From 30e1f5ec77530fad053730a2ffd10b8286420899 Mon Sep 17 00:00:00 2001 From: Andreas Rheinhardt Date: Wed, 22 Jan 2020 00:55:22 +0100 Subject: [PATCH] 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 Signed-off-by: Andreas Rheinhardt --- libavcodec/startcode.c | 9 +++++---- 1 file 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 */ +#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