> Subject: Re: [RFC] rtw88: fix subscript above array bounds compiler warning
>
> On Fri, May 03, 2019 at 12:01:05PM +0000, Tony Chuang wrote:
> > > Subject: [RFC] rtw88: fix subscript above array bounds compiler warning
> > >
> > > My compiler complain about:
> > >
> > > drivers/net/wireless/realtek/rtw88/phy.c: In function
> > > ‘rtw_phy_rf_power_2_rssi’:
> > > drivers/net/wireless/realtek/rtw88/phy.c:430:26: warning: array subscript is
> > > above array bounds [-Warray-bounds]
> > > linear = db_invert_table[i][j];
> > >
> > > According to comment power_db should be in range 1 ~ 96 .
> > > Correct rtw_phy_power_2_db() to make max power 96 db
> > > (still min is 0). This make the warning gone.
> > >
> > > However power >= 20 check still looks somewhat suspicious to me.
> > >
> > > Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
> > > ---
> > > drivers/net/wireless/realtek/rtw88/phy.c | 6 +++---
> > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/wireless/realtek/rtw88/phy.c
> > > b/drivers/net/wireless/realtek/rtw88/phy.c
> > > index 35a35dbca85f..a716a44d78b0 100644
> > > --- a/drivers/net/wireless/realtek/rtw88/phy.c
> > > +++ b/drivers/net/wireless/realtek/rtw88/phy.c
> > > @@ -410,12 +410,12 @@ void rtw_phy_dynamic_mechanism(struct
> rtw_dev
> > > *rtwdev)
> > >
> > > static u8 rtw_phy_power_2_db(s8 power)
> > > {
> > > - if (power <= -100 || power >= 20)
> > > + if (power <= -96 || power >= 20)
> > > return 0;
> > > else if (power >= 0)
> > > - return 100;
> > > + return 96;
> > > else
> > > - return 100 + power;
> > > + return 96 + power;
> > > }
> > >
> > > static u64 rtw_phy_db_2_linear(u8 power_db)
> > > --
> >
> > I think I should check with the radio team, that if the power from the
> > rx descriptor generated by hardware can possibly get >= 20
> >
> > And also check what the actual logic they expected to deal with the power.
> > Thanks for reporting it.
>
> Yeah, this could be just teoretical issue as we can not get power
> values >= 0 from HW. However I think compiler correctly complains, as
> for power_db=100 we get i = ((100 - 1) >> 3) = 12 , what exceed by one
> max first index of db_invert_table[][], which should be in range
> 0 - 11.
>
I checked it. The power sum could actually be like 20 or something.
And the recommended modification is to restrict the value used for array
subscript between 1~96 before access the array. Such as:
@@ -578,6 +578,11 @@ static u64 rtw_phy_db_2_linear(u8 power_db)
u8 i, j;
u64 linear;
+ if (power_db > 96)
+ power_db = 96;
+ else if (power_db < 1)
+ return 1;
+
/* 1dB ~ 96dB */
i = (power_db - 1) >> 3;
j = (power_db - 1) - (i << 3);
Yan-Hsuan
