On Mon, Mar 12, 2018 at 4:57 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Mon, Mar 12, 2018 at 3:55 PM, Andrew Morton > <a...@linux-foundation.org> wrote: >> >> Replacing the __builtin_choose_expr() with ?: works of course. > > Hmm. That sounds like the right thing to do. We were so myopically > staring at the __builtin_choose_expr() problem that we overlooked the > obvious solution. > > Using __builtin_constant_p() together with a ?: is in fact our common > pattern, so that should be fine. The only real reason to use > __builtin_choose_expr() is if you want to get the *type* to vary > depending on which side you choose, but that's not an issue for > min/max.
This doesn't solve it for -Wvla, unfortunately. That was the point of Josh's original suggestion of __builtin_choose_expr(). Try building with KCFLAGS=-Wval and checking net/ipv6/proc.c: net/ipv6/proc.c: In function ‘snmp6_seq_show_item’: net/ipv6/proc.c:198:2: warning: ISO C90 forbids array ‘buff’ whose size can’t be evaluated [-Wvla] unsigned long buff[SNMP_MIB_MAX]; ^~~~~~~~ -Kees -- Kees Cook Pixel Security
