Gustavo A. R. Silva
2020-Mar-09 20:19 UTC
[Ocfs2-devel] [PATCH][next] 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!NzMr-YRl2zy-K3lwLVVatz7x0uD2z7-ykQag4GrGigxmfWU8TWzDy6xrkTiW3hYl00czlw$
[2]
https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!NzMr-YRl2zy-K3lwLVVatz7x0uD2z7-ykQag4GrGigxmfWU8TWzDy6xrkTiW3hYHG1nAnw$
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>
---
fs/ocfs2/cluster/tcp.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/ocfs2/cluster/tcp.h b/fs/ocfs2/cluster/tcp.h
index de87cbffd175..736338f45c59 100644
--- a/fs/ocfs2/cluster/tcp.h
+++ b/fs/ocfs2/cluster/tcp.h
@@ -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,
--
2.25.0
Joseph Qi
2020-Mar-10 01:06 UTC
[Ocfs2-devel] [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member
On 2020/3/10 04:19, Gustavo A. R. Silva wrote:> 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://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] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>Acked-by: Joseph Qi <joseph.qi at linux.alibaba.com>> --- > fs/ocfs2/cluster/tcp.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ocfs2/cluster/tcp.h b/fs/ocfs2/cluster/tcp.h > index de87cbffd175..736338f45c59 100644 > --- a/fs/ocfs2/cluster/tcp.h > +++ b/fs/ocfs2/cluster/tcp.h > @@ -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, >