[FFmpeg-devel] [PATCH] x86: cabac: Disable the inline asm on clang on windows on i386

[Martin Storsjö]

On Mon, 25 May 2020, Martin Storsjö wrote:

> On Sun, 24 May 2020, Carl Eugen Hoyos wrote:
>
>> Am So., 24. Mai 2020 um 21:53 Uhr schrieb Martin Storsjö 
> <martin at martin.st>:
>>
>>> configure --enable-gpl --arch=i686 --cc=clang-cl --ld=lld-link
>>> --target-os=win32 --toolchain=msvc --enable-cross-compile --ar=llvm-ar
>>> --nm=llvm-nm --disable-stripping --extra-cflags=-m32
>>
>> Why are you cross-compiling?
>> On which system are you testing this?
>
> Because I normally only ever cross compile for windows.
>
> There seems to be a subtle difference in this case, between using clang-cl 
> and "clang -target i686-win32-msvc"; clang-cl passes "-mdisable-fp-elim" 
> to the compiler internals, while "clang -target i686-win32-msvc" doesn't.
>
> And cross compiling does seem to affect this particular case; there's a 
> check for whether ebp is available, which requires running the built 
> executable. When cross compiling, it's assumed the built executable is ok 
> and it isn't test run.
>
> So with clang-cl running on windows, you'll end up with "#define 
> HAVE_EBP_AVAILABLE 0" in config.h, and the x86 cabac code won't end up 
> used at all - i.e. this patch wouldn't make any difference.
>
> With clang-cl in cross compilation, and other invocations of "clang" 
> instead of "clang-cl", targeting i686 windows, you'll end up with 
> ebp_available enabled.
>
> For a case where it does make a difference, in the same setup, try 
> configuring this way instead:
>
> --cc='clang -target i686-win32-msvc' --ld=lld-link 
> --extra-ldflags='msvcrt.lib oldnames.lib' --toolchain=msvc
>
> In this case, the ebp_available test will succeed, it will proceed to 
> trying to build the x86 inline cabac code, which fails.

Any further comments on this patch?

// Martin