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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB4A7C169C4 for ; Mon, 11 Feb 2019 15:25:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A7E7620869 for ; Mon, 11 Feb 2019 15:25:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1549898733; bh=3mCx52JXCu+l7XQ29W7eDYIKFca993Orui2FU4GYNzw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=jA7xmJYjzSSwlhYhCzKY9QlU3NLMwUqUS6v5vaRQjR01p6MuZjyfyOOPgxBwjV2eb eiCwrvusz5GITbNQNVudSJBVQ/dw/JoPjyhOeYfsPvTTqz2dUJz4vmNvy6FuTZ3EsI 6cBOCkKBoIi3R+KcOG8WfWzfAuacn4CZmjwiGUOs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390206AbfBKPZb (ORCPT ); Mon, 11 Feb 2019 10:25:31 -0500 Received: from mail.kernel.org ([198.145.29.99]:49264 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390147AbfBKPBP (ORCPT ); Mon, 11 Feb 2019 10:01:15 -0500 Received: from linux-8ccs (ip5f5ade6b.dynamic.kabel-deutschland.de [95.90.222.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1EA3421773; Mon, 11 Feb 2019 15:01:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1549897274; bh=3mCx52JXCu+l7XQ29W7eDYIKFca993Orui2FU4GYNzw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=a/f0nnUXNOpKTlr3CJ1EOT4Z8K9F34SNrqPUkCP8vnRwuG+nazPiisjUy8fa/R/QS bAmOjU928sx6DhKEcWlEIdUtjFfkXcgqYk70CBAkvx/RFvcfRBUTol5XLQu2m7nx+6 i2OFVPjTFcOey6ckCfi3G/Mt+EUaW2B5uaI+i+Mo= Date: Mon, 11 Feb 2019 16:01:09 +0100 From: Jessica Yu To: Miguel Ojeda Cc: Laura Abbott , Martin Sebor , Arnd Bergmann , Masahiro Yamada , James Morris , Mathieu Desnoyers , Borislav Petkov , Kees Cook , Matt Mullins , Vincent Whitchurch , WANG Chao , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] include/linux/module.h: copy __init/__exit attrs to init/cleanup_module Message-ID: <20190211150108.GB20732@linux-8ccs> References: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com> <20190209000840.11018-4-miguel.ojeda.sandonis@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20190209000840.11018-4-miguel.ojeda.sandonis@gmail.com> X-OS: Linux linux-8ccs 4.12.14-lp150.12.28-default x86_64 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +++ Miguel Ojeda [09/02/19 01:08 +0100]: >The upcoming GCC 9 release extends the -Wmissing-attributes warnings >(enabled by -Wall) to C and aliases: it warns when particular function >attributes are missing in the aliases but not in their target. > >In particular, it triggers for all the init/cleanup_module >aliases in the kernel (defined by the module_init/exit macros), >ending up being very noisy. > >These aliases point to the __init/__exit functions of a module, >which are defined as __cold (among other attributes). However, >the aliases themselves do not have the __cold attribute. > >Since the compiler behaves differently when compiling a __cold >function as well as when compiling paths leading to calls >to __cold functions, the warning is trying to point out >the possibly-forgotten attribute in the alias. > >In order to keep the warning enabled, we decided to silence >this case. Ideally, we would mark the aliases directly >as __init/__exit. However, there are currently around 132 modules >in the kernel which are missing __init/__exit in their init/cleanup >functions (either because they are missing, or for other reasons, >e.g. the functions being called from somewhere else); and >a section mismatch is a hard error. > >A conservative alternative was to mark the aliases as __cold only. >However, since we would like to eventually enforce __init/__exit >to be always marked, we chose to use the new __copy function >attribute (introduced by GCC 9 as well to deal with this). >With it, we copy the attributes used by the target functions >into the aliases. This way, functions that were not marked >as __init/__exit won't have their aliases marked either, >and therefore there won't be a section mismatch. > >Note that the warning would go away marking either the extern >declaration, the definition, or both. However, we only mark >the definition of the alias, since we do not want callers >(which only see the declaration) to be compiled as if the function >was __cold (and therefore the paths leading to those calls >would be assumed to be unlikely). > >Link: https://lore.kernel.org/lkml/20190123173707.GA16603@gmail.com/ >Link: https://lore.kernel.org/lkml/20190206175627.GA20399@gmail.com/ >Suggested-by: Martin Sebor >Signed-off-by: Miguel Ojeda Acked-by: Jessica Yu Thanks! >--- > include/linux/module.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > >diff --git a/include/linux/module.h b/include/linux/module.h >index 8fa38d3e7538..f5bc4c046461 100644 >--- a/include/linux/module.h >+++ b/include/linux/module.h >@@ -129,13 +129,13 @@ extern void cleanup_module(void); > #define module_init(initfn) \ > static inline initcall_t __maybe_unused __inittest(void) \ > { return initfn; } \ >- int init_module(void) __attribute__((alias(#initfn))); >+ int init_module(void) __copy(initfn) __attribute__((alias(#initfn))); > > /* This is only required if you want to be unloadable. */ > #define module_exit(exitfn) \ > static inline exitcall_t __maybe_unused __exittest(void) \ > { return exitfn; } \ >- void cleanup_module(void) __attribute__((alias(#exitfn))); >+ void cleanup_module(void) __copy(exitfn) __attribute__((alias(#exitfn))); > > #endif > >-- >2.17.1 >