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

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Date:   Tue, 23 Mar 2021 07:19:00 -0700
From:   Joe Perches <joe@...ches.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Liu Ying <victor.liu@....com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/imx: fix out of bounds array access warning

On Tue, 2021-03-23 at 14:05 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.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.
[]
> diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
[]
> @@ -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));

> @@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,
[]
> +	if (mux < 0) {
> +		dev_warn(ldb->dev,
> +			 "%s: invalid mux\n", __func__);

etc...