linux-kernel - Re: [PATCH] ALSA: mips: avoid potential uninitialized variable use

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Date:   Mon, 16 Jan 2017 13:28:56 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     "Arnd Bergmann" <arnd@...db.de>
Cc:     "Jaroslav Kysela" <perex@...ex.cz>, <alsa-devel@...a-project.org>,
        <linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: mips: avoid potential uninitialized variable use

On Mon, 16 Jan 2017 12:04:56 +0100,
Arnd Bergmann wrote:
> 
> MIPS allmodconfig results in this warning:
> 
> sound/mips/hal2.c: In function 'hal2_gain_get':
> sound/mips/hal2.c:224:35: error: 'r' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> sound/mips/hal2.c:223:35: error: 'l' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> sound/mips/hal2.c: In function 'hal2_gain_put':
> sound/mips/hal2.c:260:13: error: 'new' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> sound/mips/hal2.c:260:13: error: 'old' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> It's easy enough to avoid by adding a 'default' clause to the switch
> statements here. I assume that in practice no other case can happen,
> but adding a default puts us on the safe side and shuts up the warnings.

Well, these cases are logical errors that must not happen, so
returning an error would be a "safer", IMO.


thanks,

Takashi

> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  sound/mips/hal2.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/sound/mips/hal2.c b/sound/mips/hal2.c
> index ede449f0b50d..0af4f7a9b3e7 100644
> --- a/sound/mips/hal2.c
> +++ b/sound/mips/hal2.c
> @@ -219,6 +219,9 @@ static int hal2_gain_get(struct snd_kcontrol *kcontrol,
>  		l = (tmp >> H2I_C2_L_GAIN_SHIFT) & 15;
>  		r = (tmp >> H2I_C2_R_GAIN_SHIFT) & 15;
>  		break;
> +	default:
> +		l = 0;
> +		r = 0;
>  	}
>  	ucontrol->value.integer.value[0] = l;
>  	ucontrol->value.integer.value[1] = r;
> @@ -256,6 +259,9 @@ static int hal2_gain_put(struct snd_kcontrol *kcontrol,
>  		new |= (r << H2I_C2_R_GAIN_SHIFT);
>  		hal2_i_write32(hal2, H2I_ADC_C2, new);
>  		break;
> +	default:
> +		new = 0;
> +		old = 0;
>  	}
>  	return old != new;
>  }
> -- 
> 2.9.0
> 
>