[llvm-dev] Dynamic VMA in Sanitizers for AArch64

[Jakub Jelinek via llvm-dev]

On Fri, Sep 25, 2015 at 01:19:48AM -0700, Renato Golin wrote:
> After long talks with lots of people, I think we have a winning
> strategy to deal with the variable nature of VMA address in AArch64.
> It seems that the best way forward is to try the dynamic calculation
> at runtime, evaluate the performance, and then, only if the hit is too
> great, think about compile-time alternatives. I'd like to know if
> everyone is in agreement, so we could get cracking.

You mean you want a dynamic shadow offset on aarch64 as opposed to
fixed kAArch64_ShadowOffset64 (1UL << 36) one?
I think this is completely unnecessary, all you need to change is
libsanitizer internals IMNSHO, all that is needed is to make runtime
decisions during libasan initialization on the memory layout, and
also (because 39 bit VMA is too slow), dynamic decision whether to use
32-bit or 64-bit allocator.  See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64435
for details.

	Jakub