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

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

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@xxxxxxxx>
---
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