linux-kernel - Re: WARNING: can't access registers at asm_common

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Message-ID: <20201111203941.GP2628@hirez.programming.kicks-ass.net>
Date:   Wed, 11 Nov 2020 21:39:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Damien Le Moal <Damien.LeMoal@....com>, jgross@...e.com,
        x86@...nel.org
Subject: Re: WARNING: can't access registers at asm_common_interrupt

On Wed, Nov 11, 2020 at 08:25:36PM +0000, Andrew Cooper wrote:

> > Right, it makes objtool's job a _little_ easier, since it already knows
> > how to read alternatives.  But it still has to learn to deal with the
> > conflicting stack layouts.
> 
> I suppose the needed abstraction is "these blocks will start and end
> with the same stack layout", while allowing the internals to diverge.

It's a little more complicated than that due to the fact that there is
only a single ORC table.

So something like:

	alt0		alt1
	0x00 push	0x00 nop
	0x01 nop	0x01 push

is impossible to correctly unwind.