[FFmpeg-devel] [PATCH] avcodec/put_bits: Restore x64 ABI compatibility with releases <= 4.3

[James Almer]

On 3/22/2021 3:35 AM, Andreas Rheinhardt wrote:
> 88d80cb97528d52dac3178cf5393d6095eca6200 changed the type of
> PutBitContext.BitBuf to uint64_t; it used to be an uint32_t.
> While said structure is not public, it is nevertheless used by
> certain avpriv functions and therefore crosses library boundaries:
> avpriv_align_put_bits and avpriv_copy_bits were used in other libraries
> in release 4.3 (and at the time of 88d80cb9) and so this commit broke
> ABI.
> 
> This commit mitigates the trouble caused by this by using an uint32_t
> again, but only for the 4.4 release branch and not the master branch,
> as doing so for master, would break the ABI of master again, although
> it is very unlikely that anyone would be helped by this (there don't
> seem to be any users that combine libavcodec built from master and
> libavformat from an old release: otherwise we would have received bug
> reports about said ABI break).

So basically, this would only be a problem if your application loads 
lavf <= 4.3 (that was linked to lavc <= 4.3) alongside lavc 4.4 at 
runtime, right?

> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
> Important: This is only intended for the 4.4 release branch.
> 
>   libavcodec/put_bits.h | 7 -------
>   1 file changed, 7 deletions(-)
> 
> diff --git a/libavcodec/put_bits.h b/libavcodec/put_bits.h
> index cd66a82a44..f07944a8fb 100644
> --- a/libavcodec/put_bits.h
> +++ b/libavcodec/put_bits.h
> @@ -35,16 +35,9 @@
>   
>   #include "version.h"
>   
> -#if ARCH_X86_64
> -// TODO: Benchmark and optionally enable on other 64-bit architectures.
> -typedef uint64_t BitBuf;
> -#define AV_WBBUF AV_WB64
> -#define AV_WLBUF AV_WL64
> -#else
>   typedef uint32_t BitBuf;
>   #define AV_WBBUF AV_WB32
>   #define AV_WLBUF AV_WL32
> -#endif
>   
>   static const int BUF_BITS = 8 * sizeof(BitBuf);

LGTM