From: Arnd Bergmann <arnd@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tejun Heo <tj@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Nathan Chancellor <natechancellor@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
Amir Goldstein <amir73il@gmail.com>, Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
clang-built-linux@googlegroups.com
Subject: [PATCH] seq_file: fix clang warning for NULL pointer arithmetic
Date: Mon, 26 Oct 2020 22:52:56 +0100 [thread overview]
Message-ID: <20201026215321.3894419-1-arnd@kernel.org> (raw)
From: Arnd Bergmann <arnd@arndb.de>
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 function to do the same thing without triggering that
warning. Linux already relies on a specific binary representation
of NULL, so it makes no real difference here. 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 <arnd@arndb.de>
---
fs/kernfs/file.c | 2 +-
fs/seq_file.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index f277d023ebcd..b55e6ef4d677 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -124,7 +124,7 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
* The same behavior and code as single_open(). Returns
* !NULL if pos is at the beginning; otherwise, NULL.
*/
- return NULL + !*ppos;
+ return (void *)(uintptr_t)!*ppos;
}
}
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 31219c1db17d..d456468eb934 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -526,7 +526,7 @@ EXPORT_SYMBOL(seq_dentry);
static void *single_start(struct seq_file *p, loff_t *pos)
{
- return NULL + (*pos == 0);
+ return (void *)(uintptr_t)(*pos == 0);
}
static void *single_next(struct seq_file *p, void *v, loff_t *pos)
--
2.27.0
next reply other threads:[~2020-10-26 21:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-26 21:52 Arnd Bergmann [this message]
2020-10-27 1:49 ` [PATCH] seq_file: fix clang warning for NULL pointer arithmetic Nathan Chancellor
2020-10-27 10:44 ` Christoph Hellwig
2020-10-27 14:51 ` Arnd Bergmann
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