Commit 5c91aa1d authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva

skbuff.h: 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: default avatarGustavo A. R. Silva <gustavo@embeddedor.com>
parent fe946db6
......@@ -4162,7 +4162,7 @@ struct skb_ext {
refcount_t refcnt;
u8 offset[SKB_EXT_NUM]; /* in chunks of 8 bytes */
u8 chunks; /* same */
char data[0] __aligned(8);
char data[] __aligned(8);
};
struct skb_ext *__skb_ext_alloc(void);
......
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