From: Arnd Bergmann
> Sent: 29 April 2020 20:02
> 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@xxxxxxxx>
> ---
> sound/isa/opti9xx/miro.c | 9 ++++++---
> sound/isa/opti9xx/opti92x-ad1848.c | 9 ++++++---
> 2 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/sound/isa/opti9xx/miro.c b/sound/isa/opti9xx/miro.c
> index e764816a8f7a..b039429e6871 100644
> --- a/sound/isa/opti9xx/miro.c
> +++ b/sound/isa/opti9xx/miro.c
> @@ -867,10 +867,13 @@ static void snd_miro_write(struct snd_miro *chip, unsigned char reg,
> spin_unlock_irqrestore(&chip->lock, flags);
> }
>
> +static inline void snd_miro_write_mask(struct snd_miro *chip,
> + unsigned char reg, unsigned char value, unsigned char mask)
> +{
> + unsigned char oldval = snd_miro_read(chip, reg);
>
> -#define snd_miro_write_mask(chip, reg, value, mask) \
> - snd_miro_write(chip, reg, \
> - (snd_miro_read(chip, reg) & ~(mask)) | ((value) & (mask)))
> + snd_miro_write(chip, reg, (oldval & ~mask) | (value & mask));
> +}
Isn't that likely to add additional masking with 0xff at the call sites?
You will probably get better code if the arguments are 'unsigned int'.
David
-
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