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netdevice: Replace zero-length array with flexible-array member

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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>
This commit is contained in:
Gustavo A. R. Silva 2020-03-02 05:59:33 -06:00 committed by David S. Miller
parent 6f2f92a9d0
commit bb4cf02d4c
1 changed files with 5 additions and 5 deletions
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10
include/linux/netdevice.h
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@ -664,7 +664,7 @@ static inline void netdev_queue_numa_node_write(struct netdev_queue *q, int node
struct rps_map {
unsigned int len;
struct rcu_head rcu;
u16 cpus[0];
u16 cpus[];
};
#define RPS_MAP_SIZE(_num) (sizeof(struct rps_map) + ((_num) * sizeof(u16)))
@ -686,7 +686,7 @@ struct rps_dev_flow {
struct rps_dev_flow_table {
unsigned int mask;
struct rcu_head rcu;
struct rps_dev_flow flows[0];
struct rps_dev_flow flows[];
};
#define RPS_DEV_FLOW_TABLE_SIZE(_num) (sizeof(struct rps_dev_flow_table) + \
((_num) * sizeof(struct rps_dev_flow)))
@ -704,7 +704,7 @@ struct rps_dev_flow_table {
struct rps_sock_flow_table {
u32 mask;
u32 ents[0] ____cacheline_aligned_in_smp;
u32 ents[] ____cacheline_aligned_in_smp;
};
#define RPS_SOCK_FLOW_TABLE_SIZE(_num) (offsetof(struct rps_sock_flow_table, ents[_num]))
@ -767,7 +767,7 @@ struct xps_map {
unsigned int len;
unsigned int alloc_len;
struct rcu_head rcu;
u16 queues[0];
u16 queues[];
};
#define XPS_MAP_SIZE(_num) (sizeof(struct xps_map) + ((_num) * sizeof(u16)))
#define XPS_MIN_MAP_ALLOC ((L1_CACHE_ALIGN(offsetof(struct xps_map, queues[1])) \
@ -778,7 +778,7 @@ struct xps_map {
*/
struct xps_dev_maps {
struct rcu_head rcu;
struct xps_map __rcu *attr_map[0]; /* Either CPUs map or RXQs map */
struct xps_map __rcu *attr_map[]; /* Either CPUs map or RXQs map */
};
#define XPS_CPU_DEV_MAPS_SIZE(_tcs) (sizeof(struct xps_dev_maps) + \