Linux -> Windows cross-compiling failed

[Ben Gamari]

Bernard de la Paz <bernard.delapaz at yandex.ru> writes:

> I try to cross-compile GHC 8.0.1 with x86_64-mingw toolchain (gcc 6.2.1) and native GHC 8.0.1. Sources are from http://downloads.haskell.org/~ghc/8.0.1/ghc-8.0.1-src.tar.xz
>
>  cp mk/build.mk.example mk/build.mk
>
>  sed -i '1iBuildFlavour = perf' mk/build.mk
>  sed -i '1iStage1Only = YES' mk/build.mk
>  sed -i '1iHADDOCK_DOCS = NO' mk/build.mk
>  ./configure --prefix=~/x86_64-mingw \
>  --target=x86_64-unknown-mingw32 \
>  --with-gcc=/usr/bin/x86_64-w64-mingw32-gcc \
>  --with-ld=/usr/bin/x86_64-w64-mingw32-ld \
>  --with-nm=/usr/bin/x86_64-w64-mingw32-nm \
>  --with-ar=/usr/bin/x86_64-w64-mingw32-ar \
>  --with-ranlib=/usr/bin/x86_64-w64-mingw32-ranlib
>  make -j8 install
>
> First encountered error is in Types.hsc:
>
>  Types.hsc: In function ‘_hsc2hs_test44’:
>  Types.hsc:219:20: error: storage size of ‘test_array’ isn’t constant
>
In general it is helpful if you include a bit more context on where in
the build these errors ocurred. Is this during the stage1 build or
stage2? Just a few lines of the surrounding build output would be helpful.

> There are testing scripts in utils/hsc2hs/CrossCodegen.hs that create such code:
>
>  void _hsc2hs_test44() {
>  static int test_array[value];
>  ...
>
> where 'value' is const int, that is forbidden by C standard. GCC older then 4.4 reject this code, but Clang doesn't (does with -pedantic-errors). But with-gcc=/usr/bin/x86_64-w64-mingw32-clang fails sooner, so it cannot help.
> So I compiled Types.hsc (and three others) with clang and go further.

Hmm, presumably it fails since the array in question is static? On
looking into this I realized that apparently VLAs have been made
optional in C11, so perhaps we should be more conservative in using
them, especially in hsc2hs.

> Second error:
>
>  rts/posix/GetTime.c:25:2: error: #error No implementation for getProcessCPUTime() available.
>  #error No implementation for getProcessCPUTime() available.
>
> In file there are such strings:
>
>  #if ! ((defined(HAVE_GETRUSAGE) && !irix_HOST_OS) || defined(HAVE_TIMES))
>  #error No implementation for getProcessCPUTime() available.
>  #endif
>
> Linux definitely hasn't such function, it's a part of Windows API.

getProcessCPUTime is a function provided by GHC's runtime system.

I believe the issue here is that the build system (rts/ghc.mk) chooses
which implementation to use based upon the host operating system. This
seems wrong. Then again, if this is wrong I don't see how
cross-compilation ever actually worked. Surely I'm missing something
here.

Cheers,

- Ben
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