From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH][next] net: inet_sock: Replace zero-length array with flexible-array member
Date: Mon, 2 Mar 2020 06:07:42 -0600 [thread overview]
Message-ID: <20200302120742.GA16158@embeddedor> (raw)
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/inet_sock.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 34c4436fd18f..a7ce00af6c44 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -52,7 +52,7 @@ struct ip_options {
unsigned char router_alert;
unsigned char cipso;
unsigned char __pad2;
- unsigned char __data[0];
+ unsigned char __data[];
};
struct ip_options_rcu {
--
2.25.0
next reply other threads:[~2020-03-02 12:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-02 12:07 Gustavo A. R. Silva [this message]
2020-03-02 19:27 ` [PATCH][next] net: inet_sock: Replace zero-length array with flexible-array member David Miller
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