From: linux-hyperv-owner@vger.kernel.org
[off-list ref] On Behalf Of Gustavo A. R. Silva
Sent: Wednesday, February 12, 2020 4:51 PM
 ...
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.

Looks good to me. Thanks, Gustavo!
 
Reviewed-by: Dexuan Cui <decui@microsoft.com>

FWIW, it looks there are a lot of more to fix in the kernel tree: the below
commands return 1373 for me:

grep -nr '\[0\];$' * | grep '\.h:' | grep -v = | wc -l

Running the commands against the kernel/ directory returns 3.

Thanks,
-- Dexuan