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| author | Yang Wang <yang.y.wang@intel.com> | 2012-07-24 00:51:10 +0200 |
|---|---|---|
| committer | Derek Buitenhuis <derek.buitenhuis@gmail.com> | 2012-07-25 14:22:18 -0400 |
| commit | 845e92fd6abf749a960354becdc5a9bc498f1f96 (patch) | |
| tree | 401c7d0bce5593d46b2f9434fb506c10384be490 /libavcodec | |
| parent | 6d1c9945dd0a539aa9017697ac7572fde3dc5b83 (diff) | |
| download | ffmpeg-845e92fd6abf749a960354becdc5a9bc498f1f96.tar.gz | |
dsputil_mmx: fix incorrect assembly code
In ff_put_pixels_clamped_mmx(), there are two assembly code blocks.
In the first block (in the unrolled loop), the instructions
"movq 8%3, %%mm1 \n\t", and so forth, have problems.
From above instruction, it is clear what the programmer wants: a load from
p + 8. But this assembly code doesn’t guarantee that. It only works if the
compiler puts p in a register to produce an instruction like this:
"movq 8(%edi), %mm1". During compiler optimization, it is possible that the
compiler will be able to constant propagate into p. Suppose p = &x[10000].
Then operand 3 can become 10000(%edi), where %edi holds &x. And the instruction
becomes "movq 810000(%edx)". That is, it will stride by 810000 instead of 8.
This will cause a segmentation fault.
This error was fixed in the second block of the assembly code, but not in
the unrolled loop.
How to reproduce:
This error is exposed when we build using Intel C++ Compiler, with
IPO+PGO optimization enabled. Crashed when decoding an MJPEG video.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Diffstat (limited to 'libavcodec')
| -rw-r--r-- | libavcodec/x86/dsputil_mmx.c | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/libavcodec/x86/dsputil_mmx.c b/libavcodec/x86/dsputil_mmx.c index 5eb4a242c0..522a5658b7 100644 --- a/libavcodec/x86/dsputil_mmx.c +++ b/libavcodec/x86/dsputil_mmx.c @@ -245,14 +245,14 @@ void ff_put_pixels_clamped_mmx(const DCTELEM *block, uint8_t *pixels, pix = pixels; /* unrolled loop */ __asm__ volatile ( - "movq %3, %%mm0 \n\t" - "movq 8%3, %%mm1 \n\t" - "movq 16%3, %%mm2 \n\t" - "movq 24%3, %%mm3 \n\t" - "movq 32%3, %%mm4 \n\t" - "movq 40%3, %%mm5 \n\t" - "movq 48%3, %%mm6 \n\t" - "movq 56%3, %%mm7 \n\t" + "movq (%3), %%mm0 \n\t" + "movq 8(%3), %%mm1 \n\t" + "movq 16(%3), %%mm2 \n\t" + "movq 24(%3), %%mm3 \n\t" + "movq 32(%3), %%mm4 \n\t" + "movq 40(%3), %%mm5 \n\t" + "movq 48(%3), %%mm6 \n\t" + "movq 56(%3), %%mm7 \n\t" "packuswb %%mm1, %%mm0 \n\t" "packuswb %%mm3, %%mm2 \n\t" "packuswb %%mm5, %%mm4 \n\t" @@ -262,7 +262,7 @@ void ff_put_pixels_clamped_mmx(const DCTELEM *block, uint8_t *pixels, "movq %%mm4, (%0, %1, 2) \n\t" "movq %%mm6, (%0, %2) \n\t" :: "r"(pix), "r"((x86_reg)line_size), "r"((x86_reg)line_size * 3), - "m"(*p) + "r"(p) : "memory"); pix += line_size * 4; p += 32; |