linux-kernel - new objtool unreachable instruction warnings

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Message-ID: <CAK8P3a0VU4Ui3-cEsd7h9U31u5zZaq3cM6Lc+Hk=wa7SD7EJ_w@mail.gmail.com>
Date:   Wed, 26 Jul 2017 16:46:40 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: new objtool unreachable instruction warnings

I only saw these warnings once, they are either very rare, or were introduced
recently:

arch/x86/kvm/vmx.o: warning: objtool: .altinstr_replacement+0x0:
unreachable instruction
arch/x86/kvm/svm.o: warning: objtool: .altinstr_replacement+0x6e:
unreachable instruction

I see this with gcc-4.6 though gcc-7, but not with gcc-4.3.

The configuration file that triggered it is
https://pastebin.com/aMn45GYP

I managed to trace the problem down to the CC_HAVE_ASM_GOTO
macro, without that, we don't run into the problem.

       Arnd