Re: [PATCH][next] mlxsw: Replace zero-length array with flexible-array member

From: Gustavo A. R. Silva
Date: Wed Feb 19 2020 - 14:56:22 EST

On 2/19/20 10:43, Ido Schimmel wrote:
> On Tue, Feb 18, 2020 at 02:57:05PM -0600, Gustavo A. R. Silva wrote:
>> 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]
>> [2]
>> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> Thanks, Gustavo. Looks good to me. Ran a few tests with a debug config
> and nothing exploded.

haha great!

> I was just about to submit some patches myself, but they will conflict
> with this patch, so I will wait :)


> Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxxxx>
> Tested-by: Ido Schimmel <idosch@xxxxxxxxxxxx>