2016-04-25 02:50:26

by Masahiro Yamada

Subject: [PATCH] clk: fix member type of struct clk_hw_onecell_data

We cannot assign any value to an array type variable. So,

hw_data->hws = kcalloc(hw_data->num, sizeof(struct clk_hw *),
GFP_KERNEL);

fails with "invalid use of flexible array member" error.

There are two ways to fix this issue.

[1] Make it a double-pointer
struct clk_hw_onecell_data {
size_t num;
struct clk_hw **hws;
};

This works as struct clk_onecell_data does.

[2] Make it a zero-sized array
struct clk_hw_onecell_data {
size_t num;
struct clk_hw *hws[0];
};

This allows one-shot memory allocation like this:

hw_data = kmalloc(sizeof(*hw_data) + clk_num * sizeof(struct clk_hw *),
GFP_KERNEL);

This commit adopts [2] because it looks like Stephen's intention
(he moved hws[] to the bottom of struct clk_hw_onecell_data).

Fixes: 0861e5b8cf80 ("clk: Add clk_hw OF clk providers")
Signed-off-by: Masahiro Yamada <[email protected]>
---

include/linux/clk-provider.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index fd2ccd5..1850e25 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -769,7 +769,7 @@ struct clk_onecell_data {

struct clk_hw_onecell_data {
size_t num;
- struct clk_hw *hws[];
+ struct clk_hw *hws[0];
};

extern struct of_device_id __clk_of_table;
--
1.9.1

2016-04-25 22:27:09

by Stephen Boyd

Subject: Re: [PATCH] clk: fix member type of struct clk_hw_onecell_data

On 04/25, Masahiro Yamada wrote:
> We cannot assign any value to an array type variable. So,
>
> hw_data->hws = kcalloc(hw_data->num, sizeof(struct clk_hw *),
> GFP_KERNEL);
>
> fails with "invalid use of flexible array member" error.

That's good. We don't want assignment to the hws member of this
structure to happen from an allocation like kcalloc.

>
> There are two ways to fix this issue.
>
> [1] Make it a double-pointer
> struct clk_hw_onecell_data {
> size_t num;
> struct clk_hw **hws;
> };
>
> This works as struct clk_onecell_data does.

True we could go back to the old style with two allocations.

>
> [2] Make it a zero-sized array
> struct clk_hw_onecell_data {
> size_t num;
> struct clk_hw *hws[0];
> };
>
> This allows one-shot memory allocation like this:
>
> hw_data = kmalloc(sizeof(*hw_data) + clk_num * sizeof(struct clk_hw *),
> GFP_KERNEL);
>

Good, that was possible before this patch wasn't it?

> This commit adopts [2] because it looks like Stephen's intention
> (he moved hws[] to the bottom of struct clk_hw_onecell_data).
>
> Fixes: 0861e5b8cf80 ("clk: Add clk_hw OF clk providers")
> Signed-off-by: Masahiro Yamada <[email protected]>
> ---

>
> include/linux/clk-provider.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index fd2ccd5..1850e25 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -769,7 +769,7 @@ struct clk_onecell_data {
>
> struct clk_hw_onecell_data {
> size_t num;
> - struct clk_hw *hws[];
> + struct clk_hw *hws[0];

I'm totally lost now. Isn't a flex array with [] or with [0] the
same? The latter being a GCC extension while the former being a
C99 standard?

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

2016-04-26 06:19:19

by Masahiro Yamada

Subject: Re: [PATCH] clk: fix member type of struct clk_hw_onecell_data

Hi Stephen,


2016-04-26 7:27 GMT+09:00 Stephen Boyd <[email protected]>:
> On 04/25, Masahiro Yamada wrote:
>> We cannot assign any value to an array type variable. So,
>>
>> hw_data->hws = kcalloc(hw_data->num, sizeof(struct clk_hw *),
>> GFP_KERNEL);
>>
>> fails with "invalid use of flexible array member" error.
>
> That's good. We don't want assignment to the hws member of this
> structure to happen from an allocation like kcalloc.
>
>>
>> There are two ways to fix this issue.
>>
>> [1] Make it a double-pointer
>> struct clk_hw_onecell_data {
>> size_t num;
>> struct clk_hw **hws;
>> };
>>
>> This works as struct clk_onecell_data does.
>
> True we could go back to the old style with two allocations.
>
>>
>> [2] Make it a zero-sized array
>> struct clk_hw_onecell_data {
>> size_t num;
>> struct clk_hw *hws[0];
>> };
>>
>> This allows one-shot memory allocation like this:
>>
>> hw_data = kmalloc(sizeof(*hw_data) + clk_num * sizeof(struct clk_hw *),
>> GFP_KERNEL);
>>
>
> Good, that was possible before this patch wasn't it?
>
>> This commit adopts [2] because it looks like Stephen's intention
>> (he moved hws[] to the bottom of struct clk_hw_onecell_data).
>>
>> Fixes: 0861e5b8cf80 ("clk: Add clk_hw OF clk providers")
>> Signed-off-by: Masahiro Yamada <[email protected]>
>> ---
>
>>
>> include/linux/clk-provider.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
>> index fd2ccd5..1850e25 100644
>> --- a/include/linux/clk-provider.h
>> +++ b/include/linux/clk-provider.h
>> @@ -769,7 +769,7 @@ struct clk_onecell_data {
>>
>> struct clk_hw_onecell_data {
>> size_t num;
>> - struct clk_hw *hws[];
>> + struct clk_hw *hws[0];
>
> I'm totally lost now. Isn't a flex array with [] or with [0] the
> same?

I was misunderstanding.

You are right. They are the same.


> The latter being a GCC extension while the former being a
> C99 standard?


Please ignore this patch. Sorry for noise.




--
Best Regards
Masahiro Yamada