linux-kernel - Re: [RFC] perf: fix building for ARCv1

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Message-ID: <HE1PR02MB13872D4A7A43E49B8440AEB5D6D20@HE1PR02MB1387.eurprd02.prod.outlook.com>
Date:	Fri, 5 Feb 2016 11:18:52 +0000
From:	Noam Camus <noamc@...hip.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
CC:	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"dvhart@...ux.intel.com" <dvhart@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"acme@...hat.com" <acme@...hat.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>,
	Gilad Ben Yossef <giladb@...hip.com>
Subject: Re: [RFC] perf: fix building for ARCv1

________________________________________
>From: Vineet Gupta <Vineet.Gupta1@...opsys.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