From bd39d11d2eaa679f09ab49fd3e4cd5511a168d1c Mon Sep 17 00:00:00 2001 From: "Yann E. MORIN" Date: Wed, 3 Jan 2018 18:39:52 +0100 Subject: [PATCH] core/infra: fix build on toolchain without C++ Autotools-based packages that do not need C++ but check for it, and use libtool, will fail to configure on distros that lack /lib/cpp. This is the case for example on Arch Linux, where expat fails to build with: configure: error: in `/home/dkc/src/buildroot/build/build/expat-2.2.4': configure: error: C++ preprocessor "/lib/cpp" fails sanity check This is because libtool uses AC_PROC_CXXCPP, which can not be avoided, and does require a cpp that passes some "sanity" checks (does not choke on valid input, but does choke on invalid input). So we can use neither /bin/false nor /bin/true... We instead need something that can digest some basic C++ preprocessor input. We can't use the target preprocessor: that does not work, because it obviously has no C++ cupport: arm-linux-cpp.br_real: error: conftest.cpp: C++ compiler not installed on this system We can however consider that the host machine does have a C++ compiler, so we use the host' cpp, which is gcc's compiler wrapper that ends up calling the host's C++ preprocessor. That would give us a valid C++ preprocessor when we don't have one, in fact. But autotools will then correctly fail anyway, because there is indeed no C++ compiler at all, as we can see in this excerpt of a configure log from expat: checking whether we are using the GNU C++ compiler... no checking whether false accepts -g... no checking dependency style of false... none checking how to run the C++ preprocessor... cpp checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes libtool.m4: error: problem compiling CXX test program checking for false option to produce PIC... -DPIC checking if false PIC flag -DPIC works... no checking if false static flag works... no checking if false supports -c -o file.o... no checking if false supports -c -o file.o... (cached) no checking whether the false linker (/home/ymorin/dev/buildroot/O/host/bin/arm-linux-ld) supports shared libraries... yes So, using the host's C++ preprocessor (by way of gcc's wrapper) leads to a working situation, where the end result is as expected. Reported-by: Damien Riegel Signed-off-by: "Yann E. MORIN" Cc: Damien Riegel Cc: Vivien Didelot Cc: Peter Korsgaard Cc: Thomas Petazzoni Signed-off-by: Thomas Petazzoni --- package/Makefile.in | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/package/Makefile.in b/package/Makefile.in index a1a5316051..61f0a8f9d0 100644 --- a/package/Makefile.in +++ b/package/Makefile.in @@ -398,7 +398,7 @@ NLS_OPTS = --disable-nls endif ifneq ($(BR2_INSTALL_LIBSTDCPP),y) -TARGET_CONFIGURE_OPTS += CXX=false +TARGET_CONFIGURE_OPTS += CXX=false CXXCPP=cpp endif ifeq ($(BR2_STATIC_LIBS),y) -- 2.39.2