Messages in this thread | | | Subject | Re: [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member | From | Joseph Qi <> | Date | Tue, 10 Mar 2020 09:06:31 +0800 |
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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://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 <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, >
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