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

Gustavo A. R. Silva
2020-02-25T15:15:48Z

On 2/25/20 07:44, Horia Geanta wrote:
> On 2/24/2020 6:18 PM, 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] 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>
> Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
>

Thank you, Horia.
--
Gustavo

> for caam driver:
>
>> drivers/crypto/caam/caamalg.c | 2 +-
>> drivers/crypto/caam/caamalg_qi.c | 4 ++--
>> drivers/crypto/caam/caamalg_qi2.h | 6 +++---
>> drivers/crypto/caam/caamhash.c | 2 +-
>
> Thanks,
> Horia
>