Re: [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member

Joseph Qi
2020-03-10T01:06:38Z

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,
>