1 This is ld.info, produced by makeinfo version 4.8 from ld.texinfo.
3 INFO-DIR-SECTION Software development
5 * Ld: (ld). The GNU linker.
8 This file documents the GNU linker LD (GNU Binutils) version 2.23.2.
10 Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
11 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free
12 Software Foundation, Inc.
14 Permission is granted to copy, distribute and/or modify this document
15 under the terms of the GNU Free Documentation License, Version 1.3 or
16 any later version published by the Free Software Foundation; with no
17 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
18 Texts. A copy of the license is included in the section entitled "GNU
19 Free Documentation License".
22 File: ld.info, Node: Top, Next: Overview, Up: (dir)
27 This file documents the GNU linker ld (GNU Binutils) version 2.23.2.
29 This document is distributed under the terms of the GNU Free
30 Documentation License version 1.3. A copy of the license is included
31 in the section entitled "GNU Free Documentation License".
36 * Invocation:: Invocation
37 * Scripts:: Linker Scripts
39 * Machine Dependent:: Machine Dependent Features
43 * Reporting Bugs:: Reporting Bugs
44 * MRI:: MRI Compatible Script Files
45 * GNU Free Documentation License:: GNU Free Documentation License
49 File: ld.info, Node: Overview, Next: Invocation, Prev: Top, Up: Top
54 `ld' combines a number of object and archive files, relocates their
55 data and ties up symbol references. Usually the last step in compiling
56 a program is to run `ld'.
58 `ld' accepts Linker Command Language files written in a superset of
59 AT&T's Link Editor Command Language syntax, to provide explicit and
60 total control over the linking process.
62 This version of `ld' uses the general purpose BFD libraries to
63 operate on object files. This allows `ld' to read, combine, and write
64 object files in many different formats--for example, COFF or `a.out'.
65 Different formats may be linked together to produce any available kind
66 of object file. *Note BFD::, for more information.
68 Aside from its flexibility, the GNU linker is more helpful than other
69 linkers in providing diagnostic information. Many linkers abandon
70 execution immediately upon encountering an error; whenever possible,
71 `ld' continues executing, allowing you to identify other errors (or, in
72 some cases, to get an output file in spite of the error).
75 File: ld.info, Node: Invocation, Next: Scripts, Prev: Overview, Up: Top
80 The GNU linker `ld' is meant to cover a broad range of situations, and
81 to be as compatible as possible with other linkers. As a result, you
82 have many choices to control its behavior.
86 * Options:: Command Line Options
87 * Environment:: Environment Variables
90 File: ld.info, Node: Options, Next: Environment, Up: Invocation
92 2.1 Command Line Options
93 ========================
95 The linker supports a plethora of command-line options, but in actual
96 practice few of them are used in any particular context. For instance,
97 a frequent use of `ld' is to link standard Unix object files on a
98 standard, supported Unix system. On such a system, to link a file
101 ld -o OUTPUT /lib/crt0.o hello.o -lc
103 This tells `ld' to produce a file called OUTPUT as the result of
104 linking the file `/lib/crt0.o' with `hello.o' and the library `libc.a',
105 which will come from the standard search directories. (See the
106 discussion of the `-l' option below.)
108 Some of the command-line options to `ld' may be specified at any
109 point in the command line. However, options which refer to files, such
110 as `-l' or `-T', cause the file to be read at the point at which the
111 option appears in the command line, relative to the object files and
112 other file options. Repeating non-file options with a different
113 argument will either have no further effect, or override prior
114 occurrences (those further to the left on the command line) of that
115 option. Options which may be meaningfully specified more than once are
116 noted in the descriptions below.
118 Non-option arguments are object files or archives which are to be
119 linked together. They may follow, precede, or be mixed in with
120 command-line options, except that an object file argument may not be
121 placed between an option and its argument.
123 Usually the linker is invoked with at least one object file, but you
124 can specify other forms of binary input files using `-l', `-R', and the
125 script command language. If _no_ binary input files at all are
126 specified, the linker does not produce any output, and issues the
127 message `No input files'.
129 If the linker cannot recognize the format of an object file, it will
130 assume that it is a linker script. A script specified in this way
131 augments the main linker script used for the link (either the default
132 linker script or the one specified by using `-T'). This feature
133 permits the linker to link against a file which appears to be an object
134 or an archive, but actually merely defines some symbol values, or uses
135 `INPUT' or `GROUP' to load other objects. Specifying a script in this
136 way merely augments the main linker script, with the extra commands
137 placed after the main script; use the `-T' option to replace the
138 default linker script entirely, but note the effect of the `INSERT'
139 command. *Note Scripts::.
141 For options whose names are a single letter, option arguments must
142 either follow the option letter without intervening whitespace, or be
143 given as separate arguments immediately following the option that
146 For options whose names are multiple letters, either one dash or two
147 can precede the option name; for example, `-trace-symbol' and
148 `--trace-symbol' are equivalent. Note--there is one exception to this
149 rule. Multiple letter options that start with a lower case 'o' can
150 only be preceded by two dashes. This is to reduce confusion with the
151 `-o' option. So for example `-omagic' sets the output file name to
152 `magic' whereas `--omagic' sets the NMAGIC flag on the output.
154 Arguments to multiple-letter options must either be separated from
155 the option name by an equals sign, or be given as separate arguments
156 immediately following the option that requires them. For example,
157 `--trace-symbol foo' and `--trace-symbol=foo' are equivalent. Unique
158 abbreviations of the names of multiple-letter options are accepted.
160 Note--if the linker is being invoked indirectly, via a compiler
161 driver (e.g. `gcc') then all the linker command line options should be
162 prefixed by `-Wl,' (or whatever is appropriate for the particular
163 compiler driver) like this:
165 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
167 This is important, because otherwise the compiler driver program may
168 silently drop the linker options, resulting in a bad link. Confusion
169 may also arise when passing options that require values through a
170 driver, as the use of a space between option and argument acts as a
171 separator, and causes the driver to pass only the option to the linker
172 and the argument to the compiler. In this case, it is simplest to use
173 the joined forms of both single- and multiple-letter options, such as:
175 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
177 Here is a table of the generic command line switches accepted by the
181 Read command-line options from FILE. The options read are
182 inserted in place of the original @FILE option. If FILE does not
183 exist, or cannot be read, then the option will be treated
184 literally, and not removed.
186 Options in FILE are separated by whitespace. A whitespace
187 character may be included in an option by surrounding the entire
188 option in either single or double quotes. Any character
189 (including a backslash) may be included by prefixing the character
190 to be included with a backslash. The FILE may itself contain
191 additional @FILE options; any such options will be processed
195 This option is supported for HP/UX compatibility. The KEYWORD
196 argument must be one of the strings `archive', `shared', or
197 `default'. `-aarchive' is functionally equivalent to `-Bstatic',
198 and the other two keywords are functionally equivalent to
199 `-Bdynamic'. This option may be used any number of times.
202 Adds AUDITLIB to the `DT_AUDIT' entry of the dynamic section.
203 AUDITLIB is not checked for existence, nor will it use the
204 DT_SONAME specified in the library. If specified multiple times
205 `DT_AUDIT' will contain a colon separated list of audit interfaces
206 to use. If the linker finds an object with an audit entry while
207 searching for shared libraries, it will add a corresponding
208 `DT_DEPAUDIT' entry in the output file. This option is only
209 meaningful on ELF platforms supporting the rtld-audit interface.
212 `--architecture=ARCHITECTURE'
213 In the current release of `ld', this option is useful only for the
214 Intel 960 family of architectures. In that `ld' configuration, the
215 ARCHITECTURE argument identifies the particular architecture in
216 the 960 family, enabling some safeguards and modifying the
217 archive-library search path. *Note `ld' and the Intel 960 family:
220 Future releases of `ld' may support similar functionality for
221 other architecture families.
224 `--format=INPUT-FORMAT'
225 `ld' may be configured to support more than one kind of object
226 file. If your `ld' is configured this way, you can use the `-b'
227 option to specify the binary format for input object files that
228 follow this option on the command line. Even when `ld' is
229 configured to support alternative object formats, you don't
230 usually need to specify this, as `ld' should be configured to
231 expect as a default input format the most usual format on each
232 machine. INPUT-FORMAT is a text string, the name of a particular
233 format supported by the BFD libraries. (You can list the
234 available binary formats with `objdump -i'.) *Note BFD::.
236 You may want to use this option if you are linking files with an
237 unusual binary format. You can also use `-b' to switch formats
238 explicitly (when linking object files of different formats), by
239 including `-b INPUT-FORMAT' before each group of object files in a
242 The default format is taken from the environment variable
243 `GNUTARGET'. *Note Environment::. You can also define the input
244 format from a script, using the command `TARGET'; see *Note Format
248 `--mri-script=MRI-COMMANDFILE'
249 For compatibility with linkers produced by MRI, `ld' accepts script
250 files written in an alternate, restricted command language,
251 described in *Note MRI Compatible Script Files: MRI. Introduce
252 MRI script files with the option `-c'; use the `-T' option to run
253 linker scripts written in the general-purpose `ld' scripting
254 language. If MRI-CMDFILE does not exist, `ld' looks for it in the
255 directories specified by any `-L' options.
260 These three options are equivalent; multiple forms are supported
261 for compatibility with other linkers. They assign space to common
262 symbols even if a relocatable output file is specified (with
263 `-r'). The script command `FORCE_COMMON_ALLOCATION' has the same
264 effect. *Note Miscellaneous Commands::.
266 `--depaudit AUDITLIB'
268 Adds AUDITLIB to the `DT_DEPAUDIT' entry of the dynamic section.
269 AUDITLIB is not checked for existence, nor will it use the
270 DT_SONAME specified in the library. If specified multiple times
271 `DT_DEPAUDIT' will contain a colon separated list of audit
272 interfaces to use. This option is only meaningful on ELF
273 platforms supporting the rtld-audit interface. The -P option is
274 provided for Solaris compatibility.
278 Use ENTRY as the explicit symbol for beginning execution of your
279 program, rather than the default entry point. If there is no
280 symbol named ENTRY, the linker will try to parse ENTRY as a number,
281 and use that as the entry address (the number will be interpreted
282 in base 10; you may use a leading `0x' for base 16, or a leading
283 `0' for base 8). *Note Entry Point::, for a discussion of defaults
284 and other ways of specifying the entry point.
286 `--exclude-libs LIB,LIB,...'
287 Specifies a list of archive libraries from which symbols should
288 not be automatically exported. The library names may be delimited
289 by commas or colons. Specifying `--exclude-libs ALL' excludes
290 symbols in all archive libraries from automatic export. This
291 option is available only for the i386 PE targeted port of the
292 linker and for ELF targeted ports. For i386 PE, symbols
293 explicitly listed in a .def file are still exported, regardless of
294 this option. For ELF targeted ports, symbols affected by this
295 option will be treated as hidden.
297 `--exclude-modules-for-implib MODULE,MODULE,...'
298 Specifies a list of object files or archive members, from which
299 symbols should not be automatically exported, but which should be
300 copied wholesale into the import library being generated during
301 the link. The module names may be delimited by commas or colons,
302 and must match exactly the filenames used by `ld' to open the
303 files; for archive members, this is simply the member name, but
304 for object files the name listed must include and match precisely
305 any path used to specify the input file on the linker's
306 command-line. This option is available only for the i386 PE
307 targeted port of the linker. Symbols explicitly listed in a .def
308 file are still exported, regardless of this option.
312 `--no-export-dynamic'
313 When creating a dynamically linked executable, using the `-E'
314 option or the `--export-dynamic' option causes the linker to add
315 all symbols to the dynamic symbol table. The dynamic symbol table
316 is the set of symbols which are visible from dynamic objects at
319 If you do not use either of these options (or use the
320 `--no-export-dynamic' option to restore the default behavior), the
321 dynamic symbol table will normally contain only those symbols
322 which are referenced by some dynamic object mentioned in the link.
324 If you use `dlopen' to load a dynamic object which needs to refer
325 back to the symbols defined by the program, rather than some other
326 dynamic object, then you will probably need to use this option when
327 linking the program itself.
329 You can also use the dynamic list to control what symbols should
330 be added to the dynamic symbol table if the output format supports
331 it. See the description of `--dynamic-list'.
333 Note that this option is specific to ELF targeted ports. PE
334 targets support a similar function to export all symbols from a
335 DLL or EXE; see the description of `--export-all-symbols' below.
338 Link big-endian objects. This affects the default output format.
341 Link little-endian objects. This affects the default output
346 When creating an ELF shared object, set the internal DT_AUXILIARY
347 field to the specified name. This tells the dynamic linker that
348 the symbol table of the shared object should be used as an
349 auxiliary filter on the symbol table of the shared object NAME.
351 If you later link a program against this filter object, then, when
352 you run the program, the dynamic linker will see the DT_AUXILIARY
353 field. If the dynamic linker resolves any symbols from the filter
354 object, it will first check whether there is a definition in the
355 shared object NAME. If there is one, it will be used instead of
356 the definition in the filter object. The shared object NAME need
357 not exist. Thus the shared object NAME may be used to provide an
358 alternative implementation of certain functions, perhaps for
359 debugging or for machine specific performance.
361 This option may be specified more than once. The DT_AUXILIARY
362 entries will be created in the order in which they appear on the
367 When creating an ELF shared object, set the internal DT_FILTER
368 field to the specified name. This tells the dynamic linker that
369 the symbol table of the shared object which is being created
370 should be used as a filter on the symbol table of the shared
373 If you later link a program against this filter object, then, when
374 you run the program, the dynamic linker will see the DT_FILTER
375 field. The dynamic linker will resolve symbols according to the
376 symbol table of the filter object as usual, but it will actually
377 link to the definitions found in the shared object NAME. Thus the
378 filter object can be used to select a subset of the symbols
379 provided by the object NAME.
381 Some older linkers used the `-F' option throughout a compilation
382 toolchain for specifying object-file format for both input and
383 output object files. The GNU linker uses other mechanisms for
384 this purpose: the `-b', `--format', `--oformat' options, the
385 `TARGET' command in linker scripts, and the `GNUTARGET'
386 environment variable. The GNU linker will ignore the `-F' option
387 when not creating an ELF shared object.
390 When creating an ELF executable or shared object, call NAME when
391 the executable or shared object is unloaded, by setting DT_FINI to
392 the address of the function. By default, the linker uses `_fini'
393 as the function to call.
396 Ignored. Provided for compatibility with other tools.
400 Set the maximum size of objects to be optimized using the GP
401 register to SIZE. This is only meaningful for object file formats
402 such as MIPS ECOFF which supports putting large and small objects
403 into different sections. This is ignored for other object file
408 When creating an ELF shared object, set the internal DT_SONAME
409 field to the specified name. When an executable is linked with a
410 shared object which has a DT_SONAME field, then when the
411 executable is run the dynamic linker will attempt to load the
412 shared object specified by the DT_SONAME field rather than the
413 using the file name given to the linker.
416 Perform an incremental link (same as option `-r').
419 When creating an ELF executable or shared object, call NAME when
420 the executable or shared object is loaded, by setting DT_INIT to
421 the address of the function. By default, the linker uses `_init'
422 as the function to call.
426 Add the archive or object file specified by NAMESPEC to the list
427 of files to link. This option may be used any number of times.
428 If NAMESPEC is of the form `:FILENAME', `ld' will search the
429 library path for a file called FILENAME, otherwise it will search
430 the library path for a file called `libNAMESPEC.a'.
432 On systems which support shared libraries, `ld' may also search for
433 files other than `libNAMESPEC.a'. Specifically, on ELF and SunOS
434 systems, `ld' will search a directory for a library called
435 `libNAMESPEC.so' before searching for one called `libNAMESPEC.a'.
436 (By convention, a `.so' extension indicates a shared library.)
437 Note that this behavior does not apply to `:FILENAME', which
438 always specifies a file called FILENAME.
440 The linker will search an archive only once, at the location where
441 it is specified on the command line. If the archive defines a
442 symbol which was undefined in some object which appeared before
443 the archive on the command line, the linker will include the
444 appropriate file(s) from the archive. However, an undefined
445 symbol in an object appearing later on the command line will not
446 cause the linker to search the archive again.
448 See the `-(' option for a way to force the linker to search
449 archives multiple times.
451 You may list the same archive multiple times on the command line.
453 This type of archive searching is standard for Unix linkers.
454 However, if you are using `ld' on AIX, note that it is different
455 from the behaviour of the AIX linker.
458 `--library-path=SEARCHDIR'
459 Add path SEARCHDIR to the list of paths that `ld' will search for
460 archive libraries and `ld' control scripts. You may use this
461 option any number of times. The directories are searched in the
462 order in which they are specified on the command line.
463 Directories specified on the command line are searched before the
464 default directories. All `-L' options apply to all `-l' options,
465 regardless of the order in which the options appear. `-L' options
466 do not affect how `ld' searches for a linker script unless `-T'
469 If SEARCHDIR begins with `=', then the `=' will be replaced by the
470 "sysroot prefix", a path specified when the linker is configured.
472 The default set of paths searched (without being specified with
473 `-L') depends on which emulation mode `ld' is using, and in some
474 cases also on how it was configured. *Note Environment::.
476 The paths can also be specified in a link script with the
477 `SEARCH_DIR' command. Directories specified this way are searched
478 at the point in which the linker script appears in the command
482 Emulate the EMULATION linker. You can list the available
483 emulations with the `--verbose' or `-V' options.
485 If the `-m' option is not used, the emulation is taken from the
486 `LDEMULATION' environment variable, if that is defined.
488 Otherwise, the default emulation depends upon how the linker was
493 Print a link map to the standard output. A link map provides
494 information about the link, including the following:
496 * Where object files are mapped into memory.
498 * How common symbols are allocated.
500 * All archive members included in the link, with a mention of
501 the symbol which caused the archive member to be brought in.
503 * The values assigned to symbols.
505 Note - symbols whose values are computed by an expression
506 which involves a reference to a previous value of the same
507 symbol may not have correct result displayed in the link map.
508 This is because the linker discards intermediate results and
509 only retains the final value of an expression. Under such
510 circumstances the linker will display the final value
511 enclosed by square brackets. Thus for example a linker
518 will produce the following output in the link map if the `-M'
522 [0x0000000c] foo = (foo * 0x4)
523 [0x0000000c] foo = (foo + 0x8)
525 See *Note Expressions:: for more information about
526 expressions in linker scripts.
530 Turn off page alignment of sections, and disable linking against
531 shared libraries. If the output format supports Unix style magic
532 numbers, mark the output as `NMAGIC'.
536 Set the text and data sections to be readable and writable. Also,
537 do not page-align the data segment, and disable linking against
538 shared libraries. If the output format supports Unix style magic
539 numbers, mark the output as `OMAGIC'. Note: Although a writable
540 text section is allowed for PE-COFF targets, it does not conform
541 to the format specification published by Microsoft.
544 This option negates most of the effects of the `-N' option. It
545 sets the text section to be read-only, and forces the data segment
546 to be page-aligned. Note - this option does not enable linking
547 against shared libraries. Use `-Bdynamic' for this.
551 Use OUTPUT as the name for the program produced by `ld'; if this
552 option is not specified, the name `a.out' is used by default. The
553 script command `OUTPUT' can also specify the output file name.
556 If LEVEL is a numeric values greater than zero `ld' optimizes the
557 output. This might take significantly longer and therefore
558 probably should only be enabled for the final binary. At the
559 moment this option only affects ELF shared library generation.
560 Future releases of the linker may make more use of this option.
561 Also currently there is no difference in the linker's behaviour
562 for different non-zero values of this option. Again this may
563 change with future releases.
567 Leave relocation sections and contents in fully linked executables.
568 Post link analysis and optimization tools may need this
569 information in order to perform correct modifications of
570 executables. This results in larger executables.
572 This option is currently only supported on ELF platforms.
575 Force the output file to have dynamic sections. This option is
576 specific to VxWorks targets.
580 Generate relocatable output--i.e., generate an output file that
581 can in turn serve as input to `ld'. This is often called "partial
582 linking". As a side effect, in environments that support standard
583 Unix magic numbers, this option also sets the output file's magic
584 number to `OMAGIC'. If this option is not specified, an absolute
585 file is produced. When linking C++ programs, this option _will
586 not_ resolve references to constructors; to do that, use `-Ur'.
588 When an input file does not have the same format as the output
589 file, partial linking is only supported if that input file does
590 not contain any relocations. Different output formats can have
591 further restrictions; for example some `a.out'-based formats do
592 not support partial linking with input files in other formats at
595 This option does the same thing as `-i'.
598 `--just-symbols=FILENAME'
599 Read symbol names and their addresses from FILENAME, but do not
600 relocate it or include it in the output. This allows your output
601 file to refer symbolically to absolute locations of memory defined
602 in other programs. You may use this option more than once.
604 For compatibility with other ELF linkers, if the `-R' option is
605 followed by a directory name, rather than a file name, it is
606 treated as the `-rpath' option.
610 Omit all symbol information from the output file.
614 Omit debugger symbol information (but not all symbols) from the
619 Print the names of the input files as `ld' processes them.
622 `--script=SCRIPTFILE'
623 Use SCRIPTFILE as the linker script. This script replaces `ld''s
624 default linker script (rather than adding to it), so COMMANDFILE
625 must specify everything necessary to describe the output file.
626 *Note Scripts::. If SCRIPTFILE does not exist in the current
627 directory, `ld' looks for it in the directories specified by any
628 preceding `-L' options. Multiple `-T' options accumulate.
631 `--default-script=SCRIPTFILE'
632 Use SCRIPTFILE as the default linker script. *Note Scripts::.
634 This option is similar to the `--script' option except that
635 processing of the script is delayed until after the rest of the
636 command line has been processed. This allows options placed after
637 the `--default-script' option on the command line to affect the
638 behaviour of the linker script, which can be important when the
639 linker command line cannot be directly controlled by the user.
640 (eg because the command line is being constructed by another tool,
645 Force SYMBOL to be entered in the output file as an undefined
646 symbol. Doing this may, for example, trigger linking of additional
647 modules from standard libraries. `-u' may be repeated with
648 different option arguments to enter additional undefined symbols.
649 This option is equivalent to the `EXTERN' linker script command.
652 For anything other than C++ programs, this option is equivalent to
653 `-r': it generates relocatable output--i.e., an output file that
654 can in turn serve as input to `ld'. When linking C++ programs,
655 `-Ur' _does_ resolve references to constructors, unlike `-r'. It
656 does not work to use `-Ur' on files that were themselves linked
657 with `-Ur'; once the constructor table has been built, it cannot
658 be added to. Use `-Ur' only for the last partial link, and `-r'
662 Creates a separate output section for every input section matching
663 SECTION, or if the optional wildcard SECTION argument is missing,
664 for every orphan input section. An orphan section is one not
665 specifically mentioned in a linker script. You may use this option
666 multiple times on the command line; It prevents the normal
667 merging of input sections with the same name, overriding output
668 section assignments in a linker script.
673 Display the version number for `ld'. The `-V' option also lists
674 the supported emulations.
678 Delete all local symbols.
682 Delete all temporary local symbols. (These symbols start with
683 system-specific local label prefixes, typically `.L' for ELF
684 systems or `L' for traditional a.out systems.)
687 `--trace-symbol=SYMBOL'
688 Print the name of each linked file in which SYMBOL appears. This
689 option may be given any number of times. On many systems it is
690 necessary to prepend an underscore.
692 This option is useful when you have an undefined symbol in your
693 link but don't know where the reference is coming from.
696 Add PATH to the default library search path. This option exists
697 for Solaris compatibility.
700 The recognized keywords are:
702 Combines multiple reloc sections and sorts them to make
703 dynamic symbol lookup caching possible.
706 Disallows undefined symbols in object files. Undefined
707 symbols in shared libraries are still allowed.
710 Marks the object as requiring executable stack.
713 This option is only meaningful when building a shared object.
714 It marks the object so that its runtime initialization will
715 occur before the runtime initialization of any other objects
716 brought into the process at the same time. Similarly the
717 runtime finalization of the object will occur after the
718 runtime finalization of any other objects.
721 Marks the object that its symbol table interposes before all
722 symbols but the primary executable.
725 When generating an executable or shared library, mark it to
726 tell the dynamic linker to defer function call resolution to
727 the point when the function is called (lazy binding), rather
728 than at load time. Lazy binding is the default.
731 Marks the object that its filters be processed immediately at
735 Allows multiple definitions.
738 Disables multiple reloc sections combining.
741 Disables production of copy relocs.
744 Marks the object that the search for dependencies of this
745 object will ignore any default library search paths.
748 Marks the object shouldn't be unloaded at runtime.
751 Marks the object not available to `dlopen'.
754 Marks the object can not be dumped by `dldump'.
757 Marks the object as not requiring executable stack.
760 Don't create an ELF `PT_GNU_RELRO' segment header in the
764 When generating an executable or shared library, mark it to
765 tell the dynamic linker to resolve all symbols when the
766 program is started, or when the shared library is linked to
767 using dlopen, instead of deferring function call resolution
768 to the point when the function is first called.
771 Marks the object may contain $ORIGIN.
774 Create an ELF `PT_GNU_RELRO' segment header in the object.
776 `max-page-size=VALUE'
777 Set the emulation maximum page size to VALUE.
779 `common-page-size=VALUE'
780 Set the emulation common page size to VALUE.
783 Other keywords are ignored for Solaris compatibility.
786 `--start-group ARCHIVES --end-group'
787 The ARCHIVES should be a list of archive files. They may be
788 either explicit file names, or `-l' options.
790 The specified archives are searched repeatedly until no new
791 undefined references are created. Normally, an archive is
792 searched only once in the order that it is specified on the
793 command line. If a symbol in that archive is needed to resolve an
794 undefined symbol referred to by an object in an archive that
795 appears later on the command line, the linker would not be able to
796 resolve that reference. By grouping the archives, they all be
797 searched repeatedly until all possible references are resolved.
799 Using this option has a significant performance cost. It is best
800 to use it only when there are unavoidable circular references
801 between two or more archives.
803 `--accept-unknown-input-arch'
804 `--no-accept-unknown-input-arch'
805 Tells the linker to accept input files whose architecture cannot be
806 recognised. The assumption is that the user knows what they are
807 doing and deliberately wants to link in these unknown input files.
808 This was the default behaviour of the linker, before release
809 2.14. The default behaviour from release 2.14 onwards is to
810 reject such input files, and so the `--accept-unknown-input-arch'
811 option has been added to restore the old behaviour.
815 This option affects ELF DT_NEEDED tags for dynamic libraries
816 mentioned on the command line after the `--as-needed' option.
817 Normally the linker will add a DT_NEEDED tag for each dynamic
818 library mentioned on the command line, regardless of whether the
819 library is actually needed or not. `--as-needed' causes a
820 DT_NEEDED tag to only be emitted for a library that satisfies an
821 undefined symbol reference from a regular object file or, if the
822 library is not found in the DT_NEEDED lists of other libraries
823 linked up to that point, an undefined symbol reference from
824 another dynamic library. `--no-as-needed' restores the default
829 These two options have been deprecated because of the similarity of
830 their names to the `--as-needed' and `--no-as-needed' options.
831 They have been replaced by `--copy-dt-needed-entries' and
832 `--no-copy-dt-needed-entries'.
835 This option is ignored for SunOS compatibility.
840 Link against dynamic libraries. This is only meaningful on
841 platforms for which shared libraries are supported. This option
842 is normally the default on such platforms. The different variants
843 of this option are for compatibility with various systems. You
844 may use this option multiple times on the command line: it affects
845 library searching for `-l' options which follow it.
848 Set the `DF_1_GROUP' flag in the `DT_FLAGS_1' entry in the dynamic
849 section. This causes the runtime linker to handle lookups in this
850 object and its dependencies to be performed only inside the group.
851 `--unresolved-symbols=report-all' is implied. This option is only
852 meaningful on ELF platforms which support shared libraries.
858 Do not link against shared libraries. This is only meaningful on
859 platforms for which shared libraries are supported. The different
860 variants of this option are for compatibility with various
861 systems. You may use this option multiple times on the command
862 line: it affects library searching for `-l' options which follow
863 it. This option also implies `--unresolved-symbols=report-all'.
864 This option can be used with `-shared'. Doing so means that a
865 shared library is being created but that all of the library's
866 external references must be resolved by pulling in entries from
870 When creating a shared library, bind references to global symbols
871 to the definition within the shared library, if any. Normally, it
872 is possible for a program linked against a shared library to
873 override the definition within the shared library. This option is
874 only meaningful on ELF platforms which support shared libraries.
876 `-Bsymbolic-functions'
877 When creating a shared library, bind references to global function
878 symbols to the definition within the shared library, if any. This
879 option is only meaningful on ELF platforms which support shared
882 `--dynamic-list=DYNAMIC-LIST-FILE'
883 Specify the name of a dynamic list file to the linker. This is
884 typically used when creating shared libraries to specify a list of
885 global symbols whose references shouldn't be bound to the
886 definition within the shared library, or creating dynamically
887 linked executables to specify a list of symbols which should be
888 added to the symbol table in the executable. This option is only
889 meaningful on ELF platforms which support shared libraries.
891 The format of the dynamic list is the same as the version node
892 without scope and node name. See *Note VERSION:: for more
895 `--dynamic-list-data'
896 Include all global data symbols to the dynamic list.
898 `--dynamic-list-cpp-new'
899 Provide the builtin dynamic list for C++ operator new and delete.
900 It is mainly useful for building shared libstdc++.
902 `--dynamic-list-cpp-typeinfo'
903 Provide the builtin dynamic list for C++ runtime type
907 `--no-check-sections'
908 Asks the linker _not_ to check section addresses after they have
909 been assigned to see if there are any overlaps. Normally the
910 linker will perform this check, and if it finds any overlaps it
911 will produce suitable error messages. The linker does know about,
912 and does make allowances for sections in overlays. The default
913 behaviour can be restored by using the command line switch
914 `--check-sections'. Section overlap is not usually checked for
915 relocatable links. You can force checking in that case by using
916 the `--check-sections' option.
918 `--copy-dt-needed-entries'
919 `--no-copy-dt-needed-entries'
920 This option affects the treatment of dynamic libraries referred to
921 by DT_NEEDED tags _inside_ ELF dynamic libraries mentioned on the
922 command line. Normally the linker won't add a DT_NEEDED tag to the
923 output binary for each library mentioned in a DT_NEEDED tag in an
924 input dynamic library. With `--copy-dt-needed-entries' specified
925 on the command line however any dynamic libraries that follow it
926 will have their DT_NEEDED entries added. The default behaviour
927 can be restored with `--no-copy-dt-needed-entries'.
929 This option also has an effect on the resolution of symbols in
930 dynamic libraries. With `--copy-dt-needed-entries' dynamic
931 libraries mentioned on the command line will be recursively
932 searched, following their DT_NEEDED tags to other libraries, in
933 order to resolve symbols required by the output binary. With the
934 default setting however the searching of dynamic libraries that
935 follow it will stop with the dynamic library itself. No DT_NEEDED
936 links will be traversed to resolve symbols.
939 Output a cross reference table. If a linker map file is being
940 generated, the cross reference table is printed to the map file.
941 Otherwise, it is printed on the standard output.
943 The format of the table is intentionally simple, so that it may be
944 easily processed by a script if necessary. The symbols are
945 printed out, sorted by name. For each symbol, a list of file
946 names is given. If the symbol is defined, the first file listed
947 is the location of the definition. The remaining files contain
948 references to the symbol.
951 This option inhibits the assignment of addresses to common symbols.
952 The script command `INHIBIT_COMMON_ALLOCATION' has the same effect.
953 *Note Miscellaneous Commands::.
955 The `--no-define-common' option allows decoupling the decision to
956 assign addresses to Common symbols from the choice of the output
957 file type; otherwise a non-Relocatable output type forces
958 assigning addresses to Common symbols. Using `--no-define-common'
959 allows Common symbols that are referenced from a shared library to
960 be assigned addresses only in the main program. This eliminates
961 the unused duplicate space in the shared library, and also
962 prevents any possible confusion over resolving to the wrong
963 duplicate when there are many dynamic modules with specialized
964 search paths for runtime symbol resolution.
966 `--defsym=SYMBOL=EXPRESSION'
967 Create a global symbol in the output file, containing the absolute
968 address given by EXPRESSION. You may use this option as many
969 times as necessary to define multiple symbols in the command line.
970 A limited form of arithmetic is supported for the EXPRESSION in
971 this context: you may give a hexadecimal constant or the name of
972 an existing symbol, or use `+' and `-' to add or subtract
973 hexadecimal constants or symbols. If you need more elaborate
974 expressions, consider using the linker command language from a
975 script (*note Assignment: Symbol Definitions: Assignments.).
976 _Note:_ there should be no white space between SYMBOL, the equals
977 sign ("<=>"), and EXPRESSION.
981 These options control whether to demangle symbol names in error
982 messages and other output. When the linker is told to demangle,
983 it tries to present symbol names in a readable fashion: it strips
984 leading underscores if they are used by the object file format,
985 and converts C++ mangled symbol names into user readable names.
986 Different compilers have different mangling styles. The optional
987 demangling style argument can be used to choose an appropriate
988 demangling style for your compiler. The linker will demangle by
989 default unless the environment variable `COLLECT_NO_DEMANGLE' is
990 set. These options may be used to override the default.
993 `--dynamic-linker=FILE'
994 Set the name of the dynamic linker. This is only meaningful when
995 generating dynamically linked ELF executables. The default dynamic
996 linker is normally correct; don't use this unless you know what
1000 `--no-fatal-warnings'
1001 Treat all warnings as errors. The default behaviour can be
1002 restored with the option `--no-fatal-warnings'.
1004 `--force-exe-suffix'
1005 Make sure that an output file has a .exe suffix.
1007 If a successfully built fully linked output file does not have a
1008 `.exe' or `.dll' suffix, this option forces the linker to copy the
1009 output file to one of the same name with a `.exe' suffix. This
1010 option is useful when using unmodified Unix makefiles on a
1011 Microsoft Windows host, since some versions of Windows won't run
1012 an image unless it ends in a `.exe' suffix.
1016 Enable garbage collection of unused input sections. It is ignored
1017 on targets that do not support this option. The default behaviour
1018 (of not performing this garbage collection) can be restored by
1019 specifying `--no-gc-sections' on the command line.
1021 `--gc-sections' decides which input sections are used by examining
1022 symbols and relocations. The section containing the entry symbol
1023 and all sections containing symbols undefined on the command-line
1024 will be kept, as will sections containing symbols referenced by
1025 dynamic objects. Note that when building shared libraries, the
1026 linker must assume that any visible symbol is referenced. Once
1027 this initial set of sections has been determined, the linker
1028 recursively marks as used any section referenced by their
1029 relocations. See `--entry' and `--undefined'.
1031 This option can be set when doing a partial link (enabled with
1032 option `-r'). In this case the root of symbols kept must be
1033 explicitly specified either by an `--entry' or `--undefined'
1034 option or by a `ENTRY' command in the linker script.
1036 `--print-gc-sections'
1037 `--no-print-gc-sections'
1038 List all sections removed by garbage collection. The listing is
1039 printed on stderr. This option is only effective if garbage
1040 collection has been enabled via the `--gc-sections') option. The
1041 default behaviour (of not listing the sections that are removed)
1042 can be restored by specifying `--no-print-gc-sections' on the
1045 `--print-output-format'
1046 Print the name of the default output format (perhaps influenced by
1047 other command-line options). This is the string that would appear
1048 in an `OUTPUT_FORMAT' linker script command (*note File
1052 Print a summary of the command-line options on the standard output
1056 Print a summary of all target specific options on the standard
1060 Print a link map to the file MAPFILE. See the description of the
1064 `ld' normally optimizes for speed over memory usage by caching the
1065 symbol tables of input files in memory. This option tells `ld' to
1066 instead optimize for memory usage, by rereading the symbol tables
1067 as necessary. This may be required if `ld' runs out of memory
1068 space while linking a large executable.
1072 Report unresolved symbol references from regular object files.
1073 This is done even if the linker is creating a non-symbolic shared
1074 library. The switch `--[no-]allow-shlib-undefined' controls the
1075 behaviour for reporting unresolved references found in shared
1076 libraries being linked in.
1078 `--allow-multiple-definition'
1080 Normally when a symbol is defined multiple times, the linker will
1081 report a fatal error. These options allow multiple definitions and
1082 the first definition will be used.
1084 `--allow-shlib-undefined'
1085 `--no-allow-shlib-undefined'
1086 Allows or disallows undefined symbols in shared libraries. This
1087 switch is similar to `--no-undefined' except that it determines
1088 the behaviour when the undefined symbols are in a shared library
1089 rather than a regular object file. It does not affect how
1090 undefined symbols in regular object files are handled.
1092 The default behaviour is to report errors for any undefined symbols
1093 referenced in shared libraries if the linker is being used to
1094 create an executable, but to allow them if the linker is being
1095 used to create a shared library.
1097 The reasons for allowing undefined symbol references in shared
1098 libraries specified at link time are that:
1100 * A shared library specified at link time may not be the same
1101 as the one that is available at load time, so the symbol
1102 might actually be resolvable at load time.
1104 * There are some operating systems, eg BeOS and HPPA, where
1105 undefined symbols in shared libraries are normal.
1107 The BeOS kernel for example patches shared libraries at load
1108 time to select whichever function is most appropriate for the
1109 current architecture. This is used, for example, to
1110 dynamically select an appropriate memset function.
1112 `--no-undefined-version'
1113 Normally when a symbol has an undefined version, the linker will
1114 ignore it. This option disallows symbols with undefined version
1115 and a fatal error will be issued instead.
