Re: [FFmpeg-devel] [PATCH] avcodec/x86/simple_idct: Empty MMX state in ff_simple_idct_mmx
> Will apply this patch tomorrow unless there are objections. > LGTM ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-devel] [PATCH] avcodec/x86/simple_idct: Empty MMX state in ff_simple_idct_mmx
Andreas Rheinhardt: > We currently mostly do not empty the MMX state in our MMX > DSP functions; instead we only do so before code that might > be using x87 code. This is a violation of the System V i386 ABI > (and maybe of other ABIs, too): > "The CPU shall be in x87 mode upon entry to a function. Therefore, > every function that uses the MMX registers is required to issue an > emms or femms instruction after using MMX registers, before returning > or calling another function." (See 2.2.1 in [1]) > This patch does not intend to change all these functions to abide > by the ABI; it only does so for ff_simple_idct_mmx, as this > function can by called by external users, because it is exported > via the avdct API. Without this, the following fragment will > assert (on x86_32, as ff_simple_idct_mmx is not used on x64): > int16_t __attribute__ ((aligned (16))) block[64]; > AVDCT *dct = avcodec_dct_alloc(); > dct->idct_algo = FF_IDCT_AUTO; > avcodec_dct_init(dct); > dct->idct(block); > av_assert0_fpu(); > > [1]: > https://raw.githubusercontent.com/wiki/hjl-tools/x86-psABI/intel386-psABI-1.1.pdf > > Signed-off-by: Andreas Rheinhardt > --- > libavcodec/x86/simple_idct.asm | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/libavcodec/x86/simple_idct.asm b/libavcodec/x86/simple_idct.asm > index 982b2f0bbb..4139b6dab5 100644 > --- a/libavcodec/x86/simple_idct.asm > +++ b/libavcodec/x86/simple_idct.asm > @@ -845,6 +845,7 @@ INIT_MMX mmx > > cglobal simple_idct, 1, 2, 8, 128, block, t0 > IDCT > +emms > RET > > INIT_XMM sse2 Will apply this patch tomorrow unless there are objections. - Andreas ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
[FFmpeg-devel] [PATCH] avcodec/x86/simple_idct: Empty MMX state in ff_simple_idct_mmx
We currently mostly do not empty the MMX state in our MMX DSP functions; instead we only do so before code that might be using x87 code. This is a violation of the System V i386 ABI (and maybe of other ABIs, too): "The CPU shall be in x87 mode upon entry to a function. Therefore, every function that uses the MMX registers is required to issue an emms or femms instruction after using MMX registers, before returning or calling another function." (See 2.2.1 in [1]) This patch does not intend to change all these functions to abide by the ABI; it only does so for ff_simple_idct_mmx, as this function can by called by external users, because it is exported via the avdct API. Without this, the following fragment will assert (on x86_32, as ff_simple_idct_mmx is not used on x64): int16_t __attribute__ ((aligned (16))) block[64]; AVDCT *dct = avcodec_dct_alloc(); dct->idct_algo = FF_IDCT_AUTO; avcodec_dct_init(dct); dct->idct(block); av_assert0_fpu(); [1]: https://raw.githubusercontent.com/wiki/hjl-tools/x86-psABI/intel386-psABI-1.1.pdf Signed-off-by: Andreas Rheinhardt --- libavcodec/x86/simple_idct.asm | 1 + 1 file changed, 1 insertion(+) diff --git a/libavcodec/x86/simple_idct.asm b/libavcodec/x86/simple_idct.asm index 982b2f0bbb..4139b6dab5 100644 --- a/libavcodec/x86/simple_idct.asm +++ b/libavcodec/x86/simple_idct.asm @@ -845,6 +845,7 @@ INIT_MMX mmx cglobal simple_idct, 1, 2, 8, 128, block, t0 IDCT +emms RET INIT_XMM sse2 -- 2.34.1 ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
