From e32ac2459cdac01f9b177eed526a3ffa1797039d Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 9 Mar 2020 10:48:38 -0500 Subject: [PATCH] ext4: use flexible-array member in struct fname 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 Link: https://lore.kernel.org/r/20200309154838.GA31559@embeddedor Signed-off-by: Theodore Ts'o --- fs/ext4/dir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c index 9aa1f75409b0..c654205f648d 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -392,7 +392,7 @@ struct fname { __u32 inode; __u8 name_len; __u8 file_type; - char name[0]; + char name[]; }; /*