kernel_optimize_test/include/net/mip6.h
Gustavo A. R. Silva 2e83abdcb3 net: mip6: 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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-03-02 11:16:27 -08:00

42 lines
1016 B
C

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Copyright (C)2003-2006 Helsinki University of Technology
* Copyright (C)2003-2006 USAGI/WIDE Project
*/
/*
* Authors:
* Noriaki TAKAMIYA @USAGI
* Masahide NAKAMURA @USAGI
* YOSHIFUJI Hideaki @USAGI
*/
#ifndef _NET_MIP6_H
#define _NET_MIP6_H
#include <linux/skbuff.h>
#include <net/sock.h>
/*
* Mobility Header
*/
struct ip6_mh {
__u8 ip6mh_proto;
__u8 ip6mh_hdrlen;
__u8 ip6mh_type;
__u8 ip6mh_reserved;
__u16 ip6mh_cksum;
/* Followed by type specific messages */
__u8 data[];
} __packed;
#define IP6_MH_TYPE_BRR 0 /* Binding Refresh Request */
#define IP6_MH_TYPE_HOTI 1 /* HOTI Message */
#define IP6_MH_TYPE_COTI 2 /* COTI Message */
#define IP6_MH_TYPE_HOT 3 /* HOT Message */
#define IP6_MH_TYPE_COT 4 /* COT Message */
#define IP6_MH_TYPE_BU 5 /* Binding Update */
#define IP6_MH_TYPE_BACK 6 /* Binding ACK */
#define IP6_MH_TYPE_BERROR 7 /* Binding Error */
#define IP6_MH_TYPE_MAX IP6_MH_TYPE_BERROR
#endif