From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Gustavo A. R. Silva" Subject: [PATCH] ceph: cache: Replace zero-length array with flexible-array member Date: Thu, 13 Feb 2020 10:00:04 -0600 Message-ID: <20200213160004.GA4334@embeddedor> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Jeff Layton , Sage Weil , Ilya Dryomov Cc: ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" List-Id: ceph-devel.vger.kernel.org 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 --- fs/ceph/cache.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ceph/cache.c b/fs/ceph/cache.c index 270b769607a2..2f5cb6bc78e1 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 = { -- 2.25.0