[cfe-dev] clangd/libclang: how to emulate other compilers?

[Manuel Klimek via cfe-dev]

On Thu, Apr 19, 2018 at 12:57 PM Milian Wolff <mail at milianw.de> wrote:

> On Donnerstag, 19. April 2018 14:12:21 CEST Manuel Klimek wrote:
> <snip>
>
> > Ah, sorry, I missed the neon part. So this works if we add
> > -mcpu=cortex-a15. The problem is that the gcc cross compiler apparently
> has
> > that configured at build time, and I'm not sure what the best way is to
> > figure out the full settings for cpu / fpu and float-abi, but I think
> we'll
> > need to find some way to gather them from the underlying cross compiler.
>
> OK, thanks. This brings us one more step closer towards emulation and
> should
> be sufficient for the example I have given. So, we now end up with these
> steps:
>
> #1: query the target compiler
> $ ./gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-
> gnueabihf-gcc -xc++ -E -v -dM - < /dev/null
>
> #2: parse the output for the target:
> Target: arm-linux-gnueabihf
>
> #3: parse the default march GCC argument from:
> COLLECT_GCC_OPTIONS='-E' '-v' '-dM' '-march=armv7-a' '-mtune=cortex-a9' '-
> mfloat-abi=hard' '-mfpu=vfpv3-d16' '-mthumb' '-mtls-dialect=gnu'
>
> #4: parse the include paths:
> #include <...> search starts here:
>
>  /home/milian/Downloads/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf/
> bin/../lib/gcc/arm-linux-gnueabihf/7.2.1/include
>
>  /home/milian/Downloads/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf/
> bin/../lib/gcc/arm-linux-gnueabihf/7.2.1/include-fixed
>
>  /home/milian/Downloads/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf/
> bin/../lib/gcc/arm-linux-gnueabihf/7.2.1/../../../../arm-linux-gnueabihf/
> include
>
>  /home/milian/Downloads/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf/
> bin/../arm-linux-gnueabihf/libc/usr/include
>
> #5: exclude the GCC builtin include path, i.e.:
>
>  /home/milian/Downloads/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf/
> bin/../lib/gcc/arm-linux-gnueabihf/7.2.1/include
>
> For now, this can be done by some heuristics, like checking whether the
> folder
> contains a "varargs.h" file.
>
> #6: parse the defines and write all into a file that starts with `#pragma
> clang system_header`
>

This might still break if you define things that the compiler wants to
define on its own, so you might need a filter, but overall this looks
reasonable now :)


>
> #7 parse the file with clang:
>
> clang -Xclang -ast-dump -fsyntax-only -xc++ \
>   -target arm-linux-gnueabihf \ (from #2)
>   -march=armv7-a \ (from #3)
>   -isystem... \ (from #4, 5)
>   -imacros... \ (from #6)
>   file.cpp
>
> This seems to work! Thanks for the help Manuel!
>
> --
> Milian Wolff
> mail at milianw.de
> http://milianw.de
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