From patchwork Tue Oct 27 14:52:23 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arnd Bergmann X-Patchwork-Id: 11861151 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 1DB321130 for ; Tue, 27 Oct 2020 17:26:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F1CBA2224A for ; Tue, 27 Oct 2020 17:26:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603819611; bh=lRyihQET4wWx+8eZkdWW/pEjjC0GgzuvTCnX9bjWC58=; h=From:To:Cc:Subject:Date:List-ID:From; b=bpKehdZO/U5x5U2HBZwjiUPHGhK4kj2udPE7opLjD5+DLt8kSYITLZwALno0SDgeL TIB6oPunRt3vNtp2z4e7nB2ISHX02dYqnCJ/iZv9qhna3+2+qXS61xml2Hkzi5q4SP cKmzKAsfLYFAvYH7heKZYjUsY0VH6F/su7JOU+Ls= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S369870AbgJ0R0s (ORCPT ); Tue, 27 Oct 2020 13:26:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:53488 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1775650AbgJ0OxA (ORCPT ); Tue, 27 Oct 2020 10:53:00 -0400 Received: from localhost.localdomain (unknown [192.30.34.233]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7D8B322265; Tue, 27 Oct 2020 14:52:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603810379; bh=lRyihQET4wWx+8eZkdWW/pEjjC0GgzuvTCnX9bjWC58=; h=From:To:Cc:Subject:Date:From; b=vWHtUIU3xS3y972jDvabA7wU5uusJLJNPIqvCNH4++kQmDLjEujYO2dT0z5CE3CnJ GFh2fD2xao/N4nvwRK4YspksIahDl9wNyDBja9hX6n96y8Vp0iK7RlOqrL7aeyUU/K ohk+KEh4/8n/NwztAYfPHTFnucqTtAs/s+C+7XNw= From: Arnd Bergmann To: Christoph Hellwig , Greg Kroah-Hartman , Tejun Heo , Alexander Viro Cc: Arnd Bergmann , Nathan Chancellor , Nick Desaulniers , Jan Kara , Amir Goldstein , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: [PATCH v2] seq_file: fix clang warning for NULL pointer arithmetic Date: Tue, 27 Oct 2020 15:52:23 +0100 Message-Id: <20201027145252.3976138-1-arnd@kernel.org> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Arnd Bergmann Clang points out that adding something to NULL is notallowed in standard C: fs/kernfs/file.c:127:15: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic] return NULL + !*ppos; ~~~~ ^ fs/seq_file.c:529:14: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic] return NULL + (*pos == 0); Rephrase the code to be extra explicit about the valid, giving them named SEQ_OPEN_EOF and SEQ_OPEN_SINGLE definitions. The instance in kernfs was copied from single_start, so fix both at once. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Fixes: c2b19daf6760 ("sysfs, kernfs: prepare read path for kernfs") Signed-off-by: Arnd Bergmann --- v2: add the named macros after Christoph Hellwig pointed out that my original logic was too ugly. Suggestions for better names welcome --- fs/kernfs/file.c | 8 ++++---- fs/seq_file.c | 4 ++-- include/linux/seq_file.h | 3 +++ 3 files changed, 9 insertions(+), 6 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index f277d023ebcd..eafeb8bf4fe4 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -121,10 +121,10 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) return next; } else { /* - * The same behavior and code as single_open(). Returns - * !NULL if pos is at the beginning; otherwise, NULL. + * The same behavior and code as single_open(). Continues + * if pos is at the beginning; otherwise, EOF. */ - return NULL + !*ppos; + return *ppos ? SEQ_OPEN_SINGLE : SEQ_OPEN_EOF; } } @@ -145,7 +145,7 @@ static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos) * terminate after the initial read. */ ++*ppos; - return NULL; + return SEQ_OPEN_EOF; } } diff --git a/fs/seq_file.c b/fs/seq_file.c index 31219c1db17d..203cd86136ad 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -526,13 +526,13 @@ EXPORT_SYMBOL(seq_dentry); static void *single_start(struct seq_file *p, loff_t *pos) { - return NULL + (*pos == 0); + return *pos == 0 ? SEQ_OPEN_SINGLE : SEQ_OPEN_EOF; } static void *single_next(struct seq_file *p, void *v, loff_t *pos) { ++*pos; - return NULL; + return SEQ_OPEN_EOF; } static void single_stop(struct seq_file *p, void *v) diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h index 813614d4b71f..26f0758b6551 100644 --- a/include/linux/seq_file.h +++ b/include/linux/seq_file.h @@ -37,6 +37,9 @@ struct seq_operations { #define SEQ_SKIP 1 +#define SEQ_OPEN_EOF (void *)0 +#define SEQ_OPEN_SINGLE (void *)1 + /** * seq_has_overflowed - check if the buffer has overflowed * @m: the seq_file handle