linux-kernel - Re: [PATCH 5/7] x86/speculation: Annotate intra-function calls

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Message-ID: <20200403182005.GC20730@hirez.programming.kicks-ass.net>
Date:   Fri, 3 Apr 2020 20:20:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Alexandre Chartre <alexandre.chartre@...cle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, jthierry@...hat.com,
        tglx@...utronix.de
Subject: Re: [PATCH 5/7] x86/speculation: Annotate intra-function calls

On Fri, Apr 03, 2020 at 12:24:08PM -0500, Josh Poimboeuf wrote:
> On Fri, Apr 03, 2020 at 07:18:36PM +0200, Peter Zijlstra wrote:
> > What we need in this case though is only a different stack layout inside
> > the alternative, and that is doable.
> 
> I'm not sure what you mean... any stack changes within the alternative
> have to match exactly the stack changes at the same offsets of the
> original code because ORC doesn't know the difference between the two.

I mean that the ORC entries on either side of the alternative have to be
invariant wrt the specific alternative chosen, but that -- provded you
whip up that ORC alternative stuff -- stack layout inside of an
alternative could possibly be different.