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Message-ID: <CAGXu5j+T2v1R8monUJMdCYtU5hqB2mqxm_a1737bRQVAzwuC4Q@mail.gmail.com>
Date: Thu, 15 Mar 2018 16:31:59 -0700
From: Kees Cook <keescook@...omium.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>, Randy Dunlap <rdunlap@...radead.org>,
Ingo Molnar <mingo@...nel.org>, David Laight <David.Laight@...lab.com>,
Ian Abbott <abbotti@....co.uk>, linux-input <linux-input@...r.kernel.org>,
linux-btrfs <linux-btrfs@...r.kernel.org>, Network Development <netdev@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v4 1/2] kernel.h: Introduce const_max() for VLA removal
On Thu, Mar 15, 2018 at 4:17 PM, Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>> The full one, using your naming convention:
>>
>> #define const_max(x, y) \
>> ({ \
>> if (!__builtin_constant_p(x)) \
>> __error_not_const_arg(); \
>> if (!__builtin_constant_p(y)) \
>> __error_not_const_arg(); \
>> if (!__builtin_types_compatible_p(typeof(x), typeof(y))) \
>> __error_incompatible_types(); \
>> if ((x) < 0) \
>> __error_not_positive_arg(); \
>> if ((y) < 0) \
>> __error_not_positive_arg(); \
>> __builtin_choose_expr((x) > (y), (x), (y)); \
>> })
>>
>
> Nevermind... gcc doesn't take that as a constant expr, even if it
> compiles as one at -O0.
Yeah, unfortunately. :(
-Kees
--
Kees Cook
Pixel Security
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