linux-kernel - Re: [PATCH 03/13] x86/paravirt: Convert native patch assembly code strings to macros

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Date:   Sat, 18 Nov 2017 07:17:00 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...izon.com>,
        live-patching@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        virtualization@...ts.linux-foundation.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/13] x86/paravirt: Convert native patch assembly code
 strings to macros

On Sat, Nov 18, 2017 at 11:20:06AM +0100, Juergen Gross wrote:
> >>>> +#define NATIVE_ZERO			"xor " _REG_ARG1 ", " _REG_ARG1
> >>>
> >>> NATIVE_ZERO_OUT
> >>>
> >>> I guess. NATIVE_ZERO reads like the native representation of 0 :-)
> >>
> >> NATIVE_ZERO_ARG1?
> > 
> > On a slight tangent, does anybody know why it zeros the arg?
> 
> Why are _you_ asking? You've introduced it.

So I did.  Touché!

> > The only place it's used is here:
> > 
> > #if defined(CONFIG_PARAVIRT_SPINLOCKS)
> > DEF_NATIVE(pv_lock_ops,	queued_spin_unlock,	NATIVE_QUEUED_SPIN_UNLOCK);
> > DEF_NATIVE(pv_lock_ops,	vcpu_is_preempted,	NATIVE_ZERO);
> > #endif
> > 
> > Isn't that a bug?  Seems like it should _return_ zero.  Zeroing the arg
> > shouldn't have any effect.
> 
> Right. Before that patch it _did_ return zero instead of zeroing arg1.

Oops!

> > If I'm right, we could call it NATIVE_FALSE.
> 
> I'd prefer NATIVE_ZERO, as it will be usable for non-boolean cases, too.

NATIVE_ZERO works for me.

-- 
Josh