1118 Create and use a default symbol version (the soname) for
1119 unversioned exported symbols.
1121 `--default-imported-symver'
1122 Create and use a default symbol version (the soname) for
1123 unversioned imported symbols.
1125 `--no-warn-mismatch'
1126 Normally `ld' will give an error if you try to link together input
1127 files that are mismatched for some reason, perhaps because they
1128 have been compiled for different processors or for different
1129 endiannesses. This option tells `ld' that it should silently
1130 permit such possible errors. This option should only be used with
1131 care, in cases when you have taken some special action that
1132 ensures that the linker errors are inappropriate.
1134 `--no-warn-search-mismatch'
1135 Normally `ld' will give a warning if it finds an incompatible
1136 library during a library search. This option silences the warning.
1138 `--no-whole-archive'
1139 Turn off the effect of the `--whole-archive' option for subsequent
1143 Retain the executable output file whenever it is still usable.
1144 Normally, the linker will not produce an output file if it
1145 encounters errors during the link process; it exits without
1146 writing an output file when it issues any error whatsoever.
1149 Only search library directories explicitly specified on the
1150 command line. Library directories specified in linker scripts
1151 (including linker scripts specified on the command line) are
1154 `--oformat=OUTPUT-FORMAT'
1155 `ld' may be configured to support more than one kind of object
1156 file. If your `ld' is configured this way, you can use the
1157 `--oformat' option to specify the binary format for the output
1158 object file. Even when `ld' is configured to support alternative
1159 object formats, you don't usually need to specify this, as `ld'
1160 should be configured to produce as a default output format the most
1161 usual format on each machine. OUTPUT-FORMAT is a text string, the
1162 name of a particular format supported by the BFD libraries. (You
1163 can list the available binary formats with `objdump -i'.) The
1164 script command `OUTPUT_FORMAT' can also specify the output format,
1165 but this option overrides it. *Note BFD::.
1169 Create a position independent executable. This is currently only
1170 supported on ELF platforms. Position independent executables are
1171 similar to shared libraries in that they are relocated by the
1172 dynamic linker to the virtual address the OS chooses for them
1173 (which can vary between invocations). Like normal dynamically
1174 linked executables they can be executed and symbols defined in the
1175 executable cannot be overridden by shared libraries.
1178 This option is ignored for Linux compatibility.
1181 This option is ignored for SVR4 compatibility.
1185 An option with machine dependent effects. This option is only
1186 supported on a few targets. *Note `ld' and the H8/300: H8/300.
1187 *Note `ld' and the Intel 960 family: i960. *Note `ld' and Xtensa
1188 Processors: Xtensa. *Note `ld' and the 68HC11 and 68HC12:
1189 M68HC11/68HC12. *Note `ld' and PowerPC 32-bit ELF Support:
1192 On some platforms the `--relax' option performs target specific,
1193 global optimizations that become possible when the linker resolves
1194 addressing in the program, such as relaxing address modes,
1195 synthesizing new instructions, selecting shorter version of current
1196 instructions, and combinig constant values.
1198 On some platforms these link time global optimizations may make
1199 symbolic debugging of the resulting executable impossible. This
1200 is known to be the case for the Matsushita MN10200 and MN10300
1201 family of processors.
1203 On platforms where this is not supported, `--relax' is accepted,
1206 On platforms where `--relax' is accepted the option `--no-relax'
1207 can be used to disable the feature.
1209 `--retain-symbols-file=FILENAME'
1210 Retain _only_ the symbols listed in the file FILENAME, discarding
1211 all others. FILENAME is simply a flat file, with one symbol name
1212 per line. This option is especially useful in environments (such
1213 as VxWorks) where a large global symbol table is accumulated
1214 gradually, to conserve run-time memory.
1216 `--retain-symbols-file' does _not_ discard undefined symbols, or
1217 symbols needed for relocations.
1219 You may only specify `--retain-symbols-file' once in the command
1220 line. It overrides `-s' and `-S'.
1223 Add a directory to the runtime library search path. This is used
1224 when linking an ELF executable with shared objects. All `-rpath'
1225 arguments are concatenated and passed to the runtime linker, which
1226 uses them to locate shared objects at runtime. The `-rpath'
1227 option is also used when locating shared objects which are needed
1228 by shared objects explicitly included in the link; see the
1229 description of the `-rpath-link' option. If `-rpath' is not used
1230 when linking an ELF executable, the contents of the environment
1231 variable `LD_RUN_PATH' will be used if it is defined.
1233 The `-rpath' option may also be used on SunOS. By default, on
1234 SunOS, the linker will form a runtime search patch out of all the
1235 `-L' options it is given. If a `-rpath' option is used, the
1236 runtime search path will be formed exclusively using the `-rpath'
1237 options, ignoring the `-L' options. This can be useful when using
1238 gcc, which adds many `-L' options which may be on NFS mounted file
1241 For compatibility with other ELF linkers, if the `-R' option is
1242 followed by a directory name, rather than a file name, it is
1243 treated as the `-rpath' option.
1246 When using ELF or SunOS, one shared library may require another.
1247 This happens when an `ld -shared' link includes a shared library
1248 as one of the input files.
1250 When the linker encounters such a dependency when doing a
1251 non-shared, non-relocatable link, it will automatically try to
1252 locate the required shared library and include it in the link, if
1253 it is not included explicitly. In such a case, the `-rpath-link'
1254 option specifies the first set of directories to search. The
1255 `-rpath-link' option may specify a sequence of directory names
1256 either by specifying a list of names separated by colons, or by
1257 appearing multiple times.
1259 This option should be used with caution as it overrides the search
1260 path that may have been hard compiled into a shared library. In
1261 such a case it is possible to use unintentionally a different
1262 search path than the runtime linker would do.
1264 The linker uses the following search paths to locate required
1266 1. Any directories specified by `-rpath-link' options.
1268 2. Any directories specified by `-rpath' options. The difference
1269 between `-rpath' and `-rpath-link' is that directories
1270 specified by `-rpath' options are included in the executable
1271 and used at runtime, whereas the `-rpath-link' option is only
1272 effective at link time. Searching `-rpath' in this way is
1273 only supported by native linkers and cross linkers which have
1274 been configured with the `--with-sysroot' option.
1276 3. On an ELF system, for native linkers, if the `-rpath' and
1277 `-rpath-link' options were not used, search the contents of
1278 the environment variable `LD_RUN_PATH'.
1280 4. On SunOS, if the `-rpath' option was not used, search any
1281 directories specified using `-L' options.
1283 5. For a native linker, the search the contents of the
1284 environment variable `LD_LIBRARY_PATH'.
1286 6. For a native ELF linker, the directories in `DT_RUNPATH' or
1287 `DT_RPATH' of a shared library are searched for shared
1288 libraries needed by it. The `DT_RPATH' entries are ignored if
1289 `DT_RUNPATH' entries exist.
1291 7. The default directories, normally `/lib' and `/usr/lib'.
1293 8. For a native linker on an ELF system, if the file
1294 `/etc/ld.so.conf' exists, the list of directories found in
1297 If the required shared library is not found, the linker will issue
1298 a warning and continue with the link.
1302 Create a shared library. This is currently only supported on ELF,
1303 XCOFF and SunOS platforms. On SunOS, the linker will
1304 automatically create a shared library if the `-e' option is not
1305 used and there are undefined symbols in the link.
1308 `--sort-common=ascending'
1309 `--sort-common=descending'
1310 This option tells `ld' to sort the common symbols by alignment in
1311 ascending or descending order when it places them in the
1312 appropriate output sections. The symbol alignments considered are
1313 sixteen-byte or larger, eight-byte, four-byte, two-byte, and
1314 one-byte. This is to prevent gaps between symbols due to alignment
1315 constraints. If no sorting order is specified, then descending
1318 `--sort-section=name'
1319 This option will apply `SORT_BY_NAME' to all wildcard section
1320 patterns in the linker script.
1322 `--sort-section=alignment'
1323 This option will apply `SORT_BY_ALIGNMENT' to all wildcard section
1324 patterns in the linker script.
1326 `--split-by-file[=SIZE]'
1327 Similar to `--split-by-reloc' but creates a new output section for
1328 each input file when SIZE is reached. SIZE defaults to a size of
1331 `--split-by-reloc[=COUNT]'
1332 Tries to creates extra sections in the output file so that no
1333 single output section in the file contains more than COUNT
1334 relocations. This is useful when generating huge relocatable
1335 files for downloading into certain real time kernels with the COFF
1336 object file format; since COFF cannot represent more than 65535
1337 relocations in a single section. Note that this will fail to work
1338 with object file formats which do not support arbitrary sections.
1339 The linker will not split up individual input sections for
1340 redistribution, so if a single input section contains more than
1341 COUNT relocations one output section will contain that many
1342 relocations. COUNT defaults to a value of 32768.
1345 Compute and display statistics about the operation of the linker,
1346 such as execution time and memory usage.
1348 `--sysroot=DIRECTORY'
1349 Use DIRECTORY as the location of the sysroot, overriding the
1350 configure-time default. This option is only supported by linkers
1351 that were configured using `--with-sysroot'.
1353 `--traditional-format'
1354 For some targets, the output of `ld' is different in some ways from
1355 the output of some existing linker. This switch requests `ld' to
1356 use the traditional format instead.
1358 For example, on SunOS, `ld' combines duplicate entries in the
1359 symbol string table. This can reduce the size of an output file
1360 with full debugging information by over 30 percent.
1361 Unfortunately, the SunOS `dbx' program can not read the resulting
1362 program (`gdb' has no trouble). The `--traditional-format' switch
1363 tells `ld' to not combine duplicate entries.
1365 `--section-start=SECTIONNAME=ORG'
1366 Locate a section in the output file at the absolute address given
1367 by ORG. You may use this option as many times as necessary to
1368 locate multiple sections in the command line. ORG must be a
1369 single hexadecimal integer; for compatibility with other linkers,
1370 you may omit the leading `0x' usually associated with hexadecimal
1371 values. _Note:_ there should be no white space between
1372 SECTIONNAME, the equals sign ("<=>"), and ORG.
1377 Same as `--section-start', with `.bss', `.data' or `.text' as the
1380 `-Ttext-segment=ORG'
1381 When creating an ELF executable or shared object, it will set the
1382 address of the first byte of the text segment.
1384 `-Trodata-segment=ORG'
1385 When creating an ELF executable or shared object for a target where
1386 the read-only data is in its own segment separate from the
1387 executable text, it will set the address of the first byte of the
1388 read-only data segment.
1390 `--unresolved-symbols=METHOD'
1391 Determine how to handle unresolved symbols. There are four
1392 possible values for `method':
1395 Do not report any unresolved symbols.
1398 Report all unresolved symbols. This is the default.
1400 `ignore-in-object-files'
1401 Report unresolved symbols that are contained in shared
1402 libraries, but ignore them if they come from regular object
1405 `ignore-in-shared-libs'
1406 Report unresolved symbols that come from regular object
1407 files, but ignore them if they come from shared libraries.
1408 This can be useful when creating a dynamic binary and it is
1409 known that all the shared libraries that it should be
1410 referencing are included on the linker's command line.
1412 The behaviour for shared libraries on their own can also be
1413 controlled by the `--[no-]allow-shlib-undefined' option.
1415 Normally the linker will generate an error message for each
1416 reported unresolved symbol but the option
1417 `--warn-unresolved-symbols' can change this to a warning.
1420 `--verbose[=NUMBER]'
1421 Display the version number for `ld' and list the linker emulations
1422 supported. Display which input files can and cannot be opened.
1423 Display the linker script being used by the linker. If the
1424 optional NUMBER argument > 1, plugin symbol status will also be
1427 `--version-script=VERSION-SCRIPTFILE'
1428 Specify the name of a version script to the linker. This is
1429 typically used when creating shared libraries to specify
1430 additional information about the version hierarchy for the library
1431 being created. This option is only fully supported on ELF
1432 platforms which support shared libraries; see *Note VERSION::. It
1433 is partially supported on PE platforms, which can use version
1434 scripts to filter symbol visibility in auto-export mode: any
1435 symbols marked `local' in the version script will not be exported.
1439 Warn when a common symbol is combined with another common symbol
1440 or with a symbol definition. Unix linkers allow this somewhat
1441 sloppy practise, but linkers on some other operating systems do
1442 not. This option allows you to find potential problems from
1443 combining global symbols. Unfortunately, some C libraries use
1444 this practise, so you may get some warnings about symbols in the
1445 libraries as well as in your programs.
1447 There are three kinds of global symbols, illustrated here by C
1451 A definition, which goes in the initialized data section of
1455 An undefined reference, which does not allocate space. There
1456 must be either a definition or a common symbol for the
1460 A common symbol. If there are only (one or more) common
1461 symbols for a variable, it goes in the uninitialized data
1462 area of the output file. The linker merges multiple common
1463 symbols for the same variable into a single symbol. If they
1464 are of different sizes, it picks the largest size. The
1465 linker turns a common symbol into a declaration, if there is
1466 a definition of the same variable.
1468 The `--warn-common' option can produce five kinds of warnings.
1469 Each warning consists of a pair of lines: the first describes the
1470 symbol just encountered, and the second describes the previous
1471 symbol encountered with the same name. One or both of the two
1472 symbols will be a common symbol.
1474 1. Turning a common symbol into a reference, because there is
1475 already a definition for the symbol.
1476 FILE(SECTION): warning: common of `SYMBOL'
1477 overridden by definition
1478 FILE(SECTION): warning: defined here
1480 2. Turning a common symbol into a reference, because a later
1481 definition for the symbol is encountered. This is the same
1482 as the previous case, except that the symbols are encountered
1483 in a different order.
1484 FILE(SECTION): warning: definition of `SYMBOL'
1486 FILE(SECTION): warning: common is here
1488 3. Merging a common symbol with a previous same-sized common
1490 FILE(SECTION): warning: multiple common
1492 FILE(SECTION): warning: previous common is here
1494 4. Merging a common symbol with a previous larger common symbol.
1495 FILE(SECTION): warning: common of `SYMBOL'
1496 overridden by larger common
1497 FILE(SECTION): warning: larger common is here
1499 5. Merging a common symbol with a previous smaller common
1500 symbol. This is the same as the previous case, except that
1501 the symbols are encountered in a different order.
1502 FILE(SECTION): warning: common of `SYMBOL'
1503 overriding smaller common
1504 FILE(SECTION): warning: smaller common is here
1506 `--warn-constructors'
1507 Warn if any global constructors are used. This is only useful for
1508 a few object file formats. For formats like COFF or ELF, the
1509 linker can not detect the use of global constructors.
1511 `--warn-multiple-gp'
1512 Warn if multiple global pointer values are required in the output
1513 file. This is only meaningful for certain processors, such as the
1514 Alpha. Specifically, some processors put large-valued constants
1515 in a special section. A special register (the global pointer)
1516 points into the middle of this section, so that constants can be
1517 loaded efficiently via a base-register relative addressing mode.
1518 Since the offset in base-register relative mode is fixed and
1519 relatively small (e.g., 16 bits), this limits the maximum size of
1520 the constant pool. Thus, in large programs, it is often necessary
1521 to use multiple global pointer values in order to be able to
1522 address all possible constants. This option causes a warning to
1523 be issued whenever this case occurs.
1526 Only warn once for each undefined symbol, rather than once per
1527 module which refers to it.
1529 `--warn-section-align'
1530 Warn if the address of an output section is changed because of
1531 alignment. Typically, the alignment will be set by an input
1532 section. The address will only be changed if it not explicitly
1533 specified; that is, if the `SECTIONS' command does not specify a
1534 start address for the section (*note SECTIONS::).
1536 `--warn-shared-textrel'
1537 Warn if the linker adds a DT_TEXTREL to a shared object.
1539 `--warn-alternate-em'
1540 Warn if an object has alternate ELF machine code.
1542 `--warn-unresolved-symbols'
1543 If the linker is going to report an unresolved symbol (see the
1544 option `--unresolved-symbols') it will normally generate an error.
1545 This option makes it generate a warning instead.
1547 `--error-unresolved-symbols'
1548 This restores the linker's default behaviour of generating errors
1549 when it is reporting unresolved symbols.
1552 For each archive mentioned on the command line after the
1553 `--whole-archive' option, include every object file in the archive
1554 in the link, rather than searching the archive for the required
1555 object files. This is normally used to turn an archive file into
1556 a shared library, forcing every object to be included in the
1557 resulting shared library. This option may be used more than once.
1559 Two notes when using this option from gcc: First, gcc doesn't know
1560 about this option, so you have to use `-Wl,-whole-archive'.
1561 Second, don't forget to use `-Wl,-no-whole-archive' after your
1562 list of archives, because gcc will add its own list of archives to
1563 your link and you may not want this flag to affect those as well.
1566 Use a wrapper function for SYMBOL. Any undefined reference to
1567 SYMBOL will be resolved to `__wrap_SYMBOL'. Any undefined
1568 reference to `__real_SYMBOL' will be resolved to SYMBOL.
1570 This can be used to provide a wrapper for a system function. The
1571 wrapper function should be called `__wrap_SYMBOL'. If it wishes
1572 to call the system function, it should call `__real_SYMBOL'.
1574 Here is a trivial example:
1577 __wrap_malloc (size_t c)
1579 printf ("malloc called with %zu\n", c);
1580 return __real_malloc (c);
1583 If you link other code with this file using `--wrap malloc', then
1584 all calls to `malloc' will call the function `__wrap_malloc'
1585 instead. The call to `__real_malloc' in `__wrap_malloc' will call
1586 the real `malloc' function.
1588 You may wish to provide a `__real_malloc' function as well, so that
1589 links without the `--wrap' option will succeed. If you do this,
1590 you should not put the definition of `__real_malloc' in the same
1591 file as `__wrap_malloc'; if you do, the assembler may resolve the
1592 call before the linker has a chance to wrap it to `malloc'.
1595 Request creation of `.eh_frame_hdr' section and ELF
1596 `PT_GNU_EH_FRAME' segment header.
1598 `--no-ld-generated-unwind-info'
1599 Request creation of `.eh_frame' unwind info for linker generated
1600 code sections like PLT. This option is on by default if linker
1601 generated unwind info is supported.
1603 `--enable-new-dtags'
1604 `--disable-new-dtags'
1605 This linker can create the new dynamic tags in ELF. But the older
1606 ELF systems may not understand them. If you specify
1607 `--enable-new-dtags', the dynamic tags will be created as needed.
1608 If you specify `--disable-new-dtags', no new dynamic tags will be
1609 created. By default, the new dynamic tags are not created. Note
1610 that those options are only available for ELF systems.
1612 `--hash-size=NUMBER'
1613 Set the default size of the linker's hash tables to a prime number
1614 close to NUMBER. Increasing this value can reduce the length of
1615 time it takes the linker to perform its tasks, at the expense of
1616 increasing the linker's memory requirements. Similarly reducing
1617 this value can reduce the memory requirements at the expense of
1620 `--hash-style=STYLE'
1621 Set the type of linker's hash table(s). STYLE can be either
1622 `sysv' for classic ELF `.hash' section, `gnu' for new style GNU
1623 `.gnu.hash' section or `both' for both the classic ELF `.hash' and
1624 new style GNU `.gnu.hash' hash tables. The default is `sysv'.
1626 `--reduce-memory-overheads'
1627 This option reduces memory requirements at ld runtime, at the
1628 expense of linking speed. This was introduced to select the old
1629 O(n^2) algorithm for link map file generation, rather than the new
1630 O(n) algorithm which uses about 40% more memory for symbol storage.
1632 Another effect of the switch is to set the default hash table size
1633 to 1021, which again saves memory at the cost of lengthening the
1634 linker's run time. This is not done however if the `--hash-size'
1635 switch has been used.
1637 The `--reduce-memory-overheads' switch may be also be used to
1638 enable other tradeoffs in future versions of the linker.
1642 Request creation of `.note.gnu.build-id' ELF note section. The
1643 contents of the note are unique bits identifying this linked file.
1644 STYLE can be `uuid' to use 128 random bits, `sha1' to use a
1645 160-bit SHA1 hash on the normative parts of the output contents,
1646 `md5' to use a 128-bit MD5 hash on the normative parts of the
1647 output contents, or `0xHEXSTRING' to use a chosen bit string
1648 specified as an even number of hexadecimal digits (`-' and `:'
1649 characters between digit pairs are ignored). If STYLE is omitted,
1652 The `md5' and `sha1' styles produces an identifier that is always
1653 the same in an identical output file, but will be unique among all
1654 nonidentical output files. It is not intended to be compared as a
1655 checksum for the file's contents. A linked file may be changed
1656 later by other tools, but the build ID bit string identifying the
1657 original linked file does not change.
1659 Passing `none' for STYLE disables the setting from any
1660 `--build-id' options earlier on the command line.
1662 2.1.1 Options Specific to i386 PE Targets
1663 -----------------------------------------
1665 The i386 PE linker supports the `-shared' option, which causes the
1666 output to be a dynamically linked library (DLL) instead of a normal
1667 executable. You should name the output `*.dll' when you use this
1668 option. In addition, the linker fully supports the standard `*.def'
1669 files, which may be specified on the linker command line like an object
1670 file (in fact, it should precede archives it exports symbols from, to
1671 ensure that they get linked in, just like a normal object file).
1673 In addition to the options common to all targets, the i386 PE linker
1674 support additional command line options that are specific to the i386
1675 PE target. Options that take values may be separated from their values
1676 by either a space or an equals sign.
1678 `--add-stdcall-alias'
1679 If given, symbols with a stdcall suffix (@NN) will be exported
1680 as-is and also with the suffix stripped. [This option is specific
1681 to the i386 PE targeted port of the linker]
1684 Use FILE as the name of a file in which to save the base addresses
1685 of all the relocations needed for generating DLLs with `dlltool'.
1686 [This is an i386 PE specific option]
1689 Create a DLL instead of a regular executable. You may also use
1690 `-shared' or specify a `LIBRARY' in a given `.def' file. [This
1691 option is specific to the i386 PE targeted port of the linker]
1693 `--enable-long-section-names'
1694 `--disable-long-section-names'
1695 The PE variants of the Coff object format add an extension that
1696 permits the use of section names longer than eight characters, the
1697 normal limit for Coff. By default, these names are only allowed
1698 in object files, as fully-linked executable images do not carry
1699 the Coff string table required to support the longer names. As a
1700 GNU extension, it is possible to allow their use in executable
1701 images as well, or to (probably pointlessly!) disallow it in
1702 object files, by using these two options. Executable images
1703 generated with these long section names are slightly non-standard,
1704 carrying as they do a string table, and may generate confusing
1705 output when examined with non-GNU PE-aware tools, such as file
1706 viewers and dumpers. However, GDB relies on the use of PE long
1707 section names to find Dwarf-2 debug information sections in an
1708 executable image at runtime, and so if neither option is specified
1709 on the command-line, `ld' will enable long section names,
1710 overriding the default and technically correct behaviour, when it
1711 finds the presence of debug information while linking an executable
1712 image and not stripping symbols. [This option is valid for all PE
1713 targeted ports of the linker]
1715 `--enable-stdcall-fixup'
1716 `--disable-stdcall-fixup'
1717 If the link finds a symbol that it cannot resolve, it will attempt
1718 to do "fuzzy linking" by looking for another defined symbol that
1719 differs only in the format of the symbol name (cdecl vs stdcall)
1720 and will resolve that symbol by linking to the match. For
1721 example, the undefined symbol `_foo' might be linked to the
1722 function `_foo@12', or the undefined symbol `_bar@16' might be
1723 linked to the function `_bar'. When the linker does this, it
1724 prints a warning, since it normally should have failed to link,
1725 but sometimes import libraries generated from third-party dlls may
1726 need this feature to be usable. If you specify
1727 `--enable-stdcall-fixup', this feature is fully enabled and
1728 warnings are not printed. If you specify
1729 `--disable-stdcall-fixup', this feature is disabled and such
1730 mismatches are considered to be errors. [This option is specific
1731 to the i386 PE targeted port of the linker]
1733 `--leading-underscore'
1734 `--no-leading-underscore'
1735 For most targets default symbol-prefix is an underscore and is
1736 defined in target's description. By this option it is possible to
1737 disable/enable the default underscore symbol-prefix.
1739 `--export-all-symbols'
1740 If given, all global symbols in the objects used to build a DLL
1741 will be exported by the DLL. Note that this is the default if
1742 there otherwise wouldn't be any exported symbols. When symbols are
1743 explicitly exported via DEF files or implicitly exported via
1744 function attributes, the default is to not export anything else
1745 unless this option is given. Note that the symbols `DllMain@12',
1746 `DllEntryPoint@0', `DllMainCRTStartup@12', and `impure_ptr' will
1747 not be automatically exported. Also, symbols imported from other
1748 DLLs will not be re-exported, nor will symbols specifying the
1749 DLL's internal layout such as those beginning with `_head_' or
1750 ending with `_iname'. In addition, no symbols from `libgcc',
1751 `libstd++', `libmingw32', or `crtX.o' will be exported. Symbols
1752 whose names begin with `__rtti_' or `__builtin_' will not be
1753 exported, to help with C++ DLLs. Finally, there is an extensive
1754 list of cygwin-private symbols that are not exported (obviously,
1755 this applies on when building DLLs for cygwin targets). These
1756 cygwin-excludes are: `_cygwin_dll_entry@12',
1757 `_cygwin_crt0_common@8', `_cygwin_noncygwin_dll_entry@12',
1758 `_fmode', `_impure_ptr', `cygwin_attach_dll', `cygwin_premain0',
1759 `cygwin_premain1', `cygwin_premain2', `cygwin_premain3', and
1760 `environ'. [This option is specific to the i386 PE targeted port
1763 `--exclude-symbols SYMBOL,SYMBOL,...'
1764 Specifies a list of symbols which should not be automatically
1765 exported. The symbol names may be delimited by commas or colons.
1766 [This option is specific to the i386 PE targeted port of the
1769 `--exclude-all-symbols'
1770 Specifies no symbols should be automatically exported. [This
1771 option is specific to the i386 PE targeted port of the linker]
1774 Specify the file alignment. Sections in the file will always
1775 begin at file offsets which are multiples of this number. This
1776 defaults to 512. [This option is specific to the i386 PE targeted
1780 `--heap RESERVE,COMMIT'
1781 Specify the number of bytes of memory to reserve (and optionally
1782 commit) to be used as heap for this program. The default is 1Mb
1783 reserved, 4K committed. [This option is specific to the i386 PE
1784 targeted port of the linker]
1786 `--image-base VALUE'
1787 Use VALUE as the base address of your program or dll. This is the
1788 lowest memory location that will be used when your program or dll
1789 is loaded. To reduce the need to relocate and improve performance
1790 of your dlls, each should have a unique base address and not
1791 overlap any other dlls. The default is 0x400000 for executables,
1792 and 0x10000000 for dlls. [This option is specific to the i386 PE
1793 targeted port of the linker]
1796 If given, the stdcall suffixes (@NN) will be stripped from symbols
1797 before they are exported. [This option is specific to the i386 PE
1798 targeted port of the linker]
1800 `--large-address-aware'
1801 If given, the appropriate bit in the "Characteristics" field of
1802 the COFF header is set to indicate that this executable supports
1803 virtual addresses greater than 2 gigabytes. This should be used
1804 in conjunction with the /3GB or /USERVA=VALUE megabytes switch in
1805 the "[operating systems]" section of the BOOT.INI. Otherwise,
1806 this bit has no effect. [This option is specific to PE targeted
1807 ports of the linker]
1809 `--major-image-version VALUE'
1810 Sets the major number of the "image version". Defaults to 1.
1811 [This option is specific to the i386 PE targeted port of the
1814 `--major-os-version VALUE'
1815 Sets the major number of the "os version". Defaults to 4. [This
1816 option is specific to the i386 PE targeted port of the linker]
1818 `--major-subsystem-version VALUE'
1819 Sets the major number of the "subsystem version". Defaults to 4.
1820 [This option is specific to the i386 PE targeted port of the
1823 `--minor-image-version VALUE'
1824 Sets the minor number of the "image version". Defaults to 0.
1825 [This option is specific to the i386 PE targeted port of the
1828 `--minor-os-version VALUE'
1829 Sets the minor number of the "os version". Defaults to 0. [This
1830 option is specific to the i386 PE targeted port of the linker]
1832 `--minor-subsystem-version VALUE'
1833 Sets the minor number of the "subsystem version". Defaults to 0.
1834 [This option is specific to the i386 PE targeted port of the
1838 The linker will create the file FILE which will contain a DEF file
1839 corresponding to the DLL the linker is generating. This DEF file
1840 (which should be called `*.def') may be used to create an import
1841 library with `dlltool' or may be used as a reference to
1842 automatically or implicitly exported symbols. [This option is
1843 specific to the i386 PE targeted port of the linker]
1846 The linker will create the file FILE which will contain an import
1847 lib corresponding to the DLL the linker is generating. This import
1848 lib (which should be called `*.dll.a' or `*.a' may be used to link
1849 clients against the generated DLL; this behaviour makes it
1850 possible to skip a separate `dlltool' import library creation step.
1851 [This option is specific to the i386 PE targeted port of the
1854 `--enable-auto-image-base'
1855 Automatically choose the image base for DLLs, unless one is
1856 specified using the `--image-base' argument. By using a hash
1857 generated from the dllname to create unique image bases for each
1858 DLL, in-memory collisions and relocations which can delay program
1859 execution are avoided. [This option is specific to the i386 PE
1860 targeted port of the linker]
1862 `--disable-auto-image-base'
1863 Do not automatically generate a unique image base. If there is no
1864 user-specified image base (`--image-base') then use the platform
1865 default. [This option is specific to the i386 PE targeted port of
1868 `--dll-search-prefix STRING'
1869 When linking dynamically to a dll without an import library,
1870 search for `<string><basename>.dll' in preference to
1871 `lib<basename>.dll'. This behaviour allows easy distinction
1872 between DLLs built for the various "subplatforms": native, cygwin,
1873 uwin, pw, etc. For instance, cygwin DLLs typically use
1874 `--dll-search-prefix=cyg'. [This option is specific to the i386
1875 PE targeted port of the linker]
1877 `--enable-auto-import'
1878 Do sophisticated linking of `_symbol' to `__imp__symbol' for DATA
1879 imports from DLLs, and create the necessary thunking symbols when
1880 building the import libraries with those DATA exports. Note: Use
1881 of the 'auto-import' extension will cause the text section of the
1882 image file to be made writable. This does not conform to the
1883 PE-COFF format specification published by Microsoft.
1885 Note - use of the 'auto-import' extension will also cause read only
1886 data which would normally be placed into the .rdata section to be
1887 placed into the .data section instead. This is in order to work
1888 around a problem with consts that is described here:
1889 http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
1891 Using 'auto-import' generally will 'just work' - but sometimes you
1892 may see this message:
1894 "variable '<var>' can't be auto-imported. Please read the
1895 documentation for ld's `--enable-auto-import' for details."
1897 This message occurs when some (sub)expression accesses an address
1898 ultimately given by the sum of two constants (Win32 import tables
1899 only allow one). Instances where this may occur include accesses
1900 to member fields of struct variables imported from a DLL, as well
1901 as using a constant index into an array variable imported from a
1902 DLL. Any multiword variable (arrays, structs, long long, etc) may
1903 trigger this error condition. However, regardless of the exact
1904 data type of the offending exported variable, ld will always
1905 detect it, issue the warning, and exit.
1907 There are several ways to address this difficulty, regardless of
1908 the data type of the exported variable:
1910 One way is to use -enable-runtime-pseudo-reloc switch. This leaves
1911 the task of adjusting references in your client code for runtime
1912 environment, so this method works only when runtime environment
1913 supports this feature.
1915 A second solution is to force one of the 'constants' to be a
1916 variable - that is, unknown and un-optimizable at compile time.
1917 For arrays, there are two possibilities: a) make the indexee (the
1918 array's address) a variable, or b) make the 'constant' index a
1921 extern type extern_array[];
1923 { volatile type *t=extern_array; t[1] }
1927 extern type extern_array[];
1929 { volatile int t=1; extern_array[t] }
1931 For structs (and most other multiword data types) the only option
1932 is to make the struct itself (or the long long, or the ...)
1935 extern struct s extern_struct;
1936 extern_struct.field -->
1937 { volatile struct s *t=&extern_struct; t->field }
1941 extern long long extern_ll;
1943 { volatile long long * local_ll=&extern_ll; *local_ll }
1945 A third method of dealing with this difficulty is to abandon
1946 'auto-import' for the offending symbol and mark it with
1947 `__declspec(dllimport)'. However, in practise that requires using
1948 compile-time #defines to indicate whether you are building a DLL,
1949 building client code that will link to the DLL, or merely
1950 building/linking to a static library. In making the choice
1951 between the various methods of resolving the 'direct address with
1952 constant offset' problem, you should consider typical real-world
1960 void main(int argc, char **argv){
1961 printf("%d\n",arr[1]);
1969 void main(int argc, char **argv){
1970 /* This workaround is for win32 and cygwin; do not "optimize" */
1971 volatile int *parr = arr;
1972 printf("%d\n",parr[1]);
1977 /* Note: auto-export is assumed (no __declspec(dllexport)) */
1978 #if (defined(_WIN32) || defined(__CYGWIN__)) && \
1979 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
1980 #define FOO_IMPORT __declspec(dllimport)
1984 extern FOO_IMPORT int arr[];
1987 void main(int argc, char **argv){
1988 printf("%d\n",arr[1]);
1991 A fourth way to avoid this problem is to re-code your library to
1992 use a functional interface rather than a data interface for the
1993 offending variables (e.g. set_foo() and get_foo() accessor
1994 functions). [This option is specific to the i386 PE targeted port
1997 `--disable-auto-import'
1998 Do not attempt to do sophisticated linking of `_symbol' to
1999 `__imp__symbol' for DATA imports from DLLs. [This option is
2000 specific to the i386 PE targeted port of the linker]
2002 `--enable-runtime-pseudo-reloc'
2003 If your code contains expressions described in -enable-auto-import
2004 section, that is, DATA imports from DLL with non-zero offset, this
2005 switch will create a vector of 'runtime pseudo relocations' which
2006 can be used by runtime environment to adjust references to such
2007 data in your client code. [This option is specific to the i386 PE
2008 targeted port of the linker]
2010 `--disable-runtime-pseudo-reloc'
2011 Do not create pseudo relocations for non-zero offset DATA imports
2012 from DLLs. This is the default. [This option is specific to the
2013 i386 PE targeted port of the linker]
2015 `--enable-extra-pe-debug'
2016 Show additional debug info related to auto-import symbol thunking.
2017 [This option is specific to the i386 PE targeted port of the
2020 `--section-alignment'
2021 Sets the section alignment. Sections in memory will always begin
2022 at addresses which are a multiple of this number. Defaults to
2023 0x1000. [This option is specific to the i386 PE targeted port of
2027 `--stack RESERVE,COMMIT'
2028 Specify the number of bytes of memory to reserve (and optionally
2029 commit) to be used as stack for this program. The default is 2Mb
2030 reserved, 4K committed. [This option is specific to the i386 PE
2031 targeted port of the linker]
2034 `--subsystem WHICH:MAJOR'
2035 `--subsystem WHICH:MAJOR.MINOR'
2036 Specifies the subsystem under which your program will execute. The
2037 legal values for WHICH are `native', `windows', `console',
2038 `posix', and `xbox'. You may optionally set the subsystem version
2039 also. Numeric values are also accepted for WHICH. [This option
2040 is specific to the i386 PE targeted port of the linker]
2042 The following options set flags in the `DllCharacteristics' field
2043 of the PE file header: [These options are specific to PE targeted
2044 ports of the linker]
2047 The image base address may be relocated using address space layout
2048 randomization (ASLR). This feature was introduced with MS Windows
2049 Vista for i386 PE targets.
2052 Code integrity checks are enforced.
2055 The image is compatible with the Data Execution Prevention. This
2056 feature was introduced with MS Windows XP SP2 for i386 PE targets.
2059 Although the image understands isolation, do not isolate the image.
2062 The image does not use SEH. No SE handler may be called from this
2066 Do not bind this image.
2069 The driver uses the MS Windows Driver Model.
2072 The image is Terminal Server aware.
2075 2.1.2 Options specific to C6X uClinux targets
2076 ---------------------------------------------
2078 The C6X uClinux target uses a binary format called DSBT to support
2079 shared libraries. Each shared library in the system needs to have a
2080 unique index; all executables use an index of 0.
2083 This option sets the number of entires in the DSBT of the current
2084 executable or shared library to SIZE. The default is to create a
2085 table with 64 entries.
2087 `--dsbt-index INDEX'
2088 This option sets the DSBT index of the current executable or
2089 shared library to INDEX. The default is 0, which is appropriate
2090 for generating executables. If a shared library is generated with
2091 a DSBT index of 0, the `R_C6000_DSBT_INDEX' relocs are copied into
2094 The `--no-merge-exidx-entries' switch disables the merging of
2095 adjacent exidx entries in frame unwind info.
2098 2.1.3 Options specific to Motorola 68HC11 and 68HC12 targets
2099 ------------------------------------------------------------
2101 The 68HC11 and 68HC12 linkers support specific options to control the
2102 memory bank switching mapping and trampoline code generation.
2105 This option disables the generation of trampoline. By default a
2106 trampoline is generated for each far function which is called
2107 using a `jsr' instruction (this happens when a pointer to a far
2110 `--bank-window NAME'
2111 This option indicates to the linker the name of the memory region
2112 in the `MEMORY' specification that describes the memory bank
2113 window. The definition of such region is then used by the linker
2114 to compute paging and addresses within the memory window.
