On Mon, 22 Mar 2021, Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> 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.
But this seems like the easiest fix for the warning.
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 26d69d06aa6d..3567602e0a35 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1095,11 +1095,11 @@ struct drm_i915_private {
> * in 0.5us units for WM1+.
> */
> /* primary */
> - u16 pri_latency[5];
> + u16 pri_latency[8];
> /* sprite */
> - u16 spr_latency[5];
> + u16 spr_latency[8];
> /* cursor */
> - u16 cur_latency[5];
> + u16 cur_latency[8];
> /*
> * Raw watermark memory latency values
> * for SKL for all 8 levels
--
Jani Nikula, Intel Open Source Graphics Center
