Re: [PATCH] media: mediatek: vcodec: mark vdec_vp9_slice_map_counts_eob_coef noinline

Sebastian Fricke
2024-12-18T12:46:41Z

Hey Nathan,

On 17.12.2024 10:46, Nathan Chancellor wrote:
>Hi Sebastian,
>
>On Tue, Nov 19, 2024 at 12:02:26PM +0100, Sebastian Fricke wrote:
>> Hey Nathan,
>>
>> On 18.11.2024 13:06, Nathan Chancellor wrote:
>> > On Fri, Oct 18, 2024 at 03:14:42PM +0000, Arnd Bergmann wrote:
>> > > From: Arnd Bergmann <arnd@arndb.de>
>> > >
>> > > With KASAN enabled, clang fails to optimize the inline version of
>> > > vdec_vp9_slice_map_counts_eob_coef() properly, leading to kilobytes
>> > > of temporary values spilled to the stack:
>> > >
>> > > drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c:1526:12: error: stack frame size (2160) exceeds limit (2048) in 'vdec_vp9_slice_update_prob' [-Werror,-Wframe-larger-than]
>> > >
>> > > This seems to affect all versions of clang including the latest (clang-20),
>> > > but the degree of stack overhead is different per release.
>> > >
>> > > Marking the function as noinline_for_stack is harmless here and avoids
>> > > the problem completely.
>> > >
>> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>> >
>> > Unfortunately, I have seen no moment on my upstream report and this
>> > warning is breaking allmodconfig builds because of -Werror. Can this be
>> > applied as a workaround for now (preferrably with a Cc: stable on it)?
>> >
>> > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
>>
>> I'll handle it asap, it will be part of 6.13
>
>Is there any update here? I don't see this patch applied in -next.

I have sent out the PR and it has been applied to the -fixes branch in
the media tree, due to the holiday period there might be some delays but
I expect the change to soon land in Linux-next.

>
>Cheers,
>Nathan

Regards,
Sebastian

>
>> > > ---
>> > > I have not come to a conclusion on how exactly clang fails to do this
>> > > right, but can provide the .config and/or preprocessed source files
>> > > and command line if we think this should be fixed in clang.
>> > > ---
>> > > .../mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c | 3 ++-
>> > > 1 file changed, 2 insertions(+), 1 deletion(-)
>> > >
>> > > diff --git a/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c b/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c
>> > > index eea709d93820..47c302745c1d 100644
>> > > --- a/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c
>> > > +++ b/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c
>> > > @@ -1188,7 +1188,8 @@ static int vdec_vp9_slice_setup_lat(struct vdec_vp9_slice_instance *instance,
>> > > return ret;
>> > > }
>> > >
>> > > -static
>> > > +/* clang stack usage explodes if this is inlined */
>> > > +static noinline_for_stack
>> > > void vdec_vp9_slice_map_counts_eob_coef(unsigned int i, unsigned int j, unsigned int k,
>> > > struct vdec_vp9_slice_frame_counts *counts,
>> > > struct v4l2_vp9_frame_symbol_counts *counts_helper)
>> > > --
>> > > 2.39.5
>> > >
>> >
Sebastian Fricke
Consultant Software Engineer

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