From: "Ronald S. Bultje" <[email protected]>
Based on work (for GCI) by Aneesh Dogra <[email protected]>, and
inspired by patch in Chromium by Chris Evans <[email protected]>.
When turned on, H264/CAVLC gets ~15% (CVPCMNL1_SVA_C.264) slower for
ultra-high-bitrate files, or ~2.5% (CVFI1_SVA_C.264) for lower-bitrate
files. Other codecs are affected to a lesser extent because they are
less optimized; e.g., VC-1 slows down by less than 1% (all on x86).
The patch generated 3 extra instructions (cmp, cmovae and mov) per
call to get_bits().
---
configure | 2 ++
libavcodec/get_bits.h | 37 ++++++++++++++++++++++++++++++++++++-
libavcodec/wmavoice.c | 2 ++
3 files changed, 40 insertions(+), 1 deletions(-)
diff --git a/configure b/configure
index 974e75f..0349862 100755
--- a/configure
+++ b/configure
@@ -113,6 +113,7 @@ Configuration options:
--disable-dxva2 disable DXVA2 code
--enable-runtime-cpudetect detect cpu capabilities at runtime (bigger binary)
--enable-hardcoded-tables use hardcoded tables instead of runtime generation
+ --disable-safe-bitstream-reader disable buffer boundary checking in
bitreaders (faster, but may crash)
--enable-memalign-hack emulate memalign, interferes with memory debuggers
--disable-everything disable all components listed below
--disable-encoder=NAME disable encoder NAME
@@ -976,6 +977,7 @@ CONFIG_LIST="
rdft
rtpdec
runtime_cpudetect
+ safe_bitstream_reader
shared
sinewin
small
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index 684cc99..91afe34 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -35,12 +35,32 @@
#include "libavutil/log.h"
#include "mathops.h"
+/*
+ * Safe bitstream reading:
+ * optionally, the get_bits API can check to ensure that we
+ * don't read past input buffer boundaries. This is protected
+ * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
+ * then below that with UNCHECKED_BITSTREAM_READER at the per-
+ * decoder level. This means that decoders that check internally
+ * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
+ * overread checks.
+ * Boundary checking causes a minor performance penalty so for
+ * applications that won't want/need this, it can be disabled
+ * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
+ */
+#ifndef UNCHECKED_BITSTREAM_READER
+#define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
+#endif
+
/* bit input */
/* buffer, buffer_end and size_in_bits must be present and used by every
reader */
typedef struct GetBitContext {
const uint8_t *buffer, *buffer_end;
int index;
int size_in_bits;
+#if !UNCHECKED_BITSTREAM_READER
+ int size_in_bits_plus1;
+#endif
} GetBitContext;
#define VLC_TYPE int16_t
@@ -137,7 +157,12 @@ for examples see get_bits, show_bits, skip_bits, get_vlc
# endif
// FIXME name?
+#if UNCHECKED_BITSTREAM_READER
# define SKIP_COUNTER(name, gb, num) name##_index += (num)
+#else
+# define SKIP_COUNTER(name, gb, num) name##_index = \
+ FFMIN((gb)->size_in_bits_plus1, name##_index + num)
+#endif
# define SKIP_BITS(name, gb, num) do { \
SKIP_CACHE(name, gb, num); \
@@ -164,7 +189,11 @@ static inline int get_bits_count(const GetBitContext *s){
}
static inline void skip_bits_long(GetBitContext *s, int n){
+#if UNCHECKED_BITSTREAM_READER
s->index += n;
+#else
+ s->index += av_clip(n, -s->index, s->size_in_bits_plus1 - s->index);
+#endif
}
/**
@@ -237,7 +266,10 @@ static inline unsigned int get_bits1(GetBitContext *s){
result <<= index & 7;
result >>= 8 - 1;
#endif
- index++;
+#if !UNCHECKED_BITSTREAM_READER
+ if (s->index < s->size_in_bits_plus1)
+#endif
+ index++;
s->index = index;
return result;
@@ -314,6 +346,9 @@ static inline void init_get_bits(GetBitContext *s,
s->buffer = buffer;
s->size_in_bits = bit_size;
+#if !UNCHECKED_BITSTREAM_READER
+ s->size_in_bits_plus1 = bit_size + 1;
+#endif
s->buffer_end = buffer + buffer_size;
s->index = 0;
}
diff --git a/libavcodec/wmavoice.c b/libavcodec/wmavoice.c
index 00e985d..8854e35 100644
--- a/libavcodec/wmavoice.c
+++ b/libavcodec/wmavoice.c
@@ -25,6 +25,8 @@
* @author Ronald S. Bultje <[email protected]>
*/
+#define UNCHECKED_BITSTREAM_READER 1
+
#include <math.h>
#include "avcodec.h"
#include "get_bits.h"
--
1.7.8
_______________________________________________
libav-devel mailing list
[email protected]
https://lists.libav.org/mailman/listinfo/libav-devel
