[PATCH] Add Prefer_MAP_32BIT_EXEC for Silvermont

[Florian Weimer]

On 12/11/2015 06:02 PM, Adhemerval Zanella wrote:

> Another issue is this is basically limiting ALSR really hard on x86_64.

Looking at my Fedora 22 system, it seems that most (all?) processes map
their DSOs into a single 31-bit window.  I don't know why it's
implemented this way and if it's also about silicon limitations.

Non-relocatable and PIE executables and the vDSO are stilled mapped
outside of this window, though.  A conservative fix would change that
aspect only.

I'm worried that mapping a lot of things into the first 2 GiB of address
space breaks application expectations.  LuaJIT applications might be
restricted to smaller-sized heaps, and Hotspot might not be able to use
unscaled compressed oops, resulting in a performance loss.

Florian