From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AEB7C04AA5 for ; Mon, 15 Oct 2018 14:23:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B314F20644 for ; Mon, 15 Oct 2018 14:23:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B314F20644 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726869AbeJOWIb (ORCPT ); Mon, 15 Oct 2018 18:08:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37468 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726561AbeJOWIb (ORCPT ); Mon, 15 Oct 2018 18:08:31 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 501FAA82C; Mon, 15 Oct 2018 14:23:01 +0000 (UTC) Received: from treble (ovpn-125-6.rdu2.redhat.com [10.10.125.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DF3CB1057075; Mon, 15 Oct 2018 14:22:58 +0000 (UTC) Date: Mon, 15 Oct 2018 09:22:52 -0500 From: Josh Poimboeuf To: Nathan Chancellor Cc: Andy Lutomirski , nick.desaulniers@gmail.com, Dave Hansen , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , X86 ML , LKML Subject: Re: [PATCH] x86/mm: annotate no_context with UNWIND_HINTS Message-ID: <20181015142252.6p2zgkznj26jzdwl@treble> References: <20181015003726.29103-1-nick.desaulniers@gmail.com> <20181015051705.GA20687@flashbox> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181015051705.GA20687@flashbox> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 15 Oct 2018 14:23:01 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 14, 2018 at 10:17:05PM -0700, Nathan Chancellor wrote: > On Sun, Oct 14, 2018 at 08:43:18PM -0700, Andy Lutomirski wrote: > > On Sun, Oct 14, 2018 at 5:37 PM Nick Desaulniers > > wrote: > > > > > > Fixes the objtool warning: > > > arch/x86/mm/fault.o: warning: objtool: no_context()+0x220: unreachable > > > instruction > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/204 > > > Signed-off-by: Nick Desaulniers > > > --- > > > arch/x86/mm/fault.c | 6 ++++-- > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > > > index 47bebfe6efa7..057d2178fa19 100644 > > > --- a/arch/x86/mm/fault.c > > > +++ b/arch/x86/mm/fault.c > > > @@ -760,9 +760,11 @@ no_context(struct pt_regs *regs, unsigned long error_code, > > > * and then double-fault, though, because we're likely to > > > * break the console driver and lose most of the stack dump. > > > */ > > > - asm volatile ("movq %[stack], %%rsp\n\t" > > > + asm volatile (UNWIND_HINT_SAVE > > > + "movq %[stack], %%rsp\n\t" > > > "call handle_stack_overflow\n\t" > > > - "1: jmp 1b" > > > + "1: jmp 1b\n\t" > > > + UNWIND_HINT_RESTORE > > > : ASM_CALL_CONSTRAINT > > > : "D" ("kernel stack overflow (page fault)"), > > > "S" (regs), "d" (address), > > > > NAK. Just below this snippet is unreachable(); > > > > Can you reply with objtool -dr output on a problematic fault.o? Josh, > > it *looks* like annotate_unreachable() should be doing the right > > thing, but something is clearly busted. > > > > Also, shouldn't compiler-clang.h contain a reasonable definition of > > unreachable()? > > > > --Andy > > Hi Andy, > > Did you mean 'objdump -dr'? If so, here you go (rather long, sorry if I > should have pasted it here instead): > https://gist.github.com/nathanchance/f038bb0a6653b975bb8a4e64fcd5503e As Andy said, I think compiler-clang.h needs an unreachable() definition. Without that, I'm guessing you're getting this: #ifndef unreachable # define unreachable() do { annotate_reachable(); do { } while (1); } while (0) #endif which converts "unreachable" to "reachable". That used to be needed for pre-4.5 versions of GCC when we supported them, but it's the wrong behavior for this piece of code (and I should remove all those old GCC hacks soon...) -- Josh