From 17b238acf7c665e5c1eb44a31be10299fcbf8858 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Fri, 6 Mar 2020 10:49:12 -0600 Subject: [PATCH] btrfs: delayed-inode: 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 Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/delayed-inode.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h index 74ae226ffaf0..ca96ef007d8f 100644 --- a/fs/btrfs/delayed-inode.h +++ b/fs/btrfs/delayed-inode.h @@ -70,7 +70,7 @@ struct btrfs_delayed_item { refcount_t refs; int ins_or_del; u32 data_len; - char data[0]; + char data[]; }; static inline void btrfs_init_delayed_root(