Lift the type restrictions on seq_trace token labels

OTP-14899

14 files changed, 203 insertions, 77 deletions

diff --git a/erts/emulator/beam/dist.c b/erts/emulator/beam/dist.c
index fdf307da1b..f203d85ca9 100644
--- a/erts/emulator/beam/dist.c
+++ b/erts/emulator/beam/dist.c
@@ -937,6 +937,24 @@ erts_dsig_send_demonitor(ErtsDSigData *dsdp, Eterm watcher,
     return res;
 }
 
+static int can_send_seqtrace_token(ErtsSendContext* ctx, Eterm token) {
+    Eterm label;
+
+    if (ctx->dep->flags & DFLAG_BIG_SEQTRACE_LABELS) {
+        /* The other end is capable of handling arbitrary seq_trace labels. */
+        return 1;
+    }
+
+    /* The other end only tolerates smalls, but since we could potentially be
+     * talking to an old 32-bit emulator from a 64-bit one, we have to check
+     * whether the label is small on any emulator. */
+    label = SEQ_TRACE_T_LABEL(token);
+
+    return is_small(label) &&
+        signed_val(label) <= (ERTS_SINT32_MAX >> _TAG_IMMED1_SIZE) &&
+        signed_val(label) >= (ERTS_SINT32_MIN >> _TAG_IMMED1_SIZE);
+}
+
 int
 erts_dsig_send_msg(Eterm remote, Eterm message, ErtsSendContext* ctx)
 {
@@ -970,37 +988,38 @@ erts_dsig_send_msg(Eterm remote, Eterm message, ErtsSendContext* ctx)
                       "%T", remote);
         msize = size_object(message);
         if (have_seqtrace(token)) {
-            tok_label = signed_val(SEQ_TRACE_T_LABEL(token));
+            tok_label = SEQ_TRACE_T_DTRACE_LABEL(token);
             tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token));
             tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token));
         }
     }
 #endif
 
-    if (token != NIL) {
-        Eterm el1, el2;
-        if (ctx->dep->flags & DFLAG_SEND_SENDER) {
-            el1 = make_small(DOP_SEND_SENDER_TT);
-            el2 = sender->common.id;
-        }
-        else {
-            el1 = make_small(DOP_SEND_TT);
-            el2 = am_Empty;
-        }
-	ctl = TUPLE4(&ctx->ctl_heap[0], el1, el2, remote, token);
-    }
-    else {
-        Eterm el1, el2;
+    {
+        Eterm dist_op, sender_id;
+        int send_token;
+
+        send_token = (token != NIL && can_send_seqtrace_token(ctx, token));
+
         if (ctx->dep->flags & DFLAG_SEND_SENDER) {
-            el1 = make_small(DOP_SEND_SENDER);
-            el2 = sender->common.id;
+            dist_op = make_small(send_token ?
+                                 DOP_SEND_SENDER_TT :
+                                 DOP_SEND_SENDER);
+            sender_id = sender->common.id;
+        } else {
+            dist_op = make_small(send_token ?
+                                 DOP_SEND_TT :
+                                 DOP_SEND);
+            sender_id = am_Empty;
         }
-        else {
-            el1 = make_small(DOP_SEND);
-            el2 = am_Empty;
+
+        if (send_token) {
+            ctl = TUPLE4(&ctx->ctl_heap[0], dist_op, sender_id, remote, token);
+        } else {
+            ctl = TUPLE3(&ctx->ctl_heap[0], dist_op, sender_id, remote);
         }
-	ctl = TUPLE3(&ctx->ctl_heap[0], el1, el2, remote);
     }
+
     DTRACE6(message_send, sender_name, receiver_name,
             msize, tok_label, tok_lastcnt, tok_serial);
     DTRACE7(message_send_remote, sender_name, node_name, receiver_name,
@@ -1046,19 +1065,20 @@ erts_dsig_send_reg_msg(Eterm remote_name, Eterm message,
                       "{%T,%s}", remote_name, node_name);
         msize = size_object(message);
         if (have_seqtrace(token)) {
-            tok_label = signed_val(SEQ_TRACE_T_LABEL(token));
+            tok_label = SEQ_TRACE_T_DTRACE_LABEL(token);
             tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token));
             tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token));
         }
     }
 #endif
 
