| Message ID | 20200309201907.GA8005@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] ocfs2: cluster: Replace zero-length array with flexible-array member | expand |
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@embeddedor.com> Acked-by: Joseph Qi <joseph.qi@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, >
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,
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@embeddedor.com> --- fs/ocfs2/cluster/tcp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)