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

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Message-ID: <20200403171836.GB20730@hirez.programming.kicks-ass.net>
Date:   Fri, 3 Apr 2020 19:18:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.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 10:14:49AM -0700, Alexandre Chartre wrote:

> So that means that any alternative that does a stack manipulation isn't
> currently supported?

It's fundamentally impossible to correctly unwind through.

Instructions before and after the alternative need to have the same
stack layout irrespective of the alternative chosen.

What we need in this case though is only a different stack layout inside
the alternative, and that is doable.