[PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

[PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

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>
---
 drivers/platform/x86/i2c-multi-instantiate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
index ffb8d5d1eb5f..6acc8457866e 100644
--- a/drivers/platform/x86/i2c-multi-instantiate.c
+++ b/drivers/platform/x86/i2c-multi-instantiate.c
@@ -28,7 +28,7 @@ struct i2c_inst_data {
 
 struct i2c_multi_inst_data {
 	int num_clients;
-	struct i2c_client *clients[0];
+	struct i2c_client *clients[];
 };
 
 static int i2c_multi_inst_count(struct acpi_resource *ares, void *data)
-- 
2.23.0

Re: [PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

Hi all,

Friendly ping: who can take this?

Thanks
--
Gustavo

On 2/12/20 18:55, 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>
> ---
>  drivers/platform/x86/i2c-multi-instantiate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
> index ffb8d5d1eb5f..6acc8457866e 100644
> --- a/drivers/platform/x86/i2c-multi-instantiate.c
> +++ b/drivers/platform/x86/i2c-multi-instantiate.c
> @@ -28,7 +28,7 @@ struct i2c_inst_data {
>  
>  struct i2c_multi_inst_data {
>  	int num_clients;
> -	struct i2c_client *clients[0];
> +	struct i2c_client *clients[];
>  };
>  
>  static int i2c_multi_inst_count(struct acpi_resource *ares, void *data)
> 

Re: [PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

[Hans de Goede]

Hi,


On 2/27/20 8:03 PM, Gustavo A. R. Silva wrote:
> Hi all,
> 
> Friendly ping: who can take this?

FWIW, the patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Regards,

Hans



> On 2/12/20 18:55, 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>
>> ---
>>   drivers/platform/x86/i2c-multi-instantiate.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
>> index ffb8d5d1eb5f..6acc8457866e 100644
>> --- a/drivers/platform/x86/i2c-multi-instantiate.c
>> +++ b/drivers/platform/x86/i2c-multi-instantiate.c
>> @@ -28,7 +28,7 @@ struct i2c_inst_data {
>>   
>>   struct i2c_multi_inst_data {
>>   	int num_clients;
>> -	struct i2c_client *clients[0];
>> +	struct i2c_client *clients[];
>>   };
>>   
>>   static int i2c_multi_inst_count(struct acpi_resource *ares, void *data)
>>
> 

Re: [PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

On 2/27/20 13:01, Hans de Goede wrote:
> Hi,
> 
> 
> On 2/27/20 8:03 PM, Gustavo A. R. Silva wrote:
>> Hi all,
>>
>> Friendly ping: who can take this?
> 
> FWIW, the patch looks good to me:
> 
> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
> 

Thanks, Hans.
--
Gustavo

> Regards,
> 
> Hans
> 
> 
> 
>> On 2/12/20 18:55, 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>
>>> ---
>>>   drivers/platform/x86/i2c-multi-instantiate.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
>>> index ffb8d5d1eb5f..6acc8457866e 100644
>>> --- a/drivers/platform/x86/i2c-multi-instantiate.c
>>> +++ b/drivers/platform/x86/i2c-multi-instantiate.c
>>> @@ -28,7 +28,7 @@ struct i2c_inst_data {
>>>     struct i2c_multi_inst_data {
>>>       int num_clients;
>>> -    struct i2c_client *clients[0];
>>> +    struct i2c_client *clients[];
>>>   };
>>>     static int i2c_multi_inst_count(struct acpi_resource *ares, void *data)
>>>
>>
>