lkml.org 
[lkml]   [2018]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v5 0/2] Remove false-positive VLAs when using max()
On Sat, Mar 17, 2018 at 11:52 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> So the above is completely insane, bit there is actually a chance that
> using that completely crazy "x -> sizeof(char[x])" conversion actually
> helps, because it really does have a (very odd) evaluation-time
> change. sizeof() has to be evaluated as part of the constant
> expression evaluation, in ways that "__builtin_constant_p()" isn't
> specified to be done.
>
> But it is also definitely me grasping at straws. If that doesn't work
> for 4.4, there's nothing else I can possibly see.

No luck! :( gcc 4.4 refuses to play along. And, hilariously, not only
does it not change the complaint about __builtin_choose_expr(), it
also thinks that's a VLA now.

./include/linux/mm.h: In function ‘get_mm_hiwater_rss’:
./include/linux/mm.h:1567: warning: variable length array is used
./include/linux/mm.h:1567: error: first argument to
‘__builtin_choose_expr’ not a constant

6.8 is happy with it (of course).

I do think the earlier version (without the
sizeof-hiding-builting_constant_p) provides a template for a
const_max() that both you and Rasmus would be happy with, though!

-Kees

--
Kees Cook
Pixel Security

\
 
 \ /
  Last update: 2018-03-17 21:08    [W:0.112 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site