linux-kernel - [PATCH 4.19 16/30] drm/i915: Fix -Wstringop-overflow warning in call to intel_read_wm

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Date:   Fri,  3 Jun 2022 19:39:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: [PATCH 4.19 16/30] drm/i915: Fix -Wstringop-overflow warning in call to intel_read_wm_latency()

From: Gustavo A. R. Silva <gustavoars@...nel.org>

commit 336feb502a715909a8136eb6a62a83d7268a353b upstream.

Fix the following -Wstringop-overflow warnings when building with GCC-11:

drivers/gpu/drm/i915/intel_pm.c:3106:9: warning: ‘intel_read_wm_latency’ accessing 16 bytes in a region of size 10 [-Wstringop-overflow=]
 3106 |         intel_read_wm_latency(dev_priv, dev_priv->wm.pri_latency);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/intel_pm.c:3106:9: note: referencing argument 2 of type ‘u16 *’ {aka ‘short unsigned int *’}
drivers/gpu/drm/i915/intel_pm.c:2861:13: note: in a call to function ‘intel_read_wm_latency’
 2861 | static void intel_read_wm_latency(struct drm_i915_private *dev_priv,
      |             ^~~~~~~~~~~~~~~~~~~~~

by removing the over-specified array size from the argument declarations.

It seems that this code is actually safe because the size of the
array depends on the hardware generation, and the function checks
for that.

Notice that wm can be an array of 5 elements:
drivers/gpu/drm/i915/intel_pm.c:3109:   intel_read_wm_latency(dev_priv, dev_priv->wm.pri_latency);

or an array of 8 elements:
drivers/gpu/drm/i915/intel_pm.c:3131:   intel_read_wm_latency(dev_priv, dev_priv->wm.skl_latency);

and the compiler legitimately complains about that.

This helps with the ongoing efforts to globally enable
-Wstringop-overflow.

Link: https://github.com/KSPP/linux/issues/181
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/i915/intel_pm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2814,7 +2814,7 @@ hsw_compute_linetime_wm(const struct int
 }
 
 static void intel_read_wm_latency(struct drm_i915_private *dev_priv,
-				  uint16_t wm[8])
+				  uint16_t wm[])
 {
 	if (INTEL_GEN(dev_priv) >= 9) {
 		uint32_t val;