linux-kernel - Re: [PATCH] bpf: add missing _

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Message-Id: <5f9c89fe-df1d-4eb4-b724-08f8d90fcc59@app.fastmail.com>
Date: Tue, 03 Feb 2026 17:57:58 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Alexei Starovoitov" <alexei.starovoitov@...il.com>,
 "Arnd Bergmann" <arnd@...nel.org>
Cc: "Alexei Starovoitov" <ast@...nel.org>,
 "Daniel Borkmann" <daniel@...earbox.net>,
 "Andrii Nakryiko" <andrii@...nel.org>, "Song Liu" <song@...nel.org>,
 "KP Singh" <kpsingh@...nel.org>, "Matt Bobrowski" <mattbobrowski@...gle.com>,
 "Steven Rostedt" <rostedt@...dmis.org>,
 "Masami Hiramatsu" <mhiramat@...nel.org>,
 "Martin KaFai Lau" <martin.lau@...ux.dev>,
 "Eduard Zingerman" <eddyz87@...il.com>,
 "Yonghong Song" <yonghong.song@...ux.dev>,
 "John Fastabend" <john.fastabend@...il.com>,
 "Stanislav Fomichev" <sdf@...ichev.me>, "Hao Luo" <haoluo@...gle.com>,
 "Jiri Olsa" <jolsa@...nel.org>,
 "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>,
 "Mykyta Yatsenko" <yatsenko@...a.com>,
 "Kumar Kartikeya Dwivedi" <memxor@...il.com>, bpf <bpf@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>,
 linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: add missing __printf attributes

On Tue, Feb 3, 2026, at 17:34, Alexei Starovoitov wrote:
> On Tue, Feb 3, 2026 at 8:27 AM Arnd Bergmann <arnd@...nel.org> wrote:
>>
>> From: Arnd Bergmann <arnd@...db.de>
>>
>> Some internal functions in bpf produce a warning when -Wsuggest-attribute=format
>> is passed to the compiler, e.g. in 'make W=1':
>>
>> kernel/trace/bpf_trace.c: In function '____bpf_trace_printk':
>> kernel/trace/bpf_trace.c:377:9: error: function '____bpf_trace_printk' might be a candidate for 'gnu_printf' format attribute [-Werror=suggest-attribute=format]
>>   377 |         ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt, data.bin_args);
>>       |         ^~~
>>
>> The attribute here is useless since there are no callers from C code,
>> but it helps to shut up the output anyway so we can eventually turn
>> the warning option on by default.
>>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> This was discussed and it's incorrect.

Do you have a reference to why it's incorrect?  It seems harmless
and gives me a clean kernel build in combination with a handful
of other fixes after enabling the option by default, but I assume
I'm missing something,

> Commit 7bf819aa992f ("vsnprintf: Mark binary printing functions with
> __printf() attribute") should be reverted instead.

Reverting that one would appear to introduce warnings elsewhere,
so that would not be a complete fix either.

      Arnd