-    if (token != NIL)
+    if (token != NIL && can_send_seqtrace_token(ctx, token))
 	ctl = TUPLE5(&ctx->ctl_heap[0], make_small(DOP_REG_SEND_TT),
 		     sender->common.id, am_Empty, remote_name, token);
     else
 	ctl = TUPLE4(&ctx->ctl_heap[0], make_small(DOP_REG_SEND),
 		     sender->common.id, am_Empty, remote_name);
+
     DTRACE6(message_send, sender_name, receiver_name,
             msize, tok_label, tok_lastcnt, tok_serial);
     DTRACE7(message_send_remote, sender_name, node_name, receiver_name,
@@ -1110,7 +1130,7 @@ erts_dsig_send_exit_tt(ErtsDSigData *dsdp, Eterm local, Eterm remote,
         erts_snprintf(reason_str, sizeof(DTRACE_CHARBUF_NAME(reason_str)),
                       "%T", reason);
         if (have_seqtrace(token)) {
-            tok_label = signed_val(SEQ_TRACE_T_LABEL(token));
+            tok_label = SEQ_TRACE_T_DTRACE_LABEL(token);
             tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token));
             tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token));
         }
diff --git a/erts/emulator/beam/dist.h b/erts/emulator/beam/dist.h
index c608fef816..dda2029a4c 100644
--- a/erts/emulator/beam/dist.h
+++ b/erts/emulator/beam/dist.h
@@ -45,7 +45,8 @@
 #define DFLAG_MAP_TAG             0x20000
 #define DFLAG_BIG_CREATION        0x40000
 #define DFLAG_SEND_SENDER         0x80000
-#define DFLAG_NO_MAGIC            0x100000 /* internal for pending connection */
+#define DFLAG_BIG_SEQTRACE_LABELS 0x100000
+#define DFLAG_NO_MAGIC            0x200000 /* internal for pending connection */
 
 /* Mandatory flags for distribution */
 #define DFLAG_DIST_MANDATORY (DFLAG_EXTENDED_REFERENCES         \
@@ -73,7 +74,8 @@
                             | DFLAG_UTF8_ATOMS                \
                             | DFLAG_MAP_TAG                   \
                             | DFLAG_BIG_CREATION              \
-                            | DFLAG_SEND_SENDER)
+                            | DFLAG_SEND_SENDER               \
+                            | DFLAG_BIG_SEQTRACE_LABELS)
 
