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 <gustavoars@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/drivers/block/rbd_types.h b/drivers/block/rbd_types.h
index ac98ab6..a600e0e 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 dbb8a69..ce4ffeb 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 5474129..38b0e4d5 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) + \