ntfs3: work around false-postive -Wmaybe-uninitialized warnings

[PATCH] ntfs3: work around false-postive -Wmaybe-uninitialized warnings

Posted by Arnd Bergmann 3 weeks, 4 days ago

From: Arnd Bergmann <arnd@arndb.de>

gcc sometimes fails to analyse how two local variables in ntfs_write_bh()
are initialized, as the initialization happens only in the first pass
through the main loop:

fs/ntfs3/fsntfs.c: In function 'ntfs_write_bh':
fs/ntfs3/fsntfs.c:1443:17: error: 'fixup' may be used uninitialized [-Werror=maybe-uninitialized]
 1443 |         __le16 *fixup;
      |                 ^~~~~
fs/ntfs3/fsntfs.c:1443:17: note: 'fixup' was declared here
 1443 |         __le16 *fixup;
      |                 ^~~~~
fs/ntfs3/fsntfs.c:1487:30: error: 'sample' may be used uninitialized [-Werror=maybe-uninitialized]
 1487 |                         *ptr = sample;
      |                         ~~~~~^~~~~~~~
fs/ntfs3/fsntfs.c:1444:16: note: 'sample' was declared here
 1444 |         __le16 sample;

Initializing the two variables to bogus values shuts up the warning and
makes it clear that those cannot be used. I tried rearranging the loop to
move the initialization in front of it, but couldn't quite figure it out.

Fixes: 48d9b57b169f ("fs/ntfs3: add a subset of W=1 warnings for stricter checks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
I don't know how the set of warnings for ntfs3 was picked, this seems to
be based on what W=1 used to do many years ago. -Wmaybe-uninitialized is
no longer part of it, and some of the other warnings enabled here are
turned on by default now.
---
 fs/ntfs3/fsntfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs3/fsntfs.c b/fs/ntfs3/fsntfs.c
index 0df2aa81d884..d0434756029b 100644
--- a/fs/ntfs3/fsntfs.c
+++ b/fs/ntfs3/fsntfs.c
@@ -1440,8 +1440,8 @@ int ntfs_write_bh(struct ntfs_sb_info *sbi, struct NTFS_RECORD_HEADER *rhdr,
 	u16 fo = le16_to_cpu(rhdr->fix_off);
 	u16 fn = le16_to_cpu(rhdr->fix_num);
 	u32 idx;
-	__le16 *fixup;
-	__le16 sample;
+	__le16 *fixup = NULL;
+	__le16 sample = cpu_to_le16(-1u);
 
 	if ((fo & 1) || fo + fn * sizeof(short) > SECTOR_SIZE || !fn-- ||
 	    fn * SECTOR_SIZE > bytes) {
-- 
2.39.5

Re: [PATCH] ntfs3: work around false-postive -Wmaybe-uninitialized warnings

Posted by Konstantin Komarov 1 week, 6 days ago

On 3/12/26 17:49, Arnd Bergmann wrote:

> From: Arnd Bergmann <arnd@arndb.de>
>
> gcc sometimes fails to analyse how two local variables in ntfs_write_bh()
> are initialized, as the initialization happens only in the first pass
> through the main loop:
>
> fs/ntfs3/fsntfs.c: In function 'ntfs_write_bh':
> fs/ntfs3/fsntfs.c:1443:17: error: 'fixup' may be used uninitialized [-Werror=maybe-uninitialized]
>   1443 |         __le16 *fixup;
>        |                 ^~~~~
> fs/ntfs3/fsntfs.c:1443:17: note: 'fixup' was declared here
>   1443 |         __le16 *fixup;
>        |                 ^~~~~
> fs/ntfs3/fsntfs.c:1487:30: error: 'sample' may be used uninitialized [-Werror=maybe-uninitialized]
>   1487 |                         *ptr = sample;
>        |                         ~~~~~^~~~~~~~
> fs/ntfs3/fsntfs.c:1444:16: note: 'sample' was declared here
>   1444 |         __le16 sample;
>
> Initializing the two variables to bogus values shuts up the warning and
> makes it clear that those cannot be used. I tried rearranging the loop to
> move the initialization in front of it, but couldn't quite figure it out.
>
> Fixes: 48d9b57b169f ("fs/ntfs3: add a subset of W=1 warnings for stricter checks")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> I don't know how the set of warnings for ntfs3 was picked, this seems to
> be based on what W=1 used to do many years ago. -Wmaybe-uninitialized is
> no longer part of it, and some of the other warnings enabled here are
> turned on by default now.
> ---
>   fs/ntfs3/fsntfs.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ntfs3/fsntfs.c b/fs/ntfs3/fsntfs.c
> index 0df2aa81d884..d0434756029b 100644
> --- a/fs/ntfs3/fsntfs.c
> +++ b/fs/ntfs3/fsntfs.c
> @@ -1440,8 +1440,8 @@ int ntfs_write_bh(struct ntfs_sb_info *sbi, struct NTFS_RECORD_HEADER *rhdr,
>   	u16 fo = le16_to_cpu(rhdr->fix_off);
>   	u16 fn = le16_to_cpu(rhdr->fix_num);
>   	u32 idx;
> -	__le16 *fixup;
> -	__le16 sample;
> +	__le16 *fixup = NULL;
> +	__le16 sample = cpu_to_le16(-1u);
>   
>   	if ((fo & 1) || fo + fn * sizeof(short) > SECTOR_SIZE || !fn-- ||
>   	    fn * SECTOR_SIZE > bytes) {

Hello,

Thanks for the patch, applied.

Regards,
Konstantin