From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] avcodec/qpeldsp: copy less for the mc0x cases
Date: Mon, 27 Jun 2022 14:40:04 +0200
Message-ID: <20220627124004.GS396728@pb2> (raw)
In-Reply-To: <DB6PR0101MB22148DA559EE851AB03B5D9F8FB99@DB6PR0101MB2214.eurprd01.prod.exchangelabs.com>
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On Mon, Jun 27, 2022 at 07:57:06AM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > Fixes: out of array access
> > Fixes: 47936/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5745039940124672
> >
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> > libavcodec/qpeldsp.c | 12 ++++++------
> > 1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/libavcodec/qpeldsp.c b/libavcodec/qpeldsp.c
> > index 2b9146ceb1..5f937f9d9e 100644
> > --- a/libavcodec/qpeldsp.c
> > +++ b/libavcodec/qpeldsp.c
> > @@ -199,7 +199,7 @@ static void OPNAME ## qpel8_mc01_c(uint8_t *dst, const uint8_t *src, \
> > uint8_t full[16 * 9]; \
> > uint8_t half[64]; \
> > \
> > - copy_block9(full, src, 16, stride, 9); \
> > + copy_block8(full, src, 16, stride, 9); \
> > put ## RND ## mpeg4_qpel8_v_lowpass(half, full, 8, 16); \
> > OPNAME ## pixels8_l2_8(dst, full, half, stride, 16, 8, 8); \
> > } \
> > @@ -209,7 +209,7 @@ static void OPNAME ## qpel8_mc02_c(uint8_t *dst, const uint8_t *src, \
> > { \
> > uint8_t full[16 * 9]; \
> > \
> > - copy_block9(full, src, 16, stride, 9); \
> > + copy_block8(full, src, 16, stride, 9); \
> > OPNAME ## mpeg4_qpel8_v_lowpass(dst, full, stride, 16); \
> > } \
> > \
> > @@ -219,7 +219,7 @@ static void OPNAME ## qpel8_mc03_c(uint8_t *dst, const uint8_t *src, \
> > uint8_t full[16 * 9]; \
> > uint8_t half[64]; \
> > \
> > - copy_block9(full, src, 16, stride, 9); \
> > + copy_block8(full, src, 16, stride, 9); \
> > put ## RND ## mpeg4_qpel8_v_lowpass(half, full, 8, 16); \
> > OPNAME ## pixels8_l2_8(dst, full + 16, half, stride, 16, 8, 8); \
> > } \
> > @@ -459,7 +459,7 @@ static void OPNAME ## qpel16_mc01_c(uint8_t *dst, const uint8_t *src, \
> > uint8_t full[24 * 17]; \
> > uint8_t half[256]; \
> > \
> > - copy_block17(full, src, 24, stride, 17); \
> > + copy_block16(full, src, 24, stride, 17); \
> > put ## RND ## mpeg4_qpel16_v_lowpass(half, full, 16, 24); \
> > OPNAME ## pixels16_l2_8(dst, full, half, stride, 24, 16, 16); \
> > } \
> > @@ -469,7 +469,7 @@ static void OPNAME ## qpel16_mc02_c(uint8_t *dst, const uint8_t *src, \
> > { \
> > uint8_t full[24 * 17]; \
> > \
> > - copy_block17(full, src, 24, stride, 17); \
> > + copy_block16(full, src, 24, stride, 17); \
> > OPNAME ## mpeg4_qpel16_v_lowpass(dst, full, stride, 24); \
> > } \
> > \
> > @@ -479,7 +479,7 @@ static void OPNAME ## qpel16_mc03_c(uint8_t *dst, const uint8_t *src, \
> > uint8_t full[24 * 17]; \
> > uint8_t half[256]; \
> > \
> > - copy_block17(full, src, 24, stride, 17); \
> > + copy_block16(full, src, 24, stride, 17); \
> > put ## RND ## mpeg4_qpel16_v_lowpass(half, full, 16, 24); \
> > OPNAME ## pixels16_l2_8(dst, full + 24, half, stride, 24, 16, 16); \
> > } \
>
> Are the arch-specific dsp functions affected by this, too?
the fuzzer sample does not cause a anomaly in the x86 functions
> Do you happen to know why copy_block9/17 has been used in this code?
probably because there was asm anyway so it was unused code or maybe it
was oversight or some sort of code sharing/code cache use reduction but
these hypothesis dont fit entirely. so i dont really know/rememeber
> (After all, using copy_block8/16 should result in a slight speedup, so I
> using copy_block9/17 must have been intentional.)
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Homeopathy is like voting while filling the ballot out with transparent ink.
Sometimes the outcome one wanted occurs. Rarely its worse than filling out
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next prev parent reply other threads:[~2022-06-27 12:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-26 13:51 Michael Niedermayer
2022-06-27 5:57 ` Andreas Rheinhardt
2022-06-27 12:40 ` Michael Niedermayer [this message]
2022-07-12 18:13 ` Michael Niedermayer
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