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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>,
	akpm@linux-foundation.org, broonie@kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-next@vger.kernel.org, mhocko@suse.cz,
	mm-commits@vger.kernel.org, sfr@canb.auug.org.au
Subject: Re: mmotm 2020-05-05-15-28 uploaded (objtool warning)
Date: Fri, 8 May 2020 11:01:22 -0500	[thread overview]
Message-ID: <20200508160122.hsqb25lzhd2xkisv@treble> (raw)
In-Reply-To: <20200508103830.GZ5298@hirez.programming.kicks-ass.net>

On Fri, May 08, 2020 at 12:38:30PM +0200, Peter Zijlstra wrote:
> Subject: objtool: Allow no-op CFI ops in alternatives
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Fri May 8 12:34:33 CEST 2020
> 
> Randy reported a false-positive: "alternative modifies stack".
> 
> What happens is that:
> 
> 	alternative_io("movl %0, %P1", "xchgl %0, %P1", X86_BUG_11AP,
>  13d:   89 9d 00 d0 7f ff       mov    %ebx,-0x803000(%rbp)
> 
> decodes to an instruction with CFI-ops because it modifies RBP.
> However, due to this being a !frame-pointer build, that should not in
> fact change the CFI state.
> 
> So instead of dis-allowing any CFI-op, verify the op would've actually
> changed the CFI state.
> 
> Fixes: 7117f16bf460 ("objtool: Fix ORC vs alternatives")
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

It helps to put an example of the fixed warning in the commit log, like:

This fixes the following warning:

  arch/x86/hyperv/hv_apic.o: warning: objtool: hv_apic_write()+0x25: alternative modifies stack

Otherwise it looks good.

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

-- 
Josh


  reply	other threads:[~2020-05-08 16:01 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 22:29 mmotm 2020-05-05-15-28 uploaded akpm
     [not found] ` <36dc367a-f647-4ee8-a327-d1c3457a7940@infradead.org>
2020-05-08 10:38   ` mmotm 2020-05-05-15-28 uploaded (objtool warning) Peter Zijlstra
2020-05-08 16:01     ` Josh Poimboeuf [this message]
2020-05-08 17:28     ` Randy Dunlap

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