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| author | Andreas Rheinhardt <andreas.rheinhardt@outlook.com> | 2024-02-13 12:30:05 +0100 |
|---|---|---|
| committer | Andreas Rheinhardt <andreas.rheinhardt@outlook.com> | 2024-02-16 14:58:12 +0100 |
| commit | 7ed1e806e76092df27d7f984a554546a1cf1a175 (patch) | |
| tree | 1bc2850d3ade82b4b8d4482c7e380a673bb30ca9 | |
| parent | acacf8a313f74d0cc83ae790d39341f471ef47b8 (diff) | |
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
Reviewed-by: Kieran Kunhya <kierank@obe.tv>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
| -rw-r--r-- | libavcodec/x86/simple_idct.asm | 1 |
1 files changed, 1 insertions, 0 deletions
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 |