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From: Jani Nikula <jani.nikula@linux.intel.com>
To: Arnd Bergmann <arnd@kernel.org>,
	linux-kernel@vger.kernel.org, Martin Sebor <msebor@gcc.gnu.org>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
	x86@kernel.org, "Ning Sun" <ning.sun@intel.com>,
	"Kalle Valo" <kvalo@codeaurora.org>,
	"Simon Kelley" <simon@thekelleys.org.uk>,
	"James Smart" <james.smart@broadcom.com>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Anders Larsen" <al@alarsen.net>, "Tejun Heo" <tj@kernel.org>,
	"Serge Hallyn" <serge@hallyn.com>,
	"Imre Deak" <imre.deak@intel.com>,
	linux-arm-kernel@lists.infradead.org,
	tboot-devel@lists.sourceforge.net,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	ath11k@lists.infradead.org, linux-wireless@vger.kernel.org,
	netdev@vger.kernel.org, linux-scsi@vger.kernel.org,
	cgroups@vger.kernel.org, linux-security-module@vger.kernel.org,
	"Chris Wilson" <chris@chris-wilson.co.uk>,
	"José Roberto de Souza" <jose.souza@intel.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Matt Roper" <matthew.d.roper@intel.com>,
	"Aditya Swarup" <aditya.swarup@intel.com>
Subject: Re: [PATCH 10/11] drm/i915: avoid stringop-overread warning on pri_latency
Date: Wed, 24 Mar 2021 17:30:24 +0200
Message-ID: <874kh04lin.fsf@intel.com> (raw)
In-Reply-To: <20210322160253.4032422-11-arnd@kernel.org>

On Mon, 22 Mar 2021, Arnd Bergmann <arnd@kernel.org> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> 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@intel.com>


> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  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

  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-22 16:02 [PATCH 00/11] treewide: address gcc-11 -Wstringop-overread warnings Arnd Bergmann
2021-03-22 16:02 ` [PATCH 01/11] x86: compressed: avoid gcc-11 -Wstringop-overread warning Arnd Bergmann
2021-03-22 16:02 ` [PATCH 02/11] x86: tboot: avoid Wstringop-overread-warning Arnd Bergmann
2021-03-22 20:29   ` Ingo Molnar
2021-03-22 21:39     ` Arnd Bergmann
2021-03-22 22:07     ` Martin Sebor
2021-03-22 22:49       ` Arnd Bergmann
2021-03-22 23:13       ` Ingo Molnar
2021-03-24  9:11       ` David Laight
2021-03-24 10:39         ` David Laight
2021-03-22 16:02 ` [PATCH 03/11] security: commoncap: fix -Wstringop-overread warning Arnd Bergmann
2021-03-22 16:31   ` Christian Brauner
2021-03-24 20:50   ` James Morris
2021-03-22 16:02 ` [PATCH 04/11] ath11: Wstringop-overread warning Arnd Bergmann
2021-03-22 16:02 ` [PATCH 05/11] qnx: avoid -Wstringop-overread warning Arnd Bergmann
2021-03-22 16:02 ` [PATCH 06/11] cgroup: fix -Wzero-length-bounds warnings Arnd Bergmann
2021-03-30  8:41   ` Michal Koutný
2021-03-30  9:00     ` Arnd Bergmann
2021-03-30 14:44       ` Michal Koutný
2021-03-22 16:02 ` [PATCH 07/11] ARM: sharpsl_param: work around -Wstringop-overread warning Arnd Bergmann
2021-03-22 16:02 ` [PATCH 08/11] atmel: avoid gcc -Wstringop-overflow warning Arnd Bergmann
2021-03-22 16:02 ` [PATCH 09/11] scsi: lpfc: fix gcc -Wstringop-overread warning Arnd Bergmann
2021-03-22 16:02 ` [PATCH 10/11] drm/i915: avoid stringop-overread warning on pri_latency Arnd Bergmann
2021-03-24 15:30   ` Jani Nikula [this message]
2021-03-24 17:22     ` Ville Syrjälä
2021-03-22 16:02 ` [PATCH 11/11] [RFC] drm/i915/dp: fix array overflow warning Arnd Bergmann
2021-03-25  8:05   ` Jani Nikula
2021-03-25  9:53     ` Arnd Bergmann
2021-03-25 14:49       ` Martin Sebor
2021-03-30 10:56   ` Hans de Goede
2021-04-06  4:53 ` [PATCH 00/11] treewide: address gcc-11 -Wstringop-overread warnings Martin K. Petersen

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