Re: [FFmpeg-devel] [PATCH] checkasm/v210enc.c: Use checkasm_check_type

[Kieran Kunhya via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

On Mon, Feb 10, 2025 at 12:40 PM Martin Storsjö <martin@martin.st> wrote:
>
> On Sat, 8 Feb 2025, Kieran Kunhya via ffmpeg-devel wrote:
>
> > $subj
>
> > -            if (memcmp(y0, y1, BUF_SIZE * sizeof(type))                            \
> > -                    || memcmp(u0, u1, BUF_SIZE * sizeof(type) / 2)                 \
> > -                    || memcmp(v0, v1, BUF_SIZE * sizeof(type) / 2)                 \
> > -                    || memcmp(dst0, dst1, width * 8 / 3))                          \
> > +            if (checkasm_check_##type(NULL, 0, y0, 0, y1, 0, BUF_SIZE, 0, NULL)                     \
> > +                    || checkasm_check_##type(NULL, 0, u0, 0, u1, 0, BUF_SIZE / 2, 0, NULL)          \
> > +                    || checkasm_check_##type(NULL, 0, v0, 0, v1, 0, BUF_SIZE / 2, 0, NULL)          \
> > +                    || checkasm_check_uint8_t(NULL, 0, dst0, 0, dst1, 0, (width * 8 / 3), 0, NULL)) \
>
> This actually doesn't detect any failures at all; you're passing it
> parameters for checking a buffer of BUF_SIZE width and 0 height, so it
> doesn't check anything.
>
> By passing height 1, it does seem to work as intended (detecting an
> intentionally added error in the asm).
>
> It feels a little bit unwieldy to check (and print out, if checkasm is run
> with "-v") the whole BUF_SIZE, but it's good to have testing for potential
> writes out of bounds at least, like before.
>
> Further in dav1d there are more improvements to these checkasm helpers,
> which we haven't backported to ffmpeg yet, that helps with allocating
> padded buffers and checking that the padding isn't overwritten; that would
> allow reducing the size of the checked area, to make it easier to read on
> errors too.
>
> But until that's backported, I guess this is fine, if you change the
> height to 1.
>
> // Martin
>

Sorry yes I had that fixed locally. I also noticed it was a lot of
data to print the whole BUF_SIZE.

Kieran
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