linux-kernel - [PATCH 10/11] drm/i915: avoid stringop-overread warning on pri

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Date:   Mon, 22 Mar 2021 17:02:48 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     linux-kernel@...r.kernel.org, Martin Sebor <msebor@....gnu.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Arnd Bergmann <arnd@...db.de>, x86@...nel.org,
        Ning Sun <ning.sun@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Simon Kelley <simon@...kelleys.org.uk>,
        James Smart <james.smart@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Anders Larsen <al@...rsen.net>, Tejun Heo <tj@...nel.org>,
        Serge Hallyn <serge@...lyn.com>,
        Imre Deak <imre.deak@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        tboot-devel@...ts.sourceforge.net, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, ath11k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-scsi@...r.kernel.org, cgroups@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        José Roberto de Souza <jose.souza@...el.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Matt Roper <matthew.d.roper@...el.com>,
        Aditya Swarup <aditya.swarup@...el.com>
Subject: [PATCH 10/11] drm/i915: avoid stringop-overread warning on pri_latency

From: Arnd Bergmann <arnd@...db.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.

Signed-off-by: Arnd Bergmann <arnd@...db.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
-- 
2.29.2