 /* Flags addable by local distr implementations */
 #define DFLAG_DIST_ADDABLE    DFLAG_DIST_DEFAULT
diff --git a/erts/emulator/beam/erl_bif_trace.c b/erts/emulator/beam/erl_bif_trace.c
index a076f0bf54..1953f79d79 100644
--- a/erts/emulator/beam/erl_bif_trace.c
+++ b/erts/emulator/beam/erl_bif_trace.c
@@ -1807,9 +1807,6 @@ Eterm erts_seq_trace(Process *p, Eterm arg1, Eterm arg2,
 	return old_value;
     }
     else if (arg1 == am_label) {
-	if (! is_small(arg2)) {
-	    return THE_NON_VALUE;
-	}
         new_seq_trace_token(p);
 	if (build_result) {
 	    old_value = SEQ_TRACE_TOKEN_LABEL(p);
diff --git a/erts/emulator/beam/erl_db_util.c b/erts/emulator/beam/erl_db_util.c
index 1e8e9e5e94..3836f28aa4 100644
--- a/erts/emulator/beam/erl_db_util.c
+++ b/erts/emulator/beam/erl_db_util.c
@@ -2508,25 +2508,20 @@ restart:
             if (have_no_seqtrace(SEQ_TRACE_TOKEN(c_p)))
 		*esp++ = NIL;
 	    else {
-		Eterm sender = SEQ_TRACE_TOKEN_SENDER(c_p);
-		Uint sender_sz = is_immed(sender) ? 0 : size_object(sender);
-		ehp = HAllocX(build_proc, 6 + sender_sz, HEAP_XTRA);
-		if (sender_sz) {
-		    sender = copy_struct(sender, sender_sz, &ehp, &MSO(build_proc));
-		}
- 		*esp++ = make_tuple(ehp);
- 		ehp[0] = make_arityval(5);
- 		ehp[1] = SEQ_TRACE_TOKEN_FLAGS(c_p);
- 		ehp[2] = SEQ_TRACE_TOKEN_LABEL(c_p);
- 		ehp[3] = SEQ_TRACE_TOKEN_SERIAL(c_p);
-		ehp[4] = sender;
- 		ehp[5] = SEQ_TRACE_TOKEN_LASTCNT(c_p);
-		ASSERT(SEQ_TRACE_TOKEN_ARITY(c_p) == 5);
-		ASSERT(is_immed(ehp[1]));
-		ASSERT(is_immed(ehp[2]));
-		ASSERT(is_immed(ehp[3]));
-		ASSERT(is_immed(ehp[5]));
-	    } 
+                Eterm token;
+                Uint token_sz;
+
+                ASSERT(SEQ_TRACE_TOKEN_ARITY(c_p) == 5);
+                ASSERT(is_immed(SEQ_TRACE_TOKEN_FLAGS(c_p)));
+                ASSERT(is_immed(SEQ_TRACE_TOKEN_SERIAL(c_p)));
+                ASSERT(is_immed(SEQ_TRACE_TOKEN_LASTCNT(c_p)));
+
+                token = SEQ_TRACE_TOKEN(c_p);
+                token_sz = size_object(token);
+
+                ehp = HAllocX(build_proc, token_sz, HEAP_XTRA);
+                *esp++ = copy_struct(token, token_sz, &ehp, &MSO(build_proc));
+	    }
 	    break;
         case matchEnableTrace:
             ASSERT(c_p == self);
diff --git a/erts/emulator/beam/erl_message.c b/erts/emulator/beam/erl_message.c
index ed7a9d37c2..0565e01f06 100644
--- a/erts/emulator/beam/erl_message.c
+++ b/erts/emulator/beam/erl_message.c
@@ -315,7 +315,7 @@ erts_queue_dist_message(Process *rcvr,
 
             dtrace_proc_str(rcvr, receiver_name);
             if (have_seqtrace(token)) {
-                tok_label = signed_val(SEQ_TRACE_T_LABEL(token));
+                tok_label = SEQ_TRACE_T_DTRACE_LABEL(token);
                 tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token));
                 tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token));
             }
@@ -640,7 +640,8 @@ erts_send_message(Process* sender,
 	    seq_trace_update_send(sender);
 	    seq_trace_output(stoken, message, SEQ_TRACE_SEND,
 			     receiver->common.id, sender);
-	    seq_trace_size = 6; /* TUPLE5 */
+
+	    seq_trace_size = size_object(stoken);
 	}
 #ifdef USE_VM_PROBES
         if (DT_UTAG_FLAGS(sender) & DT_UTAG_SPREADING) {
@@ -689,7 +690,7 @@ erts_send_message(Process* sender,
 	}
         if (DTRACE_ENABLED(message_send)) {
             if (have_seqtrace(stoken)) {
-		tok_label = signed_val(SEQ_TRACE_T_LABEL(stoken));
+                tok_label = SEQ_TRACE_T_DTRACE_LABEL(stoken);
 		tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(stoken));
 		tok_serial = signed_val(SEQ_TRACE_T_SERIAL(stoken));
 	    }
diff --git a/erts/emulator/beam/erl_proc_sig_queue.c b/erts/emulator/beam/erl_proc_sig_queue.c
index 1b5cbb1919..f07bd32723 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.c
+++ b/erts/emulator/beam/erl_proc_sig_queue.c
@@ -3069,7 +3069,7 @@ handle_message_enqueued_tracing(Process *c_p,
         Eterm seq_trace_token = ERL_MESSAGE_TOKEN(msg);
 
