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| author | Andreas Rheinhardt <andreas.rheinhardt@outlook.com> | 2020-01-22 00:55:22 +0100 |
|---|---|---|
| committer | Andreas Rheinhardt <andreas.rheinhardt@outlook.com> | 2022-10-19 13:48:31 +0200 |
| commit | 30e1f5ec77530fad053730a2ffd10b8286420899 (patch) | |
| tree | 3a69d4d07bdd5f4dfb6c9a0f2e476016c1c87016 | |
| parent | b9058765d7422bb801af0e67fb58ba47e523f831 (diff) | |
| download | ffmpeg-30e1f5ec77530fad053730a2ffd10b8286420899.tar.gz | |
avcodec/startcode: Avoid unaligned accesses
Up until now, ff_startcode_find_candidate_c() simply casts
an uint8_t* to uint64_t*/uint32_t* to read 64/32 bits at a time
in case HAVE_FAST_UNALIGNED is true. Yet this ignores the
alignment requirement of these types as well as effective type
rules of the C standard. This commit therefore replaces these
direct accesses with AV_RN64/32; this also improves
readability.
UBSan reported these unaligned accesses which happened in 233
FATE-tests involving H.264 and VC-1 (this has also been reported
in tickets #8138 and #8485); these tests are fixed by this commit.
The output of GCC with -O3 is unchanged for aarch64, loongarch,
ppc and x64 (as well as for arches like alpha for which
HAVE_FAST_UNALIGNED is never true in the first place).
There was only a slight difference for mips and arm.
I don't know about the speed impact of them.
Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
| -rw-r--r-- | libavcodec/startcode.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/libavcodec/startcode.c b/libavcodec/startcode.c index 9efdffe8c6..d84f326521 100644 --- a/libavcodec/startcode.c +++ b/libavcodec/startcode.c @@ -25,6 +25,7 @@ * @author Michael Niedermayer <michaelni@gmx.at> */ +#include "libavutil/intreadwrite.h" #include "startcode.h" #include "config.h" @@ -38,14 +39,14 @@ int ff_startcode_find_candidate_c(const uint8_t *buf, int size) */ #if HAVE_FAST_64BIT while (i < size && - !((~*(const uint64_t *)(buf + i) & - (*(const uint64_t *)(buf + i) - 0x0101010101010101ULL)) & + !((~AV_RN64(buf + i) & + (AV_RN64(buf + i) - 0x0101010101010101ULL)) & 0x8080808080808080ULL)) i += 8; #else while (i < size && - !((~*(const uint32_t *)(buf + i) & - (*(const uint32_t *)(buf + i) - 0x01010101U)) & + !((~AV_RN32(buf + i) & + (AV_RN32(buf + i) - 0x01010101U)) & 0x80808080U)) i += 4; #endif |