linux-kernel - Re: [PATCH][next] net/mlx5: IPsec, Replace zero-length array with flexible-array member

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Message-ID: <2c0b59b6-7897-6618-a72c-8306f42709f6@embeddedor.com>
Date:   Tue, 18 Feb 2020 14:19:51 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Boris Pismenny <borisp@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] net/mlx5: IPsec, Replace zero-length array with
 flexible-array member



On 2/18/20 10:35, Leon Romanovsky wrote:
> On Mon, Feb 17, 2020 at 01:54:34PM -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] 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@...eddedor.com>
>> ---
>>  drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Can you please do one patch for whole mlx5,
> instead of many identical patches?
> 

Sure thing. I can do that.

Thanks
--
Gustavo