linux-kernel - Re: [PATCH] media: davinci-isif: avoid uninitialized variable use

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Date:   Fri, 22 Mar 2019 09:01:40 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Wenwen Wang <wang6495@....edu>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: davinci-isif: avoid uninitialized variable use

On Fri, Mar 22, 2019 at 03:34:22PM +0100, Arnd Bergmann wrote:
> clang warns about a possible variable use that gcc never
> complained about:
> 
> drivers/media/platform/davinci/isif.c:982:32: error: variable 'frame_size' is uninitialized when used here
>       [-Werror,-Wuninitialized]
>                 dm365_vpss_set_pg_frame_size(frame_size);
>                                              ^~~~~~~~~~
> drivers/media/platform/davinci/isif.c:887:2: note: variable 'frame_size' is declared here
>         struct vpss_pg_frame_size frame_size;
>         ^
> 1 error generated.
> 
> There is no initialization for this variable at all, and there
> has never been one in the mainline kernel, so we really should
> not put that stack data into an mmio register.
> 
> On the other hand, I suspect that gcc checks the condition
> more closely and notices that the global
> isif_cfg.bayer.config_params.test_pat_gen flag is initialized
> to zero and never written to from any code path, so anything
> depending on it can be eliminated.
> 
> To shut up the clang warning, just remove the dead code manually,
> it has probably never been used because any attempt to do so
> would have resulted in undefined behavior.
> 
> Fixes: 63e3ab142fa3 ("V4L/DVB: V4L - vpfe capture - source for ISIF driver on DM365")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  drivers/media/platform/davinci/isif.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/media/platform/davinci/isif.c b/drivers/media/platform/davinci/isif.c
> index 47cecd10eb9f..2dee9af6d413 100644
> --- a/drivers/media/platform/davinci/isif.c
> +++ b/drivers/media/platform/davinci/isif.c
> @@ -884,9 +884,7 @@ static int isif_set_hw_if_params(struct vpfe_hw_if_param *params)
>  static int isif_config_ycbcr(void)
>  {
>  	struct isif_ycbcr_config *params = &isif_cfg.ycbcr;
> -	struct vpss_pg_frame_size frame_size;
>  	u32 modeset = 0, ccdcfg = 0;
> -	struct vpss_sync_pol sync;
>  
>  	dev_dbg(isif_cfg.dev, "\nStarting isif_config_ycbcr...");
>  
> @@ -974,13 +972,6 @@ static int isif_config_ycbcr(void)
>  		/* two fields are interleaved in memory */
>  		regw(0x00000249, SDOFST);
>  
> -	/* Setup test pattern if enabled */
> -	if (isif_cfg.bayer.config_params.test_pat_gen) {
> -		sync.ccdpg_hdpol = params->hd_pol;
> -		sync.ccdpg_vdpol = params->vd_pol;
> -		dm365_vpss_set_sync_pol(sync);
> -		dm365_vpss_set_pg_frame_size(frame_size);
> -	}
>  	return 0;
>  }
>  
> -- 
> 2.20.0
>