linux-kernel - Re: [PATCH] perf core: Replace offsetof() with struct

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Message-ID: <20250902072550.GJ3245006@noisy.programming.kicks-ass.net>
Date: Tue, 2 Sep 2025 09:25:50 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Xichao Zhao <zhao.xichao@...o.com>
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf core: Replace offsetof() with struct_size()

On Tue, Sep 02, 2025 at 11:43:49AM +0800, Xichao Zhao wrote:
> When dealing with structures containing flexible arrays, struct_size()
> provides additional compile-time checks compared to offsetof(). This
> enhances code robustness and reduces the risk of potential errors.
> 
> Signed-off-by: Xichao Zhao <zhao.xichao@...o.com>
> ---
>  kernel/events/callchain.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 6c83ad674d01..0f88e44af664 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -80,7 +80,7 @@ static int alloc_callchain_buffers(void)
>  	 * accessed from NMI. Use a temporary manual per cpu allocation
>  	 * until that gets sorted out.
>  	 */
> -	size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
> +	size = struct_size(entries, cpu_entries, nr_cpu_ids);

None of this code is needed anymore; that issue with NMI not being able
to access vmalloc memory should be long fixed.