[FFmpeg-devel] [PATCH] lavu/video_enc_params: make sure blocks are properly aligned

[Anton Khirnov]

Quoting Andreas Rheinhardt (2021-04-08 12:27:03)
> Anton Khirnov:
> > Quoting Andreas Rheinhardt (2021-04-08 11:41:41)
> >> Anton Khirnov:
> >>> ---
> >>>  libavutil/video_enc_params.c | 6 +++---
> >>>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/libavutil/video_enc_params.c b/libavutil/video_enc_params.c
> >>> index 635176ab91..1779a8799a 100644
> >>> --- a/libavutil/video_enc_params.c
> >>> +++ b/libavutil/video_enc_params.c
> >>> @@ -30,9 +30,9 @@ AVVideoEncParams *av_video_enc_params_alloc(enum AVVideoEncParamsType type,
> >>>                                              unsigned int nb_blocks, size_t *out_size)
> >>>  {
> >>>      AVVideoEncParams *par;
> >>> -    size_t size;
> >>> +    size_t blocks_offset = FFALIGN(sizeof(*par), 8);
> >>> +    size_t size          = blocks_offset;
> >>>  
> >>> -    size = sizeof(*par);
> >>>      if (nb_blocks > (SIZE_MAX - size) / sizeof(AVVideoBlockParams))
> >>>          return NULL;
> >>>      size += sizeof(AVVideoBlockParams) * nb_blocks;
> >>> @@ -44,7 +44,7 @@ AVVideoEncParams *av_video_enc_params_alloc(enum AVVideoEncParamsType type,
> >>>      par->type          = type;
> >>>      par->nb_blocks     = nb_blocks;
> >>>      par->block_size    = sizeof(AVVideoBlockParams);
> >>> -    par->blocks_offset = sizeof(*par);
> >>> +    par->blocks_offset = blocks_offset;
> >>>  
> >>>      if (out_size)
> >>>          *out_size = size;
> >>>
> >> Wouldn't it be safer to just define a struct { AVVideoEncParams header;
> >> AVVideoBlockParams blocks[1]; } and use the offset of blocks in that?
> > 
> > I don't see how it would be safer and it prevents you from adding new
> > fields to AVVideoEncParams
> > 
> Safer: You are making assumptions about the alignment of
> AVVideoBlockParams; these assumptions may or may not be fulfilled in
> practice.
> And I really don't get your point about this preventing the addition of
> new fields to AVVideoEncParams. If something is added to
> AVVideoEncParams, sizeof(header) and offsetof(blocks) will grow
> automatically as required.

Nevermind, I misunderstood your suggestion. I suppose it works better
indeed.

-- 
Anton Khirnov