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* [PATCH v1 1/1] bpf: Mark BPF printing functions with __printf() attribute
@ 2025-12-08 16:18 Andy Shevchenko
  2025-12-09  9:12 ` Alexei Starovoitov
  0 siblings, 1 reply; 5+ messages in thread
From: Andy Shevchenko @ 2025-12-08 16:18 UTC (permalink / raw)
  To: Alexei Starovoitov, bpf, linux-kernel, linux-trace-kernel
  Cc: Daniel Borkmann, John Fastabend, Andrii Nakryiko,
	Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
	KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa, Matt Bobrowski,
	Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers, Alan Maguire,
	Andy Shevchenko, kernel test robot

The printing functions in BPF code are using printf() type of format,
and compiler is not happy about them as is:

kernel/bpf/helpers.c:1069:9: error: function ‘____bpf_snprintf’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
 1069 |         err = bstr_printf(str, str_size, fmt, data.bin_args);
      |         ^~~

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);
      |         ^~~

kernel/trace/bpf_trace.c:433:9: error: function ‘____bpf_trace_vprintk’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
  433 |         ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt, data.bin_args);
      |         ^~~

kernel/trace/bpf_trace.c:475:9: error: function ‘____bpf_seq_printf’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
  475 |         seq_bprintf(m, fmt, data.bin_args);
      |         ^~~~~~~~~~~

Fix the compilation errors by adding __printf() attribute. For that
we need to pass it down to the BPF_CALL_x() and wrap into PRINTF_BPF_CALL_*()
to make code neater.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512061425.x0qTt9ww-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202512061640.9hKTnB8p-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202512081321.2h9ThWTg-lkp@intel.com/
Fixes: 10aceb629e19 ("bpf: Add bpf_trace_vprintk helper")
Fixes: 7b15523a989b ("bpf: Add a bpf_snprintf helper")
Fixes: 492e639f0c22 ("bpf: Add bpf_seq_printf and bpf_seq_write helpers")
Fixes: f3694e001238 ("bpf: add BPF_CALL_x macros for declaring helpers")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---

This is combined change and I think there is no need to split it, but if required
I can do it in a four changes. Note, the culprits are older than 4 years and stable
kernels anyway don't go that deep nowadays.

 include/linux/filter.h   | 24 +++++++++++++++---------
 kernel/bpf/helpers.c     |  2 +-
 kernel/trace/bpf_trace.c |  6 +++---
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index fd54fed8f95f..31034a74af22 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -607,9 +607,9 @@ static inline bool insn_is_cast_user(const struct bpf_insn *insn)
 	__BPF_MAP(n, __BPF_DECL_ARGS, __BPF_N, u64, __ur_1, u64, __ur_2,       \
 		  u64, __ur_3, u64, __ur_4, u64, __ur_5)
 
-#define BPF_CALL_x(x, attr, name, ...)					       \
+#define BPF_CALL_x(x, __attr, attr, name, ...)				       \
 	static __always_inline						       \
-	u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__));   \
+	__attr u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__));     \
 	typedef u64 (*btf_##name)(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__)); \
 	attr u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__));    \
 	attr u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__))     \
@@ -620,14 +620,20 @@ static inline bool insn_is_cast_user(const struct bpf_insn *insn)
 	u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__))
 
 #define __NOATTR
-#define BPF_CALL_0(name, ...)	BPF_CALL_x(0, __NOATTR, name, __VA_ARGS__)
-#define BPF_CALL_1(name, ...)	BPF_CALL_x(1, __NOATTR, name, __VA_ARGS__)
-#define BPF_CALL_2(name, ...)	BPF_CALL_x(2, __NOATTR, name, __VA_ARGS__)
-#define BPF_CALL_3(name, ...)	BPF_CALL_x(3, __NOATTR, name, __VA_ARGS__)
-#define BPF_CALL_4(name, ...)	BPF_CALL_x(4, __NOATTR, name, __VA_ARGS__)
-#define BPF_CALL_5(name, ...)	BPF_CALL_x(5, __NOATTR, name, __VA_ARGS__)
+#define BPF_CALL_0(name, ...)	BPF_CALL_x(0, __NOATTR, __NOATTR, name, __VA_ARGS__)
+#define BPF_CALL_1(name, ...)	BPF_CALL_x(1, __NOATTR, __NOATTR, name, __VA_ARGS__)
+#define BPF_CALL_2(name, ...)	BPF_CALL_x(2, __NOATTR, __NOATTR, name, __VA_ARGS__)
+#define BPF_CALL_3(name, ...)	BPF_CALL_x(3, __NOATTR, __NOATTR, name, __VA_ARGS__)
+#define BPF_CALL_4(name, ...)	BPF_CALL_x(4, __NOATTR, __NOATTR, name, __VA_ARGS__)
+#define BPF_CALL_5(name, ...)	BPF_CALL_x(5, __NOATTR, __NOATTR, name, __VA_ARGS__)
 
-#define NOTRACE_BPF_CALL_1(name, ...)	BPF_CALL_x(1, notrace, name, __VA_ARGS__)
+#define PRINTF_BPF_CALL_x(p, name, x, ...)				       \
+	BPF_CALL_x(x, __printf(p, 0), __NOATTR, name, __VA_ARGS__)
+
+#define PRINTF_BPF_CALL_4(p, name, ...)		PRINTF_BPF_CALL_x(p, name, 4, __VA_ARGS__)
+#define PRINTF_BPF_CALL_5(p, name, ...)		PRINTF_BPF_CALL_x(p, name, 5, __VA_ARGS__)
+
+#define NOTRACE_BPF_CALL_1(name, ...)	BPF_CALL_x(1, __NOATTR, notrace, name, __VA_ARGS__)
 
 #define bpf_ctx_range(TYPE, MEMBER)						\
 	offsetof(TYPE, MEMBER) ... offsetofend(TYPE, MEMBER) - 1
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index db72b96f9c8c..cbc66865e3dc 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1046,7 +1046,7 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
 	return err;
 }
 
-BPF_CALL_5(bpf_snprintf, char *, str, u32, str_size, char *, fmt,
+PRINTF_BPF_CALL_5(3, bpf_snprintf, char *, str, u32, str_size, char *, fmt,
 	   const void *, args, u32, data_len)
 {
 	struct bpf_bprintf_data data = {
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d57727abaade..5fd46b4bcf48 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -359,7 +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
 
-BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
+PRINTF_BPF_CALL_5(1, bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
 	   u64, arg2, u64, arg3)
 {
 	u64 args[MAX_TRACE_PRINTK_VARARGS] = { arg1, arg2, arg3 };
@@ -412,7 +412,7 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
 	return &bpf_trace_printk_proto;
 }
 
-BPF_CALL_4(bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, args,
+PRINTF_BPF_CALL_4(1, bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, args,
 	   u32, data_len)
 {
 	struct bpf_bprintf_data data = {
@@ -455,7 +455,7 @@ const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void)
 	return &bpf_trace_vprintk_proto;
 }
 
-BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
+PRINTF_BPF_CALL_5(2, bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
 	   const void *, args, u32, data_len)
 {
 	struct bpf_bprintf_data data = {
-- 
2.50.1


^ permalink raw reply related	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2025-12-10 13:13 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2025-12-08 16:18 [PATCH v1 1/1] bpf: Mark BPF printing functions with __printf() attribute Andy Shevchenko
2025-12-09  9:12 ` Alexei Starovoitov
2025-12-09 13:37   ` Andy Shevchenko
2025-12-10  7:09     ` Alexei Starovoitov
2025-12-10 13:13       ` Andy Shevchenko

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