On 7/8/17 11:48 PM, Luca Barbato wrote:
> Do not use skip_remaining to fully wipe the cache.
> Thanks to Uoti for pointing out the problem.
>
> CC: libav-sta...@libav.org
> ---
> libavcodec/bitstream.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h
> index d6dd2b9411..1b23cb2fa7 100644
> --- a/libavcodec/bitstream.h
> +++ b/libavcodec/bitstream.h
> @@ -239,11 +239,13 @@ static inline void skip_remaining(BitstreamContext *bc,
> unsigned n)
> /* Skip n bits in the buffer. */
> static inline void bitstream_skip(BitstreamContext *bc, unsigned n)
> {
> - if (n <= bc->bits_left)
> + if (n < bc->bits_left)
> skip_remaining(bc, n);
> else {
> n -= bc->bits_left;
> - skip_remaining(bc, bc->bits_left);
> + bc->bits = 0;
> + bc->bits_left = 0;
> +
> if (n >= 64) {
> unsigned skip = n / 8;
>
>
Uoti suggested:
bitstream: Avoid undefined behavior in bitstream_skip
Do not use skip_remaining to fully wipe the cache, as this could do
a 64-bit shift of a 64-bit variable which is undefined behavior in
C.
Instead set the related variables to zero directly.
Thanks to Uoti for pointing out the problem.
CC: libav-sta...@libav.org
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