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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4FCC3C6FA8A for ; Wed, 14 Sep 2022 14:28:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229813AbiINO2v (ORCPT ); Wed, 14 Sep 2022 10:28:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230042AbiINO23 (ORCPT ); Wed, 14 Sep 2022 10:28:29 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D73393ED5C; Wed, 14 Sep 2022 07:28:28 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 884331FAC1; Wed, 14 Sep 2022 14:28:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1663165707; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rNlI3zlemkHtad6UJYVAQefl5OerSoDA86fMBi08vO4=; b=IMcU+sMzPrtf2swXGKoltws1DQ4PgrmVnuO6T/Q8delDYm0q8pNrJpq1MOP7xd6pZAf/Jb Fj9kKS+pmhqrUq9gHQbLKe9xjwQzs0XXFM41HygdB74Nb7ZvF9w5/0sBD/TJQ6ijUhNld2 ovmAUy7zEQzNfJwAOOA+Lerl2Xz07qg= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1663165707; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rNlI3zlemkHtad6UJYVAQefl5OerSoDA86fMBi08vO4=; b=3fJIRsrioi8AmmHGURizF9ChVKr3QoUbkZwIJ7IgJ5my1PvR3SHrnTkZipLA9y0w31fOb6 QBhZcoLjuWM9F4Bw== Received: from wotan.suse.de (wotan.suse.de [10.160.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 0A94B2C141; Wed, 14 Sep 2022 14:28:27 +0000 (UTC) Received: by wotan.suse.de (Postfix, from userid 10510) id EFA0E62AF; Wed, 14 Sep 2022 14:28:26 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by wotan.suse.de (Postfix) with ESMTP id EDC3C62AE; Wed, 14 Sep 2022 14:28:26 +0000 (UTC) Date: Wed, 14 Sep 2022 14:28:26 +0000 (UTC) From: Michael Matz To: Peter Zijlstra cc: Josh Poimboeuf , Borislav Petkov , linux-toolchains@vger.kernel.org, Indu Bhagat , Nick Desaulniers , linux-kernel@vger.kernel.org, "Jose E. Marchesi" , Miroslav Benes , Mark Rutland , Will Deacon , x86@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Ard Biesheuvel , Chen Zhongjin , Sathvika Vasireddy , Christophe Leroy , Mark Brown Subject: Re: [RFC] Objtool toolchain proposal: -fannotate-{jump-table,noreturn} In-Reply-To: Message-ID: References: <20220909180704.jwwed4zhwvin7uyi@treble> <20220914000416.daxbgccbxwpknn2q@treble> User-Agent: Alpine 2.20 (LSU 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-toolchains@vger.kernel.org Hello, On Wed, 14 Sep 2022, Peter Zijlstra wrote: > > Maybe this is semantics, but I wouldn't characterize objtool's existence > > as being based on the mistrust of tools. It's main motivation is to > > fill in the toolchain's blind spots in asm and inline-asm, which exist > > by design. > > That and a fairly deep seated loathing for the regular CFI annotations > and DWARF in general. Linus was fairly firm he didn't want anything to > do with DWARF for in-kernel unwinding. I was referring only to the check-stuff functionality of objtool, not to its other parts. Altough, of course, "deep seated loathing" is a special form of mistrust as well ;-) > That left us in a spot that we needed unwind information in a 'better' > format than DWARF. > > Objtool was born out of those contraints. ORC not needing the CFI > annotations and ORC being *much* faster at unwiding and generation > (debug builds are slow) were all good. 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 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. Ciao, Michael.