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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 BB017C433DF for ; Mon, 18 May 2020 17:52:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9216720715 for ; Mon, 18 May 2020 17:52:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824339; bh=miDcrF9d0NgroOIR43hUyItCPnWvb7dfrxKBI3G+1HQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=u/swhf6AumjSAZODdU/Wuok9dAnvaiOFfSIhxkLaZ2tQD2hmZWxj7WBoeXEgEhGnd wmsehfvEQxjChh7WPYAe5R5fI4vRITR1X92MlZ6GFIjBFxfcrn25CI5gMDy/XzwxL6 YBD+ZYcoRNHY9zgXVEyiXRvfMB2GYyfV4xZWxPdE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730958AbgERRwS (ORCPT ); Mon, 18 May 2020 13:52:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:55470 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730954AbgERRwR (ORCPT ); Mon, 18 May 2020 13:52:17 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 3146920715; Mon, 18 May 2020 17:52:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824336; bh=miDcrF9d0NgroOIR43hUyItCPnWvb7dfrxKBI3G+1HQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=y0aif4JZL4+YPOFrzxk3EBKh+ftEePt4vFkQ8IdiYWzZLjK5uFhTJ67P1knjX9IMs x7xCD4ajQQPF4OxufmIA9H6O7ZoYqt/vhazr3n4lSAOeXGTROEkCEvr0WCC35IcW8U LhKjzmO4zT0/CAo1Ho6AuvxMPqAMpsKTXVMFl1hc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Linus Torvalds Subject: [PATCH 4.19 51/80] gcc-10: disable restrict warning for now Date: Mon, 18 May 2020 19:37:09 +0200 Message-Id: <20200518173500.773423994@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173450.097837707@linuxfoundation.org> References: <20200518173450.097837707@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Linus Torvalds commit adc71920969870dfa54e8f40dac8616284832d02 upstream. gcc-10 now warns about passing aliasing pointers to functions that take restricted pointers. That's actually a great warning, and if we ever start using 'restrict' in the kernel, it might be quite useful. But right now we don't, and it turns out that the only thing this warns about is an idiom where we have declared a few functions to be "printf-like" (which seems to make gcc pick up the restricted pointer thing), and then we print to the same buffer that we also use as an input. And people do that as an odd concatenation pattern, with code like this: #define sysfs_show_gen_prop(buffer, fmt, ...) \ snprintf(buffer, PAGE_SIZE, "%s"fmt, buffer, __VA_ARGS__) where we have 'buffer' as both the destination of the final result, and as the initial argument. Yes, it's a bit questionable. And outside of the kernel, people do have standard declarations like int snprintf( char *restrict buffer, size_t bufsz, const char *restrict format, ... ); where that output buffer is marked as a restrict pointer that cannot alias with any other arguments. But in the context of the kernel, that 'use snprintf() to concatenate to the end result' does work, and the pattern shows up in multiple places. And we have not marked our own version of snprintf() as taking restrict pointers, so the warning is incorrect for now, and gcc picks it up on its own. If we do start using 'restrict' in the kernel (and it might be a good idea if people find places where it matters), we'll need to figure out how to avoid this issue for snprintf and friends. But in the meantime, this warning is not useful. Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- Makefile | 3 +++ 1 file changed, 3 insertions(+) --- a/Makefile +++ b/Makefile @@ -797,6 +797,9 @@ KBUILD_CFLAGS += $(call cc-disable-warni KBUILD_CFLAGS += $(call cc-disable-warning, array-bounds) KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow) +# Another good warning that we'll want to enable eventually +KBUILD_CFLAGS += $(call cc-disable-warning, restrict) + # Enabled with W=2, disabled by default as noisy KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized)