From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:36218 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728449AbfCAQ3P (ORCPT ); Fri, 1 Mar 2019 11:29:15 -0500 Date: Fri, 1 Mar 2019 10:29:11 -0600 From: Josh Poimboeuf Subject: Re: [PATCH 2/2] x86/unwind: add hardcoded ORC entry for NULL Message-ID: <20190301162911.ucd6diddioqnthc2@treble> References: <20190301031201.7416-1-jannh@google.com> <20190301031201.7416-2-jannh@google.com> <20190301162418.sbhth5tycd6znxin@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190301162418.sbhth5tycd6znxin@treble> Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Jann Horn Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andrew Morton , syzbot , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Masahiro Yamada , Michal Marek , linux-kbuild@vger.kernel.org On Fri, Mar 01, 2019 at 10:24:18AM -0600, Josh Poimboeuf wrote: > > Is there a reason why the top-level Makefile only sets > > -fno-optimize-sibling-calls if CONFIG_FRAME_POINTER is set? > > I suspect that this is just a historical thing, because reliable > > unwinding didn't work without frame pointers until ORC came along. > > I'm not quite sure how best to express "don't do tail optimization if > > either frame pointers are used or ORC is used" in a Makefile, and > > whether we want an indirection through Kconfig for that, so I'm not > > doing anything about it in this series. > > Can someone send a patch to deal with it properly? > > Why would sibling calls be a problem for ORC? Once a function does a > sibling call, it has effectively returned and shouldn't show up on the > stack trace anyway. Answering my own question, I guess some people might find it confusing to have a caller skipped in the stack trace. But nobody has ever complained about it. It's not a problem for livepatch since we only care about the return path. -- Josh