         if (seq_trace_token != NIL && is_tuple(seq_trace_token)) {
-            tok_label = signed_val(SEQ_TRACE_T_LABEL(seq_trace_token));
+            tok_label = SEQ_TRACE_T_DTRACE_LABEL(seq_trace_token);
             tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(seq_trace_token));
             tok_serial = signed_val(SEQ_TRACE_T_SERIAL(seq_trace_token));
         }
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index 0550fb05b5..256b8b7d16 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -1250,7 +1250,24 @@ void erts_check_for_holes(Process* p);
 #define SEQ_TRACE_T_SENDER(token)   (*(tuple_val(token) + 4))
 #define SEQ_TRACE_T_LASTCNT(token)  (*(tuple_val(token) + 5))
 
+#ifdef USE_VM_PROBES
+/* The dtrace probe for seq_trace only supports 'int' labels, so we represent
+ * all values that won't fit into a 32-bit signed integer as ERTS_SINT32_MIN
+ * (bigints, tuples, etc). */
+
+#define SEQ_TRACE_T_DTRACE_LABEL(token) \
+    DTRACE_SEQ_TRACE_LABEL__(SEQ_TRACE_T_LABEL(token))
+
+#define DTRACE_SEQ_TRACE_LABEL__(label_term) \
+    (is_small((label_term)) ? \
+        ((signed_val((label_term)) <= ERTS_SINT32_MAX && \
+          signed_val((label_term)) >= ERTS_SINT32_MIN) ? \
+             signed_val((label_term)) : ERTS_SINT32_MIN) \
+        : ERTS_SINT32_MIN)
+#endif
+
 /*
+
  * Possible flags for the flags field in ErlSpawnOpts below.
  */
 
