[llvm-dev] Dynamic VMA in Sanitizers for AArch64

[Yury Gribov via llvm-dev]

On 09/25/2015 11:53 AM, Jakub Jelinek via llvm-dev wrote:
> 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.

Added kcc.

FYI optional dynamic offset would also help in not-so-rare situations 
when ASan's shadow range is stolen by early constructors in unsanitized 
libraries.

-Y