Re: [PATCH v4 1/2] kernel.h: Introduce const_max() for VLA removal

[Kees Cook]

On Thu, Mar 15, 2018 at 4:17 PM, Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> 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