linux-kernel - Re: [PATCH v1 1/1] bpf: Disable -Wsuggest-attribute=format

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Message-ID: <20251215171832.2b0b24d5@gandalf.local.home>
Date: Mon, 15 Dec 2025 17:18:32 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>, Andy Shevchenko
 <andriy.shevchenko@...ux.intel.com>, Alexei Starovoitov <ast@...nel.org>,
 bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, Daniel Borkmann
 <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai
 Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
 <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend
 <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, kernel test robot
 <lkp@...el.com>
Subject: Re: [PATCH v1 1/1] bpf: Disable -Wsuggest-attribute=format

On Mon, 15 Dec 2025 10:40:16 -0800
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> > But I think instead of Makefile changes we should fix the root cause
> > here. And that seems to be just wrong __printf annotations for
> > seq_bprintf and bstr_printf. They are not printf-like, they should not
> > be marked as such, and then the compiler won't be wrongly suggesting
> > bpf_stream_vprintk_impl (and others that make use of either
> > bstr_printf or seq_bprintf) to be marked with __printf.  
> 
> yeah. commit 7bf819aa992f ("vsnprintf: Mark binary printing functions
> with __printf() attribute")
> should be reverted,
> but that somebody else problem and the revert would need to silence
> that incorrect warning in lib/vsprintf.c too.

From what I understand, the __printf(X, 0) simply quiets the warning, which
is why those two are:

__printf(3, 0) int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);
__printf(3, 0) int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf);

Hence, it's not a big deal to have that. Actually, it does document that
the printf format is different than a normal printf, and that the arguments
are not the same as a normal printf.

I complained about this at first too (and never gave an acked-by), but
because it does quiet a warning, I also didn't nack it.

-- Steve