On 2012.11.29 at 11:19 -0800, Paul E. McKenney wrote: > On Thu, Nov 29, 2012 at 07:22:54PM +0100, Markus Trippelsdorf wrote: > > On 2012.11.29 at 10:10 -0800, Paul E. McKenney wrote: > > > On Thu, Nov 29, 2012 at 06:43:58PM +0100, Markus Trippelsdorf wrote: > > > > On 2012.11.29 at 09:02 -0800, Paul E. McKenney wrote: > > > > > On Thu, Nov 29, 2012 at 02:47:52PM +0100, Markus Trippelsdorf wrote: > > > > > > With gcc-4.8 I get: > > > > > > > > > > > > CC kernel/rcutree.o > > > > > > kernel/rcutree.c: In function ‘rcu_init_one’: > > > > > > kernel/rcutree.c:2850:13: warning: array subscript is above array > > > > > > bounds [-Warray-bounds] > > > > > > rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1]; > > > > > > ^ > > > > > > 2849 for (i = 1; i < rcu_num_lvls; i++) > > > > > > 2850 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i > > > > > > - 1]; > > > > > > > > > > > > At first I thought that the warning was bogus, but rcu_num_lvls > > > > > > isn't static > > > > > > and gets modified prior to the for loop. > > > > > > > > > So, in your opinion, what would be the best way to silence this warning? > > > > > > Good question. Are you saying that if the compiler cannot prove that > > > the index is in bounds, it is going to throw a warning? > > > > Yes, it does seem to be the case. See also my gcc bug report (closed as > > invalid): http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55529 > > > > > If that is the case, perhaps telling the compiler to cool it via the > > > command line would be best. > > > Or is this really one of a very few places in the kernel where the > > > compiler is complaining? > > > > Yes. With my (admittedly minimal) config this is only place. > > Hmmmm... In that case... > > Given that this is initialization code that is far from any fastpath, > could you try putting something like this at the beginning of > rcu_init_one()? > > if (rcu_num_lvls > RCU_NUM_LVLS) > panic("rcu_num_lvls overflow"); > > If the compiler doesn't know that panic() never returns (despite the > __noreturn), you could add a "return" after the panic(). > > Does that help?
Yes. This fixes the issue. Many thanks. (Perhaps not surprisingly the warning never occurred for CONFIG_NR_CPUS>64. I've also built a allyesconfig config and there was no -Warray-bounds warning at all.) -- Markus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