2117 2.1.4 Options specific to Motorola 68K target
2118 ---------------------------------------------
2120 The following options are supported to control handling of GOT
2121 generation when linking for 68K targets.
2124 This option tells the linker which GOT generation scheme to use.
2125 TYPE should be one of `single', `negative', `multigot' or
2126 `target'. For more information refer to the Info entry for `ld'.
2130 File: ld.info, Node: Environment, Prev: Options, Up: Invocation
2132 2.2 Environment Variables
2133 =========================
2135 You can change the behaviour of `ld' with the environment variables
2136 `GNUTARGET', `LDEMULATION' and `COLLECT_NO_DEMANGLE'.
2138 `GNUTARGET' determines the input-file object format if you don't use
2139 `-b' (or its synonym `--format'). Its value should be one of the BFD
2140 names for an input format (*note BFD::). If there is no `GNUTARGET' in
2141 the environment, `ld' uses the natural format of the target. If
2142 `GNUTARGET' is set to `default' then BFD attempts to discover the input
2143 format by examining binary input files; this method often succeeds, but
2144 there are potential ambiguities, since there is no method of ensuring
2145 that the magic number used to specify object-file formats is unique.
2146 However, the configuration procedure for BFD on each system places the
2147 conventional format for that system first in the search-list, so
2148 ambiguities are resolved in favor of convention.
2150 `LDEMULATION' determines the default emulation if you don't use the
2151 `-m' option. The emulation can affect various aspects of linker
2152 behaviour, particularly the default linker script. You can list the
2153 available emulations with the `--verbose' or `-V' options. If the `-m'
2154 option is not used, and the `LDEMULATION' environment variable is not
2155 defined, the default emulation depends upon how the linker was
2158 Normally, the linker will default to demangling symbols. However, if
2159 `COLLECT_NO_DEMANGLE' is set in the environment, then it will default
2160 to not demangling symbols. This environment variable is used in a
2161 similar fashion by the `gcc' linker wrapper program. The default may
2162 be overridden by the `--demangle' and `--no-demangle' options.
2165 File: ld.info, Node: Scripts, Next: Machine Dependent, Prev: Invocation, Up: Top
2170 Every link is controlled by a "linker script". This script is written
2171 in the linker command language.
2173 The main purpose of the linker script is to describe how the
2174 sections in the input files should be mapped into the output file, and
2175 to control the memory layout of the output file. Most linker scripts
2176 do nothing more than this. However, when necessary, the linker script
2177 can also direct the linker to perform many other operations, using the
2178 commands described below.
2180 The linker always uses a linker script. If you do not supply one
2181 yourself, the linker will use a default script that is compiled into the
2182 linker executable. You can use the `--verbose' command line option to
2183 display the default linker script. Certain command line options, such
2184 as `-r' or `-N', will affect the default linker script.
2186 You may supply your own linker script by using the `-T' command line
2187 option. When you do this, your linker script will replace the default
2190 You may also use linker scripts implicitly by naming them as input
2191 files to the linker, as though they were files to be linked. *Note
2192 Implicit Linker Scripts::.
2196 * Basic Script Concepts:: Basic Linker Script Concepts
2197 * Script Format:: Linker Script Format
2198 * Simple Example:: Simple Linker Script Example
2199 * Simple Commands:: Simple Linker Script Commands
2200 * Assignments:: Assigning Values to Symbols
2201 * SECTIONS:: SECTIONS Command
2202 * MEMORY:: MEMORY Command
2203 * PHDRS:: PHDRS Command
2204 * VERSION:: VERSION Command
2205 * Expressions:: Expressions in Linker Scripts
2206 * Implicit Linker Scripts:: Implicit Linker Scripts
2209 File: ld.info, Node: Basic Script Concepts, Next: Script Format, Up: Scripts
2211 3.1 Basic Linker Script Concepts
2212 ================================
2214 We need to define some basic concepts and vocabulary in order to
2215 describe the linker script language.
2217 The linker combines input files into a single output file. The
2218 output file and each input file are in a special data format known as an
2219 "object file format". Each file is called an "object file". The
2220 output file is often called an "executable", but for our purposes we
2221 will also call it an object file. Each object file has, among other
2222 things, a list of "sections". We sometimes refer to a section in an
2223 input file as an "input section"; similarly, a section in the output
2224 file is an "output section".
2226 Each section in an object file has a name and a size. Most sections
2227 also have an associated block of data, known as the "section contents".
2228 A section may be marked as "loadable", which mean that the contents
2229 should be loaded into memory when the output file is run. A section
2230 with no contents may be "allocatable", which means that an area in
2231 memory should be set aside, but nothing in particular should be loaded
2232 there (in some cases this memory must be zeroed out). A section which
2233 is neither loadable nor allocatable typically contains some sort of
2234 debugging information.
2236 Every loadable or allocatable output section has two addresses. The
2237 first is the "VMA", or virtual memory address. This is the address the
2238 section will have when the output file is run. The second is the
2239 "LMA", or load memory address. This is the address at which the
2240 section will be loaded. In most cases the two addresses will be the
2241 same. An example of when they might be different is when a data section
2242 is loaded into ROM, and then copied into RAM when the program starts up
2243 (this technique is often used to initialize global variables in a ROM
2244 based system). In this case the ROM address would be the LMA, and the
2245 RAM address would be the VMA.
2247 You can see the sections in an object file by using the `objdump'
2248 program with the `-h' option.
2250 Every object file also has a list of "symbols", known as the "symbol
2251 table". A symbol may be defined or undefined. Each symbol has a name,
2252 and each defined symbol has an address, among other information. If
2253 you compile a C or C++ program into an object file, you will get a
2254 defined symbol for every defined function and global or static
2255 variable. Every undefined function or global variable which is
2256 referenced in the input file will become an undefined symbol.
2258 You can see the symbols in an object file by using the `nm' program,
2259 or by using the `objdump' program with the `-t' option.
2262 File: ld.info, Node: Script Format, Next: Simple Example, Prev: Basic Script Concepts, Up: Scripts
2264 3.2 Linker Script Format
2265 ========================
2267 Linker scripts are text files.
2269 You write a linker script as a series of commands. Each command is
2270 either a keyword, possibly followed by arguments, or an assignment to a
2271 symbol. You may separate commands using semicolons. Whitespace is
2274 Strings such as file or format names can normally be entered
2275 directly. If the file name contains a character such as a comma which
2276 would otherwise serve to separate file names, you may put the file name
2277 in double quotes. There is no way to use a double quote character in a
2280 You may include comments in linker scripts just as in C, delimited by
2281 `/*' and `*/'. As in C, comments are syntactically equivalent to
2285 File: ld.info, Node: Simple Example, Next: Simple Commands, Prev: Script Format, Up: Scripts
2287 3.3 Simple Linker Script Example
2288 ================================
2290 Many linker scripts are fairly simple.
2292 The simplest possible linker script has just one command:
2293 `SECTIONS'. You use the `SECTIONS' command to describe the memory
2294 layout of the output file.
2296 The `SECTIONS' command is a powerful command. Here we will describe
2297 a simple use of it. Let's assume your program consists only of code,
2298 initialized data, and uninitialized data. These will be in the
2299 `.text', `.data', and `.bss' sections, respectively. Let's assume
2300 further that these are the only sections which appear in your input
2303 For this example, let's say that the code should be loaded at address
2304 0x10000, and that the data should start at address 0x8000000. Here is a
2305 linker script which will do that:
2309 .text : { *(.text) }
2311 .data : { *(.data) }
2315 You write the `SECTIONS' command as the keyword `SECTIONS', followed
2316 by a series of symbol assignments and output section descriptions
2317 enclosed in curly braces.
2319 The first line inside the `SECTIONS' command of the above example
2320 sets the value of the special symbol `.', which is the location
2321 counter. If you do not specify the address of an output section in some
2322 other way (other ways are described later), the address is set from the
2323 current value of the location counter. The location counter is then
2324 incremented by the size of the output section. At the start of the
2325 `SECTIONS' command, the location counter has the value `0'.
2327 The second line defines an output section, `.text'. The colon is
2328 required syntax which may be ignored for now. Within the curly braces
2329 after the output section name, you list the names of the input sections
2330 which should be placed into this output section. The `*' is a wildcard
2331 which matches any file name. The expression `*(.text)' means all
2332 `.text' input sections in all input files.
2334 Since the location counter is `0x10000' when the output section
2335 `.text' is defined, the linker will set the address of the `.text'
2336 section in the output file to be `0x10000'.
2338 The remaining lines define the `.data' and `.bss' sections in the
2339 output file. The linker will place the `.data' output section at
2340 address `0x8000000'. After the linker places the `.data' output
2341 section, the value of the location counter will be `0x8000000' plus the
2342 size of the `.data' output section. The effect is that the linker will
2343 place the `.bss' output section immediately after the `.data' output
2346 The linker will ensure that each output section has the required
2347 alignment, by increasing the location counter if necessary. In this
2348 example, the specified addresses for the `.text' and `.data' sections
2349 will probably satisfy any alignment constraints, but the linker may
2350 have to create a small gap between the `.data' and `.bss' sections.
2352 That's it! That's a simple and complete linker script.
2355 File: ld.info, Node: Simple Commands, Next: Assignments, Prev: Simple Example, Up: Scripts
2357 3.4 Simple Linker Script Commands
2358 =================================
2360 In this section we describe the simple linker script commands.
2364 * Entry Point:: Setting the entry point
2365 * File Commands:: Commands dealing with files
2367 * Format Commands:: Commands dealing with object file formats
2369 * REGION_ALIAS:: Assign alias names to memory regions
2370 * Miscellaneous Commands:: Other linker script commands
2373 File: ld.info, Node: Entry Point, Next: File Commands, Up: Simple Commands
2375 3.4.1 Setting the Entry Point
2376 -----------------------------
2378 The first instruction to execute in a program is called the "entry
2379 point". You can use the `ENTRY' linker script command to set the entry
2380 point. The argument is a symbol name:
2383 There are several ways to set the entry point. The linker will set
2384 the entry point by trying each of the following methods in order, and
2385 stopping when one of them succeeds:
2386 * the `-e' ENTRY command-line option;
2388 * the `ENTRY(SYMBOL)' command in a linker script;
2390 * the value of a target specific symbol, if it is defined; For many
2391 targets this is `start', but PE and BeOS based systems for example
2392 check a list of possible entry symbols, matching the first one
2395 * the address of the first byte of the `.text' section, if present;
2400 File: ld.info, Node: File Commands, Next: Format Commands, Prev: Entry Point, Up: Simple Commands
2402 3.4.2 Commands Dealing with Files
2403 ---------------------------------
2405 Several linker script commands deal with files.
2408 Include the linker script FILENAME at this point. The file will
2409 be searched for in the current directory, and in any directory
2410 specified with the `-L' option. You can nest calls to `INCLUDE'
2411 up to 10 levels deep.
2413 You can place `INCLUDE' directives at the top level, in `MEMORY' or
2414 `SECTIONS' commands, or in output section descriptions.
2416 `INPUT(FILE, FILE, ...)'
2417 `INPUT(FILE FILE ...)'
2418 The `INPUT' command directs the linker to include the named files
2419 in the link, as though they were named on the command line.
2421 For example, if you always want to include `subr.o' any time you do
2422 a link, but you can't be bothered to put it on every link command
2423 line, then you can put `INPUT (subr.o)' in your linker script.
2425 In fact, if you like, you can list all of your input files in the
2426 linker script, and then invoke the linker with nothing but a `-T'
2429 In case a "sysroot prefix" is configured, and the filename starts
2430 with the `/' character, and the script being processed was located
2431 inside the "sysroot prefix", the filename will be looked for in
2432 the "sysroot prefix". Otherwise, the linker will try to open the
2433 file in the current directory. If it is not found, the linker
2434 will search through the archive library search path. See the
2435 description of `-L' in *Note Command Line Options: Options.
2437 If you use `INPUT (-lFILE)', `ld' will transform the name to
2438 `libFILE.a', as with the command line argument `-l'.
2440 When you use the `INPUT' command in an implicit linker script, the
2441 files will be included in the link at the point at which the linker
2442 script file is included. This can affect archive searching.
2444 `GROUP(FILE, FILE, ...)'
2445 `GROUP(FILE FILE ...)'
2446 The `GROUP' command is like `INPUT', except that the named files
2447 should all be archives, and they are searched repeatedly until no
2448 new undefined references are created. See the description of `-('
2449 in *Note Command Line Options: Options.
2451 `AS_NEEDED(FILE, FILE, ...)'
2452 `AS_NEEDED(FILE FILE ...)'
2453 This construct can appear only inside of the `INPUT' or `GROUP'
2454 commands, among other filenames. The files listed will be handled
2455 as if they appear directly in the `INPUT' or `GROUP' commands,
2456 with the exception of ELF shared libraries, that will be added only
2457 when they are actually needed. This construct essentially enables
2458 `--as-needed' option for all the files listed inside of it and
2459 restores previous `--as-needed' resp. `--no-as-needed' setting
2463 The `OUTPUT' command names the output file. Using
2464 `OUTPUT(FILENAME)' in the linker script is exactly like using `-o
2465 FILENAME' on the command line (*note Command Line Options:
2466 Options.). If both are used, the command line option takes
2469 You can use the `OUTPUT' command to define a default name for the
2470 output file other than the usual default of `a.out'.
2473 The `SEARCH_DIR' command adds PATH to the list of paths where `ld'
2474 looks for archive libraries. Using `SEARCH_DIR(PATH)' is exactly
2475 like using `-L PATH' on the command line (*note Command Line
2476 Options: Options.). If both are used, then the linker will search
2477 both paths. Paths specified using the command line option are
2481 The `STARTUP' command is just like the `INPUT' command, except
2482 that FILENAME will become the first input file to be linked, as
2483 though it were specified first on the command line. This may be
2484 useful when using a system in which the entry point is always the
2485 start of the first file.
2488 File: ld.info, Node: Format Commands, Next: REGION_ALIAS, Prev: File Commands, Up: Simple Commands
2490 3.4.3 Commands Dealing with Object File Formats
2491 -----------------------------------------------
2493 A couple of linker script commands deal with object file formats.
2495 `OUTPUT_FORMAT(BFDNAME)'
2496 `OUTPUT_FORMAT(DEFAULT, BIG, LITTLE)'
2497 The `OUTPUT_FORMAT' command names the BFD format to use for the
2498 output file (*note BFD::). Using `OUTPUT_FORMAT(BFDNAME)' is
2499 exactly like using `--oformat BFDNAME' on the command line (*note
2500 Command Line Options: Options.). If both are used, the command
2501 line option takes precedence.
2503 You can use `OUTPUT_FORMAT' with three arguments to use different
2504 formats based on the `-EB' and `-EL' command line options. This
2505 permits the linker script to set the output format based on the
2508 If neither `-EB' nor `-EL' are used, then the output format will
2509 be the first argument, DEFAULT. If `-EB' is used, the output
2510 format will be the second argument, BIG. If `-EL' is used, the
2511 output format will be the third argument, LITTLE.
2513 For example, the default linker script for the MIPS ELF target
2515 OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips)
2516 This says that the default format for the output file is
2517 `elf32-bigmips', but if the user uses the `-EL' command line
2518 option, the output file will be created in the `elf32-littlemips'
2522 The `TARGET' command names the BFD format to use when reading input
2523 files. It affects subsequent `INPUT' and `GROUP' commands. This
2524 command is like using `-b BFDNAME' on the command line (*note
2525 Command Line Options: Options.). If the `TARGET' command is used
2526 but `OUTPUT_FORMAT' is not, then the last `TARGET' command is also
2527 used to set the format for the output file. *Note BFD::.
2530 File: ld.info, Node: REGION_ALIAS, Next: Miscellaneous Commands, Prev: Format Commands, Up: Simple Commands
2532 3.4.4 Assign alias names to memory regions
2533 ------------------------------------------
2535 Alias names can be added to existing memory regions created with the
2536 *Note MEMORY:: command. Each name corresponds to at most one memory
2539 REGION_ALIAS(ALIAS, REGION)
2541 The `REGION_ALIAS' function creates an alias name ALIAS for the
2542 memory region REGION. This allows a flexible mapping of output sections
2543 to memory regions. An example follows.
2545 Suppose we have an application for embedded systems which come with
2546 various memory storage devices. All have a general purpose, volatile
2547 memory `RAM' that allows code execution or data storage. Some may have
2548 a read-only, non-volatile memory `ROM' that allows code execution and
2549 read-only data access. The last variant is a read-only, non-volatile
2550 memory `ROM2' with read-only data access and no code execution
2551 capability. We have four output sections:
2553 * `.text' program code;
2555 * `.rodata' read-only data;
2557 * `.data' read-write initialized data;
2559 * `.bss' read-write zero initialized data.
2561 The goal is to provide a linker command file that contains a system
2562 independent part defining the output sections and a system dependent
2563 part mapping the output sections to the memory regions available on the
2564 system. Our embedded systems come with three different memory setups
2566 Section Variant A Variant B Variant C
2568 .rodata RAM ROM ROM2
2569 .data RAM RAM/ROM RAM/ROM2
2571 The notation `RAM/ROM' or `RAM/ROM2' means that this section is
2572 loaded into region `ROM' or `ROM2' respectively. Please note that the
2573 load address of the `.data' section starts in all three variants at the
2574 end of the `.rodata' section.
2576 The base linker script that deals with the output sections follows.
2577 It includes the system dependent `linkcmds.memory' file that describes
2579 INCLUDE linkcmds.memory
2592 .data : AT (rodata_end)
2597 data_size = SIZEOF(.data);
2598 data_load_start = LOADADDR(.data);
2605 Now we need three different `linkcmds.memory' files to define memory
2606 regions and alias names. The content of `linkcmds.memory' for the three
2607 variants `A', `B' and `C':
2609 Here everything goes into the `RAM'.
2612 RAM : ORIGIN = 0, LENGTH = 4M
2615 REGION_ALIAS("REGION_TEXT", RAM);
2616 REGION_ALIAS("REGION_RODATA", RAM);
2617 REGION_ALIAS("REGION_DATA", RAM);
2618 REGION_ALIAS("REGION_BSS", RAM);
2621 Program code and read-only data go into the `ROM'. Read-write
2622 data goes into the `RAM'. An image of the initialized data is
2623 loaded into the `ROM' and will be copied during system start into
2627 ROM : ORIGIN = 0, LENGTH = 3M
2628 RAM : ORIGIN = 0x10000000, LENGTH = 1M
2631 REGION_ALIAS("REGION_TEXT", ROM);
2632 REGION_ALIAS("REGION_RODATA", ROM);
2633 REGION_ALIAS("REGION_DATA", RAM);
2634 REGION_ALIAS("REGION_BSS", RAM);
2637 Program code goes into the `ROM'. Read-only data goes into the
2638 `ROM2'. Read-write data goes into the `RAM'. An image of the
2639 initialized data is loaded into the `ROM2' and will be copied
2640 during system start into the `RAM'.
2643 ROM : ORIGIN = 0, LENGTH = 2M
2644 ROM2 : ORIGIN = 0x10000000, LENGTH = 1M
2645 RAM : ORIGIN = 0x20000000, LENGTH = 1M
2648 REGION_ALIAS("REGION_TEXT", ROM);
2649 REGION_ALIAS("REGION_RODATA", ROM2);
2650 REGION_ALIAS("REGION_DATA", RAM);
2651 REGION_ALIAS("REGION_BSS", RAM);
2653 It is possible to write a common system initialization routine to
2654 copy the `.data' section from `ROM' or `ROM2' into the `RAM' if
2658 extern char data_start [];
2659 extern char data_size [];
2660 extern char data_load_start [];
2662 void copy_data(void)
2664 if (data_start != data_load_start)
2666 memcpy(data_start, data_load_start, (size_t) data_size);
2671 File: ld.info, Node: Miscellaneous Commands, Prev: REGION_ALIAS, Up: Simple Commands
2673 3.4.5 Other Linker Script Commands
2674 ----------------------------------
2676 There are a few other linker scripts commands.
2678 `ASSERT(EXP, MESSAGE)'
2679 Ensure that EXP is non-zero. If it is zero, then exit the linker
2680 with an error code, and print MESSAGE.
2682 `EXTERN(SYMBOL SYMBOL ...)'
2683 Force SYMBOL to be entered in the output file as an undefined
2684 symbol. Doing this may, for example, trigger linking of additional
2685 modules from standard libraries. You may list several SYMBOLs for
2686 each `EXTERN', and you may use `EXTERN' multiple times. This
2687 command has the same effect as the `-u' command-line option.
2689 `FORCE_COMMON_ALLOCATION'
2690 This command has the same effect as the `-d' command-line option:
2691 to make `ld' assign space to common symbols even if a relocatable
2692 output file is specified (`-r').
2694 `INHIBIT_COMMON_ALLOCATION'
2695 This command has the same effect as the `--no-define-common'
2696 command-line option: to make `ld' omit the assignment of addresses
2697 to common symbols even for a non-relocatable output file.
2699 `INSERT [ AFTER | BEFORE ] OUTPUT_SECTION'
2700 This command is typically used in a script specified by `-T' to
2701 augment the default `SECTIONS' with, for example, overlays. It
2702 inserts all prior linker script statements after (or before)
2703 OUTPUT_SECTION, and also causes `-T' to not override the default
2704 linker script. The exact insertion point is as for orphan
2705 sections. *Note Location Counter::. The insertion happens after
2706 the linker has mapped input sections to output sections. Prior to
2707 the insertion, since `-T' scripts are parsed before the default
2708 linker script, statements in the `-T' script occur before the
2709 default linker script statements in the internal linker
2710 representation of the script. In particular, input section
2711 assignments will be made to `-T' output sections before those in
2712 the default script. Here is an example of how a `-T' script using
2713 `INSERT' might look:
2719 .ov1 { ov1*(.text) }
2720 .ov2 { ov2*(.text) }
2725 `NOCROSSREFS(SECTION SECTION ...)'
2726 This command may be used to tell `ld' to issue an error about any
2727 references among certain output sections.
2729 In certain types of programs, particularly on embedded systems when
2730 using overlays, when one section is loaded into memory, another
2731 section will not be. Any direct references between the two
2732 sections would be errors. For example, it would be an error if
2733 code in one section called a function defined in the other section.
2735 The `NOCROSSREFS' command takes a list of output section names. If
2736 `ld' detects any cross references between the sections, it reports
2737 an error and returns a non-zero exit status. Note that the
2738 `NOCROSSREFS' command uses output section names, not input section
2741 `OUTPUT_ARCH(BFDARCH)'
2742 Specify a particular output machine architecture. The argument is
2743 one of the names used by the BFD library (*note BFD::). You can
2744 see the architecture of an object file by using the `objdump'
2745 program with the `-f' option.
2747 `LD_FEATURE(STRING)'
2748 This command may be used to modify `ld' behavior. If STRING is
2749 `"SANE_EXPR"' then absolute symbols and numbers in a script are
2750 simply treated as numbers everywhere. *Note Expression Section::.
2753 File: ld.info, Node: Assignments, Next: SECTIONS, Prev: Simple Commands, Up: Scripts
2755 3.5 Assigning Values to Symbols
2756 ===============================
2758 You may assign a value to a symbol in a linker script. This will define
2759 the symbol and place it into the symbol table with a global scope.
2763 * Simple Assignments:: Simple Assignments
2766 * PROVIDE_HIDDEN:: PROVIDE_HIDDEN
2767 * Source Code Reference:: How to use a linker script defined symbol in source code
2770 File: ld.info, Node: Simple Assignments, Next: HIDDEN, Up: Assignments
2772 3.5.1 Simple Assignments
2773 ------------------------
2775 You may assign to a symbol using any of the C assignment operators:
2777 `SYMBOL = EXPRESSION ;'
2778 `SYMBOL += EXPRESSION ;'
2779 `SYMBOL -= EXPRESSION ;'
2780 `SYMBOL *= EXPRESSION ;'
2781 `SYMBOL /= EXPRESSION ;'
2782 `SYMBOL <<= EXPRESSION ;'
2783 `SYMBOL >>= EXPRESSION ;'
2784 `SYMBOL &= EXPRESSION ;'
2785 `SYMBOL |= EXPRESSION ;'
2787 The first case will define SYMBOL to the value of EXPRESSION. In
2788 the other cases, SYMBOL must already be defined, and the value will be
2789 adjusted accordingly.
2791 The special symbol name `.' indicates the location counter. You may
2792 only use this within a `SECTIONS' command. *Note Location Counter::.
2794 The semicolon after EXPRESSION is required.
2796 Expressions are defined below; see *Note Expressions::.
2798 You may write symbol assignments as commands in their own right, or
2799 as statements within a `SECTIONS' command, or as part of an output
2800 section description in a `SECTIONS' command.
2802 The section of the symbol will be set from the section of the
2803 expression; for more information, see *Note Expression Section::.
2805 Here is an example showing the three different places that symbol
2806 assignments may be used:
2816 _bdata = (. + 3) & ~ 3;
2817 .data : { *(.data) }
2819 In this example, the symbol `floating_point' will be defined as
2820 zero. The symbol `_etext' will be defined as the address following the
2821 last `.text' input section. The symbol `_bdata' will be defined as the
2822 address following the `.text' output section aligned upward to a 4 byte
2826 File: ld.info, Node: HIDDEN, Next: PROVIDE, Prev: Simple Assignments, Up: Assignments
2831 For ELF targeted ports, define a symbol that will be hidden and won't be
2832 exported. The syntax is `HIDDEN(SYMBOL = EXPRESSION)'.
2834 Here is the example from *Note Simple Assignments::, rewritten to use
2837 HIDDEN(floating_point = 0);
2845 HIDDEN(_bdata = (. + 3) & ~ 3);
2846 .data : { *(.data) }
2848 In this case none of the three symbols will be visible outside this
2852 File: ld.info, Node: PROVIDE, Next: PROVIDE_HIDDEN, Prev: HIDDEN, Up: Assignments
2857 In some cases, it is desirable for a linker script to define a symbol
2858 only if it is referenced and is not defined by any object included in
2859 the link. For example, traditional linkers defined the symbol `etext'.
2860 However, ANSI C requires that the user be able to use `etext' as a
2861 function name without encountering an error. The `PROVIDE' keyword may
2862 be used to define a symbol, such as `etext', only if it is referenced
2863 but not defined. The syntax is `PROVIDE(SYMBOL = EXPRESSION)'.
2865 Here is an example of using `PROVIDE' to define `etext':
2876 In this example, if the program defines `_etext' (with a leading
2877 underscore), the linker will give a multiple definition error. If, on
2878 the other hand, the program defines `etext' (with no leading
2879 underscore), the linker will silently use the definition in the program.
2880 If the program references `etext' but does not define it, the linker
2881 will use the definition in the linker script.
2884 File: ld.info, Node: PROVIDE_HIDDEN, Next: Source Code Reference, Prev: PROVIDE, Up: Assignments
2886 3.5.4 PROVIDE_HIDDEN
2887 --------------------
2889 Similar to `PROVIDE'. For ELF targeted ports, the symbol will be
2890 hidden and won't be exported.
2893 File: ld.info, Node: Source Code Reference, Prev: PROVIDE_HIDDEN, Up: Assignments
2895 3.5.5 Source Code Reference
2896 ---------------------------
2898 Accessing a linker script defined variable from source code is not
2899 intuitive. In particular a linker script symbol is not equivalent to a
2900 variable declaration in a high level language, it is instead a symbol
2901 that does not have a value.
2903 Before going further, it is important to note that compilers often
2904 transform names in the source code into different names when they are
2905 stored in the symbol table. For example, Fortran compilers commonly
2906 prepend or append an underscore, and C++ performs extensive `name
2907 mangling'. Therefore there might be a discrepancy between the name of
2908 a variable as it is used in source code and the name of the same
2909 variable as it is defined in a linker script. For example in C a
2910 linker script variable might be referred to as:
2914 But in the linker script it might be defined as:
2918 In the remaining examples however it is assumed that no name
2919 transformation has taken place.
2921 When a symbol is declared in a high level language such as C, two
2922 things happen. The first is that the compiler reserves enough space in
2923 the program's memory to hold the _value_ of the symbol. The second is
2924 that the compiler creates an entry in the program's symbol table which
2925 holds the symbol's _address_. ie the symbol table contains the address
2926 of the block of memory holding the symbol's value. So for example the
2927 following C declaration, at file scope:
2931 creates a entry called `foo' in the symbol table. This entry holds
2932 the address of an `int' sized block of memory where the number 1000 is
2935 When a program references a symbol the compiler generates code that
2936 first accesses the symbol table to find the address of the symbol's
2937 memory block and then code to read the value from that memory block.
2942 looks up the symbol `foo' in the symbol table, gets the address
2943 associated with this symbol and then writes the value 1 into that
2948 looks up the symbol `foo' in the symbol table, gets it address and
2949 then copies this address into the block of memory associated with the
2952 Linker scripts symbol declarations, by contrast, create an entry in
2953 the symbol table but do not assign any memory to them. Thus they are
2954 an address without a value. So for example the linker script
2959 creates an entry in the symbol table called `foo' which holds the
2960 address of memory location 1000, but nothing special is stored at
2961 address 1000. This means that you cannot access the _value_ of a
2962 linker script defined symbol - it has no value - all you can do is
2963 access the _address_ of a linker script defined symbol.
2965 Hence when you are using a linker script defined symbol in source
2966 code you should always take the address of the symbol, and never
2967 attempt to use its value. For example suppose you want to copy the
2968 contents of a section of memory called .ROM into a section called
2969 .FLASH and the linker script contains these declarations:
2971 start_of_ROM = .ROM;
2972 end_of_ROM = .ROM + sizeof (.ROM) - 1;
2973 start_of_FLASH = .FLASH;
2975 Then the C source code to perform the copy would be:
2977 extern char start_of_ROM, end_of_ROM, start_of_FLASH;
2979 memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);
2981 Note the use of the `&' operators. These are correct.
2984 File: ld.info, Node: SECTIONS, Next: MEMORY, Prev: Assignments, Up: Scripts
2986 3.6 SECTIONS Command
2987 ====================
2989 The `SECTIONS' command tells the linker how to map input sections into
2990 output sections, and how to place the output sections in memory.
2992 The format of the `SECTIONS' command is:
3000 Each SECTIONS-COMMAND may of be one of the following:
3002 * an `ENTRY' command (*note Entry command: Entry Point.)
3004 * a symbol assignment (*note Assignments::)
3006 * an output section description
3008 * an overlay description
3010 The `ENTRY' command and symbol assignments are permitted inside the
3011 `SECTIONS' command for convenience in using the location counter in
3012 those commands. This can also make the linker script easier to
3013 understand because you can use those commands at meaningful points in
3014 the layout of the output file.
3016 Output section descriptions and overlay descriptions are described
3019 If you do not use a `SECTIONS' command in your linker script, the
3020 linker will place each input section into an identically named output
3021 section in the order that the sections are first encountered in the
3022 input files. If all input sections are present in the first file, for
3023 example, the order of sections in the output file will match the order
3024 in the first input file. The first section will be at address zero.
3028 * Output Section Description:: Output section description
3029 * Output Section Name:: Output section name
3030 * Output Section Address:: Output section address
3031 * Input Section:: Input section description
3032 * Output Section Data:: Output section data
3033 * Output Section Keywords:: Output section keywords
3034 * Output Section Discarding:: Output section discarding
3035 * Output Section Attributes:: Output section attributes
3036 * Overlay Description:: Overlay description
3039 File: ld.info, Node: Output Section Description, Next: Output Section Name, Up: SECTIONS
3041 3.6.1 Output Section Description
3042 --------------------------------
3044 The full description of an output section looks like this:
3045 SECTION [ADDRESS] [(TYPE)] :
3047 [ALIGN(SECTION_ALIGN)]
3048 [SUBALIGN(SUBSECTION_ALIGN)]
3051 OUTPUT-SECTION-COMMAND
3052 OUTPUT-SECTION-COMMAND
3054 } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP]
3056 Most output sections do not use most of the optional section
3059 The whitespace around SECTION is required, so that the section name
3060 is unambiguous. The colon and the curly braces are also required. The
3061 line breaks and other white space are optional.
3063 Each OUTPUT-SECTION-COMMAND may be one of the following:
3065 * a symbol assignment (*note Assignments::)
3067 * an input section description (*note Input Section::)
3069 * data values to include directly (*note Output Section Data::)
3071 * a special output section keyword (*note Output Section Keywords::)
3074 File: ld.info, Node: Output Section Name, Next: Output Section Address, Prev: Output Section Description, Up: SECTIONS
3076 3.6.2 Output Section Name
3077 -------------------------
3079 The name of the output section is SECTION. SECTION must meet the
3080 constraints of your output format. In formats which only support a
3081 limited number of sections, such as `a.out', the name must be one of
3082 the names supported by the format (`a.out', for example, allows only
3083 `.text', `.data' or `.bss'). If the output format supports any number
3084 of sections, but with numbers and not names (as is the case for Oasys),
3085 the name should be supplied as a quoted numeric string. A section name
3086 may consist of any sequence of characters, but a name which contains
3087 any unusual characters such as commas must be quoted.
3089 The output section name `/DISCARD/' is special; *Note Output Section
3093 File: ld.info, Node: Output Section Address, Next: Input Section, Prev: Output Section Name, Up: SECTIONS
3095 3.6.3 Output Section Address
3096 ----------------------------
3098 The ADDRESS is an expression for the VMA (the virtual memory address)
3099 of the output section. This address is optional, but if it is provided
3100 then the output address will be set exactly as specified.
3102 If the output address is not specified then one will be chosen for
3103 the section, based on the heuristic below. This address will be
3104 adjusted to fit the alignment requirement of the output section. The
3105 alignment requirement is the strictest alignment of any input section
3106 contained within the output section.
3108 The output section address heuristic is as follows:
3110 * If an output memory REGION is set for the section then it is added
3111 to this region and its address will be the next free address in
3114 * If the MEMORY command has been used to create a list of memory
3115 regions then the first region which has attributes compatible with
3116 the section is selected to contain it. The section's output
3117 address will be the next free address in that region; *Note
3120 * If no memory regions were specified, or none match the section then
3121 the output address will be based on the current value of the
3126 .text . : { *(.text) }
3130 .text : { *(.text) }
3132 are subtly different. The first will set the address of the `.text'
3133 output section to the current value of the location counter. The
3134 second will set it to the current value of the location counter aligned
3135 to the strictest alignment of any of the `.text' input sections.
3137 The ADDRESS may be an arbitrary expression; *Note Expressions::.
3138 For example, if you want to align the section on a 0x10 byte boundary,
3139 so that the lowest four bits of the section address are zero, you could
3140 do something like this:
3141 .text ALIGN(0x10) : { *(.text) }
3142 This works because `ALIGN' returns the current location counter
3143 aligned upward to the specified value.
3145 Specifying ADDRESS for a section will change the value of the
3146 location counter, provided that the section is non-empty. (Empty
3147 sections are ignored).
3150 File: ld.info, Node: Input Section, Next: Output Section Data, Prev: Output Section Address, Up: SECTIONS
3152 3.6.4 Input Section Description
3153 -------------------------------
3155 The most common output section command is an input section description.
3157 The input section description is the most basic linker script
3158 operation. You use output sections to tell the linker how to lay out
3159 your program in memory. You use input section descriptions to tell the
3160 linker how to map the input files into your memory layout.
3164 * Input Section Basics:: Input section basics
3165 * Input Section Wildcards:: Input section wildcard patterns
3166 * Input Section Common:: Input section for common symbols
3167 * Input Section Keep:: Input section and garbage collection
3168 * Input Section Example:: Input section example
3171 File: ld.info, Node: Input Section Basics, Next: Input Section Wildcards, Up: Input Section
3173 3.6.4.1 Input Section Basics
3174 ............................
3176 An input section description consists of a file name optionally followed
3177 by a list of section names in parentheses.
3179 The file name and the section name may be wildcard patterns, which we
3180 describe further below (*note Input Section Wildcards::).
3182 The most common input section description is to include all input
3183 sections with a particular name in the output section. For example, to
3184 include all input `.text' sections, you would write:
3186 Here the `*' is a wildcard which matches any file name. To exclude
3187 a list of files from matching the file name wildcard, EXCLUDE_FILE may
3188 be used to match all files except the ones specified in the
3189 EXCLUDE_FILE list. For example:
3190 *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
3191 will cause all .ctors sections from all files except `crtend.o' and
3192 `otherfile.o' to be included.
3194 There are two ways to include more than one section:
3197 The difference between these is the order in which the `.text' and
3198 `.rdata' input sections will appear in the output section. In the
3199 first example, they will be intermingled, appearing in the same order as
3200 they are found in the linker input. In the second example, all `.text'
3201 input sections will appear first, followed by all `.rdata' input
3204 You can specify a file name to include sections from a particular
3205 file. You would do this if one or more of your files contain special
3206 data that needs to be at a particular location in memory. For example:
3209 To refine the sections that are included based on the section flags
3210 of an input section, INPUT_SECTION_FLAGS may be used.
3212 Here is a simple example for using Section header flags for ELF
3216 .text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) }
3217 .text2 : { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) }
3220 In this example, the output section `.text' will be comprised of any
3221 input section matching the name *(.text) whose section header flags
3222 `SHF_MERGE' and `SHF_STRINGS' are set. The output section `.text2'
3223 will be comprised of any input section matching the name *(.text) whose
3224 section header flag `SHF_WRITE' is clear.
