[PATCH] selftests: kselftest: Fix debug message formatting

[PATCH] selftests: kselftest: Fix debug message formatting

[ZhuangZhuang Wang]

ksft_print_dbg_msg() passes a va_list to ksft_print_msg() as a regular
variadic argument. As a result, format specifiers consume the va_list
representation instead of the caller's arguments and print garbage.

Add a va_list-based helper and use it from both message printing
functions. Also annotate ksft_print_dbg_msg() so the compiler can check
its format arguments.

Fixes: f2662ec26b26 ("selftests: kselftest: Create ksft_print_dbg_msg()")
Signed-off-by: ZhuangZhuang Wang <wzz_123123@163.com>
---
 tools/testing/selftests/kselftest.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
index ae18c491a..d815a8667 100644
--- a/tools/testing/selftests/kselftest.h
+++ b/tools/testing/selftests/kselftest.h
@@ -173,19 +173,25 @@ static inline void ksft_print_cnts(void)
 		ksft_cnt.ksft_xskip, ksft_cnt.ksft_error);
 }
 
-static inline __printf(1, 2) void ksft_print_msg(const char *msg, ...)
+static inline void ksft_vprint_msg(const char *msg, va_list args)
 {
 	int saved_errno = errno;
-	va_list args;
 
-	va_start(args, msg);
 	printf("# ");
 	errno = saved_errno;
 	vprintf(msg, args);
+}
+
+static inline __printf(1, 2) void ksft_print_msg(const char *msg, ...)
+{
+	va_list args;
+
+	va_start(args, msg);
+	ksft_vprint_msg(msg, args);
 	va_end(args);
 }
 
-static inline void ksft_print_dbg_msg(const char *msg, ...)
+static inline __printf(1, 2) void ksft_print_dbg_msg(const char *msg, ...)
 {
 	va_list args;
 
@@ -193,7 +199,7 @@ static inline void ksft_print_dbg_msg(const char *msg, ...)
 		return;
 
 	va_start(args, msg);
-	ksft_print_msg(msg, args);
+	ksft_vprint_msg(msg, args);
 	va_end(args);
 }
 

Re: [PATCH] selftests: kselftest: Fix debug message formatting

[André Almeida]

Em 16/09/2026 16:04, ZhuangZhuang Wang escreveu:
> ksft_print_dbg_msg() passes a va_list to ksft_print_msg() as a regular
> variadic argument. As a result, format specifiers consume the va_list
> representation instead of the caller's arguments and print garbage.
> 
> Add a va_list-based helper and use it from both message printing
> functions. Also annotate ksft_print_dbg_msg() so the compiler can check
> its format arguments.
> 
> Fixes: f2662ec26b26 ("selftests: kselftest: Create ksft_print_dbg_msg()")
> Signed-off-by: ZhuangZhuang Wang <wzz_123123@163.com>

Reviewed-by: André Almeida <andrealmeid@igalia.com>

Re: [PATCH] selftests: kselftest: Fix debug message formatting

[Shuah Khan]

On 9/22/26 14:06, André Almeida wrote:
> Em 16/09/2026 16:04, ZhuangZhuang Wang escreveu:
>> ksft_print_dbg_msg() passes a va_list to ksft_print_msg() as a regular
>> variadic argument. As a result, format specifiers consume the va_list
>> representation instead of the caller's arguments and print garbage.
>>
>> Add a va_list-based helper and use it from both message printing
>> functions. Also annotate ksft_print_dbg_msg() so the compiler can check
>> its format arguments.
>>
>> Fixes: f2662ec26b26 ("selftests: kselftest: Create ksft_print_dbg_msg()")

Does it really fix this commit? I don't see that is the case. Please don't
add fixes tag unless it fixes the problem in the commit.

>> Signed-off-by: ZhuangZhuang Wang <wzz_123123@163.com>
> 
> Reviewed-by: André Almeida <andrealmeid@igalia.com>

Also can you tell me how this problem was found and what;s the output
before and after this change?

thanks,
-- Shuah