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Date:   Mon,  4 Feb 2019 16:20:55 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     netdev@...r.kernel.org
Cc:     yhs@...com, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net, Stanislav Fomichev <sdf@...gle.com>
Subject: [PATCH bpf-next] libbpf: fix libbpf_print

With the recent print rework we now have the following problem:
pr_{warning,info,debug} expand to __pr which calls libbpf_print.
libbpf_print does va_start and calls __libbpf_pr with va_list argument.
In __base_pr we again do va_start. Because the next argument is a
va_list, we don't get correct pointer to the argument (and print noting
in my case, I don't know why it doesn't crash tbh).

Fix this by changing libbpf_print_fn_t signature to accept va_list and
remove unneeded calls to va_start in the existing users.

Alternatively, this can we solved by exporting __libbpf_pr and
changing __pr macro to (and killing libbpf_print):
{
	if (__libbpf_pr)
		__libbpf_pr(level, "libbpf: " fmt, ##__VA_ARGS__)
}

Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
---
 tools/lib/bpf/libbpf.c                         | 14 ++++----------
 tools/lib/bpf/libbpf.h                         |  3 +--
 tools/perf/util/bpf-loader.c                   | 10 ++--------
 tools/testing/selftests/bpf/test_btf.c         | 13 ++-----------
 tools/testing/selftests/bpf/test_libbpf_open.c | 10 ++--------
 tools/testing/selftests/bpf/test_progs.c       | 10 ++--------
 6 files changed, 13 insertions(+), 47 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 84ca6c2bea91..47969aa0faf8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -54,22 +54,16 @@
 
 #define __printf(a, b)	__attribute__((format(printf, a, b)))
 
-__printf(2, 3)
-static int __base_pr(enum libbpf_print_level level, const char *format, ...)
+static int __base_pr(enum libbpf_print_level level, const char *format,
+		     va_list args)
 {
-	va_list args;
-	int err;
-
 	if (level == LIBBPF_DEBUG)
 		return 0;
 
-	va_start(args, format);
-	err = vfprintf(stderr, format, args);
-	va_end(args);
-	return err;
+	return vfprintf(stderr, format, args);
 }
 
-static __printf(2, 3) libbpf_print_fn_t __libbpf_pr = __base_pr;
+static libbpf_print_fn_t __libbpf_pr = __base_pr;
 
 void libbpf_set_print(libbpf_print_fn_t fn)
 {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 19dbc1bed960..69a7c25eaccc 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -54,8 +54,7 @@ enum libbpf_print_level {
 };
 
 typedef int (*libbpf_print_fn_t)(enum libbpf_print_level level,
-				 const char *, ...)
-	__attribute__((format(printf, 2, 3)));
+				 const char *, va_list ap);
 
 LIBBPF_API void libbpf_set_print(libbpf_print_fn_t fn);
 
diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 38afdbe6a9e0..037d8ff6a634 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -25,15 +25,9 @@
 #include "c++/clang-c.h"
 
 static int libbpf_perf_print(enum libbpf_print_level level __attribute__((unused)),
-			      const char *fmt, ...)
+			      const char *fmt, va_list args)
 {
-	va_list args;
-	int ret;
-
-	va_start(args, fmt);
-	ret = veprintf(1, verbose, pr_fmt(fmt), args);
-	va_end(args);
-	return ret;
+	return veprintf(1, verbose, pr_fmt(fmt), args);
 }
 
 struct bpf_prog_priv {
diff --git a/tools/testing/selftests/bpf/test_btf.c b/tools/testing/selftests/bpf/test_btf.c
index aebaeff5a5a0..5afab823ffbe 100644
--- a/tools/testing/selftests/bpf/test_btf.c
+++ b/tools/testing/selftests/bpf/test_btf.c
@@ -52,19 +52,10 @@ static int count_result(int err)
 	return err;
 }
 
-#define __printf(a, b)	__attribute__((format(printf, a, b)))
-
-__printf(2, 3)
 static int __base_pr(enum libbpf_print_level level __attribute__((unused)),
-		     const char *format, ...)
+		     const char *format, va_list args)
 {
-	va_list args;
-	int err;
-
-	va_start(args, format);
-	err = vfprintf(stderr, format, args);
-	va_end(args);
-	return err;
+	return vfprintf(stderr, format, args);
 }
 
 #define BTF_INFO_ENC(kind, kind_flag, vlen)			\
diff --git a/tools/testing/selftests/bpf/test_libbpf_open.c b/tools/testing/selftests/bpf/test_libbpf_open.c
index b9ff3bf76544..1909ecf4d999 100644
--- a/tools/testing/selftests/bpf/test_libbpf_open.c
+++ b/tools/testing/selftests/bpf/test_libbpf_open.c
@@ -36,19 +36,13 @@ static void usage(char *argv[])
 
 static bool debug = 0;
 static int libbpf_debug_print(enum libbpf_print_level level,
-			      const char *fmt, ...)
+			      const char *fmt, va_list args)
 {
-	va_list args;
-	int ret;
-
 	if (level == LIBBPF_DEBUG && !debug)
 		return 0;
 
-	va_start(args, fmt);
 	fprintf(stderr, "[%d] ", level);
-	ret = vfprintf(stderr, fmt, args);
-	va_end(args);
-	return ret;
+	return vfprintf(stderr, fmt, args);
 }
 
 #define EXIT_FAIL_LIBBPF EXIT_FAILURE
diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index 55d05102e7bf..c52bd90fbb34 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c
@@ -1785,18 +1785,12 @@ static void test_task_fd_query_tp(void)
 }
 
 static int libbpf_debug_print(enum libbpf_print_level level,
-			      const char *format, ...)
+			      const char *format, va_list args)
 {
-	va_list args;
-	int ret;
-
 	if (level == LIBBPF_DEBUG)
 		return 0;
 
-	va_start(args, format);
-	ret = vfprintf(stderr, format, args);
-	va_end(args);
-	return ret;
+	return vfprintf(stderr, format, args);
 }
 
 static void test_reference_tracking()
-- 
2.20.1.611.gfbb209baf1-goog

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