3226 You can also specify files within archives by writing a pattern
3227 matching the archive, a colon, then the pattern matching the file, with
3228 no whitespace around the colon.
3231 matches file within archive
3234 matches the whole archive
3237 matches file but not one in an archive
3239 Either one or both of `archive' and `file' can contain shell
3240 wildcards. On DOS based file systems, the linker will assume that a
3241 single letter followed by a colon is a drive specifier, so `c:myfile.o'
3242 is a simple file specification, not `myfile.o' within an archive called
3243 `c'. `archive:file' filespecs may also be used within an
3244 `EXCLUDE_FILE' list, but may not appear in other linker script
3245 contexts. For instance, you cannot extract a file from an archive by
3246 using `archive:file' in an `INPUT' command.
3248 If you use a file name without a list of sections, then all sections
3249 in the input file will be included in the output section. This is not
3250 commonly done, but it may by useful on occasion. For example:
3253 When you use a file name which is not an `archive:file' specifier
3254 and does not contain any wild card characters, the linker will first
3255 see if you also specified the file name on the linker command line or
3256 in an `INPUT' command. If you did not, the linker will attempt to open
3257 the file as an input file, as though it appeared on the command line.
3258 Note that this differs from an `INPUT' command, because the linker will
3259 not search for the file in the archive search path.
3262 File: ld.info, Node: Input Section Wildcards, Next: Input Section Common, Prev: Input Section Basics, Up: Input Section
3264 3.6.4.2 Input Section Wildcard Patterns
3265 .......................................
3267 In an input section description, either the file name or the section
3268 name or both may be wildcard patterns.
3270 The file name of `*' seen in many examples is a simple wildcard
3271 pattern for the file name.
3273 The wildcard patterns are like those used by the Unix shell.
3276 matches any number of characters
3279 matches any single character
3282 matches a single instance of any of the CHARS; the `-' character
3283 may be used to specify a range of characters, as in `[a-z]' to
3284 match any lower case letter
3287 quotes the following character
3289 When a file name is matched with a wildcard, the wildcard characters
3290 will not match a `/' character (used to separate directory names on
3291 Unix). A pattern consisting of a single `*' character is an exception;
3292 it will always match any file name, whether it contains a `/' or not.
3293 In a section name, the wildcard characters will match a `/' character.
3295 File name wildcard patterns only match files which are explicitly
3296 specified on the command line or in an `INPUT' command. The linker
3297 does not search directories to expand wildcards.
3299 If a file name matches more than one wildcard pattern, or if a file
3300 name appears explicitly and is also matched by a wildcard pattern, the
3301 linker will use the first match in the linker script. For example, this
3302 sequence of input section descriptions is probably in error, because the
3303 `data.o' rule will not be used:
3304 .data : { *(.data) }
3305 .data1 : { data.o(.data) }
3307 Normally, the linker will place files and sections matched by
3308 wildcards in the order in which they are seen during the link. You can
3309 change this by using the `SORT_BY_NAME' keyword, which appears before a
3310 wildcard pattern in parentheses (e.g., `SORT_BY_NAME(.text*)'). When
3311 the `SORT_BY_NAME' keyword is used, the linker will sort the files or
3312 sections into ascending order by name before placing them in the output
3315 `SORT_BY_ALIGNMENT' is very similar to `SORT_BY_NAME'. The
3316 difference is `SORT_BY_ALIGNMENT' will sort sections into ascending
3317 order by alignment before placing them in the output file.
3319 `SORT_BY_INIT_PRIORITY' is very similar to `SORT_BY_NAME'. The
3320 difference is `SORT_BY_INIT_PRIORITY' will sort sections into ascending
3321 order by numerical value of the GCC init_priority attribute encoded in
3322 the section name before placing them in the output file.
3324 `SORT' is an alias for `SORT_BY_NAME'.
3326 When there are nested section sorting commands in linker script,
3327 there can be at most 1 level of nesting for section sorting commands.
3329 1. `SORT_BY_NAME' (`SORT_BY_ALIGNMENT' (wildcard section pattern)).
3330 It will sort the input sections by name first, then by alignment
3331 if 2 sections have the same name.
3333 2. `SORT_BY_ALIGNMENT' (`SORT_BY_NAME' (wildcard section pattern)).
3334 It will sort the input sections by alignment first, then by name
3335 if 2 sections have the same alignment.
3337 3. `SORT_BY_NAME' (`SORT_BY_NAME' (wildcard section pattern)) is
3338 treated the same as `SORT_BY_NAME' (wildcard section pattern).
3340 4. `SORT_BY_ALIGNMENT' (`SORT_BY_ALIGNMENT' (wildcard section
3341 pattern)) is treated the same as `SORT_BY_ALIGNMENT' (wildcard
3344 5. All other nested section sorting commands are invalid.
3346 When both command line section sorting option and linker script
3347 section sorting command are used, section sorting command always takes
3348 precedence over the command line option.
3350 If the section sorting command in linker script isn't nested, the
3351 command line option will make the section sorting command to be treated
3352 as nested sorting command.
3354 1. `SORT_BY_NAME' (wildcard section pattern ) with `--sort-sections
3355 alignment' is equivalent to `SORT_BY_NAME' (`SORT_BY_ALIGNMENT'
3356 (wildcard section pattern)).
3358 2. `SORT_BY_ALIGNMENT' (wildcard section pattern) with
3359 `--sort-section name' is equivalent to `SORT_BY_ALIGNMENT'
3360 (`SORT_BY_NAME' (wildcard section pattern)).
3362 If the section sorting command in linker script is nested, the
3363 command line option will be ignored.
3365 `SORT_NONE' disables section sorting by ignoring the command line
3366 section sorting option.
3368 If you ever get confused about where input sections are going, use
3369 the `-M' linker option to generate a map file. The map file shows
3370 precisely how input sections are mapped to output sections.
3372 This example shows how wildcard patterns might be used to partition
3373 files. This linker script directs the linker to place all `.text'
3374 sections in `.text' and all `.bss' sections in `.bss'. The linker will
3375 place the `.data' section from all files beginning with an upper case
3376 character in `.DATA'; for all other files, the linker will place the
3377 `.data' section in `.data'.
3379 .text : { *(.text) }
3380 .DATA : { [A-Z]*(.data) }
3381 .data : { *(.data) }
3386 File: ld.info, Node: Input Section Common, Next: Input Section Keep, Prev: Input Section Wildcards, Up: Input Section
3388 3.6.4.3 Input Section for Common Symbols
3389 ........................................
3391 A special notation is needed for common symbols, because in many object
3392 file formats common symbols do not have a particular input section. The
3393 linker treats common symbols as though they are in an input section
3396 You may use file names with the `COMMON' section just as with any
3397 other input sections. You can use this to place common symbols from a
3398 particular input file in one section while common symbols from other
3399 input files are placed in another section.
3401 In most cases, common symbols in input files will be placed in the
3402 `.bss' section in the output file. For example:
3403 .bss { *(.bss) *(COMMON) }
3405 Some object file formats have more than one type of common symbol.
3406 For example, the MIPS ELF object file format distinguishes standard
3407 common symbols and small common symbols. In this case, the linker will
3408 use a different special section name for other types of common symbols.
3409 In the case of MIPS ELF, the linker uses `COMMON' for standard common
3410 symbols and `.scommon' for small common symbols. This permits you to
3411 map the different types of common symbols into memory at different
3414 You will sometimes see `[COMMON]' in old linker scripts. This
3415 notation is now considered obsolete. It is equivalent to `*(COMMON)'.
3418 File: ld.info, Node: Input Section Keep, Next: Input Section Example, Prev: Input Section Common, Up: Input Section
3420 3.6.4.4 Input Section and Garbage Collection
3421 ............................................
3423 When link-time garbage collection is in use (`--gc-sections'), it is
3424 often useful to mark sections that should not be eliminated. This is
3425 accomplished by surrounding an input section's wildcard entry with
3426 `KEEP()', as in `KEEP(*(.init))' or `KEEP(SORT_BY_NAME(*)(.ctors))'.
3429 File: ld.info, Node: Input Section Example, Prev: Input Section Keep, Up: Input Section
3431 3.6.4.5 Input Section Example
3432 .............................
3434 The following example is a complete linker script. It tells the linker
3435 to read all of the sections from file `all.o' and place them at the
3436 start of output section `outputa' which starts at location `0x10000'.
3437 All of section `.input1' from file `foo.o' follows immediately, in the
3438 same output section. All of section `.input2' from `foo.o' goes into
3439 output section `outputb', followed by section `.input1' from `foo1.o'.
3440 All of the remaining `.input1' and `.input2' sections from any files
3441 are written to output section `outputc'.
3462 File: ld.info, Node: Output Section Data, Next: Output Section Keywords, Prev: Input Section, Up: SECTIONS
3464 3.6.5 Output Section Data
3465 -------------------------
3467 You can include explicit bytes of data in an output section by using
3468 `BYTE', `SHORT', `LONG', `QUAD', or `SQUAD' as an output section
3469 command. Each keyword is followed by an expression in parentheses
3470 providing the value to store (*note Expressions::). The value of the
3471 expression is stored at the current value of the location counter.
3473 The `BYTE', `SHORT', `LONG', and `QUAD' commands store one, two,
3474 four, and eight bytes (respectively). After storing the bytes, the
3475 location counter is incremented by the number of bytes stored.
3477 For example, this will store the byte 1 followed by the four byte
3478 value of the symbol `addr':
3482 When using a 64 bit host or target, `QUAD' and `SQUAD' are the same;
3483 they both store an 8 byte, or 64 bit, value. When both host and target
3484 are 32 bits, an expression is computed as 32 bits. In this case `QUAD'
3485 stores a 32 bit value zero extended to 64 bits, and `SQUAD' stores a 32
3486 bit value sign extended to 64 bits.
3488 If the object file format of the output file has an explicit
3489 endianness, which is the normal case, the value will be stored in that
3490 endianness. When the object file format does not have an explicit
3491 endianness, as is true of, for example, S-records, the value will be
3492 stored in the endianness of the first input object file.
3494 Note--these commands only work inside a section description and not
3495 between them, so the following will produce an error from the linker:
3496 SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } }
3497 whereas this will work:
3498 SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } }
3500 You may use the `FILL' command to set the fill pattern for the
3501 current section. It is followed by an expression in parentheses. Any
3502 otherwise unspecified regions of memory within the section (for example,
3503 gaps left due to the required alignment of input sections) are filled
3504 with the value of the expression, repeated as necessary. A `FILL'
3505 statement covers memory locations after the point at which it occurs in
3506 the section definition; by including more than one `FILL' statement,
3507 you can have different fill patterns in different parts of an output
3510 This example shows how to fill unspecified regions of memory with the
3514 The `FILL' command is similar to the `=FILLEXP' output section
3515 attribute, but it only affects the part of the section following the
3516 `FILL' command, rather than the entire section. If both are used, the
3517 `FILL' command takes precedence. *Note Output Section Fill::, for
3518 details on the fill expression.
3521 File: ld.info, Node: Output Section Keywords, Next: Output Section Discarding, Prev: Output Section Data, Up: SECTIONS
3523 3.6.6 Output Section Keywords
3524 -----------------------------
3526 There are a couple of keywords which can appear as output section
3529 `CREATE_OBJECT_SYMBOLS'
3530 The command tells the linker to create a symbol for each input
3531 file. The name of each symbol will be the name of the
3532 corresponding input file. The section of each symbol will be the
3533 output section in which the `CREATE_OBJECT_SYMBOLS' command
3536 This is conventional for the a.out object file format. It is not
3537 normally used for any other object file format.
3540 When linking using the a.out object file format, the linker uses an
3541 unusual set construct to support C++ global constructors and
3542 destructors. When linking object file formats which do not support
3543 arbitrary sections, such as ECOFF and XCOFF, the linker will
3544 automatically recognize C++ global constructors and destructors by
3545 name. For these object file formats, the `CONSTRUCTORS' command
3546 tells the linker to place constructor information in the output
3547 section where the `CONSTRUCTORS' command appears. The
3548 `CONSTRUCTORS' command is ignored for other object file formats.
3550 The symbol `__CTOR_LIST__' marks the start of the global
3551 constructors, and the symbol `__CTOR_END__' marks the end.
3552 Similarly, `__DTOR_LIST__' and `__DTOR_END__' mark the start and
3553 end of the global destructors. The first word in the list is the
3554 number of entries, followed by the address of each constructor or
3555 destructor, followed by a zero word. The compiler must arrange to
3556 actually run the code. For these object file formats GNU C++
3557 normally calls constructors from a subroutine `__main'; a call to
3558 `__main' is automatically inserted into the startup code for
3559 `main'. GNU C++ normally runs destructors either by using
3560 `atexit', or directly from the function `exit'.
3562 For object file formats such as `COFF' or `ELF' which support
3563 arbitrary section names, GNU C++ will normally arrange to put the
3564 addresses of global constructors and destructors into the `.ctors'
3565 and `.dtors' sections. Placing the following sequence into your
3566 linker script will build the sort of table which the GNU C++
3567 runtime code expects to see.
3570 LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
3575 LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
3580 If you are using the GNU C++ support for initialization priority,
3581 which provides some control over the order in which global
3582 constructors are run, you must sort the constructors at link time
3583 to ensure that they are executed in the correct order. When using
3584 the `CONSTRUCTORS' command, use `SORT_BY_NAME(CONSTRUCTORS)'
3585 instead. When using the `.ctors' and `.dtors' sections, use
3586 `*(SORT_BY_NAME(.ctors))' and `*(SORT_BY_NAME(.dtors))' instead of
3587 just `*(.ctors)' and `*(.dtors)'.
3589 Normally the compiler and linker will handle these issues
3590 automatically, and you will not need to concern yourself with
3591 them. However, you may need to consider this if you are using C++
3592 and writing your own linker scripts.
3596 File: ld.info, Node: Output Section Discarding, Next: Output Section Attributes, Prev: Output Section Keywords, Up: SECTIONS
3598 3.6.7 Output Section Discarding
3599 -------------------------------
3601 The linker will not create output sections with no contents. This is
3602 for convenience when referring to input sections that may or may not be
3603 present in any of the input files. For example:
3605 will only create a `.foo' section in the output file if there is a
3606 `.foo' section in at least one input file, and if the input sections
3607 are not all empty. Other link script directives that allocate space in
3608 an output section will also create the output section.
3610 The linker will ignore address assignments (*note Output Section
3611 Address::) on discarded output sections, except when the linker script
3612 defines symbols in the output section. In that case the linker will
3613 obey the address assignments, possibly advancing dot even though the
3614 section is discarded.
3616 The special output section name `/DISCARD/' may be used to discard
3617 input sections. Any input sections which are assigned to an output
3618 section named `/DISCARD/' are not included in the output file.
3621 File: ld.info, Node: Output Section Attributes, Next: Overlay Description, Prev: Output Section Discarding, Up: SECTIONS
3623 3.6.8 Output Section Attributes
3624 -------------------------------
3626 We showed above that the full description of an output section looked
3629 SECTION [ADDRESS] [(TYPE)] :
3631 [ALIGN(SECTION_ALIGN)]
3632 [SUBALIGN(SUBSECTION_ALIGN)]
3635 OUTPUT-SECTION-COMMAND
3636 OUTPUT-SECTION-COMMAND
3638 } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP]
3640 We've already described SECTION, ADDRESS, and
3641 OUTPUT-SECTION-COMMAND. In this section we will describe the remaining
3646 * Output Section Type:: Output section type
3647 * Output Section LMA:: Output section LMA
3648 * Forced Output Alignment:: Forced Output Alignment
3649 * Forced Input Alignment:: Forced Input Alignment
3650 * Output Section Constraint:: Output section constraint
3651 * Output Section Region:: Output section region
3652 * Output Section Phdr:: Output section phdr
3653 * Output Section Fill:: Output section fill
3656 File: ld.info, Node: Output Section Type, Next: Output Section LMA, Up: Output Section Attributes
3658 3.6.8.1 Output Section Type
3659 ...........................
3661 Each output section may have a type. The type is a keyword in
3662 parentheses. The following types are defined:
3665 The section should be marked as not loadable, so that it will not
3666 be loaded into memory when the program is run.
3672 These type names are supported for backward compatibility, and are
3673 rarely used. They all have the same effect: the section should be
3674 marked as not allocatable, so that no memory is allocated for the
3675 section when the program is run.
3677 The linker normally sets the attributes of an output section based on
3678 the input sections which map into it. You can override this by using
3679 the section type. For example, in the script sample below, the `ROM'
3680 section is addressed at memory location `0' and does not need to be
3681 loaded when the program is run.
3683 ROM 0 (NOLOAD) : { ... }
3688 File: ld.info, Node: Output Section LMA, Next: Forced Output Alignment, Prev: Output Section Type, Up: Output Section Attributes
3690 3.6.8.2 Output Section LMA
3691 ..........................
3693 Every section has a virtual address (VMA) and a load address (LMA); see
3694 *Note Basic Script Concepts::. The virtual address is specified by the
3695 *note Output Section Address:: described earlier. The load address is
3696 specified by the `AT' or `AT>' keywords. Specifying a load address is
3699 The `AT' keyword takes an expression as an argument. This specifies
3700 the exact load address of the section. The `AT>' keyword takes the
3701 name of a memory region as an argument. *Note MEMORY::. The load
3702 address of the section is set to the next free address in the region,
3703 aligned to the section's alignment requirements.
3705 If neither `AT' nor `AT>' is specified for an allocatable section,
3706 the linker will use the following heuristic to determine the load
3709 * If the section has a specific VMA address, then this is used as
3710 the LMA address as well.
3712 * If the section is not allocatable then its LMA is set to its VMA.
3714 * Otherwise if a memory region can be found that is compatible with
3715 the current section, and this region contains at least one
3716 section, then the LMA is set so the difference between the VMA and
3717 LMA is the same as the difference between the VMA and LMA of the
3718 last section in the located region.
3720 * If no memory regions have been declared then a default region that
3721 covers the entire address space is used in the previous step.
3723 * If no suitable region could be found, or there was no previous
3724 section then the LMA is set equal to the VMA.
3726 This feature is designed to make it easy to build a ROM image. For
3727 example, the following linker script creates three output sections: one
3728 called `.text', which starts at `0x1000', one called `.mdata', which is
3729 loaded at the end of the `.text' section even though its VMA is
3730 `0x2000', and one called `.bss' to hold uninitialized data at address
3731 `0x3000'. The symbol `_data' is defined with the value `0x2000', which
3732 shows that the location counter holds the VMA value, not the LMA value.
3736 .text 0x1000 : { *(.text) _etext = . ; }
3738 AT ( ADDR (.text) + SIZEOF (.text) )
3739 { _data = . ; *(.data); _edata = . ; }
3741 { _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;}
3744 The run-time initialization code for use with a program generated
3745 with this linker script would include something like the following, to
3746 copy the initialized data from the ROM image to its runtime address.
3747 Notice how this code takes advantage of the symbols defined by the
3750 extern char _etext, _data, _edata, _bstart, _bend;
3751 char *src = &_etext;
3754 /* ROM has data at end of text; copy it. */
3755 while (dst < &_edata)
3759 for (dst = &_bstart; dst< &_bend; dst++)
3763 File: ld.info, Node: Forced Output Alignment, Next: Forced Input Alignment, Prev: Output Section LMA, Up: Output Section Attributes
3765 3.6.8.3 Forced Output Alignment
3766 ...............................
3768 You can increase an output section's alignment by using ALIGN.
3771 File: ld.info, Node: Forced Input Alignment, Next: Output Section Constraint, Prev: Forced Output Alignment, Up: Output Section Attributes
3773 3.6.8.4 Forced Input Alignment
3774 ..............................
3776 You can force input section alignment within an output section by using
3777 SUBALIGN. The value specified overrides any alignment given by input
3778 sections, whether larger or smaller.
3781 File: ld.info, Node: Output Section Constraint, Next: Output Section Region, Prev: Forced Input Alignment, Up: Output Section Attributes
3783 3.6.8.5 Output Section Constraint
3784 .................................
3786 You can specify that an output section should only be created if all of
3787 its input sections are read-only or all of its input sections are
3788 read-write by using the keyword `ONLY_IF_RO' and `ONLY_IF_RW'
3792 File: ld.info, Node: Output Section Region, Next: Output Section Phdr, Prev: Output Section Constraint, Up: Output Section Attributes
3794 3.6.8.6 Output Section Region
3795 .............................
3797 You can assign a section to a previously defined region of memory by
3798 using `>REGION'. *Note MEMORY::.
3800 Here is a simple example:
3801 MEMORY { rom : ORIGIN = 0x1000, LENGTH = 0x1000 }
3802 SECTIONS { ROM : { *(.text) } >rom }
3805 File: ld.info, Node: Output Section Phdr, Next: Output Section Fill, Prev: Output Section Region, Up: Output Section Attributes
3807 3.6.8.7 Output Section Phdr
3808 ...........................
3810 You can assign a section to a previously defined program segment by
3811 using `:PHDR'. *Note PHDRS::. If a section is assigned to one or more
3812 segments, then all subsequent allocated sections will be assigned to
3813 those segments as well, unless they use an explicitly `:PHDR' modifier.
3814 You can use `:NONE' to tell the linker to not put the section in any
3817 Here is a simple example:
3818 PHDRS { text PT_LOAD ; }
3819 SECTIONS { .text : { *(.text) } :text }
3822 File: ld.info, Node: Output Section Fill, Prev: Output Section Phdr, Up: Output Section Attributes
3824 3.6.8.8 Output Section Fill
3825 ...........................
3827 You can set the fill pattern for an entire section by using `=FILLEXP'.
3828 FILLEXP is an expression (*note Expressions::). Any otherwise
3829 unspecified regions of memory within the output section (for example,
3830 gaps left due to the required alignment of input sections) will be
3831 filled with the value, repeated as necessary. If the fill expression
3832 is a simple hex number, ie. a string of hex digit starting with `0x'
3833 and without a trailing `k' or `M', then an arbitrarily long sequence of
3834 hex digits can be used to specify the fill pattern; Leading zeros
3835 become part of the pattern too. For all other cases, including extra
3836 parentheses or a unary `+', the fill pattern is the four least
3837 significant bytes of the value of the expression. In all cases, the
3838 number is big-endian.
3840 You can also change the fill value with a `FILL' command in the
3841 output section commands; (*note Output Section Data::).
3843 Here is a simple example:
3844 SECTIONS { .text : { *(.text) } =0x90909090 }
3847 File: ld.info, Node: Overlay Description, Prev: Output Section Attributes, Up: SECTIONS
3849 3.6.9 Overlay Description
3850 -------------------------
3852 An overlay description provides an easy way to describe sections which
3853 are to be loaded as part of a single memory image but are to be run at
3854 the same memory address. At run time, some sort of overlay manager will
3855 copy the overlaid sections in and out of the runtime memory address as
3856 required, perhaps by simply manipulating addressing bits. This approach
3857 can be useful, for example, when a certain region of memory is faster
3860 Overlays are described using the `OVERLAY' command. The `OVERLAY'
3861 command is used within a `SECTIONS' command, like an output section
3862 description. The full syntax of the `OVERLAY' command is as follows:
3863 OVERLAY [START] : [NOCROSSREFS] [AT ( LDADDR )]
3867 OUTPUT-SECTION-COMMAND
3868 OUTPUT-SECTION-COMMAND
3870 } [:PHDR...] [=FILL]
3873 OUTPUT-SECTION-COMMAND
3874 OUTPUT-SECTION-COMMAND
3876 } [:PHDR...] [=FILL]
3878 } [>REGION] [:PHDR...] [=FILL]
3880 Everything is optional except `OVERLAY' (a keyword), and each
3881 section must have a name (SECNAME1 and SECNAME2 above). The section
3882 definitions within the `OVERLAY' construct are identical to those
3883 within the general `SECTIONS' contruct (*note SECTIONS::), except that
3884 no addresses and no memory regions may be defined for sections within
3887 The sections are all defined with the same starting address. The
3888 load addresses of the sections are arranged such that they are
3889 consecutive in memory starting at the load address used for the
3890 `OVERLAY' as a whole (as with normal section definitions, the load
3891 address is optional, and defaults to the start address; the start
3892 address is also optional, and defaults to the current value of the
3895 If the `NOCROSSREFS' keyword is used, and there any references among
3896 the sections, the linker will report an error. Since the sections all
3897 run at the same address, it normally does not make sense for one
3898 section to refer directly to another. *Note NOCROSSREFS: Miscellaneous
3901 For each section within the `OVERLAY', the linker automatically
3902 provides two symbols. The symbol `__load_start_SECNAME' is defined as
3903 the starting load address of the section. The symbol
3904 `__load_stop_SECNAME' is defined as the final load address of the
3905 section. Any characters within SECNAME which are not legal within C
3906 identifiers are removed. C (or assembler) code may use these symbols
3907 to move the overlaid sections around as necessary.
3909 At the end of the overlay, the value of the location counter is set
3910 to the start address of the overlay plus the size of the largest
3913 Here is an example. Remember that this would appear inside a
3914 `SECTIONS' construct.
3915 OVERLAY 0x1000 : AT (0x4000)
3917 .text0 { o1/*.o(.text) }
3918 .text1 { o2/*.o(.text) }
3920 This will define both `.text0' and `.text1' to start at address
3921 0x1000. `.text0' will be loaded at address 0x4000, and `.text1' will
3922 be loaded immediately after `.text0'. The following symbols will be
3923 defined if referenced: `__load_start_text0', `__load_stop_text0',
3924 `__load_start_text1', `__load_stop_text1'.
3926 C code to copy overlay `.text1' into the overlay area might look
3929 extern char __load_start_text1, __load_stop_text1;
3930 memcpy ((char *) 0x1000, &__load_start_text1,
3931 &__load_stop_text1 - &__load_start_text1);
3933 Note that the `OVERLAY' command is just syntactic sugar, since
3934 everything it does can be done using the more basic commands. The above
3935 example could have been written identically as follows.
3937 .text0 0x1000 : AT (0x4000) { o1/*.o(.text) }
3938 PROVIDE (__load_start_text0 = LOADADDR (.text0));
3939 PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
3940 .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) { o2/*.o(.text) }
3941 PROVIDE (__load_start_text1 = LOADADDR (.text1));
3942 PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
3943 . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
3946 File: ld.info, Node: MEMORY, Next: PHDRS, Prev: SECTIONS, Up: Scripts
3951 The linker's default configuration permits allocation of all available
3952 memory. You can override this by using the `MEMORY' command.
3954 The `MEMORY' command describes the location and size of blocks of
3955 memory in the target. You can use it to describe which memory regions
3956 may be used by the linker, and which memory regions it must avoid. You
3957 can then assign sections to particular memory regions. The linker will
3958 set section addresses based on the memory regions, and will warn about
3959 regions that become too full. The linker will not shuffle sections
3960 around to fit into the available regions.
3962 A linker script may contain at most one use of the `MEMORY' command.
3963 However, you can define as many blocks of memory within it as you
3964 wish. The syntax is:
3967 NAME [(ATTR)] : ORIGIN = ORIGIN, LENGTH = LEN
3971 The NAME is a name used in the linker script to refer to the region.
3972 The region name has no meaning outside of the linker script. Region
3973 names are stored in a separate name space, and will not conflict with
3974 symbol names, file names, or section names. Each memory region must
3975 have a distinct name within the `MEMORY' command. However you can add
3976 later alias names to existing memory regions with the *Note
3977 REGION_ALIAS:: command.
3979 The ATTR string is an optional list of attributes that specify
3980 whether to use a particular memory region for an input section which is
3981 not explicitly mapped in the linker script. As described in *Note
3982 SECTIONS::, if you do not specify an output section for some input
3983 section, the linker will create an output section with the same name as
3984 the input section. If you define region attributes, the linker will use
3985 them to select the memory region for the output section that it creates.
3987 The ATTR string must consist only of the following characters:
4007 Invert the sense of any of the attributes that follow
4009 If a unmapped section matches any of the listed attributes other than
4010 `!', it will be placed in the memory region. The `!' attribute
4011 reverses this test, so that an unmapped section will be placed in the
4012 memory region only if it does not match any of the listed attributes.
4014 The ORIGIN is an numerical expression for the start address of the
4015 memory region. The expression must evaluate to a constant and it
4016 cannot involve any symbols. The keyword `ORIGIN' may be abbreviated to
4017 `org' or `o' (but not, for example, `ORG').
4019 The LEN is an expression for the size in bytes of the memory region.
4020 As with the ORIGIN expression, the expression must be numerical only
4021 and must evaluate to a constant. The keyword `LENGTH' may be
4022 abbreviated to `len' or `l'.
4024 In the following example, we specify that there are two memory
4025 regions available for allocation: one starting at `0' for 256 kilobytes,
4026 and the other starting at `0x40000000' for four megabytes. The linker
4027 will place into the `rom' memory region every section which is not
4028 explicitly mapped into a memory region, and is either read-only or
4029 executable. The linker will place other sections which are not
4030 explicitly mapped into a memory region into the `ram' memory region.
4034 rom (rx) : ORIGIN = 0, LENGTH = 256K
4035 ram (!rx) : org = 0x40000000, l = 4M
4038 Once you define a memory region, you can direct the linker to place
4039 specific output sections into that memory region by using the `>REGION'
4040 output section attribute. For example, if you have a memory region
4041 named `mem', you would use `>mem' in the output section definition.
4042 *Note Output Section Region::. If no address was specified for the
4043 output section, the linker will set the address to the next available
4044 address within the memory region. If the combined output sections
4045 directed to a memory region are too large for the region, the linker
4046 will issue an error message.
4048 It is possible to access the origin and length of a memory in an
4049 expression via the `ORIGIN(MEMORY)' and `LENGTH(MEMORY)' functions:
4051 _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
4054 File: ld.info, Node: PHDRS, Next: VERSION, Prev: MEMORY, Up: Scripts
4059 The ELF object file format uses "program headers", also knows as
4060 "segments". The program headers describe how the program should be
4061 loaded into memory. You can print them out by using the `objdump'
4062 program with the `-p' option.
4064 When you run an ELF program on a native ELF system, the system loader
4065 reads the program headers in order to figure out how to load the
4066 program. This will only work if the program headers are set correctly.
4067 This manual does not describe the details of how the system loader
4068 interprets program headers; for more information, see the ELF ABI.
4070 The linker will create reasonable program headers by default.
4071 However, in some cases, you may need to specify the program headers more
4072 precisely. You may use the `PHDRS' command for this purpose. When the
4073 linker sees the `PHDRS' command in the linker script, it will not
4074 create any program headers other than the ones specified.
4076 The linker only pays attention to the `PHDRS' command when
4077 generating an ELF output file. In other cases, the linker will simply
4080 This is the syntax of the `PHDRS' command. The words `PHDRS',
4081 `FILEHDR', `AT', and `FLAGS' are keywords.
4085 NAME TYPE [ FILEHDR ] [ PHDRS ] [ AT ( ADDRESS ) ]
4086 [ FLAGS ( FLAGS ) ] ;
4089 The NAME is used only for reference in the `SECTIONS' command of the
4090 linker script. It is not put into the output file. Program header
4091 names are stored in a separate name space, and will not conflict with
4092 symbol names, file names, or section names. Each program header must
4093 have a distinct name. The headers are processed in order and it is
4094 usual for them to map to sections in ascending load address order.
4096 Certain program header types describe segments of memory which the
4097 system loader will load from the file. In the linker script, you
4098 specify the contents of these segments by placing allocatable output
4099 sections in the segments. You use the `:PHDR' output section attribute
4100 to place a section in a particular segment. *Note Output Section
4103 It is normal to put certain sections in more than one segment. This
4104 merely implies that one segment of memory contains another. You may
4105 repeat `:PHDR', using it once for each segment which should contain the
4108 If you place a section in one or more segments using `:PHDR', then
4109 the linker will place all subsequent allocatable sections which do not
4110 specify `:PHDR' in the same segments. This is for convenience, since
4111 generally a whole set of contiguous sections will be placed in a single
4112 segment. You can use `:NONE' to override the default segment and tell
4113 the linker to not put the section in any segment at all.
4115 You may use the `FILEHDR' and `PHDRS' keywords after the program
4116 header type to further describe the contents of the segment. The
4117 `FILEHDR' keyword means that the segment should include the ELF file
4118 header. The `PHDRS' keyword means that the segment should include the
4119 ELF program headers themselves. If applied to a loadable segment
4120 (`PT_LOAD'), all prior loadable segments must have one of these
4123 The TYPE may be one of the following. The numbers indicate the
4124 value of the keyword.
4127 Indicates an unused program header.
4130 Indicates that this program header describes a segment to be
4131 loaded from the file.
4134 Indicates a segment where dynamic linking information can be found.
4137 Indicates a segment where the name of the program interpreter may
4141 Indicates a segment holding note information.
4144 A reserved program header type, defined but not specified by the
4148 Indicates a segment where the program headers may be found.
4151 An expression giving the numeric type of the program header. This
4152 may be used for types not defined above.
4154 You can specify that a segment should be loaded at a particular
4155 address in memory by using an `AT' expression. This is identical to the
4156 `AT' command used as an output section attribute (*note Output Section
4157 LMA::). The `AT' command for a program header overrides the output
4160 The linker will normally set the segment flags based on the sections
4161 which comprise the segment. You may use the `FLAGS' keyword to
4162 explicitly specify the segment flags. The value of FLAGS must be an
4163 integer. It is used to set the `p_flags' field of the program header.
4165 Here is an example of `PHDRS'. This shows a typical set of program
4166 headers used on a native ELF system.
4170 headers PT_PHDR PHDRS ;
4172 text PT_LOAD FILEHDR PHDRS ;
4174 dynamic PT_DYNAMIC ;
4180 .interp : { *(.interp) } :text :interp
4181 .text : { *(.text) } :text
4182 .rodata : { *(.rodata) } /* defaults to :text */
4184 . = . + 0x1000; /* move to a new page in memory */
4185 .data : { *(.data) } :data
4186 .dynamic : { *(.dynamic) } :data :dynamic
4191 File: ld.info, Node: VERSION, Next: Expressions, Prev: PHDRS, Up: Scripts
4196 The linker supports symbol versions when using ELF. Symbol versions are
4197 only useful when using shared libraries. The dynamic linker can use
4198 symbol versions to select a specific version of a function when it runs
4199 a program that may have been linked against an earlier version of the
4202 You can include a version script directly in the main linker script,
4203 or you can supply the version script as an implicit linker script. You
4204 can also use the `--version-script' linker option.
4206 The syntax of the `VERSION' command is simply
4207 VERSION { version-script-commands }
4209 The format of the version script commands is identical to that used
4210 by Sun's linker in Solaris 2.5. The version script defines a tree of
4211 version nodes. You specify the node names and interdependencies in the
4212 version script. You can specify which symbols are bound to which
4213 version nodes, and you can reduce a specified set of symbols to local
4214 scope so that they are not globally visible outside of the shared
4217 The easiest way to demonstrate the version script language is with a
4241 This example version script defines three version nodes. The first
4242 version node defined is `VERS_1.1'; it has no other dependencies. The
4243 script binds the symbol `foo1' to `VERS_1.1'. It reduces a number of
4244 symbols to local scope so that they are not visible outside of the
4245 shared library; this is done using wildcard patterns, so that any
4246 symbol whose name begins with `old', `original', or `new' is matched.
4247 The wildcard patterns available are the same as those used in the shell
4248 when matching filenames (also known as "globbing"). However, if you
4249 specify the symbol name inside double quotes, then the name is treated
4250 as literal, rather than as a glob pattern.
4252 Next, the version script defines node `VERS_1.2'. This node depends
4253 upon `VERS_1.1'. The script binds the symbol `foo2' to the version
4256 Finally, the version script defines node `VERS_2.0'. This node
4257 depends upon `VERS_1.2'. The scripts binds the symbols `bar1' and
4258 `bar2' are bound to the version node `VERS_2.0'.
4260 When the linker finds a symbol defined in a library which is not
4261 specifically bound to a version node, it will effectively bind it to an
4262 unspecified base version of the library. You can bind all otherwise
4263 unspecified symbols to a given version node by using `global: *;'
4264 somewhere in the version script. Note that it's slightly crazy to use
4265 wildcards in a global spec except on the last version node. Global
4266 wildcards elsewhere run the risk of accidentally adding symbols to the
4267 set exported for an old version. That's wrong since older versions
4268 ought to have a fixed set of symbols.
4270 The names of the version nodes have no specific meaning other than
4271 what they might suggest to the person reading them. The `2.0' version
4272 could just as well have appeared in between `1.1' and `1.2'. However,
4273 this would be a confusing way to write a version script.
4275 Node name can be omitted, provided it is the only version node in
4276 the version script. Such version script doesn't assign any versions to
4277 symbols, only selects which symbols will be globally visible out and
4280 { global: foo; bar; local: *; };
4282 When you link an application against a shared library that has
4283 versioned symbols, the application itself knows which version of each
4284 symbol it requires, and it also knows which version nodes it needs from
4285 each shared library it is linked against. Thus at runtime, the dynamic
4286 loader can make a quick check to make sure that the libraries you have
4287 linked against do in fact supply all of the version nodes that the
4288 application will need to resolve all of the dynamic symbols. In this
4289 way it is possible for the dynamic linker to know with certainty that
4290 all external symbols that it needs will be resolvable without having to
4291 search for each symbol reference.
4293 The symbol versioning is in effect a much more sophisticated way of
4294 doing minor version checking that SunOS does. The fundamental problem
4295 that is being addressed here is that typically references to external
4296 functions are bound on an as-needed basis, and are not all bound when
4297 the application starts up. If a shared library is out of date, a
4298 required interface may be missing; when the application tries to use
4299 that interface, it may suddenly and unexpectedly fail. With symbol
4300 versioning, the user will get a warning when they start their program if
4301 the libraries being used with the application are too old.
