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

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Message-Id: <20260203162746.2337002-1-arnd@kernel.org>
Date: Tue,  3 Feb 2026 17:27:08 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: 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>
Cc: Arnd Bergmann <arnd@...db.de>,
	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@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH] bpf: add missing __printf attributes

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>
---
 kernel/bpf/helpers.c     | 1 +
 kernel/bpf/stream.c      | 1 +
 kernel/trace/bpf_trace.c | 3 +++
 3 files changed, 5 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b54ec0e945aa..45d026fc4e8a 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1046,6 +1046,7 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
 	return err;
 }
 
+__printf(3, 0)
 BPF_CALL_5(bpf_snprintf, char *, str, u32, str_size, char *, fmt,
 	   const void *, args, u32, data_len)
 {
diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
index 24730df55e69..816fd7fba3d2 100644
--- a/kernel/bpf/stream.c
+++ b/kernel/bpf/stream.c
@@ -212,6 +212,7 @@ __bpf_kfunc_start_defs();
  * Avoid using enum bpf_stream_id so that kfunc users don't have to pull in the
  * enum in headers.
  */
+__printf(2, 0)
 __bpf_kfunc int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,
 				   u32 len__sz, struct bpf_prog_aux *aux)
 {
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index eadaef8592a3..2d3de71ab86a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -359,6 +359,7 @@ static const struct bpf_func_proto bpf_probe_write_user_proto = {
 #define MAX_TRACE_PRINTK_VARARGS	3
 #define BPF_TRACE_PRINTK_SIZE		1024
 
+__printf(1, 0)
 BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
 	   u64, arg2, u64, arg3)
 {
@@ -412,6 +413,7 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
 	return &bpf_trace_printk_proto;
 }
 
+__printf(1, 0)
 BPF_CALL_4(bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, args,
 	   u32, data_len)
 {
@@ -455,6 +457,7 @@ const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void)
 	return &bpf_trace_vprintk_proto;
 }
 
+__printf(2, 0)
 BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
 	   const void *, args, u32, data_len)
 {
-- 
2.39.5