From 53ab8e7cd2d47594e68951994ac083d30f82fce4 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 7 May 2020 13:51:38 -0500 Subject: libceph, rbd: replace zero-length array with flexible-array 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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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: Ilya Dryomov Signed-off-by: Ilya Dryomov --- drivers/block/rbd_types.h | 2 +- include/linux/ceph/mon_client.h | 2 +- include/linux/crush/crush.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/block/rbd_types.h b/drivers/block/rbd_types.h index ac98ab6ccd3b..a600e0eb6b6f 100644 --- a/drivers/block/rbd_types.h +++ b/drivers/block/rbd_types.h @@ -93,7 +93,7 @@ struct rbd_image_header_ondisk { __le32 snap_count; __le32 reserved; __le64 snap_names_len; - struct rbd_image_snap_ondisk snaps[0]; + struct rbd_image_snap_ondisk snaps[]; } __attribute__((packed)); diff --git a/include/linux/ceph/mon_client.h b/include/linux/ceph/mon_client.h index dbb8a6959a73..ce4ffeb384d7 100644 --- a/include/linux/ceph/mon_client.h +++ b/include/linux/ceph/mon_client.h @@ -19,7 +19,7 @@ struct ceph_monmap { struct ceph_fsid fsid; u32 epoch; u32 num_mon; - struct ceph_entity_inst mon_inst[0]; + struct ceph_entity_inst mon_inst[]; }; struct ceph_mon_client; diff --git a/include/linux/crush/crush.h b/include/linux/crush/crush.h index 54741295c70b..38b0e4d50ed9 100644 --- a/include/linux/crush/crush.h +++ b/include/linux/crush/crush.h @@ -87,7 +87,7 @@ struct crush_rule_mask { struct crush_rule { __u32 len; struct crush_rule_mask mask; - struct crush_rule_step steps[0]; + struct crush_rule_step steps[]; }; #define crush_rule_size(len) (sizeof(struct crush_rule) + \ -- cgit v1.2.3