On Mon, 12 Mar 2018 21:28:57 -0700 Kees Cook <keesc...@chromium.org> wrote:
> 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]; > ^~~~~~~~ PITA. Didn't we once have a different way of detecting VLAs? Some post-compilation asm parser, iirc. I suppose the world wouldn't end if we had a gcc version ifdef in kernel.h. We'll get to remove it in, oh, ten years.