[FFmpeg-devel] [PATCH] fix MSVC compilation errors

[James Almer]

On 12/5/2017 8:12 AM, Hendrik Leppkes wrote:
> On Tue, Dec 5, 2017 at 12:31 AM, Mateusz <mateuszb at poczta.onet.pl> wrote:
>> After some tests:
>> 1) #undef far
>> after #include <windows.h> is wrong -- in oleauto.h is declaration
>> WINOLEAUTAPI VarUI1FromI8(LONG64 i64In, _Out_ BYTE FAR* pbOut);
>> and 'FAR' is defined as 'far' which is define as empty.
> 
> Yeah generally undefing all of them might result in errors in other
> windows headers, so thats bad.
> 
>>
>> 2) #undef near
>> after #include <windows.h> works in ffmpeg but is danger -- see 1)
> 
> Doing it rather late,  ie. right before its used in the file should be
> relatively safe. If not, we can always rename the variable.
> But it seems to work so far. And from the nature of this bug, it
> should just error out instead of resulting in other breakage - if it
> happens.
> 
>>
>> 3) after
>> git revert 3701d499f8734ec5f3e7359de7311b15d92070b0
>> git revert 590136e78da3d091ea99ab5432543d47a559a461
>> and patch
>> diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
>> -    MXFPackage packages[2] = {};
>> +    MXFPackage packages[2] = {{NULL}};
>> VS 2017 can compile ffmpeg and fate stops at audiomatch-nero-16000-mono-he-m4a
>> (without reverting 590136e hangs at api-flac-test.exe)
>>
>> 4) if for any reasons commits 3701d49 and 590136e shouldn't be reverted,
>> we can apply this patch and
> 
> We can't really revert those, so fixing them is better.
> 
>> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
>> index baf09119fe..b34a3803b8 100644
>> --- a/libavcodec/utils.c
>> +++ b/libavcodec/utils.c
>> @@ -1943,7 +1943,7 @@ int av_lockmgr_register(int (*cb)(void **mutex, enum AVLockOp op))
>>
>>  int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec)
>>  {
>> -    _Bool exp = 0;
>> +    atomic_bool exp = 0;
>>      if (codec->caps_internal & FF_CODEC_CAP_INIT_THREADSAFE || !codec->init)
>>          return 0;
>>
>> @@ -1969,7 +1969,7 @@ int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec)
>>
>>  int ff_unlock_avcodec(const AVCodec *codec)
>>  {
>> -    _Bool exp = 1;
>> +    atomic_bool exp = 1;
>>      if (codec->caps_internal & FF_CODEC_CAP_INIT_THREADSAFE || !codec->init)
>>          return 0;
>>
>>
> 
> atomic_compare_exchange* usage is a bit iffy because it uses pointers,
> and the compat wrappers don't fully represent all types properly (for
> simplicity, implementing them in a generic way would be madness).
> So this work-around seems fine to me, if it builds with GCC as well.

GCC may accept it (No idea what code it would generate, though), but
chances are Clang will complain since it's stricter about correct type
usage in these functions, and making the variable to be passed as the
"expected" parameter atomic is not correct.

> 
> - Hendrik
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