linux-kernel - Re: [PATCH] arm64: LLVMLinux: Fix inline arm64 assembly for use with clang

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Date:	Tue, 9 Sep 2014 11:15:15 +0100
From:	Will Deacon <will.deacon@....com>
To:	Mark Charlebois <charlebm@...il.com>
Cc:	"behanw@...verseincode.com" <behanw@...verseincode.com>,
	"anderson@...hat.com" <anderson@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"cl@...ux.com" <cl@...ux.com>,
	"cov@...eaurora.org" <cov@...eaurora.org>,
	"jays.lee@...sung.com" <jays.lee@...sung.com>,
	"msalter@...hat.com" <msalter@...hat.com>,
	"sandeepa.prabhu@...aro.org" <sandeepa.prabhu@...aro.org>,
	"srivatsa.bhat@...ux.vnet.ibm.com" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"takahiro.akashi@...aro.org" <takahiro.akashi@...aro.org>,
	"Vijaya.Kumar@...iumnetworks.com" <Vijaya.Kumar@...iumnetworks.com>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"acme@...nel.org" <acme@...nel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Matthew Leach <Matthew.Leach@....com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"olof@...om.net" <olof@...om.net>,
	"paulus@...ba.org" <paulus@...ba.org>
Subject: Re: [PATCH] arm64: LLVMLinux: Fix inline arm64 assembly for use with
 clang

On Mon, Sep 08, 2014 at 07:35:47PM +0100, Mark Charlebois wrote:
> When I compile
> 
> int main()
> {
>         u64 foo, tmp;
> 
>        // This fails for clang but not gcc
>         asm volatile(
>         "       mrs     %0, mair_el1\n"
>         "       bfi     %0, %1, #%2, #8\n"
>         "       msr     mair_el1, %0\n"
>         "       isb\n"
>         : "=&r" (tmp)
>         : "r" (foo), "i" (MT_NORMAL * 8));
> }
> 
> Clang fails and GCC generates:
> 
> 00000000004004f0 <main>:
>   4004f0: d538a208 mrs x8, mair_el1
>   4004f4: b3601d08 bfi x8, x8, #32, #8
>   4004f8: d518a208 msr mair_el1, x8
>   4004fc: d5033fdf isb
>   400500: 2a1f03e0 mov w0, wzr
>   400504: d65f03c0 ret

Ok, so we can just drop the '#' prefix as it probably shouldn't be there
anyway. Can you send a patch making just that change, please?

Will
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