Re: [PATCH 3/3] ath9k: fix 'side effect in macro' smatch warning

[Dan Carpenter <dan.carpenter@oracle.com>]

On Fri, Jun 22, 2012 at 10:17:23AM +0300, Kalle Valo wrote:
> Rajkumar Manoharan <rmanohar@qca.qualcomm.com> writes:
> 
> > ath9k_get_et_stats() warn: side effect in macro
> > 'AWDATA' doing 'i++'
> >
> > Cc: Ben Greear <greearb@candelatech.com>
> > Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
> 
> [...]
> 
> >  	do {								\
> > -		data[i++] = sc->debug.stats.txstats[PR_QNUM(WME_AC_BE)].elem; \
> > -		data[i++] = sc->debug.stats.txstats[PR_QNUM(WME_AC_BK)].elem; \
> > -		data[i++] = sc->debug.stats.txstats[PR_QNUM(WME_AC_VI)].elem; \
> > -		data[i++] = sc->debug.stats.txstats[PR_QNUM(WME_AC_VO)].elem; \
> > +		data[i+0] = sc->debug.stats.txstats[PR_QNUM(WME_AC_BE)].elem; \
> > +		data[i+1] = sc->debug.stats.txstats[PR_QNUM(WME_AC_BK)].elem; \
> > +		data[i+2] = sc->debug.stats.txstats[PR_QNUM(WME_AC_VI)].elem; \
> > +		data[i+3] = sc->debug.stats.txstats[PR_QNUM(WME_AC_VO)].elem; \
> > +		i += 4; \
> >  	} while (0)
> 
> I agree with Ben, this is a useless change as the end result is still
> the same (the side effect is that i is increased with four). You are
> just hiding that from smatch and once smatch is fixed it will warn again
> about the same thing.
> 
> I recommend fixing this properly so that the macro doesn't have any side
> effects.

Uh.  Sorry, also I thought I had pushed a fix to add this to the
ignored macro list, but I forgot.  I've pushed it now.

I don't think this check has ever found a bug.  These bugs are very
rare and we are careful about macro side effects in the kernel.  I
have disabled the check by default and it's only enabled when you
pass --spammy.  I told the Ruby people I was going to do this
earlier in the week but I've been out of the office and delayed.

regards,
dan carpenter