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 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 37601C6FA82 for ; Wed, 14 Sep 2022 17:45:08 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4MSSQp2dz0z3cBk for ; Thu, 15 Sep 2022 03:45:06 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lists.ozlabs.org (Postfix) with ESMTP id 4MSSQK1kG7z2xgN for ; Thu, 15 Sep 2022 03:44:39 +1000 (AEST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 28EHYR2K002376; Wed, 14 Sep 2022 12:34:27 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 28EHYPMf002375; Wed, 14 Sep 2022 12:34:25 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 14 Sep 2022 12:34:25 -0500 From: Segher Boessenkool To: Peter Zijlstra Subject: Re: [RFC] Objtool toolchain proposal: -fannotate-{jump-table,noreturn} Message-ID: <20220914173425.GZ25951@gate.crashing.org> References: <20220909180704.jwwed4zhwvin7uyi@treble> <20220914000416.daxbgccbxwpknn2q@treble> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , x86@kernel.org, Sathvika Vasireddy , linuxppc-dev@lists.ozlabs.org, Chen Zhongjin , Michael Matz , Nick Desaulniers , linux-kernel@vger.kernel.org, Ard Biesheuvel , Mark Brown , Borislav Petkov , linux-toolchains@vger.kernel.org, Indu Bhagat , live-patching@vger.kernel.org, Miroslav Benes , Will Deacon , Josh Poimboeuf , linux-arm-kernel@lists.infradead.org, "Jose E. Marchesi" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Sep 14, 2022 at 04:55:27PM +0200, Peter Zijlstra wrote: > On Wed, Sep 14, 2022 at 02:28:26PM +0000, Michael Matz wrote: > > Don't mix DWARF debug info with DWARF-based unwinding info, the latter > > doesn't imply the former. Out of interest: how does ORC get around the > > need for CFI annotations (or equivalents to restore registers) and what > > Objtool 'interprets' the stackops. So it follows the call-graph and is > an interpreter for all instructions that modify the stack. Doing that it > konws what the stackframe is at 'most' places. To get correct backtraces on e.g. PowerPC you need to emulate many of the integer insns. That is why GCC enables -fasynchronous-unwind-tables by default for us. The same is true for s390, aarch64, and x86 (unless 32-bit w/ frame pointer). The problem is that you do not know how to access anything on the stack, whether in the current frame or in a previous frame, from a random point in the program. GDB has many heuristics for this, and it still does not get it right in all cases. > > makes it fast? I want faster unwinding for DWARF as well, when there's > > feature parity :-) Maybe something can be learned for integration into > > dwarf-unwind. > > I think we have some details here: > > https://www.kernel.org/doc/html/latest/x86/orc-unwinder.html It is faster because it does a whole lot less. Is that still enough? It's not clear (to me) what exact information it wants to provide :-( Segher