ocfs2: cluster: Replace zero-length array with flexible-array member
PATCH 1/1 ocfs2: cluster: 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")
--- fs/ocfs2/cluster/tcp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
fs/ocfs2/cluster/tcp.h +1 -1
@@ -32,7 +32,7 @@ struct o2net_msg__be32 status;__be32 key;__be32 msg_num; -__u8 buf[0 ]; +__u8 buf[]; }; typedef int (o2net_msg_handler_func)(struct o2net_msg *msg, u32 len, void *data,
Signature · 1 line
2.25.0
Quoted 22 lines · Gustavo A. R. Silva
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]
Quoted 7 lines
This issue was found with the help of Coccinelle.
[1] https://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!INdYafacLMiUgRrK-HDy3FhbqtTkRakuBQtEmPbN6cZAHCDBAvGOTj194lmB8udIjmmjqw$
[2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!INdYafacLMiUgRrK-HDy3FhbqtTkRakuBQtEmPbN6cZAHCDBAvGOTj194lmB8ufEoscJWg$
[3] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>
Quoted 18 lines
--- fs/ocfs2/cluster/tcp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)fs/ocfs2/cluster/tcp.h +1
-1@@ -32,7 +32,7 @@ struct o2net_msg__be32 status;__be32 key;__be32 msg_num; -__u8 buf[0 ]; +__u8 buf[]; }; typedef int (o2net_msg_handler_func)(struct o2net_msg *msg, u32 len, void *data,