Commit 5a8b7c4b authored Feb 28, 2020 by Gustavo A. R. Silva Committed by David S. Miller Feb 29, 2020

arcnet: 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: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 08ca27d0

include/uapi/linux/if_arcnet.h

+3 −3

Original line number	Diff line number	Diff line
		@@ -60,7 +60,7 @@ struct arc_rfc1201 {
		__u8 proto; /* protocol ID field - varies */
		__u8 split_flag; /* for use with split packets */
		__be16 sequence; /* sequence number */
		__u8 payload[0]; /* space remaining in packet (504 bytes)*/
		__u8 payload[]; /* space remaining in packet (504 bytes)*/
		};
		#define RFC1201_HDR_SIZE 4

		@@ -69,7 +69,7 @@ struct arc_rfc1201 {
		*/
		struct arc_rfc1051 {
		__u8 proto; /* ARC_P_RFC1051_ARP/RFC1051_IP */
		__u8 payload[0]; /* 507 bytes */
		__u8 payload[]; /* 507 bytes */
		};
		#define RFC1051_HDR_SIZE 1

		@@ -80,7 +80,7 @@ struct arc_rfc1051 {
		struct arc_eth_encap {
		__u8 proto; /* Always ARC_P_ETHER */
		struct ethhdr eth; /* standard ethernet header (yuck!) */
		__u8 payload[0]; /* 493 bytes */
		__u8 payload[]; /* 493 bytes */
		};
		#define ETH_ENCAP_HDR_SIZE 14

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