Re: [PATCH][next] ext2: xattr.h: Replace zero-length array with flexible-array member
From: Jan Kara <jack@suse.cz>
Date: 2020-03-16 14:57:39
Also in:
lkml
On Mon 09-03-20 13:04:41, Gustavo A. R. Silva wrote:
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 <redacted>Thanks. I've added the patch to my tree. Honza
quoted hunk ↗ jump to hunk
--- fs/ext2/xattr.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/fs/ext2/xattr.h b/fs/ext2/xattr.h index cee888cdc235..16272e6ddcf4 100644 --- a/fs/ext2/xattr.h +++ b/fs/ext2/xattr.h@@ -39,7 +39,7 @@ struct ext2_xattr_entry { __le32 e_value_block; /* disk block attribute is stored on (n/i) */ __le32 e_value_size; /* size of attribute value */ __le32 e_hash; /* hash value of name and value */ - char e_name[0]; /* attribute name */ + char e_name[]; /* attribute name */ }; #define EXT2_XATTR_PAD_BITS 2-- 2.25.0
-- Jan Kara [off-list ref] SUSE Labs, CR