[RFC] perf: fix building for ARCv1

[acme at redhat.com]

Em Fri, Feb 05, 2016 at 11:18:52AM +0000, Noam Camus escreveu:
> Well here for EZchip I also see the:
> undefined reference to `__sync_add_and_fetch_4'
> undefined reference to `__sync_sub_and_fetch_4'

Yeah, because there is no: tools/arch/arc/include/asm/atomic.h, can't
you guys adapt arch/arc/include/asm/atomic.h to use in userspace?

- Arnaldo
 
> This is since at file tools/include/asm/atomic.h we use the generic implementation
> If for ARC I could use just like x86 my own header file then functions like:
> atomic_inc()
> atomic_dec_and_test()
> Are easy to implement and you may see an example for such atomic methods in my patch set for the new platform.
> 
> You however wants to use some GCC flag -matomic which I assume somehow will implement the above __sync*.
> I can't find the implementation but if it uses LLSC then it won't work for me since I am not supporting LLSC.

> So seem that either I have my own header at kernel or that I need to
> change the GCC implementation for __sync* to use my atomic
> instructions.  I am personally tend to the x86 solution and not the
> generic one since changing GCC will require to have new compiler
> dependency.