linux-kernel - Re: [PATCH 2/2] ARM: futex: make futex_detect

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Message-ID: <20190308095407.zfezalaysgjialpy@shell.armlinux.org.uk>
Date:   Fri, 8 Mar 2019 09:54:07 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Mikael Pettersson <mikpe@...uu.se>,
        Mikael Pettersson <mikpelinux@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ARM: futex: make futex_detect_cmpxchg more reliable

On Thu, Mar 07, 2019 at 04:04:23PM -0800, Nick Desaulniers wrote:
> On Thu, Mar 7, 2019 at 3:49 PM Russell King - ARM Linux admin
> <linux@...linux.org.uk> wrote:
> >
> > On Thu, Mar 07, 2019 at 11:39:08AM -0800, Nick Desaulniers wrote:
> > > Underspecification of constraints to extended inline assembly is a
> > > common issue exposed by other compilers (and possibly but in-effect
> > > infrequently compiler upgrades).
> >
> > I don't see what is "underspecified" in the original constraints.
> > Please explain.
> 
> From the link:
> 
> The problem is that in the T(streq) insn, %3 and %4 MUST be different registers,
> but nothing in the asm() constrains them to be different.

Thanks, but that is not what I'm asking.  See my reply to Ard.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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