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net: core: 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 2020-02-28 07:43:24 -06:00 committed by David S. Miller
parent b0c9a2d9a8
commit d2afb41ae6
3 changed files with 3 additions and 3 deletions
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2
net/core/bpf_sk_storage.c
View File

@ -60,7 +60,7 @@ struct bpf_sk_storage_data {
* the number of cachelines access during the cache hit case.
*/
struct bpf_sk_storage_map __rcu *smap;
u8 data[0] __aligned(8);
u8 data[] __aligned(8);
};
/* Linked to bpf_sk_storage and bpf_sk_storage_map */

2
net/core/devlink.c
View File

@ -4232,7 +4232,7 @@ struct devlink_fmsg_item {
int attrtype;
u8 nla_type;
u16 len;
int value[0];
int value[];
};
struct devlink_fmsg {

2
net/core/drop_monitor.c
View File

@ -68,7 +68,7 @@ struct net_dm_hw_entry {
struct net_dm_hw_entries {
u32 num_entries;
struct net_dm_hw_entry entries[0];
struct net_dm_hw_entry entries[];
};
struct per_cpu_dm_data {