From patchwork Wed Oct 28 15:11:36 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arnd Bergmann X-Patchwork-Id: 11863607 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 6EB9114B4 for ; Wed, 28 Oct 2020 22:23:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4763520704 for ; Wed, 28 Oct 2020 22:23:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603923796; bh=lub8VFdz9y1ay4Kw8idOVilwJzgx9JVK/MSfD79W7mQ=; h=From:To:Cc:Subject:Date:List-ID:From; b=lLs33a9sohD77oUWjtCeinYplm4cAzCAKugWkYhUKkuV22N6pnrqMh7DbfO/iGEOF ZO/urvqiyMMfDGaDW1HJDhRyMWdVUeSK+xdQG9pPxQVVDR0QAbWghXZZRdk8xjNMcF KmBpa/sVxZNwnIuIoa0SZedBj9DSxH672sFmHzrY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732673AbgJ1WWl (ORCPT ); Wed, 28 Oct 2020 18:22:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:36830 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732619AbgJ1WWY (ORCPT ); Wed, 28 Oct 2020 18:22:24 -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 00CDA247B2; Wed, 28 Oct 2020 15:12:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603897930; bh=lub8VFdz9y1ay4Kw8idOVilwJzgx9JVK/MSfD79W7mQ=; h=From:To:Cc:Subject:Date:From; b=ym3WEmO2VDY3tqNE+V5DjPOajVNzG45tFzO5Xq26Fk17ahiATlI8aQ0yBcgSkxktG Ulaa2zatXB58MUZAxY2ID+nPSvAJqQSE1u3UwLBO68Qw1LIL/F+6UbuJ5a1zqSKHwk FswansWVaI4SJFX4q7vMXLMED9aRFFkRcctAODpE= From: Arnd Bergmann To: Christoph Hellwig , Alexander Viro Cc: Arnd Bergmann , Christoph Hellwig , Nathan Chancellor , Greg Kroah-Hartman , Tejun Heo , Nick Desaulniers , Amir Goldstein , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: [PATCH v4] seq_file: fix clang warning for NULL pointer arithmetic Date: Wed, 28 Oct 2020 16:11:36 +0100 Message-Id: <20201028151202.3074398-1-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 not allowed 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") Reviewed-by: Christoph Hellwig Reviewed-by: Nathan Chancellor Signed-off-by: Arnd Bergmann --- v2: add the named macros after Christoph Hellwig pointed out that my original logic was too ugly. v3: don't overload the NULL return, avoid ?: operator v4: fix changelog text (Nathan Chancellor), add comment (Christoph Hellwig) --- fs/kernfs/file.c | 9 ++++++--- fs/seq_file.c | 5 ++++- include/linux/seq_file.h | 6 ++++++ 3 files changed, 16 insertions(+), 4 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index f277d023ebcd..5a5adb03c6df 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -121,10 +121,13 @@ 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, NULL. */ - return NULL + !*ppos; + if (*ppos) + return NULL; + + return SEQ_OPEN_SINGLE; } } diff --git a/fs/seq_file.c b/fs/seq_file.c index 31219c1db17d..6b467d769501 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -526,7 +526,10 @@ EXPORT_SYMBOL(seq_dentry); static void *single_start(struct seq_file *p, loff_t *pos) { - return NULL + (*pos == 0); + if (*pos) + return NULL; + + return SEQ_OPEN_SINGLE; } static void *single_next(struct seq_file *p, void *v, loff_t *pos) diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h index 813614d4b71f..bfa34f5578b9 100644 --- a/include/linux/seq_file.h +++ b/include/linux/seq_file.h @@ -37,6 +37,12 @@ struct seq_operations { #define SEQ_SKIP 1 +/* + * op->start must return a non-NULL pointer for single_open(), + * this is used when we don't care about the specific value. + */ +#define SEQ_OPEN_SINGLE (void *)1 + /** * seq_has_overflowed - check if the buffer has overflowed * @m: the seq_file handle