Commit 53e76f48 authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva Committed by David S. Miller

ndisc: 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 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: default avatarGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c61a2a76
...@@ -80,12 +80,12 @@ extern struct neigh_table nd_tbl; ...@@ -80,12 +80,12 @@ extern struct neigh_table nd_tbl;
struct nd_msg { struct nd_msg {
struct icmp6hdr icmph; struct icmp6hdr icmph;
struct in6_addr target; struct in6_addr target;
__u8 opt[0]; __u8 opt[];
}; };
struct rs_msg { struct rs_msg {
struct icmp6hdr icmph; struct icmp6hdr icmph;
__u8 opt[0]; __u8 opt[];
}; };
struct ra_msg { struct ra_msg {
...@@ -98,7 +98,7 @@ struct rd_msg { ...@@ -98,7 +98,7 @@ struct rd_msg {
struct icmp6hdr icmph; struct icmp6hdr icmph;
struct in6_addr target; struct in6_addr target;
struct in6_addr dest; struct in6_addr dest;
__u8 opt[0]; __u8 opt[];
}; };
struct nd_opt_hdr { struct nd_opt_hdr {
......
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