linux-kernel - Re: [PATCH] ALSA: opti9xx: shut up gcc-10 range warning

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Message-ID: <s5hv9lhijt4.wl-tiwai@suse.de>
Date:   Thu, 30 Apr 2020 08:12:07 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: opti9xx: shut up gcc-10 range warning

On Wed, 29 Apr 2020 21:02:03 +0200,
Arnd Bergmann wrote:
> 
> gcc-10 points out a few instances of suspicious integer arithmetic
> leading to value truncation:
> 
> sound/isa/opti9xx/opti92x-ad1848.c: In function 'snd_opti9xx_configure':
> sound/isa/opti9xx/opti92x-ad1848.c:322:43: error: overflow in conversion from 'int' to 'unsigned char' changes value from '(int)snd_opti9xx_read(chip, 3) & -256 | 240' to '240' [-Werror=overflow]
>   322 |   (snd_opti9xx_read(chip, reg) & ~(mask)) | ((value) & (mask)))
>       |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
> sound/isa/opti9xx/opti92x-ad1848.c:351:3: note: in expansion of macro 'snd_opti9xx_write_mask'
>   351 |   snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(3), 0xf0, 0xff);
>       |   ^~~~~~~~~~~~~~~~~~~~~~
> sound/isa/opti9xx/miro.c: In function 'snd_miro_configure':
> sound/isa/opti9xx/miro.c:873:40: error: overflow in conversion from 'int' to 'unsigned char' changes value from '(int)snd_miro_read(chip, 3) & -256 | 240' to '240' [-Werror=overflow]
>   873 |   (snd_miro_read(chip, reg) & ~(mask)) | ((value) & (mask)))
>       |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
> sound/isa/opti9xx/miro.c:1010:3: note: in expansion of macro 'snd_miro_write_mask'
>  1010 |   snd_miro_write_mask(chip, OPTi9XX_MC_REG(3), 0xf0, 0xff);
>       |   ^~~~~~~~~~~~~~~~~~~
> 
> These are all harmless here as only the low 8 bit are passed down
> anyway. Change the macros to inline functions to make the code
> more readable and also avoid the warning.
> 
> Strictly speaking those functions also need locking to make the
> read/write pair atomic, but it seems unlikely that anyone would
> still run into that issue.
> 
> Fixes: 1841f613fd2e ("[ALSA] Add snd-miro driver")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Applied now, thanks.


Takashi