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Fri, 8 May 2020 16:01:26 +0000 (UTC) Received: from treble (ovpn-115-96.rdu2.redhat.com [10.10.115.96]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 544516AD13; Fri, 8 May 2020 16:01:24 +0000 (UTC) Date: Fri, 8 May 2020 11:01:22 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Randy Dunlap , 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) Message-ID: <20200508160122.hsqb25lzhd2xkisv@treble> References: <20200505222922.jajHT3b4j%akpm@linux-foundation.org> <36dc367a-f647-4ee8-a327-d1c3457a7940@infradead.org> <20200508103830.GZ5298@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200508103830.GZ5298@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > 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 > Signed-off-by: Peter Zijlstra (Intel) 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 -- Josh