f2fs: xattr.h: 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>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/xattr.h b/fs/f2fs/xattr.h
index 0153b4c..e471be7 100644 (file)
--- a/fs/f2fs/xattr.h
+++ b/fs/f2fs/xattr.h
@@ -49,7 +49,7 @@ struct f2fs_xattr_entry {
        __u8    e_name_index;
        __u8    e_name_len;
        __le16  e_value_size;   /* size of attribute value */
-       char    e_name[0];      /* attribute name */
+       char    e_name[];      /* attribute name */
 };
 
 #define XATTR_HDR(ptr)         ((struct f2fs_xattr_header *)(ptr))