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

[Milian Wolff via cfe-dev]

On Donnerstag, 19. April 2018 19:49:51 CEST Manuel Klimek wrote:
> 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-gnueabih
> >  f/
> > 
> > bin/../lib/gcc/arm-linux-gnueabihf/7.2.1/include
> > 
> >  /home/milian/Downloads/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabih
> >  f/
> > 
> > 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-gnueabih
> >  f/
> > 
> > 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-gnueabih
> >  f/
> > 
> > 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-gnueabih
> >  f/
> > 
> > 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 :)

Afaik this shouldn't be an issue: If you don't add the `#pragma clang 
system_header` line at the start of the imacro file, then you are swamped by 
redefinition errors/warnings. The pragma just silences these, but are they 
actually redefined or not? From what I've seen, they are redefined, and that's 
fine from what I've seen so far...

Can you come up with a scenario where it would break?

Thanks

-- 
Milian Wolff
mail at milianw.de
http://milianw.de
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