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Date:   Thu, 18 Feb 2021 11:53:14 -0600
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
        Miroslav Benes <mbenes@suse.cz>, x86@kernel.org
Subject: Re: [PATCH] objtool: Fix stack-swizzle for FRAME_POINTER=y
Message-ID: <20210218175314.sdrkb3272bzezw3b@treble>
References: <161298728344.23325.15458416903870844675.tip-bot2@tip-bot2>
 <YC6UC+rc9KKmQrkd@hirez.programming.kicks-ass.net>
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On Thu, Feb 18, 2021 at 05:21:31PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 10, 2021 at 08:01:23PM -0000, tip-bot2 for Peter Zijlstra wrote:
> > objtool: Support stack-swizzle
> 
> ---
> Subject: objtool: Fix stack-swizzle for FRAME_POINTER=y
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Thu Feb 18 17:14:10 CET 2021
> 
> When objtool encounters the stack-swizzle:
> 
> 	mov %rsp, (%[tos])
> 	mov %[tos], %rsp
> 	...
> 	pop %rsp
> 
> Inside a FRAME_POINTER=y build, things go a little screwy because
> clearly we're not adjusting the cfa->base. This then results in the
> pop %rsp not being detected as a restore of cfa->base so it will turn
> into a regular POP and offset the stack, resulting in:
> 
>   kernel/softirq.o: warning: objtool: do_softirq()+0xdb: return with modified stack frame
> 
> Therefore, have "mov %[tos], %rsp" act like a PUSH (it sorta is
> anyway) to balance the things out. We're not too concerned with the
> actual stack_size for frame-pointer builds, since we don't generate
> ORC data for them anyway.
> 
> Fixes: aafeb14e9da2 ("objtool: Support stack-swizzle")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

-- 
Josh