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Re: [RFC] perf: fix building for ARCv1

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  Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-02-04 05:20 +0100
    Re: [RFC] perf: fix building for ARCv1 Noam Camus <noamc@ezchip.com> - 2016-02-05 12:20 +0100

#1326393 — Re: [RFC] perf: fix building for ARCv1

+CC Noam

On Wednesday 03 February 2016 09:50 PM, Alexey Brodkin wrote:
>> I agree with the current solution to add -atomic to for arc700 builds.
>> > Although making that default for arc700 tools will be better but that will not fix
>> > things before next release of tools etc.
>> > 
>> > But we *do* need to improve generic solution
>> > 1. Add atomics detection in perf to add fall back arch stubs
>> > 2. ARC needs to add syscall for facilitating atomic r-m-w !
> So the most recent ARC GNU tools (2015.12) were just released yesterday
> and still atomics are disabled by default for ARCv1.
> That means perf will continue to fail on building for now.
> 
> Do you think we may apply my initial fix to 4.5 while it is in development and
> then to stable trees as well?

Noam, what's the atomic story for EZChip. Do you support such things for user
space in GNU tools. If -atomic is added to perf user space builds are you guys OK!

-Vineet

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#1327610

________________________________________
>From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
>Sent: Thursday, February 4, 2016 6:13 AM
>Noam, what's the atomic story for EZChip. Do you support such things for user
space in GNU tools. If -atomic is added to perf user space builds are you guys OK!

Well here for EZchip I also see the:
undefined reference to `__sync_add_and_fetch_4'
undefined reference to `__sync_sub_and_fetch_4'

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.
 
-Noam

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