diff --git a/erts/emulator/beam/erlang_dtrace.d b/erts/emulator/beam/erlang_dtrace.d
index d0b10e0306..c47a37eb62 100644
--- a/erts/emulator/beam/erlang_dtrace.d
+++ b/erts/emulator/beam/erlang_dtrace.d
@@ -55,7 +55,8 @@ provider erlang {
      * @param sender the PID (string form) of the sender
      * @param receiver the PID (string form) of the receiver
      * @param size the size of the message being delivered (words)
-     * @param token_label for the sender's sequential trace token
+     * @param token_label for the sender's sequential trace token. This will be
+     *        INT_MIN if the label does not fit into a 32-bit integer.
      * @param token_previous count for the sender's sequential trace token
      * @param token_current count for the sender's sequential trace token
      */
@@ -73,7 +74,8 @@ provider erlang {
      * @param node_name the Erlang node name (string form) of the receiver
      * @param receiver the PID/name (string form) of the receiver
      * @param size the size of the message being delivered (words)
-     * @param token_label for the sender's sequential trace token
+     * @param token_label for the sender's sequential trace token. This will be
+     *        INT_MIN if the label does not fit into a 32-bit integer.
      * @param token_previous count for the sender's sequential trace token
      * @param token_current count for the sender's sequential trace token
      */
@@ -98,7 +100,8 @@ provider erlang {
      * @param receiver the PID (string form) of the receiver
      * @param size the size of the message being delivered (words)
      * @param queue_len length of the queue of the receiving process
-     * @param token_label for the sender's sequential trace token
+     * @param token_label for the sender's sequential trace token. This will be
+     *        INT_MIN if the label does not fit into a 32-bit integer.
      * @param token_previous count for the sender's sequential trace token
      * @param token_current count for the sender's sequential trace token
      */
@@ -122,7 +125,8 @@ provider erlang {
      * @param receiver the PID (string form) of the receiver
      * @param size the size of the message being delivered (words)
      * @param queue_len length of the queue of the receiving process
-     * @param token_label for the sender's sequential trace token
+     * @param token_label for the sender's sequential trace token. This will be
+     *        INT_MIN if the label does not fit into a 32-bit integer.
      * @param token_previous count for the sender's sequential trace token
      * @param token_current count for the sender's sequential trace token
      */
@@ -273,7 +277,8 @@ provider erlang {
      * @param node_name the Erlang node name (string form) of the receiver
      * @param receiver the PID (string form) of the process receiving EXIT signal
      * @param reason the reason for the exit (may be truncated)
-     * @param token_label for the sender's sequential trace token
+     * @param token_label for the sender's sequential trace token. This will be
+     *        INT_MIN if the label does not fit into a 32-bit integer.
      * @param token_previous count for the sender's sequential trace token
      * @param token_current count for the sender's sequential trace token
      */
diff --git a/erts/emulator/beam/msg_instrs.tab b/erts/emulator/beam/msg_instrs.tab
index 88d2ef9fa3..58cad9c666 100644
--- a/erts/emulator/beam/msg_instrs.tab
+++ b/erts/emulator/beam/msg_instrs.tab
@@ -229,7 +229,7 @@ remove_message() {
         dtrace_proc_str(c_p, receiver_name);
         token2 = SEQ_TRACE_TOKEN(c_p);
         if (have_seqtrace(token2)) {
-            tok_label = signed_val(SEQ_TRACE_T_LABEL(token2));
+            tok_label = SEQ_TRACE_T_DTRACE_LABEL(token2);
             tok_lastcnt = signed_val(SEQ_TRACE_T_LASTCNT(token2));
             tok_serial = signed_val(SEQ_TRACE_T_SERIAL(token2));
         }
diff --git a/lib/kernel/doc/src/seq_trace.xml b/lib/kernel/doc/src/seq_trace.xml
index 197851021f..69eb12a8a0 100644
--- a/lib/kernel/doc/src/seq_trace.xml
+++ b/lib/kernel/doc/src/seq_trace.xml
@@ -80,13 +80,18 @@ seq_trace:set_token(OldToken), % activate the trace token again
         <p>Sets the individual <c><anno>Component</anno></c> of the trace token to
           <c><anno>Val</anno></c>. Returns the previous value of the component.</p>
         <taglist>
-          <tag><c>set_token(label, <anno>Integer</anno>)</c></tag>
+          <tag><c>set_token(label, <anno>Label</anno>)</c></tag>
           <item>
-            <p>The <c>label</c> component is an integer which
+            <p>The <c>label</c> component is a term which
               identifies all events belonging to the same sequential
               trace. If several sequential traces can be active
               simultaneously, <c>label</c> is used to identify
               the separate traces. Default is 0.</p>
+            <warning>
+              <p>Labels were restricted to small signed integers (28 bits)
+                prior to OTP 21. The trace token will be silenty dropped if it
+                crosses over to a node that does not support the label.</p>
+            </warning>
           </item>
           <tag><c>set_token(serial, SerialValue)</c></tag>
           <item>
diff --git a/lib/kernel/include/dist.hrl b/lib/kernel/include/dist.hrl
index b7c35712a6..6baaa35d72 100644
--- a/lib/kernel/include/dist.hrl
+++ b/lib/kernel/include/dist.hrl
@@ -41,6 +41,7 @@
 -define(DFLAG_MAP_TAG, 16#20000).
 -define(DFLAG_BIG_CREATION, 16#40000).
 -define(DFLAG_SEND_SENDER, 16#80000).
+-define(DFLAG_BIG_SEQTRACE_LABELS, 16#100000).
 
