Bluetooth: 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>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/bluetooth/btrtl.h b/drivers/bluetooth/btrtl.h
index 10ad40c3e42c..2a582682136d 100644
--- a/drivers/bluetooth/btrtl.h
+++ b/drivers/bluetooth/btrtl.h
@@ -38,13 +38,13 @@ struct rtl_epatch_header {
 struct rtl_vendor_config_entry {
 	__le16 offset;
 	__u8 len;
-	__u8 data[0];
+	__u8 data[];
 } __packed;
 
 struct rtl_vendor_config {
 	__le32 signature;
 	__le16 total_len;
-	struct rtl_vendor_config_entry entry[0];
+	struct rtl_vendor_config_entry entry[];
 } __packed;
 
 #if IS_ENABLED(CONFIG_BT_RTL)