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Subject[PATCH][next] net: ip_fib: 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
include/net/ip_fib.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 6a1ae49809de..dabe398bee4c 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -153,7 +153,7 @@ struct fib_info {
bool nh_updated;
struct nexthop *nh;
struct rcu_head rcu;
- struct fib_nh fib_nh[0];
+ struct fib_nh fib_nh[];
};


@@ -250,7 +250,7 @@ struct fib_table {
int tb_num_default;
struct rcu_head rcu;
unsigned long *tb_data;
- unsigned long __data[0];
+ unsigned long __data[];
};

struct fib_dump_filter {
--
2.25.0
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