jfs: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
index 3acc954f7c04b7de3ca52c1490853a4db8e87136..837d42f61464b3a7e06bd8cf625d8e1a96fbfd5e 100644 (file)
--- a/fs/jfs/jfs_dtree.c
+++ b/fs/jfs/jfs_dtree.c
@@ -2964,7 +2964,7 @@ struct jfs_dirent {
        loff_t position;
        int ino;
        u16 name_len;
-       char name[0];
+       char name[];
 };
 
 /*

diff --git a/fs/jfs/jfs_xattr.h b/fs/jfs/jfs_xattr.h
index f0558b3348dae850475e7fa3dc8996714e827d0c..c50167a7bc50c4b56adbc28ca85aaf52ed916456 100644 (file)
--- a/fs/jfs/jfs_xattr.h
+++ b/fs/jfs/jfs_xattr.h
@@ -17,12 +17,12 @@ struct jfs_ea {
        u8 flag;        /* Unused? */
        u8 namelen;     /* Length of name */
        __le16 valuelen;        /* Length of value */
-       char name[0];   /* Attribute name (includes null-terminator) */
+       char name[];    /* Attribute name (includes null-terminator) */
 };                     /* Value immediately follows name */
 
 struct jfs_ea_list {
        __le32 size;            /* overall size */
-       struct jfs_ea ea[0];    /* Variable length list */
+       struct jfs_ea ea[];     /* Variable length list */
 };
 
 /* Macros for defining maxiumum number of bytes supported for EAs */