From: Gustavo A. R. Silva Date: Thu, 13 Feb 2020 16:00:04 +0000 (-0600) Subject: ceph: replace zero-length array with flexible-array member X-Git-Tag: v5.7-rc1~39^2~34 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f682dc713c0af79effde49209f3895072579791b;p=thirdparty%2Fkernel%2Flinux.git ceph: 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: Jeff Layton Signed-off-by: Ilya Dryomov --- diff --git a/fs/ceph/cache.c b/fs/ceph/cache.c index 270b769607a2f..2f5cb6bc78e1d 100644 --- a/fs/ceph/cache.c +++ b/fs/ceph/cache.c @@ -32,7 +32,7 @@ struct ceph_fscache_entry { size_t uniq_len; /* The following members must be last */ struct ceph_fsid fsid; - char uniquifier[0]; + char uniquifier[]; }; static const struct fscache_cookie_def ceph_fscache_fsid_object_def = {