 %% Also update dflag2str() in ../src/dist_util.erl
 %% when adding flags...
diff --git a/lib/kernel/src/dist_util.erl b/lib/kernel/src/dist_util.erl
index f7a84c14b4..781397e1ee 100644
--- a/lib/kernel/src/dist_util.erl
+++ b/lib/kernel/src/dist_util.erl
@@ -113,6 +113,8 @@ dflag2str(?DFLAG_BIG_CREATION) ->
     "BIG_CREATION";
 dflag2str(?DFLAG_SEND_SENDER) ->
     "SEND_SENDER";
+dflag2str(?DFLAG_BIG_SEQTRACE_LABELS) ->
+    "BIG_SEQTRACE_LABELS";
 dflag2str(_) ->
     "UNKNOWN".
 
diff --git a/lib/kernel/src/seq_trace.erl b/lib/kernel/src/seq_trace.erl
index cc0c10909b..8d7aba0f27 100644
--- a/lib/kernel/src/seq_trace.erl
+++ b/lib/kernel/src/seq_trace.erl
@@ -41,7 +41,7 @@
 
 -type flag()       :: 'send' | 'receive' | 'print' | 'timestamp' | 'monotonic_timestamp' | 'strict_monotonic_timestamp'.
 -type component()  :: 'label' | 'serial' | flag().
--type value()      :: (Integer :: non_neg_integer())
+-type value()      :: (Label :: term())
                     | {Previous :: non_neg_integer(),
                        Current :: non_neg_integer()}
                     | (Bool :: boolean()).
@@ -59,10 +59,6 @@ set_token({Flags,Label,Serial,_From,Lastcnt}) ->
     F = decode_flags(Flags),
     set_token2([{label,Label},{serial,{Lastcnt, Serial}} | F]).
 
-%% We limit the label type to always be a small integer because erl_interface
-%% expects that, the BIF can however "unofficially" handle atoms as well, and
-%% atoms can be used if only Erlang nodes are involved
-
 -spec set_token(Component, Val) -> {Component, OldVal} when
       Component :: component(),
       Val :: value(),
diff --git a/lib/kernel/test/seq_trace_SUITE.erl b/lib/kernel/test/seq_trace_SUITE.erl
index be23a1933f..aae8a83304 100644
--- a/lib/kernel/test/seq_trace_SUITE.erl
+++ b/lib/kernel/test/seq_trace_SUITE.erl
@@ -25,7 +25,7 @@
 -export([token_set_get/1, tracer_set_get/1, print/1,
 	 send/1, distributed_send/1, recv/1, distributed_recv/1,
 	 trace_exit/1, distributed_exit/1, call/1, port/1,
-	 match_set_seq_token/1, gc_seq_token/1]).
+	 match_set_seq_token/1, gc_seq_token/1, label_capability_mismatch/1]).
 
 %% internal exports
 -export([simple_tracer/2, one_time_receiver/0, one_time_receiver/1,
@@ -47,7 +47,7 @@ all() ->
     [token_set_get, tracer_set_get, print, send,
      distributed_send, recv, distributed_recv, trace_exit,
      distributed_exit, call, port, match_set_seq_token,
-     gc_seq_token].
+     gc_seq_token, label_capability_mismatch].
 
