Re: [PATCH] drm: panel: fix excessive stack usage in td028ttec1_prepare

[Arnd Bergmann]

On Tue, Jan 7, 2020 at 11:00 PM Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Arnd,
>
> Thank you for the patch.
>
> On Tue, Jan 07, 2020 at 10:27:33PM +0100, Arnd Bergmann wrote:
> > With gcc -O3, the compiler can inline very aggressively,
> > leading to rather large stack usage:
> >
> > drivers/gpu/drm/panel/panel-tpo-td028ttec1.c: In function 'td028ttec1_prepare':
> > drivers/gpu/drm/panel/panel-tpo-td028ttec1.c:233:1: error: the frame size of 2768 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> >  }
> >
> > Marking jbt_reg_write_1() as noinline avoids the case where
> > multiple instances of this function get inlined into the same
> > stack frame and each one adds a copy of 'tx_buf'.
> >
> > Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>
> Isn't this something that should be fixed at the compiler level ?

I suspect but have not verified that structleak gcc plugin is partly at
fault here as well, it has caused similar problems elsewhere.

If you like I can try to dig deeper before that patch gets merged,
and explain more in the changelog or open a gcc bug if necessary.

      Arnd