Use __attribute__((fallthrough)) rather than magic GCC comments.

GCC added an implicit-fallthrough warning a while back, where it
would complain if you had a nontrivial "case:" block that didn't end
with break, return, or something like that.  Clang recently added
the same thing.

GCC, however, would let you annotate a fall-through as intended by
any of various magic "/* fall through */" comments.  Clang, however,
only seems to like "__attribute__((fallthrough))".  Fortunately, GCC
accepts that too.

A previous commit in this branch defined a FALLTHROUGH macro to do
the right thing if GNUC is defined; here we replace all of our "fall
through" comments with uses of that macro.

This is an automated commit, made with the following perl one-liner:

  #!/usr/bin/perl -i -p
  s#/\* *falls? ?thr.*?\*/#FALLTHROUGH;#i;

src/core/or/channeltls.c

@@ -1238,7 +1238,7 @@ channel_tls_handle_var_cell(var_cell_t *var_cell, or_connection_t *conn)
       /* But that should be happening any longer've disabled bufferevents. */
       tor_assert_nonfatal_unreached_once();
 
-      /* fall through */
+      FALLTHROUGH;
     case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
       if (!(command_allowed_before_handshake(var_cell->command))) {
         log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,

src/core/or/circuitbuild.c

@@ -2106,7 +2106,7 @@ choose_good_exit_server(origin_circuit_t *circ,
       /* For these three, we want to pick the exit like a middle hop,
        * since it should be random. */
       tor_assert_nonfatal(is_internal);
-      /* Falls through */
+      FALLTHROUGH;
     case CIRCUIT_PURPOSE_C_GENERAL:
       if (is_internal) /* pick it like a middle hop */
         return router_choose_random_node(NULL, options->ExcludeNodes, flags);

src/core/or/circuitlist.c

@@ -787,7 +787,7 @@ circuit_purpose_to_controller_hs_state_string(uint8_t purpose)
              "Unrecognized circuit purpose: %d",
              (int)purpose);
       tor_fragile_assert();
-      /* fall through */
+      FALLTHROUGH;
 
     case CIRCUIT_PURPOSE_OR:
     case CIRCUIT_PURPOSE_C_GENERAL:
@@ -2738,7 +2738,7 @@ assert_cpath_layer_ok(const crypt_path_t *cp)
     {
     case CPATH_STATE_OPEN:
       relay_crypto_assert_ok(&cp->crypto);
-      /* fall through */
+      FALLTHROUGH;
     case CPATH_STATE_CLOSED:
       /*XXXX Assert that there's no handshake_state either. */
       tor_assert(!cp->rend_dh_handshake_state);

src/core/or/circuituse.c

@@ -780,7 +780,7 @@ circuit_expire_building(void)
             TO_ORIGIN_CIRCUIT(victim)->build_state->pending_final_cpath ==
             NULL)
           break;
-        /* fallthrough! */
+        FALLTHROUGH;
       case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
       case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
         /* If we have reached this line, we want to spare the circ for now. */

src/core/or/connection_edge.c

@@ -324,7 +324,7 @@ connection_edge_process_inbuf(edge_connection_t *conn, int package_partial)
       }
       /* Fall through if the connection is on a circuit without optimistic
        * data support. */
-      /* Falls through. */
+      FALLTHROUGH;
     case EXIT_CONN_STATE_CONNECTING:
     case AP_CONN_STATE_RENDDESC_WAIT:
     case AP_CONN_STATE_CIRCUIT_WAIT:

src/core/or/onion.c

@@ -509,7 +509,7 @@ create_cell_format_impl(cell_t *cell_out, const create_cell_t *cell_in,
       p += 16;
       space -= 16;
     }
-    /* Fall through */
+    FALLTHROUGH;
   case CELL_CREATE_FAST:
     tor_assert(cell_in->handshake_len <= space);
     memcpy(p, cell_in->onionskin, cell_in->handshake_len);

src/core/or/reasons.c

@@ -489,7 +489,7 @@ end_reason_to_http_connect_response_line(int endreason)
       return "HTTP/1.0 502 Bad Gateway (tor protocol violation)\r\n\r\n";
     case END_STREAM_REASON_ENTRYPOLICY:
       return "HTTP/1.0 403 Forbidden (entry policy violation)\r\n\r\n";
-    case END_STREAM_REASON_NOTDIRECTORY: /* Fall Through */
+    case END_STREAM_REASON_NOTDIRECTORY: FALLTHROUGH;
     default:
       tor_assert_nonfatal_unreached();
       return "HTTP/1.0 500 Internal Server Error (weird end reason)\r\n\r\n";

src/core/or/relay.c

@@ -866,7 +866,7 @@ connection_ap_process_end_not_open(
           break; /* break means it'll close, below */
         /* Else fall through: expire this circuit, clear the
          * chosen_exit_name field, and try again. */
-        /* Falls through. */
+        FALLTHROUGH;
       case END_STREAM_REASON_RESOLVEFAILED:
       case END_STREAM_REASON_TIMEOUT:
       case END_STREAM_REASON_MISC:

src/core/or/scheduler.c

@@ -192,7 +192,7 @@ get_scheduler_type_string(scheduler_types_t type)
   case SCHEDULER_KIST_LITE:
     return "KISTLite";
   case SCHEDULER_NONE:
-    /* fallthrough */
+    FALLTHROUGH;
   default:
     tor_assert_unreached();
     return "(N/A)";
@@ -288,7 +288,7 @@ select_scheduler(void)
       scheduler_kist_set_lite_mode();
       goto end;
     case SCHEDULER_NONE:
-      /* fallthrough */
+      FALLTHROUGH;
     default:
       /* Our option validation should have caught this. */
       tor_assert_unreached();

src/core/proto/proto_socks.c

@@ -856,7 +856,7 @@ fetch_from_buf_socks(buf_t *buf, socks_request_t *req,
       case SOCKS_RESULT_TRUNCATED:
         if (datalen == n_pullup)
           return 0;
-        /* FALLTHRU */
+        FALLTHROUGH;
       case SOCKS_RESULT_MORE_EXPECTED:
         res = 0;
         break;
@@ -962,7 +962,7 @@ parse_socks(const char *data, size_t datalen, socks_request_t *req,
       strlcpy((char*)req->reply, SOCKS_PROXY_IS_NOT_AN_HTTP_PROXY_MSG,
               MAX_SOCKS_REPLY_LEN);
       req->replylen = strlen((char*)req->reply)+1;
-      /* fall through */
+      FALLTHROUGH;
     default: /* version is not socks4 or socks5 */
       log_warn(LD_APP,
                "Socks version %d not recognized. (This port is not an "