[drivers/clk] Question about `en7523_register_clocks` func: misuse of __counted_by

[drivers/clk] Question about `en7523_register_clocks` func: misuse of __counted_by

[Haoyu Li]

Dear Linux Developers for COMMON CLK FRAMEWORK,

We are curious about the use of `struct clk_hw_onecell_data *clk_data`
in function `en7523_register_clocks`.
The definition of `struct clk_hw_onecell_data` is at
https://elixir.bootlin.com/linux/v6.10.6/source/include/linux/clk-provider.h#L1405.
```
struct clk_hw_onecell_data {
        unsigned int num;
        struct clk_hw *hws[] __counted_by(num);
};
```

Our question is: The `hws` member of `struct clk_hw_onecell_data` is annotated
with "__counted_by", which means the size of the array is indicated by
`num`. Only if we set `num` before accessing `hws[n]`, the flexible
member `hws` can be properly bounds-checked at run-time when enabling
CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE. Or there will be a
warning from each array access that is prior to the initialization
because the number of elements is zero.

In function `en7523_register_clocks` at
https://elixir.bootlin.com/linux/v6.10.6/source/drivers/clk/clk-en7523.c#L428,
we think relocating `clk_data->num = EN7523_NUM_CLOCKS` before
accessing `clk_data->hws[EN7523_CLK_PCIE]` is needed.

Here is a fix example of a similar situation :
https://lore.kernel.org/stable/20240613113225.898955993@linuxfoundation.org/.

Please kindly correct us if we missed any key information. Looking
forward to your response!

Best,
Haoyu Li

Re: [drivers/clk] Question about `en7523_register_clocks` func: misuse of __counted_by

[Stephen Boyd]

Quoting Haoyu Li (2024-08-19 12:05:30)
> 
> Please kindly correct us if we missed any key information. Looking
> forward to your response!

Patches welcome.