Em Fri, 17 Nov 2017 09:55:44 -0500
dgopstein@xxxxxxx escreveu:
> From: Dan Gopstein <dgopstein@xxxxxxx>
>
> Two definitions of the ABS (absolute value) macro fail to parenthesize
> their parameter properly. This can lead to a bad expansion for
> low-precedence expression arguments. Add parens to protect against
> troublesome arguments.
>
> For example: ABS(1-2) currently expands to ((1-2) < 0 ? (-1-2) : (1-2))
> which evaluates to -3. But the correct expansion would be
> ((1-2) < 0 ? -(1-2) : (1-2)) which evaluates to 1.
>
> Signed-off-by: Dan Gopstein <dgopstein@xxxxxxx>
> ---
> v1->v2:
> * unmangled the patch
> * added example to commit text
>
> drivers/media/dvb-frontends/dibx000_common.h | 2 +-
> drivers/media/dvb-frontends/mb86a16.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/dvb-frontends/dibx000_common.h b/drivers/media/dvb-frontends/dibx000_common.h
> index 8784af9..ae60f5d 100644
> --- a/drivers/media/dvb-frontends/dibx000_common.h
> +++ b/drivers/media/dvb-frontends/dibx000_common.h
> @@ -223,7 +223,7 @@ struct dvb_frontend_parametersContext {
>
> #define FE_CALLBACK_TIME_NEVER 0xffffffff
>
> -#define ABS(x) ((x < 0) ? (-x) : (x))
> +#define ABS(x) (((x) < 0) ? -(x) : (x))
>
> #define DATA_BUS_ACCESS_MODE_8BIT 0x01
> #define DATA_BUS_ACCESS_MODE_16BIT 0x02
> diff --git a/drivers/media/dvb-frontends/mb86a16.c b/drivers/media/dvb-frontends/mb86a16.c
> index dfe322e..2d921c7 100644
> --- a/drivers/media/dvb-frontends/mb86a16.c
> +++ b/drivers/media/dvb-frontends/mb86a16.c
> @@ -31,7 +31,7 @@
> static unsigned int verbose = 5;
> module_param(verbose, int, 0644);
>
> -#define ABS(x) ((x) < 0 ? (-x) : (x))
> +#define ABS(x) ((x) < 0 ? -(x) : (x))
>
> struct mb86a16_state {
> struct i2c_adapter *i2c_adap;
Actually, the Kernel has already a macro for that, called abs().
So, the better would be to just remove those macros,
replacing ABS(foo) by abs(foo).
Thanks,
Mauro
