From: Arnd Bergmann <arnd@kernel.org>
To: Christoph Hellwig <hch@infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tejun Heo <tj@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>,
Nathan Chancellor <natechancellor@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
clang-built-linux@googlegroups.com
Subject: [PATCH v3] seq_file: fix clang warning for NULL pointer arithmetic
Date: Tue, 27 Oct 2020 23:18:24 +0100 [thread overview]
Message-ID: <20201027221916.463235-1-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 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 <arnd@arndb.de>
---
v2: add the named macros after Christoph Hellwig pointed out
that my original logic was too ugly.
Suggestions for better names welcome
v3: don't overload the NULL return, avoid ?: operator
---
fs/kernfs/file.c | 9 ++++++---
fs/seq_file.c | 5 ++++-
include/linux/seq_file.h | 2 ++
3 files changed, 12 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..eb344448d4da 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -37,6 +37,8 @@ struct seq_operations {
#define SEQ_SKIP 1
+#define SEQ_OPEN_SINGLE (void *)1
+
/**
* seq_has_overflowed - check if the buffer has overflowed
* @m: the seq_file handle
--
2.27.0
next reply other threads:[~2020-10-27 22:19 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-27 22:18 Arnd Bergmann [this message]
2020-10-28 6:23 ` [PATCH v3] seq_file: fix clang warning for NULL pointer arithmetic Christoph Hellwig
2020-10-28 6:51 ` Nathan Chancellor
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201027221916.463235-1-arnd@kernel.org \
--to=arnd@kernel.org \
--cc=arnd@arndb.de \
--cc=clang-built-linux@googlegroups.com \
--cc=gregkh@linuxfoundation.org \
--cc=hch@infradead.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=natechancellor@gmail.com \
--cc=ndesaulniers@google.com \
--cc=tj@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).