[llvm-dev] Dynamic VMA in Sanitizers for AArch64

Renato Golin via llvm-dev llvm-dev at lists.llvm.org
Sun Oct 4 11:28:21 PDT 2015

On 29 September 2015 at 15:00, Jakub Jelinek <jakub at redhat.com> wrote:
> You are mixing things up.  The size of virtual address space in bits is one
> thing, and another one is the chosen ASAN shadow offset.

Well, the shadow offset cannot overlap with the virtual address space,
and that's why the offset is different for different VMA values.

> All you need to do is the math how the address space needs to look out
> for the various VMA sizes, and whether it clashes with where the kernel
> will normally try to allocate shared libraries or the stack.

That's the part I'm not sure of. From my understanding, the kernel
*may* use memory beyond the stack, and that's largely based on the VMA
setting. Trying to find a value that works *well* for all alternatives
might be too restricting, or so I'm told.

I'd like the opinion of someone that understand the kernel better than
I do, however, to have a more informed decision. I'll be very happy to
be wrong, here, and start using 56-bits VMA for all AArch64 from now
on (as this may be a very likely future).


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