From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751267AbdFAOlL (ORCPT ); Thu, 1 Jun 2017 10:41:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:39880 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751089AbdFAOlJ (ORCPT ); Thu, 1 Jun 2017 10:41:09 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A62612395B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org MIME-Version: 1.0 In-Reply-To: <20170601141659.yeh6enc5nc6z363s@treble> References: <5ec63cefd2093152464b7bb1383938f6970e65eb.1496293620.git.jpoimboe@redhat.com> <20170601141659.yeh6enc5nc6z363s@treble> From: Andy Lutomirski Date: Thu, 1 Jun 2017 07:40:47 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to provide CFI hints To: Josh Poimboeuf Cc: Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , live-patching@vger.kernel.org, Linus Torvalds , Jiri Slaby , Ingo Molnar , "H. Peter Anvin" , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 1, 2017 at 7:16 AM, Josh Poimboeuf wrote: > On Thu, Jun 01, 2017 at 06:57:24AM -0700, Andy Lutomirski wrote: >> On Wed, May 31, 2017 at 10:44 PM, Josh Poimboeuf wrote: >> > Some asm (and inline asm) code does special things to the stack which >> > objtool can't understand. (Nor can GCC or GNU assembler, for that >> > matter.) In such cases we need a facility for the code to provide >> > annotations, so the unwinder can unwind through it. >> > >> > This provides such a facility, in the form of CFI hints. They're >> > similar to the GNU assembler .cfi* directives, but they give more >> > information, and are needed in far fewer places, because objtool can >> > fill in the blanks by following branches and adjusting the stack pointer >> > for pushes and pops. >> >> Two minor suggestions: >> >> Could you prefix these with something other than "CFI_"? For those of >> use who have read the binutils manual, using "CFI_" sounds awfully >> like .cfi_, and people might expect the semantics to be the same. > > The intention was that even if this undwarf thing doesn't work out, the > CFI_ macros could still be used by objtool to generate proper DWARF. > Would prefixing them with CFI_HINT_ be better? Or UNWIND_HINT_? This has nothing to do with the data format or implementation. I just think that "CFI_" suggests that they're semantically equivalent to binutils' .cfi directives. If they're not, then maybe UNWIND_HINT is better.