* [PATCH] seq_file: fix NULL pointer arithmetic warning
@ 2022-01-30 15:27 Maíra Canal
2022-01-30 17:22 ` Al Viro
0 siblings, 1 reply; 2+ messages in thread
From: Maíra Canal @ 2022-01-30 15:27 UTC (permalink / raw)
To: gregkh, tj, viro, nathan, ndesaulniers; +Cc: linux-kernel, linux-fsdevel, llvm
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: Maíra Canal <maira.canal@usp.br>
---
fs/kernfs/file.c | 6 ++++--
fs/seq_file.c | 2 +-
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 9414a7a60a9f..3a6990c7fe8e 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -120,12 +120,14 @@ 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 {
+ } else if (*ppos) {
/*
* The same behavior and code as single_open(). Returns
* !NULL if pos is at the beginning; otherwise, NULL.
*/
- return NULL + !*ppos;
+ return NULL;
+ } else {
+ return (void *) 1;
}
}
diff --git a/fs/seq_file.c b/fs/seq_file.c
index f8e1f4ee87ff..7b6165d5d829 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -556,7 +556,7 @@ EXPORT_SYMBOL(seq_dentry);
static void *single_start(struct seq_file *p, loff_t *pos)
{
- return NULL + (*pos == 0);
+ return *pos ? NULL : (void *) 1;
}
static void *single_next(struct seq_file *p, void *v, loff_t *pos)
--
2.34.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] seq_file: fix NULL pointer arithmetic warning
2022-01-30 15:27 [PATCH] seq_file: fix NULL pointer arithmetic warning Maíra Canal
@ 2022-01-30 17:22 ` Al Viro
0 siblings, 0 replies; 2+ messages in thread
From: Al Viro @ 2022-01-30 17:22 UTC (permalink / raw)
To: Maíra Canal
Cc: gregkh, tj, nathan, ndesaulniers, linux-kernel, linux-fsdevel, llvm
On Sun, Jan 30, 2022 at 12:27:00PM -0300, Maíra 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);
NAK. _If_ you want to bother with that at all, at least make it
use SEQ_START_TOKEN, rather than open-coding it; what's more,
kernfs_seq_start() should simply call single_start() instead of
open-coding it. I.e.
if (ops->seq_start) {
void *next = ops->seq_start(sf, ppos);
/* see the comment above kernfs_seq_stop_active() */
if (next == ERR_PTR(-ENODEV))
kernfs_seq_stop_active(sf, next);
return next;
} else {
return single_start(sf, ppos);
}
and
return *ppos ? NULL : SEQ_START_TOKEN;
in single_start() itself.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-01-30 15:27 [PATCH] seq_file: fix NULL pointer arithmetic warning Maíra Canal
2022-01-30 17:22 ` Al Viro
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