l4/pkg/libsdl/contrib/src/video/ataricommon/SDL_atarisuper.h

   1 /*
   2     SDL - Simple DirectMedia Layer
   3     Copyright (C) 1997-2012 Sam Lantinga
   4
   5     This library is free software; you can redistribute it and/or
   6     modify it under the terms of the GNU Lesser General Public
   7     License as published by the Free Software Foundation; either
   8     version 2.1 of the License, or (at your option) any later version.
   9
  10     This library is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13     Lesser General Public License for more details.
  14
  15     You should have received a copy of the GNU Lesser General Public
  16     License along with this library; if not, write to the Free Software
  17     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  18
  19     Sam Lantinga
  20     slouken@libsdl.org
  21 */
  22 #include "SDL_config.h"
  23
  24 #ifndef _ATARI_SUPER_h
  25 #define _ATARI_SUPER_h
  26
  27 #include "SDL_stdinc.h"
  28
  29 #ifndef SuperToUser
  30
  31 /*
  32  * Safe binding to switch back from supervisor to user mode.
  33  * On TOS or EmuTOS, if the stack pointer has changed between Super(0)
  34  * and Super(oldssp), the resulting user stack pointer is wrong.
  35  * This bug does not occur with FreeMiNT.
  36  * So the safe way to return from supervisor to user mode is to backup
  37  * the stack pointer then restore it after the trap.
  38  * Sometimes, GCC optimizes the stack usage, so this matters.
  39  */
  40 #define SuperToUser(ptr)                                                \
  41 (void)__extension__                                                     \
  42 ({                                                                      \
  43         register long retvalue __asm__("d0");                           \
  44         register long sp_backup;                                        \
  45                                                                         \
  46         __asm__ volatile                                                \
  47         (                                                               \
  48                 "movl   sp,%1\n\t"                                      \
  49                 "movl   %2,sp@-\n\t"                                    \
  50                 "movw   #0x20,sp@-\n\t"                                 \
  51                 "trap   #1\n\t"                                         \
  52                 "movl   %1,sp\n\t"                                      \
  53         : "=r"(retvalue), "=&r"(sp_backup)      /* outputs */           \
  54         : "g"((long)(ptr))                      /* inputs */            \
  55         : "d1", "d2", "a0", "a1", "a2"          \
  56         );                                                              \
  57 })
  58
  59 #endif /* SuperToUser */
  60
  61 #endif /* _ATARI_SUPER_h */