logging: fix corrupted output

Harald reported a problem in the logging:
http://lists.osmocom.org/pipermail/openbsc/2011-May/002896.html

Reverting 81e9636454294ae10ef9bc8bf149dd0248afce76 seems to
fix the problem. However, that workaround looks ugly.

Holger gives us another clue on what was wrong:
http://lists.osmocom.org/pipermail/openbsc/2011-May/002905.html

While digging in the manpage, I found this:

"The functions vprintf(), vfprintf(), vsprintf(), vsnprintf()
are equivalent to the functions printf(), fprintf(), sprintf(),
snprintf(), respectively, except that they are called with a
va_list instead of a variable number of arguments. These functions
do not call the va_end macro. Consequently, the value of ap is
undefined after the call. The application should call va_end(ap)
itself afterwards."

1 files changed, 6 insertions, 0 deletions

diff --git a/src/logging.c b/src/logging.c
index 0911010a..3c9dc03f 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -198,6 +198,7 @@ static void _logp(unsigned int subsys, int level, char *file, int line,
 	llist_for_each_entry(tar, &osmo_log_target_list, entry) {
 		struct log_category *category;
 		int output = 0;
+		va_list bp;
 
 		category = &tar->categories[subsys];
 		/* subsystem is not supposed to be logged */
@@ -224,7 +225,12 @@ static void _logp(unsigned int subsys, int level, char *file, int line,
 		if (!output)
 			continue;
 
+		/* According to the manpage, vsnprintf leaves the value of ap
+		 * in undefined state. Since _output uses vsnprintf and it may
+		 * be called several times, we have to pass a copy of ap. */
+		va_copy(bp, ap);
 		_output(tar, subsys, level, file, line, cont, format, ap);
+		va_end(bp);
 	}
 }