linux-kernel - Re: [RFC][PATCH 3/7] objtool: Allow branches within the same alternative.

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Message-ID: <20200419163219.b5dpg246xh6avsci@treble>
Date:   Sun, 19 Apr 2020 11:32:19 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     alexandre.chartre@...cle.com, linux-kernel@...r.kernel.org,
        jthierry@...hat.com, tglx@...utronix.de, x86@...nel.org
Subject: Re: [RFC][PATCH 3/7] objtool: Allow branches within the same
 alternative.

On Thu, Apr 16, 2020 at 05:07:55PM +0200, Peter Zijlstra wrote:
> From: Alexandre Chartre <alexandre.chartre@...cle.com>
> 
> Currently objtool prevents any branch to an alternative. While preventing
> branching from the outside to the middle of an alternative makes perfect
> sense, branching within the same alternative should be allowed. To do so,
> identify each alternative and check that a branch to an alternative comes
> from the same alternative.
> 
> Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/20200414103618.12657-3-alexandre.chartre@oracle.com

I I think I'd rather just drop this patch.  It adds some complexity and
I don't really see a benefit to having the warning in the first place.

Branching to the middle of an alternative group just doesn't seem like a
realistic scenario (can it even be done with the alternative macros?).

Even if it were possible, I'm not sure why somebody would attempt such a
feat.  And it seems like it would just wreck the system anyway.

-- 
Josh