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 283B9C433F5 for ; Tue, 25 Jan 2022 16:00:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1583008AbiAYQAf (ORCPT ); Tue, 25 Jan 2022 11:00:35 -0500 Received: from foss.arm.com ([217.140.110.172]:52452 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1582888AbiAYP7C (ORCPT ); Tue, 25 Jan 2022 10:59:02 -0500 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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.