On Fri, Nov 27, 2015 at 11:36:30AM +0300, Andrey Ryabinin wrote:

2015-11-25 23:39 GMT+03:00 Daniel Cashman [off-list ref]:

quoted

On 11/25/2015 04:06 AM, Catalin Marinas wrote:

quoted

For KASan, we ended up calculating KASAN_SHADOW_OFFSET in
arch/arm64/Makefile. What would the formula be for the above
ARCH_MMAP_RND_BITS_MAX?

The general formula I used ended up being:
_max = floor(log(TASK_SIZE)) - log(PAGE_SIZE) - 3

For kasan, we calculate KASAN_SHADOW_OFFSET in Makefile, because we need to use
that value in Makefiles.

For ARCH_MMAP_RND_COMPAT_BITS_MIN/MAX I don't see a reason why it has
to be in Kconfig.
Can't we just use your formula to #define ARCH_MMAP_RND_COMPAT_BITS_*
in some arch header?

Because there is another option, ARCH_MMAP_RND_BITS depending on EXPERT
which uses the MIN/MAX range defined per architecture. Since it's an
expert feature, we could as well ignore the MIN/MAX in Kconfig and just
add BUILD_BUG_ON checks to the code. This way we could simply define
them in C files.

Alternatively, add arithmetics support to kbuild ;).

-- 
Catalin