 groups() -> 
     [].
@@ -90,8 +90,8 @@ do_token_set_get(TsType) ->
     %% Test that initial seq_trace is disabled
     [] = seq_trace:get_token(),
     %% Test setting and reading the different fields
-    0 = seq_trace:set_token(label,17),
-    {label,17} = seq_trace:get_token(label),
+    0 = seq_trace:set_token(label,{my_label,1}),
+    {label,{my_label,1}} = seq_trace:get_token(label),
     false = seq_trace:set_token(print,true),
     {print,true} = seq_trace:get_token(print),
     false = seq_trace:set_token(send,true),
@@ -101,12 +101,12 @@ do_token_set_get(TsType) ->
     false = seq_trace:set_token(TsType,true),
     {TsType,true} = seq_trace:get_token(TsType),
     %% Check the whole token
-    {Flags,17,0,Self,0} = seq_trace:get_token(), % all flags are set
+    {Flags,{my_label,1},0,Self,0} = seq_trace:get_token(), % all flags are set
     %% Test setting and reading the 'serial' field
     {0,0} = seq_trace:set_token(serial,{3,5}),
     {serial,{3,5}} = seq_trace:get_token(serial),
     %% Check the whole token, test that a whole token can be set and get
-    {Flags,17,5,Self,3} = seq_trace:get_token(),
+    {Flags,{my_label,1},5,Self,3} = seq_trace:get_token(),
     seq_trace:set_token({Flags,19,7,Self,5}),
     {Flags,19,7,Self,5} = seq_trace:get_token(),
     %% Check that receive timeout does not reset token
@@ -166,11 +166,13 @@ do_send(TsType) ->
     seq_trace:reset_trace(),
     start_tracer(),
     Receiver = spawn(?MODULE,one_time_receiver,[]),
+    Label = make_ref(),
+    seq_trace:set_token(label,Label),
     set_token_flags([send, TsType]),
     Receiver ! send,
     Self = self(),
     seq_trace:reset_trace(),
-    [{0,{send,_,Self,Receiver,send}, Ts}] = stop_tracer(1),
+    [{Label,{send,_,Self,Receiver,send}, Ts}] = stop_tracer(1),
     check_ts(TsType, Ts).
 
 distributed_send(Config) when is_list(Config) ->
@@ -184,14 +186,19 @@ do_distributed_send(TsType) ->
     seq_trace:reset_trace(),
     start_tracer(),
     Receiver = spawn(Node,?MODULE,one_time_receiver,[]),
+
+    %% Make sure complex labels survive the trip.
+    Label = make_ref(),
+    seq_trace:set_token(label,Label),
     set_token_flags([send,TsType]),
+
     Receiver ! send,
     Self = self(),
     seq_trace:reset_trace(),
     stop_node(Node),
-    [{0,{send,_,Self,Receiver,send}, Ts}] = stop_tracer(1),
+    [{Label,{send,_,Self,Receiver,send}, Ts}] = stop_tracer(1),
     check_ts(TsType, Ts).
-    
+
 
 recv(Config) when is_list(Config) ->
     lists:foreach(fun do_recv/1, ?TIMESTAMP_MODES).
@@ -220,7 +227,12 @@ do_distributed_recv(TsType) ->
     seq_trace:reset_trace(),
     rpc:call(Node,?MODULE,start_tracer,[]),
     Receiver = spawn(Node,?MODULE,one_time_receiver,[]),
+
+    %% Make sure complex labels survive the trip.
+    Label = make_ref(),
+    seq_trace:set_token(label,Label),
     set_token_flags(['receive',TsType]),
+
     Receiver ! 'receive',
     %% let the other process receive the message:
     receive after 1 -> ok end,
@@ -229,7 +241,7 @@ do_distributed_recv(TsType) ->
     Result = rpc:call(Node,?MODULE,stop_tracer,[1]),
     stop_node(Node),
     ok = io:format("~p~n",[Result]),
-    [{0,{'receive',_,Self,Receiver,'receive'}, Ts}] = Result,
+    [{Label,{'receive',_,Self,Receiver,'receive'}, Ts}] = Result,
     check_ts(TsType, Ts).
 
