linux-kernel - Re: [tip: perf/core] perf/x86: Annotate struct bts_buffer with __counted

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Message-ID: <Z8gW1rihV0aIp8Oo@gmail.com>
Date: Wed, 5 Mar 2025 10:18:14 +0100
From: Ingo Molnar <mingo@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org,
	Thorsten Blum <thorsten.blum@...ux.dev>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: Re: [tip: perf/core] perf/x86: Annotate struct bts_buffer with
 __counted_by()


* tip-bot2 for Thorsten Blum <tip-bot2@...utronix.de> wrote:

> The following commit has been merged into the perf/core branch of tip:
> 
> Commit-ID:     077dcef270361089c322a969b792438b33cfb479
> Gitweb:        https://git.kernel.org/tip/077dcef270361089c322a969b792438b33cfb479
> Author:        Thorsten Blum <thorsten.blum@...ux.dev>
> AuthorDate:    Tue, 04 Mar 2025 19:30:57 +01:00
> Committer:     Ingo Molnar <mingo@...nel.org>
> CommitterDate: Tue, 04 Mar 2025 19:58:01 +01:00
> 
> perf/x86: Annotate struct bts_buffer with __counted_by()
> 
> Add the __counted_by() compiler attribute to the flexible array member
> buf to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Use struct_size() to calculate the number of bytes to allocate for a new
> bts_buffer. Compared to offsetof(), struct_size() has additional
> compile-time checks (e.g., __must_be_array()).
> 
> No functional changes intended.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Link: https://lore.kernel.org/r/20250304183056.78920-2-thorsten.blum@linux.dev
> ---
>  arch/x86/events/intel/bts.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
> index 8e09319..debfc18 100644
> --- a/arch/x86/events/intel/bts.c
> +++ b/arch/x86/events/intel/bts.c
> @@ -58,7 +58,7 @@ struct bts_buffer {
>  	local_t		head;
>  	unsigned long	end;
>  	void		**data_pages;
> -	struct bts_phys	buf[];
> +	struct bts_phys	buf[] __counted_by(nr_bufs);
>  };
>  
>  static struct pmu bts_pmu;
> @@ -101,7 +101,7 @@ bts_buffer_setup_aux(struct perf_event *event, void **pages,
>  	if (overwrite && nbuf > 1)
>  		return NULL;

Actually, on a second thought:

> -	buf = kzalloc_node(offsetof(struct bts_buffer, buf[nbuf]), GFP_KERNEL, node);
> +	buf = kzalloc_node(struct_size(buf, buf, nbuf), GFP_KERNEL, node);

Firstly, in what world is 'buf, buf' more readable? One is a member of 
a structure, the other is the name of the structure - and they match, 
which shows that this function's naming conventions are a mess.

Which should be fixed first ...

I'm also not sure the code is correct ...

So I zapped this commit from tip:perf/core.

Thanks,

	Ingo