rtos: add debug prints for qSymbol lookup

- Added two debug prints that allow to inspect the symbol
  lookup process (carried out via the qSymbol packets).

- Added a check for an edge situation when the debugger
  would send us different symbol than what we asked for
  (avoids NULL dereference).

Change-Id: I84ae1b2b66473eab76a7966c678d2777b6ef48d6
Signed-off-by: Jan Matyas <matyas@codasip.com>
Reviewed-on: http://openocd.zylin.com/6287
Tested-by: jenkins
Reviewed-by: Tim Newsome <tim@sifive.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/rtos/rtos.c

@@ -266,8 +266,17 @@ int rtos_qsymbol(struct connection *connection, char const *packet, int packet_s
 			cur_sym[0] = '\x00';
 		}
 	}
+
+	LOG_DEBUG("RTOS: Address of symbol '%s' is 0x%" PRIx64, cur_sym, addr);
+
 	next_sym = next_symbol(os, cur_sym, addr);
 
+	/* Should never happen unless the debugger misbehaves */
+	if (next_sym == NULL) {
+		LOG_WARNING("RTOS: Debugger sent us qSymbol with '%s' that we did not ask for", cur_sym);
+		goto done;
+	}
+
 	if (!next_sym->symbol_name) {
 		/* No more symbols need looking up */
 
@@ -291,6 +300,8 @@ int rtos_qsymbol(struct connection *connection, char const *packet, int packet_s
 		goto done;
 	}
 
+	LOG_DEBUG("RTOS: Requesting symbol lookup of '%s' from the debugger", next_sym->symbol_name);
+
 	reply_len = snprintf(reply, sizeof(reply), "qSymbol:");
 	reply_len += hexify(reply + reply_len,
 		(const uint8_t *)next_sym->symbol_name, strlen(next_sym->symbol_name),