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igmp.h: 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>
This commit is contained in:
Gustavo A. R. Silva 2020-03-23 17:59:00 -05:00
parent 89f60a5d9b
commit 0ead33642f
1 changed files with 1 additions and 1 deletions
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2
include/linux/igmp.h
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@ -38,7 +38,7 @@ struct ip_sf_socklist {
unsigned int sl_max; unsigned int sl_max;
unsigned int sl_count; unsigned int sl_count;
struct rcu_head rcu; struct rcu_head rcu;
__be32 sl_addr[0]; __be32 sl_addr[];
}; };
#define IP_SFLSIZE(count) (sizeof(struct ip_sf_socklist) + \ #define IP_SFLSIZE(count) (sizeof(struct ip_sf_socklist) + \