Re: [PATCH] drm/imx: fix out of bounds array access warning

On Tue, 2021-03-23 at 07:19 -0700, Joe Perches wrote:

On Tue, 2021-03-23 at 14:05 +0100, Arnd Bergmann wrote:

quoted

From: Arnd Bergmann <arnd@arndb.de>

When CONFIG_OF is disabled, building with 'make W=1' produces warnings
about out of bounds array access:

drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]

Add an error check before the index is used, which helps with the
warning, as well as any possible other error condition that may be
triggered at runtime.

[]

quoted

diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c

[]

quoted

@@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
 	int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
 	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);

+	if (mux < 0) {
+		dev_warn(ldb->dev,
+			 "%s: invalid mux\n", __func__);

trivia:

Any real reason to make this 2 lines?  It fits nicely in 80 chars.  Maybe:

		dev_warn(ldb->dev, "%s: invalid mux: %d\n", __func__, mux);

or maybe:

		dev_warn(ldb->dev, "%s: invalid mux: %pe\n",
			 __func__, ERR_PTR(mux));

+1

The second one looks better as it's more informative.

Regards,
Liu Ying

quoted

@@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,

[]

quoted

+	if (mux < 0) {
+		dev_warn(ldb->dev,
+			 "%s: invalid mux\n", __func__);

etc...

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