qtnfmac: Replace zero-length array with flexible-array

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]

sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues.

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")

---
 drivers/net/wireless/quantenna/qtnfmac/bus.h   |    2 
 drivers/net/wireless/quantenna/qtnfmac/qlink.h |   54 ++++++++++++-------------
 2 files changed, 28 insertions(+), 28 deletions(-)

index 87d048df09d1..3334c45aac13 100644
@@ -69,7 +69,7 @@ struct qtnf_bus {
 	struct notifier_block netdev_nb;
 	u8 hw_id[ETH_ALEN];
 	/* bus private data */
-	char bus_priv[0] __aligned(sizeof(void *));
+	char bus_priv[] __aligned(sizeof(void *));
 };
 
 static inline bool qtnf_fw_is_up(struct qtnf_bus *bus)

...

Regards,
Sergey

Patch applied to wireless-drivers-next.git, thanks.

55bb8a2b01a3 qtnfmac: Replace zero-length array with flexible-array

https://patchwork.kernel.org/patch/11534767/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches