linux-kernel - Re: [PATCH 16/20] objtool: Rewrite alt->skip

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Message-ID: <20190308222744.fox35ov75zxi6wis@treble>
Date:   Fri, 8 Mar 2019 16:27:44 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, luto@...nel.org,
        bp@...en8.de, dvlasenk@...hat.com, linux-kernel@...r.kernel.org,
        dvyukov@...gle.com, rostedt@...dmis.org
Subject: Re: [PATCH 16/20] objtool: Rewrite alt->skip_orig

On Fri, Mar 08, 2019 at 10:34:18PM +0100, Peter Zijlstra wrote:
> On Fri, Mar 08, 2019 at 02:15:56PM -0600, Josh Poimboeuf wrote:
> > On Thu, Mar 07, 2019 at 12:45:27PM +0100, Peter Zijlstra wrote:
> > > Really skip the original instruction flow, instead of letting it
> > > continue with NOPs.
> > > 
> > > Since the alternative code flow already continues after the original
> > > instructions, only the alt-original is skipped.
> > 
> > I like this approach.  I wonder if we can do something similar to get
> > rid of the nasty fake jumps.
> 
> This actually hard relies on those fake jumps. Or am I missing the
> point?

I was just wondering out loud if we could somehow keep the same "fake
jump" functionality, but do it in a cleaner way that doesn't require
creating fake instructions.  I'll might give it a try.

-- 
Josh