linux-kernel - Re: [PATCH] drm: panel: fix excessive stack usage in td028ttec1

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Date:   Tue, 7 Jan 2020 23:09:13 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Oleksandr Natalenko <oleksandr@...hat.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: panel: fix excessive stack usage in td028ttec1_prepare

On Tue, Jan 7, 2020 at 11:00 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> 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@...db.de>
>
> 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