log: handle LOG_*() before calling to log_init()

There are cases where LOG_*() functions are called before the logs
are initialized with log_init().
E.g. in transport_register() that is executed in gcc constructors,
thus called even before main().
With debug_level set to LOG_LVL_USER=-1 all the LOG_ERROR() get
dropped.
Properly initializing debug_level cause segmentation fault due to
log_output still not initialized.

Initialize debug_level to LOG_LVL_INFO so errors get printed.
Handle separately the case of log_output still NULL, meaning that
log_init() is not called yet.

Change-Id: I2ea32c87a4955fb44e79b38131c456e25dfbc327
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5602
Tested-by: jenkins

src/helper/log.c

@@ -40,7 +40,7 @@
 #endif
 #endif
 
-int debug_level = -1;
+int debug_level = LOG_LVL_INFO;
 
 static FILE *log_output;
 static struct log_callback *log_callbacks;
@@ -91,6 +91,14 @@ static void log_puts(enum log_levels level,
 	const char *string)
 {
 	char *f;
+
+	if (!log_output) {
+		/* log_init() not called yet; print on stderr */
+		fputs(string, stderr);
+		fflush(stderr);
+		return;
+	}
+
 	if (level == LOG_LVL_OUTPUT) {
 		/* do not prepend any headers, just print out what we were given and return */
 		fputs(string, log_output);
@@ -277,9 +285,6 @@ void log_init(void)
 {
 	/* set defaults for daemon configuration,
 	 * if not set by cmdline or cfgfile */
-	if (debug_level == -1)
-		debug_level = LOG_LVL_INFO;
-
 	char *debug_env = getenv("OPENOCD_DEBUG_LEVEL");
 	if (NULL != debug_env) {
 		int value;