4303 There are several GNU extensions to Sun's versioning approach. The
4304 first of these is the ability to bind a symbol to a version node in the
4305 source file where the symbol is defined instead of in the versioning
4306 script. This was done mainly to reduce the burden on the library
4307 maintainer. You can do this by putting something like:
4308 __asm__(".symver original_foo,foo@VERS_1.1");
4309 in the C source file. This renames the function `original_foo' to
4310 be an alias for `foo' bound to the version node `VERS_1.1'. The
4311 `local:' directive can be used to prevent the symbol `original_foo'
4312 from being exported. A `.symver' directive takes precedence over a
4315 The second GNU extension is to allow multiple versions of the same
4316 function to appear in a given shared library. In this way you can make
4317 an incompatible change to an interface without increasing the major
4318 version number of the shared library, while still allowing applications
4319 linked against the old interface to continue to function.
4321 To do this, you must use multiple `.symver' directives in the source
4322 file. Here is an example:
4324 __asm__(".symver original_foo,foo@");
4325 __asm__(".symver old_foo,foo@VERS_1.1");
4326 __asm__(".symver old_foo1,foo@VERS_1.2");
4327 __asm__(".symver new_foo,foo@@VERS_2.0");
4329 In this example, `foo@' represents the symbol `foo' bound to the
4330 unspecified base version of the symbol. The source file that contains
4331 this example would define 4 C functions: `original_foo', `old_foo',
4332 `old_foo1', and `new_foo'.
4334 When you have multiple definitions of a given symbol, there needs to
4335 be some way to specify a default version to which external references to
4336 this symbol will be bound. You can do this with the `foo@@VERS_2.0'
4337 type of `.symver' directive. You can only declare one version of a
4338 symbol as the default in this manner; otherwise you would effectively
4339 have multiple definitions of the same symbol.
4341 If you wish to bind a reference to a specific version of the symbol
4342 within the shared library, you can use the aliases of convenience
4343 (i.e., `old_foo'), or you can use the `.symver' directive to
4344 specifically bind to an external version of the function in question.
4346 You can also specify the language in the version script:
4348 VERSION extern "lang" { version-script-commands }
4350 The supported `lang's are `C', `C++', and `Java'. The linker will
4351 iterate over the list of symbols at the link time and demangle them
4352 according to `lang' before matching them to the patterns specified in
4353 `version-script-commands'. The default `lang' is `C'.
4355 Demangled names may contains spaces and other special characters. As
4356 described above, you can use a glob pattern to match demangled names,
4357 or you can use a double-quoted string to match the string exactly. In
4358 the latter case, be aware that minor differences (such as differing
4359 whitespace) between the version script and the demangler output will
4360 cause a mismatch. As the exact string generated by the demangler might
4361 change in the future, even if the mangled name does not, you should
4362 check that all of your version directives are behaving as you expect
4366 File: ld.info, Node: Expressions, Next: Implicit Linker Scripts, Prev: VERSION, Up: Scripts
4368 3.10 Expressions in Linker Scripts
4369 ==================================
4371 The syntax for expressions in the linker script language is identical to
4372 that of C expressions. All expressions are evaluated as integers. All
4373 expressions are evaluated in the same size, which is 32 bits if both the
4374 host and target are 32 bits, and is otherwise 64 bits.
4376 You can use and set symbol values in expressions.
4378 The linker defines several special purpose builtin functions for use
4383 * Constants:: Constants
4384 * Symbolic Constants:: Symbolic constants
4385 * Symbols:: Symbol Names
4386 * Orphan Sections:: Orphan Sections
4387 * Location Counter:: The Location Counter
4388 * Operators:: Operators
4389 * Evaluation:: Evaluation
4390 * Expression Section:: The Section of an Expression
4391 * Builtin Functions:: Builtin Functions
4394 File: ld.info, Node: Constants, Next: Symbolic Constants, Up: Expressions
4399 All constants are integers.
4401 As in C, the linker considers an integer beginning with `0' to be
4402 octal, and an integer beginning with `0x' or `0X' to be hexadecimal.
4403 Alternatively the linker accepts suffixes of `h' or `H' for
4404 hexadeciaml, `o' or `O' for octal, `b' or `B' for binary and `d' or `D'
4405 for decimal. Any integer value without a prefix or a suffix is
4406 considered to be decimal.
4408 In addition, you can use the suffixes `K' and `M' to scale a
4409 constant by `1024' or `1024*1024' respectively. For example, the
4410 following all refer to the same quantity:
4417 Note - the `K' and `M' suffixes cannot be used in conjunction with
4418 the base suffixes mentioned above.
4421 File: ld.info, Node: Symbolic Constants, Next: Symbols, Prev: Constants, Up: Expressions
4423 3.10.2 Symbolic Constants
4424 -------------------------
4426 It is possible to refer to target specific constants via the use of the
4427 `CONSTANT(NAME)' operator, where NAME is one of:
4430 The target's maximum page size.
4433 The target's default page size.
4437 .text ALIGN (CONSTANT (MAXPAGESIZE)) : { *(.text) }
4439 will create a text section aligned to the largest page boundary
4440 supported by the target.
4443 File: ld.info, Node: Symbols, Next: Orphan Sections, Prev: Symbolic Constants, Up: Expressions
4448 Unless quoted, symbol names start with a letter, underscore, or period
4449 and may include letters, digits, underscores, periods, and hyphens.
4450 Unquoted symbol names must not conflict with any keywords. You can
4451 specify a symbol which contains odd characters or has the same name as a
4452 keyword by surrounding the symbol name in double quotes:
4454 "with a space" = "also with a space" + 10;
4456 Since symbols can contain many non-alphabetic characters, it is
4457 safest to delimit symbols with spaces. For example, `A-B' is one
4458 symbol, whereas `A - B' is an expression involving subtraction.
4461 File: ld.info, Node: Orphan Sections, Next: Location Counter, Prev: Symbols, Up: Expressions
4463 3.10.4 Orphan Sections
4464 ----------------------
4466 Orphan sections are sections present in the input files which are not
4467 explicitly placed into the output file by the linker script. The
4468 linker will still copy these sections into the output file, but it has
4469 to guess as to where they should be placed. The linker uses a simple
4470 heuristic to do this. It attempts to place orphan sections after
4471 non-orphan sections of the same attribute, such as code vs data,
4472 loadable vs non-loadable, etc. If there is not enough room to do this
4473 then it places at the end of the file.
4475 For ELF targets, the attribute of the section includes section type
4476 as well as section flag.
4478 If an orphaned section's name is representable as a C identifier then
4479 the linker will automatically *note PROVIDE:: two symbols:
4480 __start_SECNAME and __stop_SECNAME, where SECNAME is the name of the
4481 section. These indicate the start address and end address of the
4482 orphaned section respectively. Note: most section names are not
4483 representable as C identifiers because they contain a `.' character.
4486 File: ld.info, Node: Location Counter, Next: Operators, Prev: Orphan Sections, Up: Expressions
4488 3.10.5 The Location Counter
4489 ---------------------------
4491 The special linker variable "dot" `.' always contains the current
4492 output location counter. Since the `.' always refers to a location in
4493 an output section, it may only appear in an expression within a
4494 `SECTIONS' command. The `.' symbol may appear anywhere that an
4495 ordinary symbol is allowed in an expression.
4497 Assigning a value to `.' will cause the location counter to be
4498 moved. This may be used to create holes in the output section. The
4499 location counter may not be moved backwards inside an output section,
4500 and may not be moved backwards outside of an output section if so doing
4501 creates areas with overlapping LMAs.
4514 In the previous example, the `.text' section from `file1' is located
4515 at the beginning of the output section `output'. It is followed by a
4516 1000 byte gap. Then the `.text' section from `file2' appears, also
4517 with a 1000 byte gap following before the `.text' section from `file3'.
4518 The notation `= 0x12345678' specifies what data to write in the gaps
4519 (*note Output Section Fill::).
4521 Note: `.' actually refers to the byte offset from the start of the
4522 current containing object. Normally this is the `SECTIONS' statement,
4523 whose start address is 0, hence `.' can be used as an absolute address.
4524 If `.' is used inside a section description however, it refers to the
4525 byte offset from the start of that section, not an absolute address.
4526 Thus in a script like this:
4542 The `.text' section will be assigned a starting address of 0x100 and
4543 a size of exactly 0x200 bytes, even if there is not enough data in the
4544 `.text' input sections to fill this area. (If there is too much data,
4545 an error will be produced because this would be an attempt to move `.'
4546 backwards). The `.data' section will start at 0x500 and it will have
4547 an extra 0x600 bytes worth of space after the end of the values from
4548 the `.data' input sections and before the end of the `.data' output
4551 Setting symbols to the value of the location counter outside of an
4552 output section statement can result in unexpected values if the linker
4553 needs to place orphan sections. For example, given the following:
4566 If the linker needs to place some input section, e.g. `.rodata', not
4567 mentioned in the script, it might choose to place that section between
4568 `.text' and `.data'. You might think the linker should place `.rodata'
4569 on the blank line in the above script, but blank lines are of no
4570 particular significance to the linker. As well, the linker doesn't
4571 associate the above symbol names with their sections. Instead, it
4572 assumes that all assignments or other statements belong to the previous
4573 output section, except for the special case of an assignment to `.'.
4574 I.e., the linker will place the orphan `.rodata' section as if the
4575 script was written as follows:
4584 .rodata: { *(.rodata) }
4589 This may or may not be the script author's intention for the value of
4590 `start_of_data'. One way to influence the orphan section placement is
4591 to assign the location counter to itself, as the linker assumes that an
4592 assignment to `.' is setting the start address of a following output
4593 section and thus should be grouped with that section. So you could
4608 Now, the orphan `.rodata' section will be placed between
4609 `end_of_text' and `start_of_data'.
4612 File: ld.info, Node: Operators, Next: Evaluation, Prev: Location Counter, Up: Expressions
4617 The linker recognizes the standard C set of arithmetic operators, with
4618 the standard bindings and precedence levels:
4619 precedence associativity Operators Notes
4625 5 left == != > < <= >=
4631 11 right &= += -= *= /= (2)
4633 Notes: (1) Prefix operators (2) *Note Assignments::.
4636 File: ld.info, Node: Evaluation, Next: Expression Section, Prev: Operators, Up: Expressions
4641 The linker evaluates expressions lazily. It only computes the value of
4642 an expression when absolutely necessary.
4644 The linker needs some information, such as the value of the start
4645 address of the first section, and the origins and lengths of memory
4646 regions, in order to do any linking at all. These values are computed
4647 as soon as possible when the linker reads in the linker script.
4649 However, other values (such as symbol values) are not known or needed
4650 until after storage allocation. Such values are evaluated later, when
4651 other information (such as the sizes of output sections) is available
4652 for use in the symbol assignment expression.
4654 The sizes of sections cannot be known until after allocation, so
4655 assignments dependent upon these are not performed until after
4658 Some expressions, such as those depending upon the location counter
4659 `.', must be evaluated during section allocation.
4661 If the result of an expression is required, but the value is not
4662 available, then an error results. For example, a script like the
4666 .text 9+this_isnt_constant :
4669 will cause the error message `non constant expression for initial
4673 File: ld.info, Node: Expression Section, Next: Builtin Functions, Prev: Evaluation, Up: Expressions
4675 3.10.8 The Section of an Expression
4676 -----------------------------------
4678 Addresses and symbols may be section relative, or absolute. A section
4679 relative symbol is relocatable. If you request relocatable output
4680 using the `-r' option, a further link operation may change the value of
4681 a section relative symbol. On the other hand, an absolute symbol will
4682 retain the same value throughout any further link operations.
4684 Some terms in linker expressions are addresses. This is true of
4685 section relative symbols and for builtin functions that return an
4686 address, such as `ADDR', `LOADADDR', `ORIGIN' and `SEGMENT_START'.
4687 Other terms are simply numbers, or are builtin functions that return a
4688 non-address value, such as `LENGTH'. One complication is that unless
4689 you set `LD_FEATURE ("SANE_EXPR")' (*note Miscellaneous Commands::),
4690 numbers and absolute symbols are treated differently depending on their
4691 location, for compatibility with older versions of `ld'. Expressions
4692 appearing outside an output section definition treat all numbers as
4693 absolute addresses. Expressions appearing inside an output section
4694 definition treat absolute symbols as numbers. If `LD_FEATURE
4695 ("SANE_EXPR")' is given, then absolute symbols and numbers are simply
4696 treated as numbers everywhere.
4698 In the following simple example,
4703 __executable_start = 0x100;
4707 __data_start = 0x10;
4713 both `.' and `__executable_start' are set to the absolute address
4714 0x100 in the first two assignments, then both `.' and `__data_start'
4715 are set to 0x10 relative to the `.data' section in the second two
4718 For expressions involving numbers, relative addresses and absolute
4719 addresses, ld follows these rules to evaluate terms:
4721 * Unary operations on a relative address, and binary operations on
4722 two relative addresses in the same section or between one relative
4723 address and a number, apply the operator to the offset part of the
4726 * Unary operations on an absolute address, and binary operations on
4727 one or more absolute addresses or on two relative addresses not in
4728 the same section, first convert any non-absolute term to an
4729 absolute address before applying the operator.
4731 The result section of each sub-expression is as follows:
4733 * An operation involving only numbers results in a number.
4735 * The result of comparisons, `&&' and `||' is also a number.
4737 * The result of other binary arithmetic and logical operations on two
4738 relative addresses in the same section or two absolute addresess
4739 (after above conversions) is also a number.
4741 * The result of other operations on relative addresses or one
4742 relative address and a number, is a relative address in the same
4743 section as the relative operand(s).
4745 * The result of other operations on absolute addresses (after above
4746 conversions) is an absolute address.
4748 You can use the builtin function `ABSOLUTE' to force an expression
4749 to be absolute when it would otherwise be relative. For example, to
4750 create an absolute symbol set to the address of the end of the output
4754 .data : { *(.data) _edata = ABSOLUTE(.); }
4756 If `ABSOLUTE' were not used, `_edata' would be relative to the
4759 Using `LOADADDR' also forces an expression absolute, since this
4760 particular builtin function returns an absolute address.
4763 File: ld.info, Node: Builtin Functions, Prev: Expression Section, Up: Expressions
4765 3.10.9 Builtin Functions
4766 ------------------------
4768 The linker script language includes a number of builtin functions for
4769 use in linker script expressions.
4772 Return the absolute (non-relocatable, as opposed to non-negative)
4773 value of the expression EXP. Primarily useful to assign an
4774 absolute value to a symbol within a section definition, where
4775 symbol values are normally section relative. *Note Expression
4779 Return the address (VMA) of the named SECTION. Your script must
4780 previously have defined the location of that section. In the
4781 following example, `start_of_output_1', `symbol_1' and `symbol_2'
4782 are assigned equivalent values, except that `symbol_1' will be
4783 relative to the `.output1' section while the other two will be
4788 start_of_output_1 = ABSOLUTE(.);
4793 symbol_1 = ADDR(.output1);
4794 symbol_2 = start_of_output_1;
4800 Return the location counter (`.') or arbitrary expression aligned
4801 to the next ALIGN boundary. The single operand `ALIGN' doesn't
4802 change the value of the location counter--it just does arithmetic
4803 on it. The two operand `ALIGN' allows an arbitrary expression to
4804 be aligned upwards (`ALIGN(ALIGN)' is equivalent to `ALIGN(.,
4807 Here is an example which aligns the output `.data' section to the
4808 next `0x2000' byte boundary after the preceding section and sets a
4809 variable within the section to the next `0x8000' boundary after the
4812 .data ALIGN(0x2000): {
4814 variable = ALIGN(0x8000);
4817 The first use of `ALIGN' in this example specifies the
4818 location of a section because it is used as the optional ADDRESS
4819 attribute of a section definition (*note Output Section
4820 Address::). The second use of `ALIGN' is used to defines the
4823 The builtin function `NEXT' is closely related to `ALIGN'.
4826 Return the alignment in bytes of the named SECTION, if that
4827 section has been allocated. If the section has not been allocated
4828 when this is evaluated, the linker will report an error. In the
4829 following example, the alignment of the `.output' section is
4830 stored as the first value in that section.
4833 LONG (ALIGNOF (.output))
4839 This is a synonym for `ALIGN', for compatibility with older linker
4840 scripts. It is most often seen when setting the address of an
4843 `DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE)'
4844 This is equivalent to either
4845 (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - 1)))
4847 (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - COMMONPAGESIZE)))
4848 depending on whether the latter uses fewer COMMONPAGESIZE sized
4849 pages for the data segment (area between the result of this
4850 expression and `DATA_SEGMENT_END') than the former or not. If the
4851 latter form is used, it means COMMONPAGESIZE bytes of runtime
4852 memory will be saved at the expense of up to COMMONPAGESIZE wasted
4853 bytes in the on-disk file.
4855 This expression can only be used directly in `SECTIONS' commands,
4856 not in any output section descriptions and only once in the linker
4857 script. COMMONPAGESIZE should be less or equal to MAXPAGESIZE and
4858 should be the system page size the object wants to be optimized
4859 for (while still working on system page sizes up to MAXPAGESIZE).
4862 . = DATA_SEGMENT_ALIGN(0x10000, 0x2000);
4864 `DATA_SEGMENT_END(EXP)'
4865 This defines the end of data segment for `DATA_SEGMENT_ALIGN'
4866 evaluation purposes.
4868 . = DATA_SEGMENT_END(.);
4870 `DATA_SEGMENT_RELRO_END(OFFSET, EXP)'
4871 This defines the end of the `PT_GNU_RELRO' segment when `-z relro'
4872 option is used. Second argument is returned. When `-z relro'
4873 option is not present, `DATA_SEGMENT_RELRO_END' does nothing,
4874 otherwise `DATA_SEGMENT_ALIGN' is padded so that EXP + OFFSET is
4875 aligned to the most commonly used page boundary for particular
4876 target. If present in the linker script, it must always come in
4877 between `DATA_SEGMENT_ALIGN' and `DATA_SEGMENT_END'.
4879 . = DATA_SEGMENT_RELRO_END(24, .);
4882 Return 1 if SYMBOL is in the linker global symbol table and is
4883 defined before the statement using DEFINED in the script, otherwise
4884 return 0. You can use this function to provide default values for
4885 symbols. For example, the following script fragment shows how to
4886 set a global symbol `begin' to the first location in the `.text'
4887 section--but if a symbol called `begin' already existed, its value
4892 begin = DEFINED(begin) ? begin : . ;
4899 Return the length of the memory region named MEMORY.
4902 Return the absolute LMA of the named SECTION. (*note Output
4906 Returns the maximum of EXP1 and EXP2.
4909 Returns the minimum of EXP1 and EXP2.
4912 Return the next unallocated address that is a multiple of EXP.
4913 This function is closely related to `ALIGN(EXP)'; unless you use
4914 the `MEMORY' command to define discontinuous memory for the output
4915 file, the two functions are equivalent.
4918 Return the origin of the memory region named MEMORY.
4920 `SEGMENT_START(SEGMENT, DEFAULT)'
4921 Return the base address of the named SEGMENT. If an explicit
4922 value has been given for this segment (with a command-line `-T'
4923 option) that value will be returned; otherwise the value will be
4924 DEFAULT. At present, the `-T' command-line option can only be
4925 used to set the base address for the "text", "data", and "bss"
4926 sections, but you can use `SEGMENT_START' with any segment name.
4929 Return the size in bytes of the named SECTION, if that section has
4930 been allocated. If the section has not been allocated when this is
4931 evaluated, the linker will report an error. In the following
4932 example, `symbol_1' and `symbol_2' are assigned identical values:
4939 symbol_1 = .end - .start ;
4940 symbol_2 = SIZEOF(.output);
4945 Return the size in bytes of the output file's headers. This is
4946 information which appears at the start of the output file. You
4947 can use this number when setting the start address of the first
4948 section, if you choose, to facilitate paging.
4950 When producing an ELF output file, if the linker script uses the
4951 `SIZEOF_HEADERS' builtin function, the linker must compute the
4952 number of program headers before it has determined all the section
4953 addresses and sizes. If the linker later discovers that it needs
4954 additional program headers, it will report an error `not enough
4955 room for program headers'. To avoid this error, you must avoid
4956 using the `SIZEOF_HEADERS' function, or you must rework your linker
4957 script to avoid forcing the linker to use additional program
4958 headers, or you must define the program headers yourself using the
4959 `PHDRS' command (*note PHDRS::).
4962 File: ld.info, Node: Implicit Linker Scripts, Prev: Expressions, Up: Scripts
4964 3.11 Implicit Linker Scripts
4965 ============================
4967 If you specify a linker input file which the linker can not recognize as
4968 an object file or an archive file, it will try to read the file as a
4969 linker script. If the file can not be parsed as a linker script, the
4970 linker will report an error.
4972 An implicit linker script will not replace the default linker script.
4974 Typically an implicit linker script would contain only symbol
4975 assignments, or the `INPUT', `GROUP', or `VERSION' commands.
4977 Any input files read because of an implicit linker script will be
4978 read at the position in the command line where the implicit linker
4979 script was read. This can affect archive searching.
4982 File: ld.info, Node: Machine Dependent, Next: BFD, Prev: Scripts, Up: Top
4984 4 Machine Dependent Features
4985 ****************************
4987 `ld' has additional features on some platforms; the following sections
4988 describe them. Machines where `ld' has no additional functionality are
4994 * H8/300:: `ld' and the H8/300
4996 * i960:: `ld' and the Intel 960 family
4998 * ARM:: `ld' and the ARM family
5000 * HPPA ELF32:: `ld' and HPPA 32-bit ELF
5002 * M68K:: `ld' and the Motorola 68K family
5004 * MMIX:: `ld' and MMIX
5006 * MSP430:: `ld' and MSP430
5008 * M68HC11/68HC12:: `ld' and the Motorola 68HC11 and 68HC12 families
5010 * PowerPC ELF32:: `ld' and PowerPC 32-bit ELF Support
5012 * PowerPC64 ELF64:: `ld' and PowerPC64 64-bit ELF Support
5014 * SPU ELF:: `ld' and SPU ELF Support
5016 * TI COFF:: `ld' and TI COFF
5018 * WIN32:: `ld' and WIN32 (cygwin/mingw)
5020 * Xtensa:: `ld' and Xtensa Processors
5023 File: ld.info, Node: H8/300, Next: i960, Up: Machine Dependent
5025 4.1 `ld' and the H8/300
5026 =======================
5028 For the H8/300, `ld' can perform these global optimizations when you
5029 specify the `--relax' command-line option.
5031 _relaxing address modes_
5032 `ld' finds all `jsr' and `jmp' instructions whose targets are
5033 within eight bits, and turns them into eight-bit program-counter
5034 relative `bsr' and `bra' instructions, respectively.
5036 _synthesizing instructions_
5037 `ld' finds all `mov.b' instructions which use the sixteen-bit
5038 absolute address form, but refer to the top page of memory, and
5039 changes them to use the eight-bit address form. (That is: the
5040 linker turns `mov.b `@'AA:16' into `mov.b `@'AA:8' whenever the
5041 address AA is in the top page of memory).
5043 _bit manipulation instructions_
5044 `ld' finds all bit manipulation instructions like `band, bclr,
5045 biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst,
5046 bxor' which use 32 bit and 16 bit absolute address form, but refer
5047 to the top page of memory, and changes them to use the 8 bit
5048 address form. (That is: the linker turns `bset #xx:3,`@'AA:32'
5049 into `bset #xx:3,`@'AA:8' whenever the address AA is in the top
5052 _system control instructions_
5053 `ld' finds all `ldc.w, stc.w' instructions which use the 32 bit
5054 absolute address form, but refer to the top page of memory, and
5055 changes them to use 16 bit address form. (That is: the linker
5056 turns `ldc.w `@'AA:32,ccr' into `ldc.w `@'AA:16,ccr' whenever the
5057 address AA is in the top page of memory).
5060 File: ld.info, Node: i960, Next: ARM, Prev: H8/300, Up: Machine Dependent
5062 4.2 `ld' and the Intel 960 Family
5063 =================================
5065 You can use the `-AARCHITECTURE' command line option to specify one of
5066 the two-letter names identifying members of the 960 family; the option
5067 specifies the desired output target, and warns of any incompatible
5068 instructions in the input files. It also modifies the linker's search
5069 strategy for archive libraries, to support the use of libraries
5070 specific to each particular architecture, by including in the search
5071 loop names suffixed with the string identifying the architecture.
5073 For example, if your `ld' command line included `-ACA' as well as
5074 `-ltry', the linker would look (in its built-in search paths, and in
5075 any paths you specify with `-L') for a library with the names
5082 The first two possibilities would be considered in any event; the last
5083 two are due to the use of `-ACA'.
5085 You can meaningfully use `-A' more than once on a command line, since
5086 the 960 architecture family allows combination of target architectures;
5087 each use will add another pair of name variants to search for when `-l'
5088 specifies a library.
5090 `ld' supports the `--relax' option for the i960 family. If you
5091 specify `--relax', `ld' finds all `balx' and `calx' instructions whose
5092 targets are within 24 bits, and turns them into 24-bit program-counter
5093 relative `bal' and `cal' instructions, respectively. `ld' also turns
5094 `cal' instructions into `bal' instructions when it determines that the
5095 target subroutine is a leaf routine (that is, the target subroutine does
5096 not itself call any subroutines).
5098 The `--fix-cortex-a8' switch enables a link-time workaround for an
5099 erratum in certain Cortex-A8 processors. The workaround is enabled by
5100 default if you are targeting the ARM v7-A architecture profile. It can
5101 be enabled otherwise by specifying `--fix-cortex-a8', or disabled
5102 unconditionally by specifying `--no-fix-cortex-a8'.
5104 The erratum only affects Thumb-2 code. Please contact ARM for
5107 The `--no-merge-exidx-entries' switch disables the merging of
5108 adjacent exidx entries in debuginfo.
5111 File: ld.info, Node: M68HC11/68HC12, Next: PowerPC ELF32, Prev: MSP430, Up: Machine Dependent
5113 4.3 `ld' and the Motorola 68HC11 and 68HC12 families
5114 ====================================================
5116 4.3.1 Linker Relaxation
5117 -----------------------
5119 For the Motorola 68HC11, `ld' can perform these global optimizations
5120 when you specify the `--relax' command-line option.
5122 _relaxing address modes_
5123 `ld' finds all `jsr' and `jmp' instructions whose targets are
5124 within eight bits, and turns them into eight-bit program-counter
5125 relative `bsr' and `bra' instructions, respectively.
5127 `ld' also looks at all 16-bit extended addressing modes and
5128 transforms them in a direct addressing mode when the address is in
5129 page 0 (between 0 and 0x0ff).
5131 _relaxing gcc instruction group_
5132 When `gcc' is called with `-mrelax', it can emit group of
5133 instructions that the linker can optimize to use a 68HC11 direct
5134 addressing mode. These instructions consists of `bclr' or `bset'
5138 4.3.2 Trampoline Generation
5139 ---------------------------
5141 For 68HC11 and 68HC12, `ld' can generate trampoline code to call a far
5142 function using a normal `jsr' instruction. The linker will also change
5143 the relocation to some far function to use the trampoline address
5144 instead of the function address. This is typically the case when a
5145 pointer to a function is taken. The pointer will in fact point to the
5146 function trampoline.
5149 File: ld.info, Node: ARM, Next: HPPA ELF32, Prev: i960, Up: Machine Dependent
5151 4.4 `ld' and the ARM family
5152 ===========================
5154 For the ARM, `ld' will generate code stubs to allow functions calls
5155 between ARM and Thumb code. These stubs only work with code that has
5156 been compiled and assembled with the `-mthumb-interwork' command line
5157 option. If it is necessary to link with old ARM object files or
5158 libraries, which have not been compiled with the -mthumb-interwork
5159 option then the `--support-old-code' command line switch should be
5160 given to the linker. This will make it generate larger stub functions
5161 which will work with non-interworking aware ARM code. Note, however,
5162 the linker does not support generating stubs for function calls to
5163 non-interworking aware Thumb code.
5165 The `--thumb-entry' switch is a duplicate of the generic `--entry'
5166 switch, in that it sets the program's starting address. But it also
5167 sets the bottom bit of the address, so that it can be branched to using
5168 a BX instruction, and the program will start executing in Thumb mode
5171 The `--use-nul-prefixed-import-tables' switch is specifying, that
5172 the import tables idata4 and idata5 have to be generated with a zero
5173 elememt prefix for import libraries. This is the old style to generate
5174 import tables. By default this option is turned off.
5176 The `--be8' switch instructs `ld' to generate BE8 format
5177 executables. This option is only valid when linking big-endian objects.
5178 The resulting image will contain big-endian data and little-endian code.
5180 The `R_ARM_TARGET1' relocation is typically used for entries in the
5181 `.init_array' section. It is interpreted as either `R_ARM_REL32' or
5182 `R_ARM_ABS32', depending on the target. The `--target1-rel' and
5183 `--target1-abs' switches override the default.
5185 The `--target2=type' switch overrides the default definition of the
5186 `R_ARM_TARGET2' relocation. Valid values for `type', their meanings,
5187 and target defaults are as follows:
5189 `R_ARM_REL32' (arm*-*-elf, arm*-*-eabi)
5192 `R_ARM_ABS32' (arm*-*-symbianelf)
5195 `R_ARM_GOT_PREL' (arm*-*-linux, arm*-*-*bsd)
5197 The `R_ARM_V4BX' relocation (defined by the ARM AAELF specification)
5198 enables objects compiled for the ARMv4 architecture to be
5199 interworking-safe when linked with other objects compiled for ARMv4t,
5200 but also allows pure ARMv4 binaries to be built from the same ARMv4
5203 In the latter case, the switch `--fix-v4bx' must be passed to the
5204 linker, which causes v4t `BX rM' instructions to be rewritten as `MOV
5205 PC,rM', since v4 processors do not have a `BX' instruction.
5207 In the former case, the switch should not be used, and `R_ARM_V4BX'
5208 relocations are ignored.
5210 Replace `BX rM' instructions identified by `R_ARM_V4BX' relocations
5211 with a branch to the following veneer:
5217 This allows generation of libraries/applications that work on ARMv4
5218 cores and are still interworking safe. Note that the above veneer
5219 clobbers the condition flags, so may cause incorrect progrm behavior in
5222 The `--use-blx' switch enables the linker to use ARM/Thumb BLX
5223 instructions (available on ARMv5t and above) in various situations.
5224 Currently it is used to perform calls via the PLT from Thumb code using
5225 BLX rather than using BX and a mode-switching stub before each PLT
5226 entry. This should lead to such calls executing slightly faster.
5228 This option is enabled implicitly for SymbianOS, so there is no need
5229 to specify it if you are using that target.
5231 The `--vfp11-denorm-fix' switch enables a link-time workaround for a
5232 bug in certain VFP11 coprocessor hardware, which sometimes allows
5233 instructions with denorm operands (which must be handled by support
5234 code) to have those operands overwritten by subsequent instructions
5235 before the support code can read the intended values.
5237 The bug may be avoided in scalar mode if you allow at least one
5238 intervening instruction between a VFP11 instruction which uses a
5239 register and another instruction which writes to the same register, or
5240 at least two intervening instructions if vector mode is in use. The bug
5241 only affects full-compliance floating-point mode: you do not need this
5242 workaround if you are using "runfast" mode. Please contact ARM for
5245 If you know you are using buggy VFP11 hardware, you can enable this
5246 workaround by specifying the linker option `--vfp-denorm-fix=scalar' if
5247 you are using the VFP11 scalar mode only, or `--vfp-denorm-fix=vector'
5248 if you are using vector mode (the latter also works for scalar code).
5249 The default is `--vfp-denorm-fix=none'.
5251 If the workaround is enabled, instructions are scanned for
5252 potentially-troublesome sequences, and a veneer is created for each
5253 such sequence which may trigger the erratum. The veneer consists of the
5254 first instruction of the sequence and a branch back to the subsequent
5255 instruction. The original instruction is then replaced with a branch to
5256 the veneer. The extra cycles required to call and return from the veneer
5257 are sufficient to avoid the erratum in both the scalar and vector cases.
5259 The `--fix-arm1176' switch enables a link-time workaround for an
5260 erratum in certain ARM1176 processors. The workaround is enabled by
5261 default if you are targetting ARM v6 (excluding ARM v6T2) or earlier.
5262 It can be disabled unconditionally by specifying `--no-fix-arm1176'.
5264 Further information is available in the "ARM1176JZ-S and ARM1176JZF-S
5265 Programmer Advice Notice" available on the ARM documentaion website at:
5266 http://infocenter.arm.com/.
5268 The `--no-enum-size-warning' switch prevents the linker from warning
5269 when linking object files that specify incompatible EABI enumeration
5270 size attributes. For example, with this switch enabled, linking of an
5271 object file using 32-bit enumeration values with another using
5272 enumeration values fitted into the smallest possible space will not be
5275 The `--no-wchar-size-warning' switch prevents the linker from
5276 warning when linking object files that specify incompatible EABI
5277 `wchar_t' size attributes. For example, with this switch enabled,
5278 linking of an object file using 32-bit `wchar_t' values with another
5279 using 16-bit `wchar_t' values will not be diagnosed.
5281 The `--pic-veneer' switch makes the linker use PIC sequences for
5282 ARM/Thumb interworking veneers, even if the rest of the binary is not
5283 PIC. This avoids problems on uClinux targets where `--emit-relocs' is
5284 used to generate relocatable binaries.
5286 The linker will automatically generate and insert small sequences of
5287 code into a linked ARM ELF executable whenever an attempt is made to
5288 perform a function call to a symbol that is too far away. The
5289 placement of these sequences of instructions - called stubs - is
5290 controlled by the command line option `--stub-group-size=N'. The
5291 placement is important because a poor choice can create a need for
5292 duplicate stubs, increasing the code sizw. The linker will try to
5293 group stubs together in order to reduce interruptions to the flow of
5294 code, but it needs guidance as to how big these groups should be and
5295 where they should be placed.
5297 The value of `N', the parameter to the `--stub-group-size=' option
5298 controls where the stub groups are placed. If it is negative then all
5299 stubs are placed after the first branch that needs them. If it is
5300 positive then the stubs can be placed either before or after the
5301 branches that need them. If the value of `N' is 1 (either +1 or -1)
5302 then the linker will choose exactly where to place groups of stubs,
5303 using its built in heuristics. A value of `N' greater than 1 (or
5304 smaller than -1) tells the linker that a single group of stubs can
5305 service at most `N' bytes from the input sections.
5307 The default, if `--stub-group-size=' is not specified, is `N = +1'.
5309 Farcalls stubs insertion is fully supported for the ARM-EABI target
5310 only, because it relies on object files properties not present
5314 File: ld.info, Node: HPPA ELF32, Next: M68K, Prev: ARM, Up: Machine Dependent
5316 4.5 `ld' and HPPA 32-bit ELF Support
5317 ====================================
5319 When generating a shared library, `ld' will by default generate import
5320 stubs suitable for use with a single sub-space application. The
5321 `--multi-subspace' switch causes `ld' to generate export stubs, and
5322 different (larger) import stubs suitable for use with multiple
5325 Long branch stubs and import/export stubs are placed by `ld' in stub
5326 sections located between groups of input sections. `--stub-group-size'
5327 specifies the maximum size of a group of input sections handled by one
5328 stub section. Since branch offsets are signed, a stub section may
5329 serve two groups of input sections, one group before the stub section,
5330 and one group after it. However, when using conditional branches that
5331 require stubs, it may be better (for branch prediction) that stub
5332 sections only serve one group of input sections. A negative value for
5333 `N' chooses this scheme, ensuring that branches to stubs always use a
5334 negative offset. Two special values of `N' are recognized, `1' and
5335 `-1'. These both instruct `ld' to automatically size input section
5336 groups for the branch types detected, with the same behaviour regarding
5337 stub placement as other positive or negative values of `N' respectively.
5339 Note that `--stub-group-size' does not split input sections. A
5340 single input section larger than the group size specified will of course
5341 create a larger group (of one section). If input sections are too
5342 large, it may not be possible for a branch to reach its stub.
5345 File: ld.info, Node: M68K, Next: MMIX, Prev: HPPA ELF32, Up: Machine Dependent
5347 4.6 `ld' and the Motorola 68K family
5348 ====================================
5350 The `--got=TYPE' option lets you choose the GOT generation scheme. The
5351 choices are `single', `negative', `multigot' and `target'. When
5352 `target' is selected the linker chooses the default GOT generation
5353 scheme for the current target. `single' tells the linker to generate a
5354 single GOT with entries only at non-negative offsets. `negative'
5355 instructs the linker to generate a single GOT with entries at both
5356 negative and positive offsets. Not all environments support such GOTs.
5357 `multigot' allows the linker to generate several GOTs in the output
5358 file. All GOT references from a single input object file access the
5359 same GOT, but references from different input object files might access
5360 different GOTs. Not all environments support such GOTs.
5363 File: ld.info, Node: MMIX, Next: MSP430, Prev: M68K, Up: Machine Dependent
5368 For MMIX, there is a choice of generating `ELF' object files or `mmo'
5369 object files when linking. The simulator `mmix' understands the `mmo'
5370 format. The binutils `objcopy' utility can translate between the two
5373 There is one special section, the `.MMIX.reg_contents' section.
5374 Contents in this section is assumed to correspond to that of global
5375 registers, and symbols referring to it are translated to special
5376 symbols, equal to registers. In a final link, the start address of the
5377 `.MMIX.reg_contents' section corresponds to the first allocated global
5378 register multiplied by 8. Register `$255' is not included in this
5379 section; it is always set to the program entry, which is at the symbol
5380 `Main' for `mmo' files.
