linux-kernel - Re: [PATCH] objtool: Fix stack-swizzle for FRAME

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Message-ID: <20210218175314.sdrkb3272bzezw3b@treble>
Date:   Thu, 18 Feb 2021 11:53:14 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>, x86@...nel.org
Subject: Re: [PATCH] objtool: Fix stack-swizzle for FRAME_POINTER=y

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@...radead.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@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

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

-- 
Josh