Re: [PATCH] rtc: ac100: Assign .num before accessing .hws

[Chen-Yu Tsai]

On Sun, Sep 6, 2026 at 2:40 AM Aamir Ahmed <elb12345@xxxxxxxxxxxxx> wrote:
>
> Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
> __counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
> with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS)
> about the number of elements in .hws[], so that it can warn when .hws[]
> is accessed out of bounds. As noted in that change, the __counted_by
> member must be initialized with the number of elements before the first
> array access happens, otherwise there will be a warning from each access
> prior to the initialization because the number of elements is zero.
> This occurs in ac100_rtc_register_clks() due to .num being assigned only
> after every clkout clock has been stored in .hws[]. With
> CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC
> 15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report
> during probe, and with CONFIG_UBSAN_TRAP the first store traps.
>
> Initialize .num with AC100_CLKOUT_NUM, the number of elements .hws[] was
> allocated with, right after the allocation. That is the value the loop
> counter ends up at on the success path anyway, so the provider's
> behaviour is unchanged.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
> Assisted-by: LLM
> Signed-off-by: Aamir Ahmed <elb12345@xxxxxxxxxxxxx>


Reviewed-by: Chen-Yu Tsai <wens@xxxxxxxxxx>