5382 Global symbols with the prefix `__.MMIX.start.', for example
5383 `__.MMIX.start..text' and `__.MMIX.start..data' are special. The
5384 default linker script uses these to set the default start address of a
5387 Initial and trailing multiples of zero-valued 32-bit words in a
5388 section, are left out from an mmo file.
5391 File: ld.info, Node: MSP430, Next: M68HC11/68HC12, Prev: MMIX, Up: Machine Dependent
5396 For the MSP430 it is possible to select the MPU architecture. The flag
5397 `-m [mpu type]' will select an appropriate linker script for selected
5398 MPU type. (To get a list of known MPUs just pass `-m help' option to
5401 The linker will recognize some extra sections which are MSP430
5405 Defines a portion of ROM where interrupt vectors located.
5408 Defines the bootloader portion of the ROM (if applicable). Any
5409 code in this section will be uploaded to the MPU.
5412 Defines an information memory section (if applicable). Any code in
5413 this section will be uploaded to the MPU.
5416 This is the same as the `.infomem' section except that any code in
5417 this section will not be uploaded to the MPU.
5420 Denotes a portion of RAM located above `.bss' section.
5422 The last two sections are used by gcc.
5425 File: ld.info, Node: PowerPC ELF32, Next: PowerPC64 ELF64, Prev: M68HC11/68HC12, Up: Machine Dependent
5427 4.9 `ld' and PowerPC 32-bit ELF Support
5428 =======================================
5430 Branches on PowerPC processors are limited to a signed 26-bit
5431 displacement, which may result in `ld' giving `relocation truncated to
5432 fit' errors with very large programs. `--relax' enables the generation
5433 of trampolines that can access the entire 32-bit address space. These
5434 trampolines are inserted at section boundaries, so may not themselves
5435 be reachable if an input section exceeds 33M in size. You may combine
5436 `-r' and `--relax' to add trampolines in a partial link. In that case
5437 both branches to undefined symbols and inter-section branches are also
5438 considered potentially out of range, and trampolines inserted.
5441 Current PowerPC GCC accepts a `-msecure-plt' option that generates
5442 code capable of using a newer PLT and GOT layout that has the
5443 security advantage of no executable section ever needing to be
5444 writable and no writable section ever being executable. PowerPC
5445 `ld' will generate this layout, including stubs to access the PLT,
5446 if all input files (including startup and static libraries) were
5447 compiled with `-msecure-plt'. `--bss-plt' forces the old BSS PLT
5448 (and GOT layout) which can give slightly better performance.
5451 `ld' will use the new PLT and GOT layout if it is linking new
5452 `-fpic' or `-fPIC' code, but does not do so automatically when
5453 linking non-PIC code. This option requests the new PLT and GOT
5454 layout. A warning will be given if some object file requires the
5458 The new secure PLT and GOT are placed differently relative to other
5459 sections compared to older BSS PLT and GOT placement. The
5460 location of `.plt' must change because the new secure PLT is an
5461 initialized section while the old PLT is uninitialized. The
5462 reason for the `.got' change is more subtle: The new placement
5463 allows `.got' to be read-only in applications linked with `-z
5464 relro -z now'. However, this placement means that `.sdata' cannot
5465 always be used in shared libraries, because the PowerPC ABI
5466 accesses `.sdata' in shared libraries from the GOT pointer.
5467 `--sdata-got' forces the old GOT placement. PowerPC GCC doesn't
5468 use `.sdata' in shared libraries, so this option is really only
5469 useful for other compilers that may do so.
5472 This option causes `ld' to label linker stubs with a local symbol
5473 that encodes the stub type and destination.
5476 PowerPC `ld' normally performs some optimization of code sequences
5477 used to access Thread-Local Storage. Use this option to disable
5481 File: ld.info, Node: PowerPC64 ELF64, Next: SPU ELF, Prev: PowerPC ELF32, Up: Machine Dependent
5483 4.10 `ld' and PowerPC64 64-bit ELF Support
5484 ==========================================
5487 Long branch stubs, PLT call stubs and TOC adjusting stubs are
5488 placed by `ld' in stub sections located between groups of input
5489 sections. `--stub-group-size' specifies the maximum size of a
5490 group of input sections handled by one stub section. Since branch
5491 offsets are signed, a stub section may serve two groups of input
5492 sections, one group before the stub section, and one group after
5493 it. However, when using conditional branches that require stubs,
5494 it may be better (for branch prediction) that stub sections only
5495 serve one group of input sections. A negative value for `N'
5496 chooses this scheme, ensuring that branches to stubs always use a
5497 negative offset. Two special values of `N' are recognized, `1'
5498 and `-1'. These both instruct `ld' to automatically size input
5499 section groups for the branch types detected, with the same
5500 behaviour regarding stub placement as other positive or negative
5501 values of `N' respectively.
5503 Note that `--stub-group-size' does not split input sections. A
5504 single input section larger than the group size specified will of
5505 course create a larger group (of one section). If input sections
5506 are too large, it may not be possible for a branch to reach its
5510 This option causes `ld' to label linker stubs with a local symbol
5511 that encodes the stub type and destination.
5513 `--dotsyms, --no-dotsyms'
5514 These two options control how `ld' interprets version patterns in
5515 a version script. Older PowerPC64 compilers emitted both a
5516 function descriptor symbol with the same name as the function, and
5517 a code entry symbol with the name prefixed by a dot (`.'). To
5518 properly version a function `foo', the version script thus needs
5519 to control both `foo' and `.foo'. The option `--dotsyms', on by
5520 default, automatically adds the required dot-prefixed patterns.
5521 Use `--no-dotsyms' to disable this feature.
5524 PowerPC64 `ld' normally performs some optimization of code
5525 sequences used to access Thread-Local Storage. Use this option to
5526 disable the optimization.
5529 PowerPC64 `ld' normally removes `.opd' section entries
5530 corresponding to deleted link-once functions, or functions removed
5531 by the action of `--gc-sections' or linker script `/DISCARD/'.
5532 Use this option to disable `.opd' optimization.
5534 `--non-overlapping-opd'
5535 Some PowerPC64 compilers have an option to generate compressed
5536 `.opd' entries spaced 16 bytes apart, overlapping the third word,
5537 the static chain pointer (unused in C) with the first word of the
5538 next entry. This option expands such entries to the full 24 bytes.
5541 PowerPC64 `ld' normally removes unused `.toc' section entries.
5542 Such entries are detected by examining relocations that reference
5543 the TOC in code sections. A reloc in a deleted code section marks
5544 a TOC word as unneeded, while a reloc in a kept code section marks
5545 a TOC word as needed. Since the TOC may reference itself, TOC
5546 relocs are also examined. TOC words marked as both needed and
5547 unneeded will of course be kept. TOC words without any referencing
5548 reloc are assumed to be part of a multi-word entry, and are kept or
5549 discarded as per the nearest marked preceding word. This works
5550 reliably for compiler generated code, but may be incorrect if
5551 assembly code is used to insert TOC entries. Use this option to
5552 disable the optimization.
5555 If given any toc option besides `-mcmodel=medium' or
5556 `-mcmodel=large', PowerPC64 GCC generates code for a TOC model
5557 where TOC entries are accessed with a 16-bit offset from r2. This
5558 limits the total TOC size to 64K. PowerPC64 `ld' extends this
5559 limit by grouping code sections such that each group uses less
5560 than 64K for its TOC entries, then inserts r2 adjusting stubs
5561 between inter-group calls. `ld' does not split apart input
5562 sections, so cannot help if a single input file has a `.toc'
5563 section that exceeds 64K, most likely from linking multiple files
5564 with `ld -r'. Use this option to turn off this feature.
5567 By default, `ld' sorts TOC sections so that those whose file
5568 happens to have a section called `.init' or `.fini' are placed
5569 first, followed by TOC sections referenced by code generated with
5570 PowerPC64 gcc's `-mcmodel=small', and lastly TOC sections
5571 referenced only by code generated with PowerPC64 gcc's
5572 `-mcmodel=medium' or `-mcmodel=large' options. Doing this results
5573 in better TOC grouping for multi-TOC. Use this option to turn off
5578 Use these options to control whether individual PLT call stubs are
5579 aligned to a 32-byte boundary, or to the specified power of two
5580 boundary when using `--plt-align='. By default PLT call stubs are
5583 `--plt-static-chain'
5584 `--no-plt-static-chain'
5585 Use these options to control whether PLT call stubs load the static
5586 chain pointer (r11). `ld' defaults to not loading the static
5587 chain since there is never any need to do so on a PLT call.
5591 With power7's weakly ordered memory model, it is possible when
5592 using lazy binding for ld.so to update a plt entry in one thread
5593 and have another thread see the individual plt entry words update
5594 in the wrong order, despite ld.so carefully writing in the correct
5595 order and using memory write barriers. To avoid this we need some
5596 sort of read barrier in the call stub, or use LD_BIND_NOW=1. By
5597 default, `ld' looks for calls to commonly used functions that
5598 create threads, and if seen, adds the necessary barriers. Use
5599 these options to change the default behaviour.
5602 File: ld.info, Node: SPU ELF, Next: TI COFF, Prev: PowerPC64 ELF64, Up: Machine Dependent
5604 4.11 `ld' and SPU ELF Support
5605 =============================
5608 This option marks an executable as a PIC plugin module.
5611 Normally, `ld' recognizes calls to functions within overlay
5612 regions, and redirects such calls to an overlay manager via a stub.
5613 `ld' also provides a built-in overlay manager. This option turns
5614 off all this special overlay handling.
5617 This option causes `ld' to label overlay stubs with a local symbol
5618 that encodes the stub type and destination.
5620 `--extra-overlay-stubs'
5621 This option causes `ld' to add overlay call stubs on all function
5622 calls out of overlay regions. Normally stubs are not added on
5623 calls to non-overlay regions.
5625 `--local-store=lo:hi'
5626 `ld' usually checks that a final executable for SPU fits in the
5627 address range 0 to 256k. This option may be used to change the
5628 range. Disable the check entirely with `--local-store=0:0'.
5631 SPU local store space is limited. Over-allocation of stack space
5632 unnecessarily limits space available for code and data, while
5633 under-allocation results in runtime failures. If given this
5634 option, `ld' will provide an estimate of maximum stack usage.
5635 `ld' does this by examining symbols in code sections to determine
5636 the extents of functions, and looking at function prologues for
5637 stack adjusting instructions. A call-graph is created by looking
5638 for relocations on branch instructions. The graph is then searched
5639 for the maximum stack usage path. Note that this analysis does not
5640 find calls made via function pointers, and does not handle
5641 recursion and other cycles in the call graph. Stack usage may be
5642 under-estimated if your code makes such calls. Also, stack usage
5643 for dynamic allocation, e.g. alloca, will not be detected. If a
5644 link map is requested, detailed information about each function's
5645 stack usage and calls will be given.
5648 This option, if given along with `--stack-analysis' will result in
5649 `ld' emitting stack sizing symbols for each function. These take
5650 the form `__stack_<function_name>' for global functions, and
5651 `__stack_<number>_<function_name>' for static functions.
5652 `<number>' is the section id in hex. The value of such symbols is
5653 the stack requirement for the corresponding function. The symbol
5654 size will be zero, type `STT_NOTYPE', binding `STB_LOCAL', and
5658 File: ld.info, Node: TI COFF, Next: WIN32, Prev: SPU ELF, Up: Machine Dependent
5660 4.12 `ld''s Support for Various TI COFF Versions
5661 ================================================
5663 The `--format' switch allows selection of one of the various TI COFF
5664 versions. The latest of this writing is 2; versions 0 and 1 are also
5665 supported. The TI COFF versions also vary in header byte-order format;
5666 `ld' will read any version or byte order, but the output header format
5667 depends on the default specified by the specific target.
5670 File: ld.info, Node: WIN32, Next: Xtensa, Prev: TI COFF, Up: Machine Dependent
5672 4.13 `ld' and WIN32 (cygwin/mingw)
5673 ==================================
5675 This section describes some of the win32 specific `ld' issues. See
5676 *Note Command Line Options: Options. for detailed description of the
5677 command line options mentioned here.
5680 The standard Windows linker creates and uses so-called import
5681 libraries, which contains information for linking to dll's. They
5682 are regular static archives and are handled as any other static
5683 archive. The cygwin and mingw ports of `ld' have specific support
5684 for creating such libraries provided with the `--out-implib'
5685 command line option.
5687 _exporting DLL symbols_
5688 The cygwin/mingw `ld' has several ways to export symbols for dll's.
5690 _using auto-export functionality_
5691 By default `ld' exports symbols with the auto-export
5692 functionality, which is controlled by the following command
5695 * -export-all-symbols [This is the default]
5701 * -exclude-modules-for-implib
5705 When auto-export is in operation, `ld' will export all the
5706 non-local (global and common) symbols it finds in a DLL, with
5707 the exception of a few symbols known to belong to the
5708 system's runtime and libraries. As it will often not be
5709 desirable to export all of a DLL's symbols, which may include
5710 private functions that are not part of any public interface,
5711 the command-line options listed above may be used to filter
5712 symbols out from the list for exporting. The `--output-def'
5713 option can be used in order to see the final list of exported
5714 symbols with all exclusions taken into effect.
5716 If `--export-all-symbols' is not given explicitly on the
5717 command line, then the default auto-export behavior will be
5718 _disabled_ if either of the following are true:
5720 * A DEF file is used.
5722 * Any symbol in any object file was marked with the
5723 __declspec(dllexport) attribute.
5726 Another way of exporting symbols is using a DEF file. A DEF
5727 file is an ASCII file containing definitions of symbols which
5728 should be exported when a dll is created. Usually it is
5729 named `<dll name>.def' and is added as any other object file
5730 to the linker's command line. The file's name must end in
5733 gcc -o <output> <objectfiles> <dll name>.def
5735 Using a DEF file turns off the normal auto-export behavior,
5736 unless the `--export-all-symbols' option is also used.
5738 Here is an example of a DEF file for a shared library called
5741 LIBRARY "xyz.dll" BASE=0x20000000
5747 another_foo = abc.dll.afoo
5752 This example defines a DLL with a non-default base address
5753 and seven symbols in the export table. The third exported
5754 symbol `_bar' is an alias for the second. The fourth symbol,
5755 `another_foo' is resolved by "forwarding" to another module
5756 and treating it as an alias for `afoo' exported from the DLL
5757 `abc.dll'. The final symbol `var1' is declared to be a data
5758 object. The `doo' symbol in export library is an alias of
5759 `foo', which gets the string name in export table `foo2'. The
5760 `eoo' symbol is an data export symbol, which gets in export
5761 table the name `var1'.
5763 The optional `LIBRARY <name>' command indicates the _internal_
5764 name of the output DLL. If `<name>' does not include a suffix,
5765 the default library suffix, `.DLL' is appended.
5767 When the .DEF file is used to build an application, rather
5768 than a library, the `NAME <name>' command should be used
5769 instead of `LIBRARY'. If `<name>' does not include a suffix,
5770 the default executable suffix, `.EXE' is appended.
5772 With either `LIBRARY <name>' or `NAME <name>' the optional
5773 specification `BASE = <number>' may be used to specify a
5774 non-default base address for the image.
5776 If neither `LIBRARY <name>' nor `NAME <name>' is specified,
5777 or they specify an empty string, the internal name is the
5778 same as the filename specified on the command line.
5780 The complete specification of an export symbol is:
5783 ( ( ( <name1> [ = <name2> ] )
5784 | ( <name1> = <module-name> . <external-name>))
5785 [ @ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) *
5787 Declares `<name1>' as an exported symbol from the DLL, or
5788 declares `<name1>' as an exported alias for `<name2>'; or
5789 declares `<name1>' as a "forward" alias for the symbol
5790 `<external-name>' in the DLL `<module-name>'. Optionally,
5791 the symbol may be exported by the specified ordinal
5792 `<integer>' alias. The optional `<name3>' is the to be used
5793 string in import/export table for the symbol.
5795 The optional keywords that follow the declaration indicate:
5797 `NONAME': Do not put the symbol name in the DLL's export
5798 table. It will still be exported by its ordinal alias
5799 (either the value specified by the .def specification or,
5800 otherwise, the value assigned by the linker). The symbol
5801 name, however, does remain visible in the import library (if
5802 any), unless `PRIVATE' is also specified.
5804 `DATA': The symbol is a variable or object, rather than a
5805 function. The import lib will export only an indirect
5806 reference to `foo' as the symbol `_imp__foo' (ie, `foo' must
5807 be resolved as `*_imp__foo').
5809 `CONSTANT': Like `DATA', but put the undecorated `foo' as
5810 well as `_imp__foo' into the import library. Both refer to the
5811 read-only import address table's pointer to the variable, not
5812 to the variable itself. This can be dangerous. If the user
5813 code fails to add the `dllimport' attribute and also fails to
5814 explicitly add the extra indirection that the use of the
5815 attribute enforces, the application will behave unexpectedly.
5817 `PRIVATE': Put the symbol in the DLL's export table, but do
5818 not put it into the static import library used to resolve
5819 imports at link time. The symbol can still be imported using
5820 the `LoadLibrary/GetProcAddress' API at runtime or by by
5821 using the GNU ld extension of linking directly to the DLL
5822 without an import library.
5824 See ld/deffilep.y in the binutils sources for the full
5825 specification of other DEF file statements
5827 While linking a shared dll, `ld' is able to create a DEF file
5828 with the `--output-def <file>' command line option.
5831 Another way of marking symbols for export is to modify the
5832 source code itself, so that when building the DLL each symbol
5833 to be exported is declared as:
5835 __declspec(dllexport) int a_variable
5836 __declspec(dllexport) void a_function(int with_args)
5838 All such symbols will be exported from the DLL. If, however,
5839 any of the object files in the DLL contain symbols decorated
5840 in this way, then the normal auto-export behavior is
5841 disabled, unless the `--export-all-symbols' option is also
5844 Note that object files that wish to access these symbols must
5845 _not_ decorate them with dllexport. Instead, they should use
5848 __declspec(dllimport) int a_variable
5849 __declspec(dllimport) void a_function(int with_args)
5851 This complicates the structure of library header files,
5852 because when included by the library itself the header must
5853 declare the variables and functions as dllexport, but when
5854 included by client code the header must declare them as
5855 dllimport. There are a number of idioms that are typically
5856 used to do this; often client code can omit the __declspec()
5857 declaration completely. See `--enable-auto-import' and
5858 `automatic data imports' for more information.
5860 _automatic data imports_
5861 The standard Windows dll format supports data imports from dlls
5862 only by adding special decorations (dllimport/dllexport), which
5863 let the compiler produce specific assembler instructions to deal
5864 with this issue. This increases the effort necessary to port
5865 existing Un*x code to these platforms, especially for large c++
5866 libraries and applications. The auto-import feature, which was
5867 initially provided by Paul Sokolovsky, allows one to omit the
5868 decorations to achieve a behavior that conforms to that on
5869 POSIX/Un*x platforms. This feature is enabled with the
5870 `--enable-auto-import' command-line option, although it is enabled
5871 by default on cygwin/mingw. The `--enable-auto-import' option
5872 itself now serves mainly to suppress any warnings that are
5873 ordinarily emitted when linked objects trigger the feature's use.
5875 auto-import of variables does not always work flawlessly without
5876 additional assistance. Sometimes, you will see this message
5878 "variable '<var>' can't be auto-imported. Please read the
5879 documentation for ld's `--enable-auto-import' for details."
5881 The `--enable-auto-import' documentation explains why this error
5882 occurs, and several methods that can be used to overcome this
5883 difficulty. One of these methods is the _runtime pseudo-relocs_
5884 feature, described below.
5886 For complex variables imported from DLLs (such as structs or
5887 classes), object files typically contain a base address for the
5888 variable and an offset (_addend_) within the variable-to specify a
5889 particular field or public member, for instance. Unfortunately,
5890 the runtime loader used in win32 environments is incapable of
5891 fixing these references at runtime without the additional
5892 information supplied by dllimport/dllexport decorations. The
5893 standard auto-import feature described above is unable to resolve
5896 The `--enable-runtime-pseudo-relocs' switch allows these
5897 references to be resolved without error, while leaving the task of
5898 adjusting the references themselves (with their non-zero addends)
5899 to specialized code provided by the runtime environment. Recent
5900 versions of the cygwin and mingw environments and compilers
5901 provide this runtime support; older versions do not. However, the
5902 support is only necessary on the developer's platform; the
5903 compiled result will run without error on an older system.
5905 `--enable-runtime-pseudo-relocs' is not the default; it must be
5906 explicitly enabled as needed.
5908 _direct linking to a dll_
5909 The cygwin/mingw ports of `ld' support the direct linking,
5910 including data symbols, to a dll without the usage of any import
5911 libraries. This is much faster and uses much less memory than
5912 does the traditional import library method, especially when
5913 linking large libraries or applications. When `ld' creates an
5914 import lib, each function or variable exported from the dll is
5915 stored in its own bfd, even though a single bfd could contain many
5916 exports. The overhead involved in storing, loading, and
5917 processing so many bfd's is quite large, and explains the
5918 tremendous time, memory, and storage needed to link against
5919 particularly large or complex libraries when using import libs.
5921 Linking directly to a dll uses no extra command-line switches
5922 other than `-L' and `-l', because `ld' already searches for a
5923 number of names to match each library. All that is needed from
5924 the developer's perspective is an understanding of this search, in
5925 order to force ld to select the dll instead of an import library.
5927 For instance, when ld is called with the argument `-lxxx' it will
5928 attempt to find, in the first directory of its search path,
5938 before moving on to the next directory in the search path.
5940 (*) Actually, this is not `cygxxx.dll' but in fact is
5941 `<prefix>xxx.dll', where `<prefix>' is set by the `ld' option
5942 `--dll-search-prefix=<prefix>'. In the case of cygwin, the
5943 standard gcc spec file includes `--dll-search-prefix=cyg', so in
5944 effect we actually search for `cygxxx.dll'.
5946 Other win32-based unix environments, such as mingw or pw32, may
5947 use other `<prefix>'es, although at present only cygwin makes use
5948 of this feature. It was originally intended to help avoid name
5949 conflicts among dll's built for the various win32/un*x
5950 environments, so that (for example) two versions of a zlib dll
5951 could coexist on the same machine.
5953 The generic cygwin/mingw path layout uses a `bin' directory for
5954 applications and dll's and a `lib' directory for the import
5955 libraries (using cygwin nomenclature):
5960 libxxx.dll.a (in case of dll's)
5961 libxxx.a (in case of static archive)
5963 Linking directly to a dll without using the import library can be
5966 1. Use the dll directly by adding the `bin' path to the link line
5967 gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx
5969 However, as the dll's often have version numbers appended to their
5970 names (`cygncurses-5.dll') this will often fail, unless one
5971 specifies `-L../bin -lncurses-5' to include the version. Import
5972 libs are generally not versioned, and do not have this difficulty.
5974 2. Create a symbolic link from the dll to a file in the `lib'
5975 directory according to the above mentioned search pattern. This
5976 should be used to avoid unwanted changes in the tools needed for
5979 ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a]
5981 Then you can link without any make environment changes.
5983 gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx
5985 This technique also avoids the version number problems, because
5986 the following is perfectly legal
5991 libxxx.dll.a -> ../bin/cygxxx-5.dll
5993 Linking directly to a dll without using an import lib will work
5994 even when auto-import features are exercised, and even when
5995 `--enable-runtime-pseudo-relocs' is used.
5997 Given the improvements in speed and memory usage, one might
5998 justifiably wonder why import libraries are used at all. There
6001 1. Until recently, the link-directly-to-dll functionality did _not_
6002 work with auto-imported data.
6004 2. Sometimes it is necessary to include pure static objects within
6005 the import library (which otherwise contains only bfd's for
6006 indirection symbols that point to the exports of a dll). Again,
6007 the import lib for the cygwin kernel makes use of this ability,
6008 and it is not possible to do this without an import lib.
6010 3. Symbol aliases can only be resolved using an import lib. This
6011 is critical when linking against OS-supplied dll's (eg, the win32
6012 API) in which symbols are usually exported as undecorated aliases
6013 of their stdcall-decorated assembly names.
6015 So, import libs are not going away. But the ability to replace
6016 true import libs with a simple symbolic link to (or a copy of) a
6017 dll, in many cases, is a useful addition to the suite of tools
6018 binutils makes available to the win32 developer. Given the
6019 massive improvements in memory requirements during linking, storage
6020 requirements, and linking speed, we expect that many developers
6021 will soon begin to use this feature whenever possible.
6025 _adding additional names_
6026 Sometimes, it is useful to export symbols with additional
6027 names. A symbol `foo' will be exported as `foo', but it can
6028 also be exported as `_foo' by using special directives in the
6029 DEF file when creating the dll. This will affect also the
6030 optional created import library. Consider the following DEF
6033 LIBRARY "xyz.dll" BASE=0x61000000
6039 The line `_foo = foo' maps the symbol `foo' to `_foo'.
6041 Another method for creating a symbol alias is to create it in
6042 the source code using the "weak" attribute:
6044 void foo () { /* Do something. */; }
6045 void _foo () __attribute__ ((weak, alias ("foo")));
6047 See the gcc manual for more information about attributes and
6051 Sometimes it is useful to rename exports. For instance, the
6052 cygwin kernel does this regularly. A symbol `_foo' can be
6053 exported as `foo' but not as `_foo' by using special
6054 directives in the DEF file. (This will also affect the import
6055 library, if it is created). In the following example:
6057 LIBRARY "xyz.dll" BASE=0x61000000
6062 The line `_foo = foo' maps the exported symbol `foo' to
6065 Note: using a DEF file disables the default auto-export behavior,
6066 unless the `--export-all-symbols' command line option is used.
6067 If, however, you are trying to rename symbols, then you should list
6068 _all_ desired exports in the DEF file, including the symbols that
6069 are not being renamed, and do _not_ use the `--export-all-symbols'
6070 option. If you list only the renamed symbols in the DEF file, and
6071 use `--export-all-symbols' to handle the other symbols, then the
6072 both the new names _and_ the original names for the renamed
6073 symbols will be exported. In effect, you'd be aliasing those
6074 symbols, not renaming them, which is probably not what you wanted.
6077 The Windows object format, PE, specifies a form of weak symbols
6078 called weak externals. When a weak symbol is linked and the
6079 symbol is not defined, the weak symbol becomes an alias for some
6080 other symbol. There are three variants of weak externals:
6081 * Definition is searched for in objects and libraries,
6082 historically called lazy externals.
6084 * Definition is searched for only in other objects, not in
6085 libraries. This form is not presently implemented.
6087 * No search; the symbol is an alias. This form is not presently
6089 As a GNU extension, weak symbols that do not specify an alternate
6090 symbol are supported. If the symbol is undefined when linking,
6091 the symbol uses a default value.
6093 _aligned common symbols_
6094 As a GNU extension to the PE file format, it is possible to
6095 specify the desired alignment for a common symbol. This
6096 information is conveyed from the assembler or compiler to the
6097 linker by means of GNU-specific commands carried in the object
6098 file's `.drectve' section, which are recognized by `ld' and
6099 respected when laying out the common symbols. Native tools will
6100 be able to process object files employing this GNU extension, but
6101 will fail to respect the alignment instructions, and may issue
6102 noisy warnings about unknown linker directives.
6105 File: ld.info, Node: Xtensa, Prev: WIN32, Up: Machine Dependent
6107 4.14 `ld' and Xtensa Processors
6108 ===============================
6110 The default `ld' behavior for Xtensa processors is to interpret
6111 `SECTIONS' commands so that lists of explicitly named sections in a
6112 specification with a wildcard file will be interleaved when necessary to
6113 keep literal pools within the range of PC-relative load offsets. For
6114 example, with the command:
6123 `ld' may interleave some of the `.literal' and `.text' sections from
6124 different object files to ensure that the literal pools are within the
6125 range of PC-relative load offsets. A valid interleaving might place
6126 the `.literal' sections from an initial group of files followed by the
6127 `.text' sections of that group of files. Then, the `.literal' sections
6128 from the rest of the files and the `.text' sections from the rest of
6129 the files would follow.
6131 Relaxation is enabled by default for the Xtensa version of `ld' and
6132 provides two important link-time optimizations. The first optimization
6133 is to combine identical literal values to reduce code size. A redundant
6134 literal will be removed and all the `L32R' instructions that use it
6135 will be changed to reference an identical literal, as long as the
6136 location of the replacement literal is within the offset range of all
6137 the `L32R' instructions. The second optimization is to remove
6138 unnecessary overhead from assembler-generated "longcall" sequences of
6139 `L32R'/`CALLXN' when the target functions are within range of direct
6140 `CALLN' instructions.
6142 For each of these cases where an indirect call sequence can be
6143 optimized to a direct call, the linker will change the `CALLXN'
6144 instruction to a `CALLN' instruction, remove the `L32R' instruction,
6145 and remove the literal referenced by the `L32R' instruction if it is
6146 not used for anything else. Removing the `L32R' instruction always
6147 reduces code size but can potentially hurt performance by changing the
6148 alignment of subsequent branch targets. By default, the linker will
6149 always preserve alignments, either by switching some instructions
6150 between 24-bit encodings and the equivalent density instructions or by
6151 inserting a no-op in place of the `L32R' instruction that was removed.
6152 If code size is more important than performance, the `--size-opt'
6153 option can be used to prevent the linker from widening density
6154 instructions or inserting no-ops, except in a few cases where no-ops
6155 are required for correctness.
6157 The following Xtensa-specific command-line options can be used to
6161 When optimizing indirect calls to direct calls, optimize for code
6162 size more than performance. With this option, the linker will not
6163 insert no-ops or widen density instructions to preserve branch
6164 target alignment. There may still be some cases where no-ops are
6165 required to preserve the correctness of the code.
6168 File: ld.info, Node: BFD, Next: Reporting Bugs, Prev: Machine Dependent, Up: Top
6173 The linker accesses object and archive files using the BFD libraries.
6174 These libraries allow the linker to use the same routines to operate on
6175 object files whatever the object file format. A different object file
6176 format can be supported simply by creating a new BFD back end and adding
6177 it to the library. To conserve runtime memory, however, the linker and
6178 associated tools are usually configured to support only a subset of the
6179 object file formats available. You can use `objdump -i' (*note
6180 objdump: (binutils.info)objdump.) to list all the formats available for
6183 As with most implementations, BFD is a compromise between several
6184 conflicting requirements. The major factor influencing BFD design was
6185 efficiency: any time used converting between formats is time which
6186 would not have been spent had BFD not been involved. This is partly
6187 offset by abstraction payback; since BFD simplifies applications and
6188 back ends, more time and care may be spent optimizing algorithms for a
6191 One minor artifact of the BFD solution which you should bear in mind
6192 is the potential for information loss. There are two places where
6193 useful information can be lost using the BFD mechanism: during
6194 conversion and during output. *Note BFD information loss::.
6198 * BFD outline:: How it works: an outline of BFD
6201 File: ld.info, Node: BFD outline, Up: BFD
6203 5.1 How It Works: An Outline of BFD
6204 ===================================
6206 When an object file is opened, BFD subroutines automatically determine
6207 the format of the input object file. They then build a descriptor in
6208 memory with pointers to routines that will be used to access elements of
6209 the object file's data structures.
6211 As different information from the object files is required, BFD
6212 reads from different sections of the file and processes them. For
6213 example, a very common operation for the linker is processing symbol
6214 tables. Each BFD back end provides a routine for converting between
6215 the object file's representation of symbols and an internal canonical
6216 format. When the linker asks for the symbol table of an object file, it
6217 calls through a memory pointer to the routine from the relevant BFD
6218 back end which reads and converts the table into a canonical form. The
6219 linker then operates upon the canonical form. When the link is finished
6220 and the linker writes the output file's symbol table, another BFD back
6221 end routine is called to take the newly created symbol table and
6222 convert it into the chosen output format.
6226 * BFD information loss:: Information Loss
6227 * Canonical format:: The BFD canonical object-file format
6230 File: ld.info, Node: BFD information loss, Next: Canonical format, Up: BFD outline
6232 5.1.1 Information Loss
6233 ----------------------
6235 _Information can be lost during output._ The output formats supported
6236 by BFD do not provide identical facilities, and information which can
6237 be described in one form has nowhere to go in another format. One
6238 example of this is alignment information in `b.out'. There is nowhere
6239 in an `a.out' format file to store alignment information on the
6240 contained data, so when a file is linked from `b.out' and an `a.out'
6241 image is produced, alignment information will not propagate to the
6242 output file. (The linker will still use the alignment information
6243 internally, so the link is performed correctly).
6245 Another example is COFF section names. COFF files may contain an
6246 unlimited number of sections, each one with a textual section name. If
6247 the target of the link is a format which does not have many sections
6248 (e.g., `a.out') or has sections without names (e.g., the Oasys format),
6249 the link cannot be done simply. You can circumvent this problem by
6250 describing the desired input-to-output section mapping with the linker
6253 _Information can be lost during canonicalization._ The BFD internal
6254 canonical form of the external formats is not exhaustive; there are
6255 structures in input formats for which there is no direct representation
6256 internally. This means that the BFD back ends cannot maintain all
6257 possible data richness through the transformation between external to
6258 internal and back to external formats.
6260 This limitation is only a problem when an application reads one
6261 format and writes another. Each BFD back end is responsible for
6262 maintaining as much data as possible, and the internal BFD canonical
6263 form has structures which are opaque to the BFD core, and exported only
6264 to the back ends. When a file is read in one format, the canonical form
6265 is generated for BFD and the application. At the same time, the back
6266 end saves away any information which may otherwise be lost. If the data
6267 is then written back in the same format, the back end routine will be
6268 able to use the canonical form provided by the BFD core as well as the
6269 information it prepared earlier. Since there is a great deal of
6270 commonality between back ends, there is no information lost when
6271 linking or copying big endian COFF to little endian COFF, or `a.out' to
6272 `b.out'. When a mixture of formats is linked, the information is only
6273 lost from the files whose format differs from the destination.
6276 File: ld.info, Node: Canonical format, Prev: BFD information loss, Up: BFD outline
6278 5.1.2 The BFD canonical object-file format
6279 ------------------------------------------
6281 The greatest potential for loss of information occurs when there is the
6282 least overlap between the information provided by the source format,
6283 that stored by the canonical format, and that needed by the destination
6284 format. A brief description of the canonical form may help you
6285 understand which kinds of data you can count on preserving across
6289 Information stored on a per-file basis includes target machine
6290 architecture, particular implementation format type, a demand
6291 pageable bit, and a write protected bit. Information like Unix
6292 magic numbers is not stored here--only the magic numbers' meaning,
6293 so a `ZMAGIC' file would have both the demand pageable bit and the
6294 write protected text bit set. The byte order of the target is
6295 stored on a per-file basis, so that big- and little-endian object
6296 files may be used with one another.
6299 Each section in the input file contains the name of the section,
6300 the section's original address in the object file, size and
6301 alignment information, various flags, and pointers into other BFD
6305 Each symbol contains a pointer to the information for the object
6306 file which originally defined it, its name, its value, and various
6307 flag bits. When a BFD back end reads in a symbol table, it
6308 relocates all symbols to make them relative to the base of the
6309 section where they were defined. Doing this ensures that each
6310 symbol points to its containing section. Each symbol also has a
6311 varying amount of hidden private data for the BFD back end. Since
6312 the symbol points to the original file, the private data format
6313 for that symbol is accessible. `ld' can operate on a collection
6314 of symbols of wildly different formats without problems.
6316 Normal global and simple local symbols are maintained on output,
6317 so an output file (no matter its format) will retain symbols
6318 pointing to functions and to global, static, and common variables.
6319 Some symbol information is not worth retaining; in `a.out', type
6320 information is stored in the symbol table as long symbol names.
6321 This information would be useless to most COFF debuggers; the
6322 linker has command line switches to allow users to throw it away.
6324 There is one word of type information within the symbol, so if the
6325 format supports symbol type information within symbols (for
6326 example, COFF, IEEE, Oasys) and the type is simple enough to fit
6327 within one word (nearly everything but aggregates), the
6328 information will be preserved.
6331 Each canonical BFD relocation record contains a pointer to the
6332 symbol to relocate to, the offset of the data to relocate, the
6333 section the data is in, and a pointer to a relocation type
6334 descriptor. Relocation is performed by passing messages through
6335 the relocation type descriptor and the symbol pointer. Therefore,
6336 relocations can be performed on output data using a relocation
6337 method that is only available in one of the input formats. For
6338 instance, Oasys provides a byte relocation format. A relocation
6339 record requesting this relocation type would point indirectly to a
6340 routine to perform this, so the relocation may be performed on a
6341 byte being written to a 68k COFF file, even though 68k COFF has no
6342 such relocation type.
6345 Object formats can contain, for debugging purposes, some form of
6346 mapping between symbols, source line numbers, and addresses in the
6347 output file. These addresses have to be relocated along with the
6348 symbol information. Each symbol with an associated list of line
6349 number records points to the first record of the list. The head
6350 of a line number list consists of a pointer to the symbol, which
6351 allows finding out the address of the function whose line number
6352 is being described. The rest of the list is made up of pairs:
6353 offsets into the section and line numbers. Any format which can
6354 simply derive this information can pass it successfully between
6355 formats (COFF, IEEE and Oasys).
