Yosys doesn't support libraries, so this provides the same behavior as
%m, as some other tools have opted to do.
                                                goto unsupported_format;
                                        break;
 
+                               case 'l':
+                               case 'L':
+                                       if (got_len)
+                                               goto unsupported_format;
+                                       break;
+
                                default:
                                unsupported_format:
                                        log_file_error(filename, location.first_line, "System task `%s' called with invalid/unsupported format specifier.\n", str.c_str());
                                        sout += log_id(current_module->name);
                                        break;
 
+                               case 'l':
+                               case 'L':
+                                       sout += log_id(current_module->name);
+                                       break;
+
                                default:
                                        log_abort();
                        }