From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Petazzoni Date: Sun, 7 Jan 2018 15:58:35 +0100 Subject: [Buildroot] [PATCH RFC] core/infra: fix build on toolchain without C++ In-Reply-To: <20180103173952.10834-1-yann.morin.1998@free.fr> References: <20180103173952.10834-1-yann.morin.1998@free.fr> Message-ID: <20180107155835.5bf8e8c4@windsurf> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net Hello, On Wed, 3 Jan 2018 18:39:52 +0100, Yann E. MORIN wrote: > 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 > --- > package/Makefile.in | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Applied to master, thanks. Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com