[cfe-users] C/C++ system include dirs when cross-compiling

[Jeffrey Walton via cfe-users]

On Thu, Mar 31, 2016 at 11:50 AM, Patrick Boettcher via cfe-users
<cfe-users at lists.llvm.org> wrote:
> Hi,
>
> On Thu, 24 Mar 2016 16:48:30 +0100
> Arnaud Allard de Grandmaison <arnaud.adegm at gmail.com> wrote:
>
>> Hi Patrick,
>>
>> This is a common case when cross compiling, so clang knows how to use
>> a gcc-toolchain installation: you just have to pass it the
>> "--sysroot=..." and "--toolchain=..." arguments, and it will get the
>> header files and linker / assembler for your target --- assuming your
>> gcc-toolchain has a standard layout.
>
> I'm getting back to you after (some vacations and) having compared
> linaro's latest toolchain to the one I built.
>
> Linaro provides a sysroot-package which does not contain
> c++-header-files. Instead they are located in the gcc-package, as in
> my package, in
>
>   <target>/include/c++/<gcc-version>/
>
> I'm unable to convince clang(++) to include this search-dir using any
> combination of the following options with variations on the path name.
>
>   --gcc-toolchain=
>   -B
>   --sysroot=
>
> sysroot works a little bit, but only for c-include which are located in
> <sysroot-dir>/usr/include.
>
> Using gcc-linaro-5.3-2016.02-x86_64_aarch64-elf I would highly
> appreciate an example of how to invoke clang++ for cross-compilation
> with this gcc and its includes?
>
> My current try is:
>
> TARGET=aarch64-elf \
> GCC_ROOT=~/Downloads/gcc-linaro-5.3-2016.02-x86_64_aarch64-elf \
> ~/devel/upstream/build/bin/clang++ \
>                 -v \
>                 --target=$TARGET \
>                 --gcc-toolchain=$GCC_ROOT/$TARGET \
>                 --sysroot=$GCC_ROOT/$TARGET/sysroot \
>                 -nostdlib \
>                 -o testCCompiler.cpp.obj -c \
>                 -std=c++11 \
>                 test.cpp
>
> test.cpp is empty except #include <cstdint> which it doesn't find.
>
> Linaro's gcc has all include paths in its search list.
>
> Thanks in advance for any help,

We found Ubuntu (perhaps Debian) broke the cross-compile using
--sysroot some time ago. Also see "g++-arm-linux-gnueabi cannot
compile a C++ program with --sysroot",
https://bugs.launchpad.net/ubuntu/+source/gcc-defaults-armel-cross/+bug/1375071.

We were working around the broken C++ header includes by specifically
calling them out with -I. See the comment "Fix C++ header paths for
Ubuntu" at https://github.com/weidai11/cryptopp/blob/master/setenv-embedded.sh#L96.

ARM's "GCC ARM Embedded Tools" works as expected. Its maintained by
ARM employees. Also see the PPA at
https://launchpad.net/gcc-arm-embedded.

Since the time of the Launchpad bug report, the linker no longer works, either.

Jeff