6358 File: ld.info, Node: Reporting Bugs, Next: MRI, Prev: BFD, Up: Top
6363 Your bug reports play an essential role in making `ld' reliable.
6365 Reporting a bug may help you by bringing a solution to your problem,
6366 or it may not. But in any case the principal function of a bug report
6367 is to help the entire community by making the next version of `ld' work
6368 better. Bug reports are your contribution to the maintenance of `ld'.
6370 In order for a bug report to serve its purpose, you must include the
6371 information that enables us to fix the bug.
6375 * Bug Criteria:: Have you found a bug?
6376 * Bug Reporting:: How to report bugs
6379 File: ld.info, Node: Bug Criteria, Next: Bug Reporting, Up: Reporting Bugs
6381 6.1 Have You Found a Bug?
6382 =========================
6384 If you are not sure whether you have found a bug, here are some
6387 * If the linker gets a fatal signal, for any input whatever, that is
6388 a `ld' bug. Reliable linkers never crash.
6390 * If `ld' produces an error message for valid input, that is a bug.
6392 * If `ld' does not produce an error message for invalid input, that
6393 may be a bug. In the general case, the linker can not verify that
6394 object files are correct.
6396 * If you are an experienced user of linkers, your suggestions for
6397 improvement of `ld' are welcome in any case.
6400 File: ld.info, Node: Bug Reporting, Prev: Bug Criteria, Up: Reporting Bugs
6402 6.2 How to Report Bugs
6403 ======================
6405 A number of companies and individuals offer support for GNU products.
6406 If you obtained `ld' from a support organization, we recommend you
6407 contact that organization first.
6409 You can find contact information for many support companies and
6410 individuals in the file `etc/SERVICE' in the GNU Emacs distribution.
6412 Otherwise, send bug reports for `ld' to
6413 `http://www.sourceware.org/bugzilla/'.
6415 The fundamental principle of reporting bugs usefully is this:
6416 *report all the facts*. If you are not sure whether to state a fact or
6417 leave it out, state it!
6419 Often people omit facts because they think they know what causes the
6420 problem and assume that some details do not matter. Thus, you might
6421 assume that the name of a symbol you use in an example does not matter.
6422 Well, probably it does not, but one cannot be sure. Perhaps the bug
6423 is a stray memory reference which happens to fetch from the location
6424 where that name is stored in memory; perhaps, if the name were
6425 different, the contents of that location would fool the linker into
6426 doing the right thing despite the bug. Play it safe and give a
6427 specific, complete example. That is the easiest thing for you to do,
6428 and the most helpful.
6430 Keep in mind that the purpose of a bug report is to enable us to fix
6431 the bug if it is new to us. Therefore, always write your bug reports
6432 on the assumption that the bug has not been reported previously.
6434 Sometimes people give a few sketchy facts and ask, "Does this ring a
6435 bell?" This cannot help us fix a bug, so it is basically useless. We
6436 respond by asking for enough details to enable us to investigate. You
6437 might as well expedite matters by sending them to begin with.
6439 To enable us to fix the bug, you should include all these things:
6441 * The version of `ld'. `ld' announces it if you start it with the
6442 `--version' argument.
6444 Without this, we will not know whether there is any point in
6445 looking for the bug in the current version of `ld'.
6447 * Any patches you may have applied to the `ld' source, including any
6448 patches made to the `BFD' library.
6450 * The type of machine you are using, and the operating system name
6453 * What compiler (and its version) was used to compile `ld'--e.g.
6456 * The command arguments you gave the linker to link your example and
6457 observe the bug. To guarantee you will not omit something
6458 important, list them all. A copy of the Makefile (or the output
6459 from make) is sufficient.
6461 If we were to try to guess the arguments, we would probably guess
6462 wrong and then we might not encounter the bug.
6464 * A complete input file, or set of input files, that will reproduce
6465 the bug. It is generally most helpful to send the actual object
6466 files provided that they are reasonably small. Say no more than
6467 10K. For bigger files you can either make them available by FTP
6468 or HTTP or else state that you are willing to send the object
6469 file(s) to whomever requests them. (Note - your email will be
6470 going to a mailing list, so we do not want to clog it up with
6471 large attachments). But small attachments are best.
6473 If the source files were assembled using `gas' or compiled using
6474 `gcc', then it may be OK to send the source files rather than the
6475 object files. In this case, be sure to say exactly what version of
6476 `gas' or `gcc' was used to produce the object files. Also say how
6477 `gas' or `gcc' were configured.
6479 * A description of what behavior you observe that you believe is
6480 incorrect. For example, "It gets a fatal signal."
6482 Of course, if the bug is that `ld' gets a fatal signal, then we
6483 will certainly notice it. But if the bug is incorrect output, we
6484 might not notice unless it is glaringly wrong. You might as well
6485 not give us a chance to make a mistake.
6487 Even if the problem you experience is a fatal signal, you should
6488 still say so explicitly. Suppose something strange is going on,
6489 such as, your copy of `ld' is out of sync, or you have encountered
6490 a bug in the C library on your system. (This has happened!) Your
6491 copy might crash and ours would not. If you told us to expect a
6492 crash, then when ours fails to crash, we would know that the bug
6493 was not happening for us. If you had not told us to expect a
6494 crash, then we would not be able to draw any conclusion from our
6497 * If you wish to suggest changes to the `ld' source, send us context
6498 diffs, as generated by `diff' with the `-u', `-c', or `-p' option.
6499 Always send diffs from the old file to the new file. If you even
6500 discuss something in the `ld' source, refer to it by context, not
6503 The line numbers in our development sources will not match those
6504 in your sources. Your line numbers would convey no useful
6507 Here are some things that are not necessary:
6509 * A description of the envelope of the bug.
6511 Often people who encounter a bug spend a lot of time investigating
6512 which changes to the input file will make the bug go away and which
6513 changes will not affect it.
6515 This is often time consuming and not very useful, because the way
6516 we will find the bug is by running a single example under the
6517 debugger with breakpoints, not by pure deduction from a series of
6518 examples. We recommend that you save your time for something else.
6520 Of course, if you can find a simpler example to report _instead_
6521 of the original one, that is a convenience for us. Errors in the
6522 output will be easier to spot, running under the debugger will take
6523 less time, and so on.
6525 However, simplification is not vital; if you do not want to do
6526 this, report the bug anyway and send us the entire test case you
6529 * A patch for the bug.
6531 A patch for the bug does help us if it is a good one. But do not
6532 omit the necessary information, such as the test case, on the
6533 assumption that a patch is all we need. We might see problems
6534 with your patch and decide to fix the problem another way, or we
6535 might not understand it at all.
6537 Sometimes with a program as complicated as `ld' it is very hard to
6538 construct an example that will make the program follow a certain
6539 path through the code. If you do not send us the example, we will
6540 not be able to construct one, so we will not be able to verify
6541 that the bug is fixed.
6543 And if we cannot understand what bug you are trying to fix, or why
6544 your patch should be an improvement, we will not install it. A
6545 test case will help us to understand.
6547 * A guess about what the bug is or what it depends on.
6549 Such guesses are usually wrong. Even we cannot guess right about
6550 such things without first using the debugger to find the facts.
6553 File: ld.info, Node: MRI, Next: GNU Free Documentation License, Prev: Reporting Bugs, Up: Top
6555 Appendix A MRI Compatible Script Files
6556 **************************************
6558 To aid users making the transition to GNU `ld' from the MRI linker,
6559 `ld' can use MRI compatible linker scripts as an alternative to the
6560 more general-purpose linker scripting language described in *Note
6561 Scripts::. MRI compatible linker scripts have a much simpler command
6562 set than the scripting language otherwise used with `ld'. GNU `ld'
6563 supports the most commonly used MRI linker commands; these commands are
6566 In general, MRI scripts aren't of much use with the `a.out' object
6567 file format, since it only has three sections and MRI scripts lack some
6568 features to make use of them.
6570 You can specify a file containing an MRI-compatible script using the
6571 `-c' command-line option.
6573 Each command in an MRI-compatible script occupies its own line; each
6574 command line starts with the keyword that identifies the command (though
6575 blank lines are also allowed for punctuation). If a line of an
6576 MRI-compatible script begins with an unrecognized keyword, `ld' issues
6577 a warning message, but continues processing the script.
6579 Lines beginning with `*' are comments.
6581 You can write these commands using all upper-case letters, or all
6582 lower case; for example, `chip' is the same as `CHIP'. The following
6583 list shows only the upper-case form of each command.
6586 `ABSOLUTE SECNAME, SECNAME, ... SECNAME'
6587 Normally, `ld' includes in the output file all sections from all
6588 the input files. However, in an MRI-compatible script, you can
6589 use the `ABSOLUTE' command to restrict the sections that will be
6590 present in your output program. If the `ABSOLUTE' command is used
6591 at all in a script, then only the sections named explicitly in
6592 `ABSOLUTE' commands will appear in the linker output. You can
6593 still use other input sections (whatever you select on the command
6594 line, or using `LOAD') to resolve addresses in the output file.
6596 `ALIAS OUT-SECNAME, IN-SECNAME'
6597 Use this command to place the data from input section IN-SECNAME
6598 in a section called OUT-SECNAME in the linker output file.
6600 IN-SECNAME may be an integer.
6602 `ALIGN SECNAME = EXPRESSION'
6603 Align the section called SECNAME to EXPRESSION. The EXPRESSION
6604 should be a power of two.
6607 Use the value of EXPRESSION as the lowest address (other than
6608 absolute addresses) in the output file.
6611 `CHIP EXPRESSION, EXPRESSION'
6612 This command does nothing; it is accepted only for compatibility.
6615 This command does nothing whatever; it's only accepted for
6618 `FORMAT OUTPUT-FORMAT'
6619 Similar to the `OUTPUT_FORMAT' command in the more general linker
6620 language, but restricted to one of these output formats:
6622 1. S-records, if OUTPUT-FORMAT is `S'
6624 2. IEEE, if OUTPUT-FORMAT is `IEEE'
6626 3. COFF (the `coff-m68k' variant in BFD), if OUTPUT-FORMAT is
6630 Print (to the standard output file) a link map, as produced by the
6631 `ld' command-line option `-M'.
6633 The keyword `LIST' may be followed by anything on the same line,
6634 with no change in its effect.
6637 `LOAD FILENAME, FILENAME, ... FILENAME'
6638 Include one or more object file FILENAME in the link; this has the
6639 same effect as specifying FILENAME directly on the `ld' command
6643 OUTPUT-NAME is the name for the program produced by `ld'; the
6644 MRI-compatible command `NAME' is equivalent to the command-line
6645 option `-o' or the general script language command `OUTPUT'.
6647 `ORDER SECNAME, SECNAME, ... SECNAME'
6648 `ORDER SECNAME SECNAME SECNAME'
6649 Normally, `ld' orders the sections in its output file in the order
6650 in which they first appear in the input files. In an
6651 MRI-compatible script, you can override this ordering with the
6652 `ORDER' command. The sections you list with `ORDER' will appear
6653 first in your output file, in the order specified.
6655 `PUBLIC NAME=EXPRESSION'
6656 `PUBLIC NAME,EXPRESSION'
6657 `PUBLIC NAME EXPRESSION'
6658 Supply a value (EXPRESSION) for external symbol NAME used in the
6661 `SECT SECNAME, EXPRESSION'
6662 `SECT SECNAME=EXPRESSION'
6663 `SECT SECNAME EXPRESSION'
6664 You can use any of these three forms of the `SECT' command to
6665 specify the start address (EXPRESSION) for section SECNAME. If
6666 you have more than one `SECT' statement for the same SECNAME, only
6667 the _first_ sets the start address.
6670 File: ld.info, Node: GNU Free Documentation License, Next: LD Index, Prev: MRI, Up: Top
6672 Appendix B GNU Free Documentation License
6673 *****************************************
6675 Version 1.3, 3 November 2008
6677 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
6680 Everyone is permitted to copy and distribute verbatim copies
6681 of this license document, but changing it is not allowed.
6685 The purpose of this License is to make a manual, textbook, or other
6686 functional and useful document "free" in the sense of freedom: to
6687 assure everyone the effective freedom to copy and redistribute it,
6688 with or without modifying it, either commercially or
6689 noncommercially. Secondarily, this License preserves for the
6690 author and publisher a way to get credit for their work, while not
6691 being considered responsible for modifications made by others.
6693 This License is a kind of "copyleft", which means that derivative
6694 works of the document must themselves be free in the same sense.
6695 It complements the GNU General Public License, which is a copyleft
6696 license designed for free software.
6698 We have designed this License in order to use it for manuals for
6699 free software, because free software needs free documentation: a
6700 free program should come with manuals providing the same freedoms
6701 that the software does. But this License is not limited to
6702 software manuals; it can be used for any textual work, regardless
6703 of subject matter or whether it is published as a printed book.
6704 We recommend this License principally for works whose purpose is
6705 instruction or reference.
6707 1. APPLICABILITY AND DEFINITIONS
6709 This License applies to any manual or other work, in any medium,
6710 that contains a notice placed by the copyright holder saying it
6711 can be distributed under the terms of this License. Such a notice
6712 grants a world-wide, royalty-free license, unlimited in duration,
6713 to use that work under the conditions stated herein. The
6714 "Document", below, refers to any such manual or work. Any member
6715 of the public is a licensee, and is addressed as "you". You
6716 accept the license if you copy, modify or distribute the work in a
6717 way requiring permission under copyright law.
6719 A "Modified Version" of the Document means any work containing the
6720 Document or a portion of it, either copied verbatim, or with
6721 modifications and/or translated into another language.
6723 A "Secondary Section" is a named appendix or a front-matter section
6724 of the Document that deals exclusively with the relationship of the
6725 publishers or authors of the Document to the Document's overall
6726 subject (or to related matters) and contains nothing that could
6727 fall directly within that overall subject. (Thus, if the Document
6728 is in part a textbook of mathematics, a Secondary Section may not
6729 explain any mathematics.) The relationship could be a matter of
6730 historical connection with the subject or with related matters, or
6731 of legal, commercial, philosophical, ethical or political position
6734 The "Invariant Sections" are certain Secondary Sections whose
6735 titles are designated, as being those of Invariant Sections, in
6736 the notice that says that the Document is released under this
6737 License. If a section does not fit the above definition of
6738 Secondary then it is not allowed to be designated as Invariant.
6739 The Document may contain zero Invariant Sections. If the Document
6740 does not identify any Invariant Sections then there are none.
6742 The "Cover Texts" are certain short passages of text that are
6743 listed, as Front-Cover Texts or Back-Cover Texts, in the notice
6744 that says that the Document is released under this License. A
6745 Front-Cover Text may be at most 5 words, and a Back-Cover Text may
6746 be at most 25 words.
6748 A "Transparent" copy of the Document means a machine-readable copy,
6749 represented in a format whose specification is available to the
6750 general public, that is suitable for revising the document
6751 straightforwardly with generic text editors or (for images
6752 composed of pixels) generic paint programs or (for drawings) some
6753 widely available drawing editor, and that is suitable for input to
6754 text formatters or for automatic translation to a variety of
6755 formats suitable for input to text formatters. A copy made in an
6756 otherwise Transparent file format whose markup, or absence of
6757 markup, has been arranged to thwart or discourage subsequent
6758 modification by readers is not Transparent. An image format is
6759 not Transparent if used for any substantial amount of text. A
6760 copy that is not "Transparent" is called "Opaque".
6762 Examples of suitable formats for Transparent copies include plain
6763 ASCII without markup, Texinfo input format, LaTeX input format,
6764 SGML or XML using a publicly available DTD, and
6765 standard-conforming simple HTML, PostScript or PDF designed for
6766 human modification. Examples of transparent image formats include
6767 PNG, XCF and JPG. Opaque formats include proprietary formats that
6768 can be read and edited only by proprietary word processors, SGML or
6769 XML for which the DTD and/or processing tools are not generally
6770 available, and the machine-generated HTML, PostScript or PDF
6771 produced by some word processors for output purposes only.
6773 The "Title Page" means, for a printed book, the title page itself,
6774 plus such following pages as are needed to hold, legibly, the
6775 material this License requires to appear in the title page. For
6776 works in formats which do not have any title page as such, "Title
6777 Page" means the text near the most prominent appearance of the
6778 work's title, preceding the beginning of the body of the text.
6780 The "publisher" means any person or entity that distributes copies
6781 of the Document to the public.
6783 A section "Entitled XYZ" means a named subunit of the Document
6784 whose title either is precisely XYZ or contains XYZ in parentheses
6785 following text that translates XYZ in another language. (Here XYZ
6786 stands for a specific section name mentioned below, such as
6787 "Acknowledgements", "Dedications", "Endorsements", or "History".)
6788 To "Preserve the Title" of such a section when you modify the
6789 Document means that it remains a section "Entitled XYZ" according
6792 The Document may include Warranty Disclaimers next to the notice
6793 which states that this License applies to the Document. These
6794 Warranty Disclaimers are considered to be included by reference in
6795 this License, but only as regards disclaiming warranties: any other
6796 implication that these Warranty Disclaimers may have is void and
6797 has no effect on the meaning of this License.
6801 You may copy and distribute the Document in any medium, either
6802 commercially or noncommercially, provided that this License, the
6803 copyright notices, and the license notice saying this License
6804 applies to the Document are reproduced in all copies, and that you
6805 add no other conditions whatsoever to those of this License. You
6806 may not use technical measures to obstruct or control the reading
6807 or further copying of the copies you make or distribute. However,
6808 you may accept compensation in exchange for copies. If you
6809 distribute a large enough number of copies you must also follow
6810 the conditions in section 3.
6812 You may also lend copies, under the same conditions stated above,
6813 and you may publicly display copies.
6815 3. COPYING IN QUANTITY
6817 If you publish printed copies (or copies in media that commonly
6818 have printed covers) of the Document, numbering more than 100, and
6819 the Document's license notice requires Cover Texts, you must
6820 enclose the copies in covers that carry, clearly and legibly, all
6821 these Cover Texts: Front-Cover Texts on the front cover, and
6822 Back-Cover Texts on the back cover. Both covers must also clearly
6823 and legibly identify you as the publisher of these copies. The
6824 front cover must present the full title with all words of the
6825 title equally prominent and visible. You may add other material
6826 on the covers in addition. Copying with changes limited to the
6827 covers, as long as they preserve the title of the Document and
6828 satisfy these conditions, can be treated as verbatim copying in
6831 If the required texts for either cover are too voluminous to fit
6832 legibly, you should put the first ones listed (as many as fit
6833 reasonably) on the actual cover, and continue the rest onto
6836 If you publish or distribute Opaque copies of the Document
6837 numbering more than 100, you must either include a
6838 machine-readable Transparent copy along with each Opaque copy, or
6839 state in or with each Opaque copy a computer-network location from
6840 which the general network-using public has access to download
6841 using public-standard network protocols a complete Transparent
6842 copy of the Document, free of added material. If you use the
6843 latter option, you must take reasonably prudent steps, when you
6844 begin distribution of Opaque copies in quantity, to ensure that
6845 this Transparent copy will remain thus accessible at the stated
6846 location until at least one year after the last time you
6847 distribute an Opaque copy (directly or through your agents or
6848 retailers) of that edition to the public.
6850 It is requested, but not required, that you contact the authors of
6851 the Document well before redistributing any large number of
6852 copies, to give them a chance to provide you with an updated
6853 version of the Document.
6857 You may copy and distribute a Modified Version of the Document
6858 under the conditions of sections 2 and 3 above, provided that you
6859 release the Modified Version under precisely this License, with
6860 the Modified Version filling the role of the Document, thus
6861 licensing distribution and modification of the Modified Version to
6862 whoever possesses a copy of it. In addition, you must do these
6863 things in the Modified Version:
6865 A. Use in the Title Page (and on the covers, if any) a title
6866 distinct from that of the Document, and from those of
6867 previous versions (which should, if there were any, be listed
6868 in the History section of the Document). You may use the
6869 same title as a previous version if the original publisher of
6870 that version gives permission.
6872 B. List on the Title Page, as authors, one or more persons or
6873 entities responsible for authorship of the modifications in
6874 the Modified Version, together with at least five of the
6875 principal authors of the Document (all of its principal
6876 authors, if it has fewer than five), unless they release you
6877 from this requirement.
6879 C. State on the Title page the name of the publisher of the
6880 Modified Version, as the publisher.
6882 D. Preserve all the copyright notices of the Document.
6884 E. Add an appropriate copyright notice for your modifications
6885 adjacent to the other copyright notices.
6887 F. Include, immediately after the copyright notices, a license
6888 notice giving the public permission to use the Modified
6889 Version under the terms of this License, in the form shown in
6892 G. Preserve in that license notice the full lists of Invariant
6893 Sections and required Cover Texts given in the Document's
6896 H. Include an unaltered copy of this License.
6898 I. Preserve the section Entitled "History", Preserve its Title,
6899 and add to it an item stating at least the title, year, new
6900 authors, and publisher of the Modified Version as given on
6901 the Title Page. If there is no section Entitled "History" in
6902 the Document, create one stating the title, year, authors,
6903 and publisher of the Document as given on its Title Page,
6904 then add an item describing the Modified Version as stated in
6905 the previous sentence.
6907 J. Preserve the network location, if any, given in the Document
6908 for public access to a Transparent copy of the Document, and
6909 likewise the network locations given in the Document for
6910 previous versions it was based on. These may be placed in
6911 the "History" section. You may omit a network location for a
6912 work that was published at least four years before the
6913 Document itself, or if the original publisher of the version
6914 it refers to gives permission.
6916 K. For any section Entitled "Acknowledgements" or "Dedications",
6917 Preserve the Title of the section, and preserve in the
6918 section all the substance and tone of each of the contributor
6919 acknowledgements and/or dedications given therein.
6921 L. Preserve all the Invariant Sections of the Document,
6922 unaltered in their text and in their titles. Section numbers
6923 or the equivalent are not considered part of the section
6926 M. Delete any section Entitled "Endorsements". Such a section
6927 may not be included in the Modified Version.
6929 N. Do not retitle any existing section to be Entitled
6930 "Endorsements" or to conflict in title with any Invariant
6933 O. Preserve any Warranty Disclaimers.
6935 If the Modified Version includes new front-matter sections or
6936 appendices that qualify as Secondary Sections and contain no
6937 material copied from the Document, you may at your option
6938 designate some or all of these sections as invariant. To do this,
6939 add their titles to the list of Invariant Sections in the Modified
6940 Version's license notice. These titles must be distinct from any
6941 other section titles.
6943 You may add a section Entitled "Endorsements", provided it contains
6944 nothing but endorsements of your Modified Version by various
6945 parties--for example, statements of peer review or that the text
6946 has been approved by an organization as the authoritative
6947 definition of a standard.
6949 You may add a passage of up to five words as a Front-Cover Text,
6950 and a passage of up to 25 words as a Back-Cover Text, to the end
6951 of the list of Cover Texts in the Modified Version. Only one
6952 passage of Front-Cover Text and one of Back-Cover Text may be
6953 added by (or through arrangements made by) any one entity. If the
6954 Document already includes a cover text for the same cover,
6955 previously added by you or by arrangement made by the same entity
6956 you are acting on behalf of, you may not add another; but you may
6957 replace the old one, on explicit permission from the previous
6958 publisher that added the old one.
6960 The author(s) and publisher(s) of the Document do not by this
6961 License give permission to use their names for publicity for or to
6962 assert or imply endorsement of any Modified Version.
6964 5. COMBINING DOCUMENTS
6966 You may combine the Document with other documents released under
6967 this License, under the terms defined in section 4 above for
6968 modified versions, provided that you include in the combination
6969 all of the Invariant Sections of all of the original documents,
6970 unmodified, and list them all as Invariant Sections of your
6971 combined work in its license notice, and that you preserve all
6972 their Warranty Disclaimers.
6974 The combined work need only contain one copy of this License, and
6975 multiple identical Invariant Sections may be replaced with a single
6976 copy. If there are multiple Invariant Sections with the same name
6977 but different contents, make the title of each such section unique
6978 by adding at the end of it, in parentheses, the name of the
6979 original author or publisher of that section if known, or else a
6980 unique number. Make the same adjustment to the section titles in
6981 the list of Invariant Sections in the license notice of the
6984 In the combination, you must combine any sections Entitled
6985 "History" in the various original documents, forming one section
6986 Entitled "History"; likewise combine any sections Entitled
6987 "Acknowledgements", and any sections Entitled "Dedications". You
6988 must delete all sections Entitled "Endorsements."
6990 6. COLLECTIONS OF DOCUMENTS
6992 You may make a collection consisting of the Document and other
6993 documents released under this License, and replace the individual
6994 copies of this License in the various documents with a single copy
6995 that is included in the collection, provided that you follow the
6996 rules of this License for verbatim copying of each of the
6997 documents in all other respects.
6999 You may extract a single document from such a collection, and
7000 distribute it individually under this License, provided you insert
7001 a copy of this License into the extracted document, and follow
7002 this License in all other respects regarding verbatim copying of
7005 7. AGGREGATION WITH INDEPENDENT WORKS
7007 A compilation of the Document or its derivatives with other
7008 separate and independent documents or works, in or on a volume of
7009 a storage or distribution medium, is called an "aggregate" if the
7010 copyright resulting from the compilation is not used to limit the
7011 legal rights of the compilation's users beyond what the individual
7012 works permit. When the Document is included in an aggregate, this
7013 License does not apply to the other works in the aggregate which
7014 are not themselves derivative works of the Document.
7016 If the Cover Text requirement of section 3 is applicable to these
7017 copies of the Document, then if the Document is less than one half
7018 of the entire aggregate, the Document's Cover Texts may be placed
7019 on covers that bracket the Document within the aggregate, or the
7020 electronic equivalent of covers if the Document is in electronic
7021 form. Otherwise they must appear on printed covers that bracket
7022 the whole aggregate.
7026 Translation is considered a kind of modification, so you may
7027 distribute translations of the Document under the terms of section
7028 4. Replacing Invariant Sections with translations requires special
7029 permission from their copyright holders, but you may include
7030 translations of some or all Invariant Sections in addition to the
7031 original versions of these Invariant Sections. You may include a
7032 translation of this License, and all the license notices in the
7033 Document, and any Warranty Disclaimers, provided that you also
7034 include the original English version of this License and the
7035 original versions of those notices and disclaimers. In case of a
7036 disagreement between the translation and the original version of
7037 this License or a notice or disclaimer, the original version will
7040 If a section in the Document is Entitled "Acknowledgements",
7041 "Dedications", or "History", the requirement (section 4) to
7042 Preserve its Title (section 1) will typically require changing the
7047 You may not copy, modify, sublicense, or distribute the Document
7048 except as expressly provided under this License. Any attempt
7049 otherwise to copy, modify, sublicense, or distribute it is void,
7050 and will automatically terminate your rights under this License.
7052 However, if you cease all violation of this License, then your
7053 license from a particular copyright holder is reinstated (a)
7054 provisionally, unless and until the copyright holder explicitly
7055 and finally terminates your license, and (b) permanently, if the
7056 copyright holder fails to notify you of the violation by some
7057 reasonable means prior to 60 days after the cessation.
7059 Moreover, your license from a particular copyright holder is
7060 reinstated permanently if the copyright holder notifies you of the
7061 violation by some reasonable means, this is the first time you have
7062 received notice of violation of this License (for any work) from
7063 that copyright holder, and you cure the violation prior to 30 days
7064 after your receipt of the notice.
7066 Termination of your rights under this section does not terminate
7067 the licenses of parties who have received copies or rights from
7068 you under this License. If your rights have been terminated and
7069 not permanently reinstated, receipt of a copy of some or all of
7070 the same material does not give you any rights to use it.
7072 10. FUTURE REVISIONS OF THIS LICENSE
7074 The Free Software Foundation may publish new, revised versions of
7075 the GNU Free Documentation License from time to time. Such new
7076 versions will be similar in spirit to the present version, but may
7077 differ in detail to address new problems or concerns. See
7078 `http://www.gnu.org/copyleft/'.
7080 Each version of the License is given a distinguishing version
7081 number. If the Document specifies that a particular numbered
7082 version of this License "or any later version" applies to it, you
7083 have the option of following the terms and conditions either of
7084 that specified version or of any later version that has been
7085 published (not as a draft) by the Free Software Foundation. If
7086 the Document does not specify a version number of this License,
7087 you may choose any version ever published (not as a draft) by the
7088 Free Software Foundation. If the Document specifies that a proxy
7089 can decide which future versions of this License can be used, that
7090 proxy's public statement of acceptance of a version permanently
7091 authorizes you to choose that version for the Document.
7095 "Massive Multiauthor Collaboration Site" (or "MMC Site") means any
7096 World Wide Web server that publishes copyrightable works and also
7097 provides prominent facilities for anybody to edit those works. A
7098 public wiki that anybody can edit is an example of such a server.
7099 A "Massive Multiauthor Collaboration" (or "MMC") contained in the
7100 site means any set of copyrightable works thus published on the MMC
7103 "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
7104 license published by Creative Commons Corporation, a not-for-profit
7105 corporation with a principal place of business in San Francisco,
7106 California, as well as future copyleft versions of that license
7107 published by that same organization.
7109 "Incorporate" means to publish or republish a Document, in whole or
7110 in part, as part of another Document.
7112 An MMC is "eligible for relicensing" if it is licensed under this
7113 License, and if all works that were first published under this
7114 License somewhere other than this MMC, and subsequently
7115 incorporated in whole or in part into the MMC, (1) had no cover
7116 texts or invariant sections, and (2) were thus incorporated prior
7117 to November 1, 2008.
7119 The operator of an MMC Site may republish an MMC contained in the
7120 site under CC-BY-SA on the same site at any time before August 1,
7121 2009, provided the MMC is eligible for relicensing.
7124 ADDENDUM: How to use this License for your documents
7125 ====================================================
7127 To use this License in a document you have written, include a copy of
7128 the License in the document and put the following copyright and license
7129 notices just after the title page:
7131 Copyright (C) YEAR YOUR NAME.
7132 Permission is granted to copy, distribute and/or modify this document
7133 under the terms of the GNU Free Documentation License, Version 1.3
7134 or any later version published by the Free Software Foundation;
7135 with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
7136 Texts. A copy of the license is included in the section entitled ``GNU
7137 Free Documentation License''.
7139 If you have Invariant Sections, Front-Cover Texts and Back-Cover
7140 Texts, replace the "with...Texts." line with this:
7142 with the Invariant Sections being LIST THEIR TITLES, with
7143 the Front-Cover Texts being LIST, and with the Back-Cover Texts
7146 If you have Invariant Sections without Cover Texts, or some other
7147 combination of the three, merge those two alternatives to suit the
7150 If your document contains nontrivial examples of program code, we
7151 recommend releasing these examples in parallel under your choice of
7152 free software license, such as the GNU General Public License, to
7153 permit their use in free software.
