Subject: Re: [PATCH 10/11] drm/i915: avoid stringop-overread warning on pri_latency

From: Ville Syrjälä <[email-masked]>
Date: Wed, 24 Mar 2021 19:22:48 +0200

On Wed, Mar 24, 2021 at 05:30:24PM +0200, Jani Nikula wrote:
> On Mon, 22 Mar 2021, Arnd Bergmann <[email-masked]> wrote:
> > From: Arnd Bergmann <[email-masked]>
> >
> > gcc-11 warns about what appears to be an out-of-range array access:
> >
> > In function ‘snb_wm_latency_quirk’,
> >     inlined from ‘ilk_setup_wm_latency’ at drivers/gpu/drm/i915/intel_pm.c:3108:3:
> > drivers/gpu/drm/i915/intel_pm.c:3057:9: error: ‘intel_print_wm_latency’ reading 16 bytes from a region of size 10 [-Werror=stringop-overread]
> >  3057 |         intel_print_wm_latency(dev_priv, "Primary", dev_priv->wm.pri_latency);
> >       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/gpu/drm/i915/intel_pm.c: In function ‘ilk_setup_wm_latency’:
> > drivers/gpu/drm/i915/intel_pm.c:3057:9: note: referencing argument 3 of type ‘const u16 *’ {aka ‘const short unsigned int *’}
> > drivers/gpu/drm/i915/intel_pm.c:2994:13: note: in a call to function ‘intel_print_wm_latency’
> >  2994 | static void intel_print_wm_latency(struct drm_i915_private *dev_priv,
> >       |             ^~~~~~~~~~~~~~~~~~~~~~
> >
> > My guess is that this code is actually safe because the size of the
> > array depends on the hardware generation, and the function checks for
> > that, but at the same time I would not expect the compiler to work it
> > out correctly, and the code seems a little fragile with regards to
> > future changes. Simply increasing the size of the array should help.
> 
> Agreed, I don't think there's an issue, but the code could use a bunch
> of improvements.
> 
> Like, we have intel_print_wm_latency() for debug logging and
> wm_latency_show() for debugfs, and there's a bunch of duplication and
> ugh.

There is all this ancient stuff in review limbo...
https://patchwork.freedesktop.org/series/50802/

-- 
Ville Syrjälä
Intel