Implement conditional logic in order to replace NULL pointer arithmetic.
The use of NULL pointer arithmetic was pointed out by clang with the
following warning:
fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return NULL + !*ppos;
~~~~ ^
fs/seq_file.c:559:14: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return NULL + (*pos == 0);
Signed-off-by: Ma?ra Canal <[email protected]>
---
V1 -> V2:
- Use SEQ_START_TOKEN instead of open-coding it
- kernfs_seq_start call single_start instead of open-coding it
V2 -> V3:
- Remove the EXPORT of the single_start symbol
---
fs/kernfs/file.c | 7 +------
fs/seq_file.c | 4 ++--
include/linux/seq_file.h | 1 +
3 files changed, 4 insertions(+), 8 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 9414a7a60a9f..7aefaca876a0 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -120,13 +120,8 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
if (next == ERR_PTR(-ENODEV))
kernfs_seq_stop_active(sf, next);
return next;
- } else {
- /*
- * The same behavior and code as single_open(). Returns
- * !NULL if pos is at the beginning; otherwise, NULL.
- */
- return NULL + !*ppos;
}
+ return single_start(sf, ppos);
}
static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
diff --git a/fs/seq_file.c b/fs/seq_file.c
index f8e1f4ee87ff..7ab8a58c29b6 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -554,9 +554,9 @@ int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
}
EXPORT_SYMBOL(seq_dentry);
-static void *single_start(struct seq_file *p, loff_t *pos)
+void *single_start(struct seq_file *p, loff_t *pos)
{
- return NULL + (*pos == 0);
+ return *pos ? NULL : SEQ_START_TOKEN;
}
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 88cc16444b43..60820ab511d2 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -162,6 +162,7 @@ int seq_dentry(struct seq_file *, struct dentry *, const char *);
int seq_path_root(struct seq_file *m, const struct path *path,
const struct path *root, const char *esc);
+void *single_start(struct seq_file *, loff_t *);
int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
int single_open_size(struct file *, int (*)(struct seq_file *, void *), void *, size_t);
int single_release(struct inode *, struct file *);
--
2.34.1
On Mon, Jan 31, 2022 at 03:22:42PM -0300, Ma?ra Canal wrote:
> Implement conditional logic in order to replace NULL pointer arithmetic.
>
> The use of NULL pointer arithmetic was pointed out by clang with the
> following warning:
>
> fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + !*ppos;
> ~~~~ ^
> fs/seq_file.c:559:14: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + (*pos == 0);
>
> Signed-off-by: Ma?ra Canal <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Hi Ma?ra,
On Mon, Jan 31, 2022 at 03:22:42PM -0300, Ma?ra Canal wrote:
> Implement conditional logic in order to replace NULL pointer arithmetic.
>
> The use of NULL pointer arithmetic was pointed out by clang with the
> following warning:
>
> fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + !*ppos;
> ~~~~ ^
> fs/seq_file.c:559:14: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + (*pos == 0);
>
> Signed-off-by: Ma?ra Canal <[email protected]>
Thanks a lot for the patch!
It looks like Arnd sent a similar patch but it was never picked up:
https://lore.kernel.org/r/[email protected]/
This is a cleaner solution as it uses existing defines and functions to
deduplicate the code.
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> V1 -> V2:
> - Use SEQ_START_TOKEN instead of open-coding it
> - kernfs_seq_start call single_start instead of open-coding it
> V2 -> V3:
> - Remove the EXPORT of the single_start symbol
> ---
> fs/kernfs/file.c | 7 +------
> fs/seq_file.c | 4 ++--
> include/linux/seq_file.h | 1 +
> 3 files changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
> index 9414a7a60a9f..7aefaca876a0 100644
> --- a/fs/kernfs/file.c
> +++ b/fs/kernfs/file.c
> @@ -120,13 +120,8 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
> if (next == ERR_PTR(-ENODEV))
> kernfs_seq_stop_active(sf, next);
> return next;
> - } else {
> - /*
> - * The same behavior and code as single_open(). Returns
> - * !NULL if pos is at the beginning; otherwise, NULL.
> - */
> - return NULL + !*ppos;
> }
> + return single_start(sf, ppos);
> }
>
> static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
> diff --git a/fs/seq_file.c b/fs/seq_file.c
> index f8e1f4ee87ff..7ab8a58c29b6 100644
> --- a/fs/seq_file.c
> +++ b/fs/seq_file.c
> @@ -554,9 +554,9 @@ int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
> }
> EXPORT_SYMBOL(seq_dentry);
>
> -static void *single_start(struct seq_file *p, loff_t *pos)
> +void *single_start(struct seq_file *p, loff_t *pos)
> {
> - return NULL + (*pos == 0);
> + return *pos ? NULL : SEQ_START_TOKEN;
> }
>
> 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 88cc16444b43..60820ab511d2 100644
> --- a/include/linux/seq_file.h
> +++ b/include/linux/seq_file.h
> @@ -162,6 +162,7 @@ int seq_dentry(struct seq_file *, struct dentry *, const char *);
> int seq_path_root(struct seq_file *m, const struct path *path,
> const struct path *root, const char *esc);
>
> +void *single_start(struct seq_file *, loff_t *);
> int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
> int single_open_size(struct file *, int (*)(struct seq_file *, void *), void *, size_t);
> int single_release(struct inode *, struct file *);
> --
> 2.34.1
>
On Mon, Jan 31, 2022 at 03:22:42PM -0300, Ma?ra Canal wrote:
> Implement conditional logic in order to replace NULL pointer arithmetic.
>
> The use of NULL pointer arithmetic was pointed out by clang with the
> following warning:
>
> fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + !*ppos;
> ~~~~ ^
> fs/seq_file.c:559:14: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + (*pos == 0);
>
> Signed-off-by: Ma?ra Canal <[email protected]>
> ---
> V1 -> V2:
> - Use SEQ_START_TOKEN instead of open-coding it
> - kernfs_seq_start call single_start instead of open-coding it
> V2 -> V3:
> - Remove the EXPORT of the single_start symbol
Applied.