hostap: 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")

---
 drivers/net/wireless/intersil/hostap/hostap_common.h | 2 +-
 drivers/net/wireless/intersil/hostap/hostap_wlan.h   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

index 22543538239b..dd29a8e8d349 100644
@@ -322,7 +322,7 @@ struct prism2_download_param {
 		u32 addr; /* wlan card address */
 		u32 len;
 		void __user *ptr; /* pointer to data in user space */
-	} data[0];
+	} data[];
 };
 
 #define PRISM2_MAX_DOWNLOAD_AREA_LEN 131072

index 487883fbb58c..dd2603d9b5d3 100644
@@ -615,7 +615,7 @@ struct prism2_download_data {
 		u32 addr; /* wlan card address */
 		u32 len;
 		u8 *data; /* allocated data */
-	} data[0];
+	} data[];
 };
 
 

2.25.0

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

bc1d50a1a485 hostap: Replace zero-length array with flexible-array member

https://patchwork.kernel.org/patch/11402357/

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