7156 File: ld.info, Node: LD Index, Prev: GNU Free Documentation License, Up: Top
7164 * ": Symbols. (line 6)
7165 * -(: Options. (line 696)
7166 * --accept-unknown-input-arch: Options. (line 714)
7167 * --add-needed: Options. (line 738)
7168 * --add-stdcall-alias: Options. (line 1589)
7169 * --allow-multiple-definition: Options. (line 989)
7170 * --allow-shlib-undefined: Options. (line 995)
7171 * --architecture=ARCH: Options. (line 123)
7172 * --as-needed: Options. (line 724)
7173 * --audit AUDITLIB: Options. (line 112)
7174 * --auxiliary=NAME: Options. (line 255)
7175 * --bank-window: Options. (line 2021)
7176 * --base-file: Options. (line 1594)
7177 * --be8: ARM. (line 28)
7178 * --bss-plt: PowerPC ELF32. (line 16)
7179 * --build-id: Options. (line 1551)
7180 * --build-id=STYLE: Options. (line 1551)
7181 * --check-sections: Options. (line 817)
7182 * --copy-dt-needed-entries: Options. (line 829)
7183 * --cref: Options. (line 849)
7184 * --default-imported-symver: Options. (line 1032)
7185 * --default-script=SCRIPT: Options. (line 541)
7186 * --default-symver: Options. (line 1028)
7187 * --defsym=SYMBOL=EXP: Options. (line 877)
7188 * --demangle[=STYLE]: Options. (line 890)
7189 * --depaudit AUDITLIB: Options. (line 177)
7190 * --disable-auto-image-base: Options. (line 1773)
7191 * --disable-auto-import: Options. (line 1908)
7192 * --disable-long-section-names: Options. (line 1604)
7193 * --disable-new-dtags: Options. (line 1514)
7194 * --disable-runtime-pseudo-reloc: Options. (line 1921)
7195 * --disable-stdcall-fixup: Options. (line 1626)
7196 * --discard-all: Options. (line 587)
7197 * --discard-locals: Options. (line 591)
7198 * --dll: Options. (line 1599)
7199 * --dll-search-prefix: Options. (line 1779)
7200 * --dotsyms: PowerPC64 ELF64. (line 33)
7201 * --dsbt-index: Options. (line 1998)
7202 * --dsbt-size: Options. (line 1993)
7203 * --dynamic-linker=FILE: Options. (line 903)
7204 * --dynamic-list-cpp-new: Options. (line 809)
7205 * --dynamic-list-cpp-typeinfo: Options. (line 813)
7206 * --dynamic-list-data: Options. (line 806)
7207 * --dynamic-list=DYNAMIC-LIST-FILE: Options. (line 793)
7208 * --dynamicbase: Options. (line 1957)
7209 * --eh-frame-hdr: Options. (line 1505)
7210 * --emit-relocs: Options. (line 476)
7211 * --emit-stack-syms: SPU ELF. (line 46)
7212 * --emit-stub-syms <1>: SPU ELF. (line 15)
7213 * --emit-stub-syms <2>: PowerPC ELF32. (line 47)
7214 * --emit-stub-syms: PowerPC64 ELF64. (line 29)
7215 * --enable-auto-image-base: Options. (line 1765)
7216 * --enable-auto-import: Options. (line 1788)
7217 * --enable-extra-pe-debug: Options. (line 1926)
7218 * --enable-long-section-names: Options. (line 1604)
7219 * --enable-new-dtags: Options. (line 1514)
7220 * --enable-runtime-pseudo-reloc: Options. (line 1913)
7221 * --enable-stdcall-fixup: Options. (line 1626)
7222 * --entry=ENTRY: Options. (line 187)
7223 * --error-unresolved-symbols: Options. (line 1458)
7224 * --exclude-all-symbols: Options. (line 1680)
7225 * --exclude-libs: Options. (line 197)
7226 * --exclude-modules-for-implib: Options. (line 208)
7227 * --exclude-symbols: Options. (line 1674)
7228 * --export-all-symbols: Options. (line 1650)
7229 * --export-dynamic: Options. (line 221)
7230 * --extra-overlay-stubs: SPU ELF. (line 19)
7231 * --fatal-warnings: Options. (line 910)
7232 * --file-alignment: Options. (line 1684)
7233 * --filter=NAME: Options. (line 276)
7234 * --fix-arm1176: ARM. (line 111)
7235 * --fix-cortex-a8: i960. (line 39)
7236 * --fix-v4bx: ARM. (line 49)
7237 * --fix-v4bx-interworking: ARM. (line 62)
7238 * --force-dynamic: Options. (line 485)
7239 * --force-exe-suffix: Options. (line 915)
7240 * --forceinteg: Options. (line 1962)
7241 * --format=FORMAT: Options. (line 134)
7242 * --format=VERSION: TI COFF. (line 6)
7243 * --gc-sections: Options. (line 925)
7244 * --got: Options. (line 2034)
7245 * --got=TYPE: M68K. (line 6)
7246 * --gpsize=VALUE: Options. (line 309)
7247 * --hash-size=NUMBER: Options. (line 1523)
7248 * --hash-style=STYLE: Options. (line 1531)
7249 * --heap: Options. (line 1690)
7250 * --help: Options. (line 962)
7251 * --image-base: Options. (line 1697)
7252 * --just-symbols=FILE: Options. (line 508)
7253 * --kill-at: Options. (line 1706)
7254 * --large-address-aware: Options. (line 1711)
7255 * --ld-generated-unwind-info: Options. (line 1509)
7256 * --leading-underscore: Options. (line 1644)
7257 * --library-path=DIR: Options. (line 368)
7258 * --library=NAMESPEC: Options. (line 335)
7259 * --local-store=lo:hi: SPU ELF. (line 24)
7260 * --major-image-version: Options. (line 1720)
7261 * --major-os-version: Options. (line 1725)
7262 * --major-subsystem-version: Options. (line 1729)
7263 * --merge-exidx-entries: i960. (line 48)
7264 * --minor-image-version: Options. (line 1734)
7265 * --minor-os-version: Options. (line 1739)
7266 * --minor-subsystem-version: Options. (line 1743)
7267 * --mri-script=MRI-CMDFILE: Options. (line 158)
7268 * --multi-subspace: HPPA ELF32. (line 6)
7269 * --nmagic: Options. (line 439)
7270 * --no-accept-unknown-input-arch: Options. (line 714)
7271 * --no-add-needed: Options. (line 738)
7272 * --no-allow-shlib-undefined: Options. (line 995)
7273 * --no-as-needed: Options. (line 724)
7274 * --no-bind: Options. (line 1976)
7275 * --no-check-sections: Options. (line 817)
7276 * --no-copy-dt-needed-entries: Options. (line 829)
7277 * --no-define-common: Options. (line 861)
7278 * --no-demangle: Options. (line 890)
7279 * --no-dotsyms: PowerPC64 ELF64. (line 33)
7280 * --no-enum-size-warning: ARM. (line 120)
7281 * --no-export-dynamic: Options. (line 221)
7282 * --no-fatal-warnings: Options. (line 910)
7283 * --no-fix-arm1176: ARM. (line 111)
7284 * --no-fix-cortex-a8: i960. (line 39)
7285 * --no-gc-sections: Options. (line 925)
7286 * --no-isolation: Options. (line 1969)
7287 * --no-keep-memory: Options. (line 974)
7288 * --no-leading-underscore: Options. (line 1644)
7289 * --no-merge-exidx-entries <1>: Options. (line 2005)
7290 * --no-merge-exidx-entries: i960. (line 48)
7291 * --no-multi-toc: PowerPC64 ELF64. (line 74)
7292 * --no-omagic: Options. (line 454)
7293 * --no-opd-optimize: PowerPC64 ELF64. (line 48)
7294 * --no-overlays: SPU ELF. (line 9)
7295 * --no-plt-align: PowerPC64 ELF64. (line 96)
7296 * --no-plt-static-chain: PowerPC64 ELF64. (line 103)
7297 * --no-plt-thread-safe: PowerPC64 ELF64. (line 109)
7298 * --no-print-gc-sections: Options. (line 947)
7299 * --no-seh: Options. (line 1972)
7300 * --no-tls-optimize <1>: PowerPC ELF32. (line 51)
7301 * --no-tls-optimize: PowerPC64 ELF64. (line 43)
7302 * --no-toc-optimize: PowerPC64 ELF64. (line 60)
7303 * --no-toc-sort: PowerPC64 ELF64. (line 86)
7304 * --no-trampoline: Options. (line 2015)
7305 * --no-undefined: Options. (line 981)
7306 * --no-undefined-version: Options. (line 1023)
7307 * --no-warn-mismatch: Options. (line 1036)
7308 * --no-warn-search-mismatch: Options. (line 1045)
7309 * --no-wchar-size-warning: ARM. (line 127)
7310 * --no-whole-archive: Options. (line 1049)
7311 * --noinhibit-exec: Options. (line 1053)
7312 * --non-overlapping-opd: PowerPC64 ELF64. (line 54)
7313 * --nxcompat: Options. (line 1965)
7314 * --oformat=OUTPUT-FORMAT: Options. (line 1065)
7315 * --omagic: Options. (line 445)
7316 * --out-implib: Options. (line 1756)
7317 * --output-def: Options. (line 1748)
7318 * --output=OUTPUT: Options. (line 460)
7319 * --pic-executable: Options. (line 1078)
7320 * --pic-veneer: ARM. (line 133)
7321 * --plt-align: PowerPC64 ELF64. (line 96)
7322 * --plt-static-chain: PowerPC64 ELF64. (line 103)
7323 * --plt-thread-safe: PowerPC64 ELF64. (line 109)
7324 * --plugin: SPU ELF. (line 6)
7325 * --print-gc-sections: Options. (line 947)
7326 * --print-map: Options. (line 402)
7327 * --print-output-format: Options. (line 956)
7328 * --reduce-memory-overheads: Options. (line 1537)
7329 * --relax: Options. (line 1094)
7330 * --relax on i960: i960. (line 31)
7331 * --relax on PowerPC: PowerPC ELF32. (line 6)
7332 * --relax on Xtensa: Xtensa. (line 27)
7333 * --relocatable: Options. (line 489)
7334 * --retain-symbols-file=FILENAME: Options. (line 1120)
7335 * --script=SCRIPT: Options. (line 532)
7336 * --sdata-got: PowerPC ELF32. (line 33)
7337 * --section-alignment: Options. (line 1931)
7338 * --section-start=SECTIONNAME=ORG: Options. (line 1276)
7339 * --secure-plt: PowerPC ELF32. (line 26)
7340 * --sort-common: Options. (line 1218)
7341 * --sort-section=alignment: Options. (line 1233)
7342 * --sort-section=name: Options. (line 1229)
7343 * --split-by-file: Options. (line 1237)
7344 * --split-by-reloc: Options. (line 1242)
7345 * --stack: Options. (line 1937)
7346 * --stack-analysis: SPU ELF. (line 29)
7347 * --stats: Options. (line 1255)
7348 * --strip-all: Options. (line 519)
7349 * --strip-debug: Options. (line 523)
7350 * --stub-group-size: PowerPC64 ELF64. (line 6)
7351 * --stub-group-size=N <1>: HPPA ELF32. (line 12)
7352 * --stub-group-size=N: ARM. (line 138)
7353 * --subsystem: Options. (line 1944)
7354 * --support-old-code: ARM. (line 6)
7355 * --sysroot=DIRECTORY: Options. (line 1259)
7356 * --target-help: Options. (line 966)
7357 * --target1-abs: ARM. (line 32)
7358 * --target1-rel: ARM. (line 32)
7359 * --target2=TYPE: ARM. (line 37)
7360 * --thumb-entry=ENTRY: ARM. (line 17)
7361 * --trace: Options. (line 528)
7362 * --trace-symbol=SYMBOL: Options. (line 597)
7363 * --traditional-format: Options. (line 1264)
7364 * --tsaware: Options. (line 1982)
7365 * --undefined=SYMBOL: Options. (line 554)
7366 * --unique[=SECTION]: Options. (line 572)
7367 * --unresolved-symbols: Options. (line 1301)
7368 * --use-blx: ARM. (line 74)
7369 * --use-nul-prefixed-import-tables: ARM. (line 23)
7370 * --verbose[=NUMBER]: Options. (line 1330)
7371 * --version: Options. (line 581)
7372 * --version-script=VERSION-SCRIPTFILE: Options. (line 1338)
7373 * --vfp11-denorm-fix: ARM. (line 83)
7374 * --warn-alternate-em: Options. (line 1450)
7375 * --warn-common: Options. (line 1349)
7376 * --warn-constructors: Options. (line 1417)
7377 * --warn-multiple-gp: Options. (line 1422)
7378 * --warn-once: Options. (line 1436)
7379 * --warn-section-align: Options. (line 1440)
7380 * --warn-shared-textrel: Options. (line 1447)
7381 * --warn-unresolved-symbols: Options. (line 1453)
7382 * --wdmdriver: Options. (line 1979)
7383 * --whole-archive: Options. (line 1462)
7384 * --wrap=SYMBOL: Options. (line 1476)
7385 * -A ARCH: Options. (line 122)
7386 * -a KEYWORD: Options. (line 105)
7387 * -assert KEYWORD: Options. (line 745)
7388 * -b FORMAT: Options. (line 134)
7389 * -Bdynamic: Options. (line 748)
7390 * -Bgroup: Options. (line 758)
7391 * -Bshareable: Options. (line 1211)
7392 * -Bstatic: Options. (line 765)
7393 * -Bsymbolic: Options. (line 780)
7394 * -Bsymbolic-functions: Options. (line 787)
7395 * -c MRI-CMDFILE: Options. (line 158)
7396 * -call_shared: Options. (line 748)
7397 * -d: Options. (line 168)
7398 * -dc: Options. (line 168)
7399 * -dn: Options. (line 765)
7400 * -dp: Options. (line 168)
7401 * -dT SCRIPT: Options. (line 541)
7402 * -dy: Options. (line 748)
7403 * -E: Options. (line 221)
7404 * -e ENTRY: Options. (line 187)
7405 * -EB: Options. (line 248)
7406 * -EL: Options. (line 251)
7407 * -f NAME: Options. (line 255)
7408 * -F NAME: Options. (line 276)
7409 * -fini=NAME: Options. (line 300)
7410 * -g: Options. (line 306)
7411 * -G VALUE: Options. (line 309)
7412 * -h NAME: Options. (line 317)
7413 * -i: Options. (line 326)
7414 * -IFILE: Options. (line 903)
7415 * -init=NAME: Options. (line 329)
7416 * -L DIR: Options. (line 368)
7417 * -l NAMESPEC: Options. (line 335)
7418 * -M: Options. (line 402)
7419 * -m EMULATION: Options. (line 392)
7420 * -Map=MAPFILE: Options. (line 970)
7421 * -N: Options. (line 445)
7422 * -n: Options. (line 439)
7423 * -no-relax: Options. (line 1094)
7424 * -non_shared: Options. (line 765)
7425 * -nostdlib: Options. (line 1059)
7426 * -O LEVEL: Options. (line 466)
7427 * -o OUTPUT: Options. (line 460)
7428 * -P AUDITLIB: Options. (line 177)
7429 * -pie: Options. (line 1078)
7430 * -q: Options. (line 476)
7431 * -qmagic: Options. (line 1088)
7432 * -Qy: Options. (line 1091)
7433 * -r: Options. (line 489)
7434 * -R FILE: Options. (line 508)
7435 * -rpath-link=DIR: Options. (line 1156)
7436 * -rpath=DIR: Options. (line 1134)
7437 * -S: Options. (line 523)
7438 * -s: Options. (line 519)
7439 * -shared: Options. (line 1211)
7440 * -soname=NAME: Options. (line 317)
7441 * -static: Options. (line 765)
7442 * -t: Options. (line 528)
7443 * -T SCRIPT: Options. (line 532)
7444 * -Tbss=ORG: Options. (line 1285)
7445 * -Tdata=ORG: Options. (line 1285)
7446 * -Trodata-segment=ORG: Options. (line 1295)
7447 * -Ttext-segment=ORG: Options. (line 1291)
7448 * -Ttext=ORG: Options. (line 1285)
7449 * -u SYMBOL: Options. (line 554)
7450 * -Ur: Options. (line 562)
7451 * -v: Options. (line 581)
7452 * -V: Options. (line 581)
7453 * -x: Options. (line 587)
7454 * -X: Options. (line 591)
7455 * -Y PATH: Options. (line 606)
7456 * -y SYMBOL: Options. (line 597)
7457 * -z defs: Options. (line 981)
7458 * -z KEYWORD: Options. (line 610)
7459 * -z muldefs: Options. (line 989)
7460 * .: Location Counter. (line 6)
7461 * /DISCARD/: Output Section Discarding.
7463 * :PHDR: Output Section Phdr.
7465 * =FILLEXP: Output Section Fill.
7467 * >REGION: Output Section Region.
7469 * [COMMON]: Input Section Common.
7471 * ABSOLUTE (MRI): MRI. (line 33)
7472 * absolute and relocatable symbols: Expression Section. (line 6)
7473 * absolute expressions: Expression Section. (line 6)
7474 * ABSOLUTE(EXP): Builtin Functions. (line 10)
7475 * ADDR(SECTION): Builtin Functions. (line 17)
7476 * address, section: Output Section Address.
7478 * ALIAS (MRI): MRI. (line 44)
7479 * ALIGN (MRI): MRI. (line 50)
7480 * align expression: Builtin Functions. (line 38)
7481 * align location counter: Builtin Functions. (line 38)
7482 * ALIGN(ALIGN): Builtin Functions. (line 38)
7483 * ALIGN(EXP,ALIGN): Builtin Functions. (line 38)
7484 * ALIGN(SECTION_ALIGN): Forced Output Alignment.
7486 * aligned common symbols: WIN32. (line 424)
7487 * ALIGNOF(SECTION): Builtin Functions. (line 64)
7488 * allocating memory: MEMORY. (line 6)
7489 * architecture: Miscellaneous Commands.
7491 * architectures: Options. (line 122)
7492 * archive files, from cmd line: Options. (line 335)
7493 * archive search path in linker script: File Commands. (line 74)
7494 * arithmetic: Expressions. (line 6)
7495 * arithmetic operators: Operators. (line 6)
7496 * ARM interworking support: ARM. (line 6)
7497 * ARM1176 erratum workaround: ARM. (line 111)
7498 * AS_NEEDED(FILES): File Commands. (line 54)
7499 * ASSERT: Miscellaneous Commands.
7501 * assertion in linker script: Miscellaneous Commands.
7503 * assignment in scripts: Assignments. (line 6)
7504 * AT(LMA): Output Section LMA. (line 6)
7505 * AT>LMA_REGION: Output Section LMA. (line 6)
7506 * automatic data imports: WIN32. (line 191)
7507 * back end: BFD. (line 6)
7508 * BASE (MRI): MRI. (line 54)
7509 * BE8: ARM. (line 28)
7510 * BFD canonical format: Canonical format. (line 11)
7511 * BFD requirements: BFD. (line 16)
7512 * big-endian objects: Options. (line 248)
7513 * binary input format: Options. (line 134)
7514 * BLOCK(EXP): Builtin Functions. (line 77)
7515 * bug criteria: Bug Criteria. (line 6)
7516 * bug reports: Bug Reporting. (line 6)
7517 * bugs in ld: Reporting Bugs. (line 6)
7518 * BYTE(EXPRESSION): Output Section Data.
7520 * C++ constructors, arranging in link: Output Section Keywords.
7522 * CHIP (MRI): MRI. (line 58)
7523 * COLLECT_NO_DEMANGLE: Environment. (line 29)
7524 * combining symbols, warnings on: Options. (line 1349)
7525 * command files: Scripts. (line 6)
7526 * command line: Options. (line 6)
7527 * common allocation: Options. (line 861)
7528 * common allocation in linker script: Miscellaneous Commands.
7530 * common symbol placement: Input Section Common.
7532 * COMMONPAGESIZE: Symbolic Constants. (line 13)
7533 * compatibility, MRI: Options. (line 158)
7534 * CONSTANT: Symbolic Constants. (line 6)
7535 * constants in linker scripts: Constants. (line 6)
7536 * constraints on output sections: Output Section Constraint.
7538 * constructors: Options. (line 562)
7539 * CONSTRUCTORS: Output Section Keywords.
7541 * constructors, arranging in link: Output Section Keywords.
7543 * Cortex-A8 erratum workaround: i960. (line 39)
7544 * crash of linker: Bug Criteria. (line 9)
7545 * CREATE_OBJECT_SYMBOLS: Output Section Keywords.
7547 * creating a DEF file: WIN32. (line 158)
7548 * cross reference table: Options. (line 849)
7549 * cross references: Miscellaneous Commands.
7551 * current output location: Location Counter. (line 6)
7552 * data: Output Section Data.
7554 * DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE): Builtin Functions.
7556 * DATA_SEGMENT_END(EXP): Builtin Functions. (line 103)
7557 * DATA_SEGMENT_RELRO_END(OFFSET, EXP): Builtin Functions. (line 109)
7558 * dbx: Options. (line 1269)
7559 * DEF files, creating: Options. (line 1748)
7560 * default emulation: Environment. (line 21)
7561 * default input format: Environment. (line 9)
7562 * DEFINED(SYMBOL): Builtin Functions. (line 120)
7563 * deleting local symbols: Options. (line 587)
7564 * demangling, default: Environment. (line 29)
7565 * demangling, from command line: Options. (line 890)
7566 * direct linking to a dll: WIN32. (line 239)
7567 * discarding sections: Output Section Discarding.
7569 * discontinuous memory: MEMORY. (line 6)
7570 * DLLs, creating: Options. (line 1650)
7571 * DLLs, linking to: Options. (line 1779)
7572 * dot: Location Counter. (line 6)
7573 * dot inside sections: Location Counter. (line 36)
7574 * dot outside sections: Location Counter. (line 66)
7575 * dynamic linker, from command line: Options. (line 903)
7576 * dynamic symbol table: Options. (line 221)
7577 * ELF program headers: PHDRS. (line 6)
7578 * emulation: Options. (line 392)
7579 * emulation, default: Environment. (line 21)
7580 * END (MRI): MRI. (line 62)
7581 * endianness: Options. (line 248)
7582 * entry point: Entry Point. (line 6)
7583 * entry point, from command line: Options. (line 187)
7584 * entry point, thumb: ARM. (line 17)
7585 * ENTRY(SYMBOL): Entry Point. (line 6)
7586 * error on valid input: Bug Criteria. (line 12)
7587 * example of linker script: Simple Example. (line 6)
7588 * exporting DLL symbols: WIN32. (line 19)
7589 * expression evaluation order: Evaluation. (line 6)
7590 * expression sections: Expression Section. (line 6)
7591 * expression, absolute: Builtin Functions. (line 10)
7592 * expressions: Expressions. (line 6)
7593 * EXTERN: Miscellaneous Commands.
7595 * fatal signal: Bug Criteria. (line 9)
7596 * file name wildcard patterns: Input Section Wildcards.
7598 * FILEHDR: PHDRS. (line 62)
7599 * filename symbols: Output Section Keywords.
7601 * fill pattern, entire section: Output Section Fill.
7603 * FILL(EXPRESSION): Output Section Data.
7605 * finalization function: Options. (line 300)
7606 * first input file: File Commands. (line 82)
7607 * first instruction: Entry Point. (line 6)
7608 * FIX_V4BX: ARM. (line 49)
7609 * FIX_V4BX_INTERWORKING: ARM. (line 62)
7610 * FORCE_COMMON_ALLOCATION: Miscellaneous Commands.
7612 * forcing input section alignment: Forced Input Alignment.
7614 * forcing output section alignment: Forced Output Alignment.
7616 * forcing the creation of dynamic sections: Options. (line 485)
7617 * FORMAT (MRI): MRI. (line 66)
7618 * functions in expressions: Builtin Functions. (line 6)
7619 * garbage collection <1>: Options. (line 947)
7620 * garbage collection <2>: Input Section Keep. (line 6)
7621 * garbage collection: Options. (line 925)
7622 * generating optimized output: Options. (line 466)
7623 * GNU linker: Overview. (line 6)
7624 * GNUTARGET: Environment. (line 9)
7625 * GROUP(FILES): File Commands. (line 47)
7626 * grouping input files: File Commands. (line 47)
7627 * groups of archives: Options. (line 696)
7628 * H8/300 support: H8/300. (line 6)
7629 * header size: Builtin Functions. (line 183)
7630 * heap size: Options. (line 1690)
7631 * help: Options. (line 962)
7632 * HIDDEN: HIDDEN. (line 6)
7633 * holes: Location Counter. (line 12)
7634 * holes, filling: Output Section Data.
7636 * HPPA multiple sub-space stubs: HPPA ELF32. (line 6)
7637 * HPPA stub grouping: HPPA ELF32. (line 12)
7638 * i960 support: i960. (line 6)
7639 * image base: Options. (line 1697)
7640 * implicit linker scripts: Implicit Linker Scripts.
7642 * import libraries: WIN32. (line 10)
7643 * INCLUDE FILENAME: File Commands. (line 9)
7644 * including a linker script: File Commands. (line 9)
7645 * including an entire archive: Options. (line 1462)
7646 * incremental link: Options. (line 326)
7647 * INHIBIT_COMMON_ALLOCATION: Miscellaneous Commands.
7649 * initialization function: Options. (line 329)
7650 * initialized data in ROM: Output Section LMA. (line 39)
7651 * input file format in linker script: Format Commands. (line 35)
7652 * input filename symbols: Output Section Keywords.
7654 * input files in linker scripts: File Commands. (line 19)
7655 * input files, displaying: Options. (line 528)
7656 * input format: Options. (line 134)
7657 * input object files in linker scripts: File Commands. (line 19)
7658 * input section alignment: Forced Input Alignment.
7660 * input section basics: Input Section Basics.
7662 * input section wildcards: Input Section Wildcards.
7664 * input sections: Input Section. (line 6)
7665 * INPUT(FILES): File Commands. (line 19)
7666 * INSERT: Miscellaneous Commands.
7668 * insert user script into default script: Miscellaneous Commands.
7670 * integer notation: Constants. (line 6)
7671 * integer suffixes: Constants. (line 15)
7672 * internal object-file format: Canonical format. (line 11)
7673 * invalid input: Bug Criteria. (line 14)
7674 * K and M integer suffixes: Constants. (line 15)
7675 * KEEP: Input Section Keep. (line 6)
7676 * l =: MEMORY. (line 74)
7677 * lazy evaluation: Evaluation. (line 6)
7678 * ld bugs, reporting: Bug Reporting. (line 6)
7679 * LD_FEATURE(STRING): Miscellaneous Commands.
7681 * LDEMULATION: Environment. (line 21)
7682 * len =: MEMORY. (line 74)
7683 * LENGTH =: MEMORY. (line 74)
7684 * LENGTH(MEMORY): Builtin Functions. (line 137)
7685 * library search path in linker script: File Commands. (line 74)
7686 * link map: Options. (line 402)
7687 * link-time runtime library search path: Options. (line 1156)
7688 * linker crash: Bug Criteria. (line 9)
7689 * linker script concepts: Basic Script Concepts.
7691 * linker script example: Simple Example. (line 6)
7692 * linker script file commands: File Commands. (line 6)
7693 * linker script format: Script Format. (line 6)
7694 * linker script input object files: File Commands. (line 19)
7695 * linker script simple commands: Simple Commands. (line 6)
7696 * linker scripts: Scripts. (line 6)
7697 * LIST (MRI): MRI. (line 77)
7698 * little-endian objects: Options. (line 251)
7699 * LOAD (MRI): MRI. (line 84)
7700 * load address: Output Section LMA. (line 6)
7701 * LOADADDR(SECTION): Builtin Functions. (line 140)
7702 * loading, preventing: Output Section Type.
7704 * local symbols, deleting: Options. (line 591)
7705 * location counter: Location Counter. (line 6)
7706 * LONG(EXPRESSION): Output Section Data.
7708 * M and K integer suffixes: Constants. (line 15)
7709 * M68HC11 and 68HC12 support: M68HC11/68HC12. (line 6)
7710 * machine architecture: Miscellaneous Commands.
7712 * machine dependencies: Machine Dependent. (line 6)
7713 * mapping input sections to output sections: Input Section. (line 6)
7714 * MAX: Builtin Functions. (line 143)
7715 * MAXPAGESIZE: Symbolic Constants. (line 10)
7716 * MEMORY: MEMORY. (line 6)
7717 * memory region attributes: MEMORY. (line 34)
7718 * memory regions: MEMORY. (line 6)
7719 * memory regions and sections: Output Section Region.
7721 * memory usage: Options. (line 974)
7722 * MIN: Builtin Functions. (line 146)
7723 * Motorola 68K GOT generation: M68K. (line 6)
7724 * MRI compatibility: MRI. (line 6)
7725 * MSP430 extra sections: MSP430. (line 11)
7726 * NAME (MRI): MRI. (line 90)
7727 * name, section: Output Section Name.
7729 * names: Symbols. (line 6)
7730 * naming the output file: Options. (line 460)
7731 * NEXT(EXP): Builtin Functions. (line 150)
7732 * NMAGIC: Options. (line 439)
7733 * NO_ENUM_SIZE_WARNING: ARM. (line 120)
7734 * NO_WCHAR_SIZE_WARNING: ARM. (line 127)
7735 * NOCROSSREFS(SECTIONS): Miscellaneous Commands.
7737 * NOLOAD: Output Section Type.
7739 * not enough room for program headers: Builtin Functions. (line 188)
7740 * o =: MEMORY. (line 69)
7741 * objdump -i: BFD. (line 6)
7742 * object file management: BFD. (line 6)
7743 * object files: Options. (line 29)
7744 * object formats available: BFD. (line 6)
7745 * object size: Options. (line 309)
7746 * OMAGIC: Options. (line 445)
7747 * ONLY_IF_RO: Output Section Constraint.
7749 * ONLY_IF_RW: Output Section Constraint.
7751 * opening object files: BFD outline. (line 6)
7752 * operators for arithmetic: Operators. (line 6)
7753 * options: Options. (line 6)
7754 * ORDER (MRI): MRI. (line 95)
7755 * org =: MEMORY. (line 69)
7756 * ORIGIN =: MEMORY. (line 69)
7757 * ORIGIN(MEMORY): Builtin Functions. (line 156)
7758 * orphan: Orphan Sections. (line 6)
7759 * output file after errors: Options. (line 1053)
7760 * output file format in linker script: Format Commands. (line 10)
7761 * output file name in linker script: File Commands. (line 64)
7762 * output format: Options. (line 956)
7763 * output section alignment: Forced Output Alignment.
7765 * output section attributes: Output Section Attributes.
7767 * output section data: Output Section Data.
7769 * OUTPUT(FILENAME): File Commands. (line 64)
7770 * OUTPUT_ARCH(BFDARCH): Miscellaneous Commands.
7772 * OUTPUT_FORMAT(BFDNAME): Format Commands. (line 10)
7773 * OVERLAY: Overlay Description.
7775 * overlays: Overlay Description.
7777 * partial link: Options. (line 489)
7778 * PE import table prefixing: ARM. (line 23)
7779 * PHDRS: PHDRS. (line 62)
7780 * PIC_VENEER: ARM. (line 133)
7781 * position independent executables: Options. (line 1080)
7782 * PowerPC ELF32 options: PowerPC ELF32. (line 16)
7783 * PowerPC GOT: PowerPC ELF32. (line 33)
7784 * PowerPC long branches: PowerPC ELF32. (line 6)
7785 * PowerPC PLT: PowerPC ELF32. (line 16)
7786 * PowerPC stub symbols: PowerPC ELF32. (line 47)
7787 * PowerPC TLS optimization: PowerPC ELF32. (line 51)
7788 * PowerPC64 dot symbols: PowerPC64 ELF64. (line 33)
7789 * PowerPC64 ELF64 options: PowerPC64 ELF64. (line 6)
7790 * PowerPC64 multi-TOC: PowerPC64 ELF64. (line 74)
7791 * PowerPC64 OPD optimization: PowerPC64 ELF64. (line 48)
7792 * PowerPC64 OPD spacing: PowerPC64 ELF64. (line 54)
7793 * PowerPC64 PLT call stub static chain: PowerPC64 ELF64. (line 103)
7794 * PowerPC64 PLT call stub thread safety: PowerPC64 ELF64. (line 109)
7795 * PowerPC64 PLT stub alignment: PowerPC64 ELF64. (line 96)
7796 * PowerPC64 stub grouping: PowerPC64 ELF64. (line 6)
7797 * PowerPC64 stub symbols: PowerPC64 ELF64. (line 29)
7798 * PowerPC64 TLS optimization: PowerPC64 ELF64. (line 43)
7799 * PowerPC64 TOC optimization: PowerPC64 ELF64. (line 60)
7800 * PowerPC64 TOC sorting: PowerPC64 ELF64. (line 86)
7801 * precedence in expressions: Operators. (line 6)
7802 * prevent unnecessary loading: Output Section Type.
7804 * program headers: PHDRS. (line 6)
7805 * program headers and sections: Output Section Phdr.
7807 * program headers, not enough room: Builtin Functions. (line 188)
7808 * program segments: PHDRS. (line 6)
7809 * PROVIDE: PROVIDE. (line 6)
7810 * PROVIDE_HIDDEN: PROVIDE_HIDDEN. (line 6)
7811 * PUBLIC (MRI): MRI. (line 103)
7812 * QUAD(EXPRESSION): Output Section Data.
7814 * quoted symbol names: Symbols. (line 6)
7815 * read-only text: Options. (line 439)
7816 * read/write from cmd line: Options. (line 445)
7817 * region alias: REGION_ALIAS. (line 6)
7818 * region names: REGION_ALIAS. (line 6)
7819 * REGION_ALIAS(ALIAS, REGION): REGION_ALIAS. (line 6)
7820 * regions of memory: MEMORY. (line 6)
7821 * relative expressions: Expression Section. (line 6)
7822 * relaxing addressing modes: Options. (line 1094)
7823 * relaxing on H8/300: H8/300. (line 9)
7824 * relaxing on i960: i960. (line 31)
7825 * relaxing on M68HC11: M68HC11/68HC12. (line 12)
7826 * relaxing on Xtensa: Xtensa. (line 27)
7827 * relocatable and absolute symbols: Expression Section. (line 6)
7828 * relocatable output: Options. (line 489)
7829 * removing sections: Output Section Discarding.
7831 * reporting bugs in ld: Reporting Bugs. (line 6)
7832 * requirements for BFD: BFD. (line 16)
7833 * retain relocations in final executable: Options. (line 476)
7834 * retaining specified symbols: Options. (line 1120)
7835 * rodata segment origin, cmd line: Options. (line 1296)
7836 * ROM initialized data: Output Section LMA. (line 39)
7837 * round up expression: Builtin Functions. (line 38)
7838 * round up location counter: Builtin Functions. (line 38)
7839 * runtime library name: Options. (line 317)
7840 * runtime library search path: Options. (line 1134)
7841 * runtime pseudo-relocation: WIN32. (line 217)
7842 * scaled integers: Constants. (line 15)
7843 * scommon section: Input Section Common.
7845 * script files: Options. (line 541)
7846 * scripts: Scripts. (line 6)
7847 * search directory, from cmd line: Options. (line 368)
7848 * search path in linker script: File Commands. (line 74)
7849 * SEARCH_DIR(PATH): File Commands. (line 74)
7850 * SECT (MRI): MRI. (line 109)
7851 * section address: Output Section Address.
7853 * section address in expression: Builtin Functions. (line 17)
7854 * section alignment: Builtin Functions. (line 64)
7855 * section alignment, warnings on: Options. (line 1440)
7856 * section data: Output Section Data.
7858 * section fill pattern: Output Section Fill.
7860 * section load address: Output Section LMA. (line 6)
7861 * section load address in expression: Builtin Functions. (line 140)
7862 * section name: Output Section Name.
7864 * section name wildcard patterns: Input Section Wildcards.
7866 * section size: Builtin Functions. (line 167)
7867 * section, assigning to memory region: Output Section Region.
7869 * section, assigning to program header: Output Section Phdr.
7871 * SECTIONS: SECTIONS. (line 6)
7872 * sections, discarding: Output Section Discarding.
7874 * segment origins, cmd line: Options. (line 1285)
7875 * SEGMENT_START(SEGMENT, DEFAULT): Builtin Functions. (line 159)
7876 * segments, ELF: PHDRS. (line 6)
7877 * shared libraries: Options. (line 1213)
7878 * SHORT(EXPRESSION): Output Section Data.
7880 * SIZEOF(SECTION): Builtin Functions. (line 167)
7881 * SIZEOF_HEADERS: Builtin Functions. (line 183)
7882 * small common symbols: Input Section Common.
7884 * SORT: Input Section Wildcards.
7886 * SORT_BY_ALIGNMENT: Input Section Wildcards.
7888 * SORT_BY_INIT_PRIORITY: Input Section Wildcards.
7890 * SORT_BY_NAME: Input Section Wildcards.
7892 * SORT_NONE: Input Section Wildcards.
7894 * SPU: SPU ELF. (line 29)
7895 * SPU ELF options: SPU ELF. (line 6)
7896 * SPU extra overlay stubs: SPU ELF. (line 19)
7897 * SPU local store size: SPU ELF. (line 24)
7898 * SPU overlay stub symbols: SPU ELF. (line 15)
7899 * SPU overlays: SPU ELF. (line 9)
7900 * SPU plugins: SPU ELF. (line 6)
7901 * SQUAD(EXPRESSION): Output Section Data.
7903 * stack size: Options. (line 1937)
7904 * standard Unix system: Options. (line 7)
7905 * start of execution: Entry Point. (line 6)
7906 * STARTUP(FILENAME): File Commands. (line 82)
7907 * strip all symbols: Options. (line 519)
7908 * strip debugger symbols: Options. (line 523)
7909 * stripping all but some symbols: Options. (line 1120)
7910 * STUB_GROUP_SIZE: ARM. (line 138)
7911 * SUBALIGN(SUBSECTION_ALIGN): Forced Input Alignment.
7913 * suffixes for integers: Constants. (line 15)
7914 * symbol defaults: Builtin Functions. (line 120)
7915 * symbol definition, scripts: Assignments. (line 6)
7916 * symbol names: Symbols. (line 6)
7917 * symbol tracing: Options. (line 597)
7918 * symbol versions: VERSION. (line 6)
7919 * symbol-only input: Options. (line 508)
7920 * symbolic constants: Symbolic Constants. (line 6)
7921 * symbols, from command line: Options. (line 877)
7922 * symbols, relocatable and absolute: Expression Section. (line 6)
7923 * symbols, retaining selectively: Options. (line 1120)
7924 * synthesizing linker: Options. (line 1094)
7925 * synthesizing on H8/300: H8/300. (line 14)
7926 * TARGET(BFDNAME): Format Commands. (line 35)
7927 * TARGET1: ARM. (line 32)
7928 * TARGET2: ARM. (line 37)
7929 * text segment origin, cmd line: Options. (line 1292)
7930 * thumb entry point: ARM. (line 17)
7931 * TI COFF versions: TI COFF. (line 6)
7932 * traditional format: Options. (line 1264)
7933 * trampoline generation on M68HC11: M68HC11/68HC12. (line 31)
7934 * trampoline generation on M68HC12: M68HC11/68HC12. (line 31)
7935 * unallocated address, next: Builtin Functions. (line 150)
7936 * undefined symbol: Options. (line 554)
7937 * undefined symbol in linker script: Miscellaneous Commands.
7939 * undefined symbols, warnings on: Options. (line 1436)
7940 * uninitialized data placement: Input Section Common.
7942 * unspecified memory: Output Section Data.
7944 * usage: Options. (line 962)
7945 * USE_BLX: ARM. (line 74)
7946 * using a DEF file: WIN32. (line 57)
7947 * using auto-export functionality: WIN32. (line 22)
7948 * Using decorations: WIN32. (line 162)
7949 * variables, defining: Assignments. (line 6)
7950 * verbose[=NUMBER]: Options. (line 1330)
7951 * version: Options. (line 581)
7952 * version script: VERSION. (line 6)
7953 * version script, symbol versions: Options. (line 1338)
7954 * VERSION {script text}: VERSION. (line 6)
7955 * versions of symbols: VERSION. (line 6)
7956 * VFP11_DENORM_FIX: ARM. (line 83)
7957 * warnings, on combining symbols: Options. (line 1349)
7958 * warnings, on section alignment: Options. (line 1440)
7959 * warnings, on undefined symbols: Options. (line 1436)
7960 * weak externals: WIN32. (line 407)
7961 * what is this?: Overview. (line 6)
7962 * wildcard file name patterns: Input Section Wildcards.
7964 * Xtensa options: Xtensa. (line 56)
7965 * Xtensa processors: Xtensa. (line 6)
7971 Node: Overview
\7f1600
7972 Node: Invocation
\7f2714
7973 Node: Options
\7f3122
7974 Node: Environment
\7f95055
7975 Node: Scripts
\7f96815
7976 Node: Basic Script Concepts
\7f98549
7977 Node: Script Format
\7f101256
7978 Node: Simple Example
\7f102119
7979 Node: Simple Commands
\7f105215
7980 Node: Entry Point
\7f105721
7981 Node: File Commands
\7f106654
7982 Node: Format Commands
\7f110655
7983 Node: REGION_ALIAS
\7f112611
7984 Node: Miscellaneous Commands
\7f117443
7985 Node: Assignments
\7f121051
7986 Node: Simple Assignments
\7f121562
7987 Node: HIDDEN
\7f123297
7988 Node: PROVIDE
\7f123927
7989 Node: PROVIDE_HIDDEN
\7f125120
7990 Node: Source Code Reference
\7f125364
7991 Node: SECTIONS
\7f128944
7992 Node: Output Section Description
\7f130835
7993 Node: Output Section Name
\7f131922
7994 Node: Output Section Address
\7f132798
7995 Node: Input Section
\7f135033
7996 Node: Input Section Basics
\7f135834
7997 Node: Input Section Wildcards
\7f139740
7998 Node: Input Section Common
\7f144834
7999 Node: Input Section Keep
\7f146316
8000 Node: Input Section Example
\7f146806
8001 Node: Output Section Data
\7f147774
8002 Node: Output Section Keywords
\7f150551
8003 Node: Output Section Discarding
\7f154120
8004 Node: Output Section Attributes
\7f155301
8005 Node: Output Section Type
\7f156402
8006 Node: Output Section LMA
\7f157473
8007 Node: Forced Output Alignment
\7f160544
8008 Node: Forced Input Alignment
\7f160812
8009 Node: Output Section Constraint
\7f161201
8010 Node: Output Section Region
\7f161629
8011 Node: Output Section Phdr
\7f162062
8012 Node: Output Section Fill
\7f162726
8013 Node: Overlay Description
\7f163868
8014 Node: MEMORY
\7f168171
8015 Node: PHDRS
\7f172506
8016 Node: VERSION
\7f177760
8017 Node: Expressions
\7f185853
8018 Node: Constants
\7f186782
8019 Node: Symbolic Constants
\7f187657
8020 Node: Symbols
\7f188208
8021 Node: Orphan Sections
\7f188955
8022 Node: Location Counter
\7f190120
8023 Node: Operators
\7f194556
8024 Node: Evaluation
\7f195478
8025 Node: Expression Section
\7f196842
8026 Node: Builtin Functions
\7f200499
8027 Node: Implicit Linker Scripts
\7f208460
8028 Node: Machine Dependent
\7f209235
8029 Node: H8/300
\7f210251
8031 Node: M68HC11/68HC12
\7f214080
8033 Node: HPPA ELF32
\7f223497
8036 Node: MSP430
\7f227194
8037 Node: PowerPC ELF32
\7f228243
8038 Node: PowerPC64 ELF64
\7f231079
8039 Node: SPU ELF
\7f237235
8040 Node: TI COFF
\7f239867
8041 Node: WIN32
\7f240393
8042 Node: Xtensa
\7f260518
8044 Node: BFD outline
\7f264938
8045 Node: BFD information loss
\7f266224
8046 Node: Canonical format
\7f268741
8047 Node: Reporting Bugs
\7f273098
8048 Node: Bug Criteria
\7f273792
8049 Node: Bug Reporting
\7f274491
8051 Node: GNU Free Documentation License
\7f286173
8052 Node: LD Index
\7f311329