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SubjectRe: [PATCH] regulator: da9062: Replace zero-length array with flexible-array member
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On 2/12/20 05:12, Adam Thomson wrote:
> On 11 February 2020 23:46, 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
>> inadvertenly introduced[3] to the codebase from now on.
>>
>> 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/regulator/da9062-regulator.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062-
>> regulator.c
>> index b064d8a19d4c..c3b6ba9bafdf 100644
>> --- a/drivers/regulator/da9062-regulator.c
>> +++ b/drivers/regulator/da9062-regulator.c
>> @@ -86,7 +86,7 @@ struct da9062_regulators {
>> int irq_ldo_lim;
>> unsigned n_regulators;
>> /* Array size to be defined during init. Keep at end. */
>> - struct da9062_regulator regulator[0];
>> + struct da9062_regulator regulator[];
>
> I don't think is the correct change here for this driver. In the probe
> 'struct_size()' is used to determine the actual size requested from 'malloc()'
> when allocating memory for this structure. It's not statically initialised.
> Your change will break that code I believe.
>

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]

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

Thanks
--
Gustavo

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