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Date:   Wed, 11 Nov 2020 21:39:41 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andrew Cooper <andrew.cooper3@citrix.com>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Damien Le Moal <Damien.LeMoal@wdc.com>, jgross@suse.com,
        x86@kernel.org
Subject: Re: WARNING: can't access registers at asm_common_interrupt
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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.