[FFmpeg-devel] [PATCH] Unbreak av_malloc_max(0) API/ABI

[Joakim Tjernlund]

On Thu, 2020-10-15 at 16:18 +0800, zhilizhao(赵志立) wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> > On Oct 15, 2020, at 1:14 AM, Joakim Tjernlund <joakim.tjernlund at infinera.com> wrote:
> > 
> > On Tue, 2020-10-13 at 20:33 +0200, Joakim Tjernlund wrote:
> > > On Tue, 2020-10-13 at 20:11 +0200, Andreas Rheinhardt wrote:
> > > > 
> > > > Joakim Tjernlund:
> > > > > On Tue, 2020-10-13 at 15:24 +0100, Derek Buitenhuis wrote:
> > > > > > 
> > > > > > On 13/10/2020 15:19, Joakim Tjernlund wrote:
> > > > > > > For now just fixing av_malloc_max(0) will do, av_max_malloc2() etc. is beyond this patch.
> > > > > > 
> > > > > > As Ronald mentioned, if you're going to fix the ABI/API, you should actually
> > > > > > fix every use of that ABI/API, not just the one you care about (0).
> > > > > > 
> > > > > > So max values of 1-31 should also be handled.
> > > > > 
> > > > > OK, how far do you want to take this, will this do?
> > > > >     if (max < 32)
> > > > >         max = INT_MAX;
> > > > > 
> > > > 
> > > > The old behaviour was to effectively limit allocations to max - 32 in
> > > > this case (near to SIZE_MAX), not to INT_MAX. And it does not restore
> > > > default behaviour (the effective default limit was INT_MAX - 32).
> > > > 
> > > > > Complete API fix would need to revert the patch that caused the break to begin with and I don't think you want that ?
> > > > > 
> > > > Actually the old behaviour was against the documented API (or where do
> > > > you see the 32 mentioned in the docs?).
> > > 
> > > The old behaviour in code, what the docs say isn't relevant to a failing app.
> > > 
> > > > 
> > > > - Andreas
> > > > 
> > > > PS: My rationale for this patch was to match actual behaviour and
> > > > documented behaviour and to make the full range of INT available for
> > > > allocations if the maximum has not been overridden by av_max_alloc().
> > > > Otherwise allocations of e.g. packets with sizes in the range (INT_MAX -
> > > > 31 - AV_INPUT_BUFFER_PADDING_SIZE)..(INT_MAX -
> > > > AV_INPUT_BUFFER_PADDING_SIZE) will fail.
> > > 
> > > Please suggest a patch to your liking, I am just trying to repair the breakage, I am not a ffmpeg dev.
> > > 
> > 
> > Gentle ping
> 
> There is little benefit to keep such compatibility. And I wonder if there is anyone still use av_max_alloc(0).
> More workaround means more burden for code maintenance. If there is no use case for av_max_alloc(0),
> I think we can add an assert(max), but not change the value quietly.

Did you read the patch description ? There are apps using this, all chrome based apps is a potential one and MS Teams in
particular does break.
ffmpeg DID change av_max_alloc(0) quietly in 4.3 (by accident) so some restoration of previous behaviour to restore
at least known breakage is what I am asking for.

  Jocke