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

[Nathan Chancellor <nathan@kernel.org>]

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.

Cheers,
Nathan

> > > ---
> > > 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
> > > 
> >