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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 <damien.riegel@savoirfairelinux.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Damien Riegel <damien.riegel@savoirfairelinux.com>
Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Buildroot is a simple, efficient and easy-to-use tool to generate embedded Linux systems through cross-compilation. The documentation can be found in docs/manual. You can generate a text document with 'make manual-text' and read output/docs/manual/manual.text. Online documentation can be found at http://buildroot.org/docs.html To build and use the buildroot stuff, do the following: 1) run 'make menuconfig' 2) select the target architecture and the packages you wish to compile 3) run 'make' 4) wait while it compiles 5) find the kernel, bootloader, root filesystem, etc. in output/images You do not need to be root to build or run buildroot. Have fun! Buildroot comes with a basic configuration for a number of boards. Run 'make list-defconfigs' to view the list of provided configurations. Please feed suggestions, bug reports, insults, and bribes back to the buildroot mailing list: buildroot@buildroot.org You can also find us on #buildroot on Freenode IRC. If you would like to contribute patches, please read https://buildroot.org/manual.html#submitting-patches