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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 C6B84C433F5 for ; Tue, 25 Jan 2022 16:14:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=vN5M7k+bssFHFOsttnnTxYsI8j+WdgBtyG7hxYni8b8=; b=1k0qwO4QIMj6qT hbXsweEQmr8cJ8ccSNmRzmWoqty8/otio6HgzpJrZRFIfY1hfj3hOErpUOzAwyK0gt1gYtTmF+uZy h6R2o6LuJ1oOecL6lj73iTuXZ84ArhZtwX81s6MBOW7QEOkGgluiKH6y76oY+5IYN0g1+ompEg+rd o3cNTZHm/dMJolA0QLpi0A2yGwNVnjFfV8Q2+AvCZ49wXgeYIYgcQ9SbeFW/E0TPLRnWlDk4d/sW4 EqNmNWbNQX727rBYAKxO9DRT5bn8qCPS9dWYV3Sy+bTdPQCngIQpAAN2yBZo6MBX3J/MZhM0/sQss JUycF/PRwjbT5cc1s0GA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCOQn-008atc-RC; Tue, 25 Jan 2022 16:12:30 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCODj-008WUm-CX for linux-arm-kernel@lists.infradead.org; Tue, 25 Jan 2022 15:59:01 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A30AA1FB; Tue, 25 Jan 2022 07:58:57 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.1.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 63F883F793; Tue, 25 Jan 2022 07:58:55 -0800 (PST) Date: Tue, 25 Jan 2022 15:58:51 +0000 From: Mark Rutland To: Ard Biesheuvel Cc: Linux Kernel Mailing List , acme@redhat.com, Borislav Petkov , Mark Brown , Catalin Marinas , Dave Hansen , Josh Poimboeuf , Jiri Slaby , Linux ARM , Russell King , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Will Deacon Subject: Re: [PATCH v2 0/7] linkage: better symbol aliasing Message-ID: References: <20220125113200.3829108-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220125_075859_556770_8AB2C4B2 X-CRM114-Status: GOOD ( 29.31 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jan 25, 2022 at 04:49:03PM +0100, Ard Biesheuvel wrote: > On Tue, 25 Jan 2022 at 16:46, Mark Rutland wrote: > > > > On Tue, Jan 25, 2022 at 04:28:11PM +0100, Ard Biesheuvel wrote: > > > On Tue, 25 Jan 2022 at 12:32, Mark Rutland wrote: > > > > > > > > This series aims to make symbol aliasing simpler and more consistent. > > > > The basic idea is to replace SYM_FUNC_START_ALIAS(alias) and > > > > SYM_FUNC_END_ALIAS(alias) with a new SYM_FUNC_ALIAS(alias, name), so > > > > that e.g. > > > > > > > > SYM_FUNC_START(func) > > > > SYM_FUNC_START_ALIAS(alias1) > > > > SYM_FUNC_START_ALIAS(alias2) > > > > ... asm insns ... > > > > SYM_FUNC_END(func) > > > > SYM_FUNC_END_ALIAS(alias1) > > > > SYM_FUNC_END_ALIAS(alias2) > > > > EXPORT_SYMBOL(alias1) > > > > EXPORT_SYMBOL(alias2) > > > > > > > > ... can become: > > > > > > > > SYM_FUNC_START(name) > > > > ... asm insns ... > > > > SYM_FUNC_END(name) > > > > > > > > SYM_FUNC_ALIAS(alias1, func) > > > > EXPORT_SYMBOL(alias1) > > > > > > > > SYM_FUNC_ALIAS(alias2, func) > > > > EXPORT_SYMBOL(alias2) > > > > > > > > This avoids repetition and hopefully make it easier to ensure > > > > consistency (e.g. so each function has a single canonical name and > > > > associated metadata). > > > > > > > > > > I take it this affects the sizes of the alias ELF symbols? Does that matter? > > > > The alias should be given the same size as the original symbol, unless I've > > made an error. If you look at patch 3: > > > > * In SYM_FUNC_START(name), via SYM_ENTRY_AT(name, ...), we create a local label > > for the start of the function: .L____sym_entry__##name > > > > * In SYM_FUNC_END(name), via SYM_END_AT(name, ...), we create a local label for > > the end of the function: .L____sym_end__##name > > > > * In SYM_FUNC_ALIAS*(alias,name), we define the start and end of the alias as > > the start and end of the original symbol using those local labels, e.g. > > > > | #define SYM_FUNC_ALIAS(alias, name) \ > > | SYM_START_AT(alias, .L____sym_entry__##name, SYM_L_GLOBAL) \ > > | SYM_END_AT(alias, .L____sym_end__##name, SYM_T_FUNC) > > > > Note that: > > > > * SYM_FUNC_START() uses SYM_START(), which uses SYM_ENTRY_AT() > > * SYM_FUNC_END() uses SYM_END(), which uses SYM_END_AT() > > > > ... so the definition of tha alias is ultimately structurally identical to the > > definition of the canoncial name, at least for now. > > > > Ah right, apologies for not looking more carefully - I assumed the > changed placement implied that the aliases had zero size. NP; I didn't make that clear in the cover letter, and now it's written up and archived for future reference. :) > And ultimately, I don't think there is an obviously correct answer > anyway, it's just the [apparently non-existent] change in behavior I > was curious about. FWIW, I hadn't really considered whether we actually need that for the aliases; it was jsut the path of least resistance implementation-wise, and I'd like to be able to use the local labls for the bounds in future for other annotations and sanity-checks. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel