[PATCH bpf-next] libbpf: fix libbpf_print

[PATCH bpf-next] libbpf: fix libbpf_print

[Stanislav Fomichev]

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@google.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

Re: [PATCH bpf-next] libbpf: fix libbpf_print

[Yonghong Song]

On 2/4/19 4:20 PM, Stanislav Fomichev wrote:
> 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@google.com>

It is my mistake. My early version did passed correctly and later
on I made some changes and did not test properly. Thanks for the fix!

Acked-by: Yonghong Song <yhs@fb.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()
> 

Re: [PATCH bpf-next] libbpf: fix libbpf_print

[Alexei Starovoitov]

On Tue, Feb 05, 2019 at 12:37:29AM +0000, Yonghong Song wrote:
> 
> 
> On 2/4/19 4:20 PM, Stanislav Fomichev wrote:
> > 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@google.com>
> 
> It is my mistake. My early version did passed correctly and later
> on I made some changes and did not test properly. Thanks for the fix!
> 
> Acked-by: Yonghong Song <yhs@fb.com>

argh.
Applied. Thanks for the fix.
Yonghong, how was the earlier patch set tested?
It sounds that nothing should have worked.
How perf changes were tested?

Re: [PATCH bpf-next] libbpf: fix libbpf_print

[Yonghong Song]

On 2/4/19 5:51 PM, Alexei Starovoitov wrote:
> On Tue, Feb 05, 2019 at 12:37:29AM +0000, Yonghong Song wrote:
>>
>>
>> On 2/4/19 4:20 PM, Stanislav Fomichev wrote:
>>> 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@google.com>
>>
>> It is my mistake. My early version did passed correctly and later
>> on I made some changes and did not test properly. Thanks for the fix!
>>
>> Acked-by: Yonghong Song <yhs@fb.com>
> 
> argh.
> Applied. Thanks for the fix.
> Yonghong, how was the earlier patch set tested?

Before the global function patch set, I have a global variable version,
which I tested and worked. Later on when changing to global
libbpf_print approach, I tested it through test_btf. That is why
I found a missing check for LIBBPF_DEBUG level in default __base_pr.
But I have to admit that I probably did not pay attention to contents 
somehow so I missed the garbled output.

> It sounds that nothing should have worked.
> How perf changes were tested?

I only tested compilation. The context is similar to a few other
bpf selftests programs and I assume with similar implementation, the
result should be similar. But really badly, they are all incorrect :-(