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

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Date:   Tue, 26 Mar 2019 10:23:46 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Wenwen Wang <wang6495@....edu>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: davinci-isif: avoid uninitialized variable use

On Fri, Mar 22, 2019 at 2:34 PM Arnd Bergmann <arnd@...db.de> 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>
> ---
>  drivers/media/platform/davinci/isif.c | 9 ---------
>  1 file changed, 9 deletions(-)
>

Acked-by: Lad, Prabhakar <prabhakar.csengg@...il.com>

Cheers,
--Prabhakar Lad

> 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
>