[FFmpeg-devel] [PATCH]lavc/svq3: Do not write into const memory

[Tomas Härdin]

On 2018-01-18 23:34, Carl Eugen Hoyos wrote:
> Hi!
>
> Attached patch fixes a warning, I suspect it makes the code more correct.
>
> Please comment, Carl Eugen
>

> --- a/libavcodec/svq3.c
> +++ b/libavcodec/svq3.c
> @@ -1048,12 +1048,12 @@ static int svq3_decode_slice_header(AVCodecContext *avctx)
>           }
>           memcpy(s->slice_buf, s->gb.buffer + s->gb.index / 8, slice_bytes);
>   
> -        init_get_bits(&s->gb_slice, s->slice_buf, slice_bits);

Unrelated change?


>           if (s->watermark_key) {
> -            uint32_t header = AV_RL32(&s->gb_slice.buffer[1]);
> -            AV_WL32(&s->gb_slice.buffer[1], header ^ s->watermark_key);

Strange that this didn't manage to break anything, or that the compiler 
let it through

> +            uint32_t header = AV_RL32(&s->slice_buf[1]);
> +            AV_WL32(&s->slice_buf[1], header ^ s->watermark_key);

Considering the memcpy() above, either this or the old code must be 
wrong. My guess is the old code must have been wrong, since to fiddle 
the same bits this AV_WL32() would need to set &s->slice_buf[1 - 
s->gb.index / 8]...

/Tomas