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."

diff --git a/src/logging.c b/src/logging.c
index 0911010..3c9dc03 100644 (file)
--- 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);
        }
 }