 trace_exit(Config) when is_list(Config) ->
@@ -240,7 +252,12 @@ do_trace_exit(TsType) ->
     start_tracer(),
     Receiver = spawn_link(?MODULE, one_time_receiver, [exit]),
     process_flag(trap_exit, true),
+
+    %% Make sure complex labels survive the trip.
+    Label = make_ref(),
+    seq_trace:set_token(label,Label),
     set_token_flags([send, TsType]),
+
     Receiver ! {before, exit},
     %% let the other process receive the message:
     receive
@@ -254,8 +271,8 @@ do_trace_exit(TsType) ->
     Result = stop_tracer(2),
     seq_trace:reset_trace(),
     ok = io:format("~p~n", [Result]),
-    [{0, {send, {0,1}, Self, Receiver, {before, exit}}, Ts0},
-	   {0, {send, {1,2}, Receiver, Self,
+    [{Label, {send, {0,1}, Self, Receiver, {before, exit}}, Ts0},
+	   {Label, {send, {1,2}, Receiver, Self,
 	       {'EXIT', Receiver, {exit, {before, exit}}}}, Ts1}] = Result,
     check_ts(TsType, Ts0),
     check_ts(TsType, Ts1).
@@ -291,6 +308,74 @@ do_distributed_exit(TsType) ->
 		{'EXIT', Receiver, {exit, {before, exit}}}}, Ts}] = Result,
     check_ts(TsType, Ts).
 
+label_capability_mismatch(Config) when is_list(Config) ->
+    Releases = ["20_latest"],
+    Available = [Rel || Rel <- Releases, test_server:is_release_available(Rel)],
+    case Available of
+        [] -> {skipped, "No incompatible releases available"};
+        _ ->
+            lists:foreach(fun do_incompatible_labels/1, Available),
+            lists:foreach(fun do_compatible_labels/1, Available),
+            ok
+    end.
+
+do_incompatible_labels(Rel) ->
+    Cookie = atom_to_list(erlang:get_cookie()),
+    {ok, Node} = test_server:start_node(
+        list_to_atom(atom_to_list(?MODULE)++"_"++Rel), peer,
+        [{args, " -setcookie "++Cookie}, {erl, [{release, Rel}]}]),
+
+    {_,Dir} = code:is_loaded(?MODULE),
+    Mdir = filename:dirname(Dir),
+    true = rpc:call(Node,code,add_patha,[Mdir]),
+    seq_trace:reset_trace(),
+    rpc:call(Node,?MODULE,start_tracer,[]),
+    Receiver = spawn(Node,?MODULE,one_time_receiver,[]),
+
+    %% This node does not support arbitrary labels, so it must fail with a
+    %% timeout as the token is dropped silently.
+    seq_trace:set_token(label,make_ref()),
+    seq_trace:set_token('receive',true),
+
+    Receiver ! 'receive',
+    %% let the other process receive the message:
+    receive after 10 -> ok end,
+    seq_trace:reset_trace(),
+
+    {error,timeout} = rpc:call(Node,?MODULE,stop_tracer,[1]),
+    stop_node(Node),
+    ok.
+
+do_compatible_labels(Rel) ->
+    Cookie = atom_to_list(erlang:get_cookie()),
+    {ok, Node} = test_server:start_node(
+        list_to_atom(atom_to_list(?MODULE)++"_"++Rel), peer,
+        [{args, " -setcookie "++Cookie}, {erl, [{release, Rel}]}]),
+
+    {_,Dir} = code:is_loaded(?MODULE),
+    Mdir = filename:dirname(Dir),
+    true = rpc:call(Node,code,add_patha,[Mdir]),
+    seq_trace:reset_trace(),
+    rpc:call(Node,?MODULE,start_tracer,[]),
+    Receiver = spawn(Node,?MODULE,one_time_receiver,[]),
+
+    %% This node does not support arbitrary labels, but small integers should
+    %% still work.
+    Label = 1234,
+    seq_trace:set_token(label,Label),
+    seq_trace:set_token('receive',true),
+
+    Receiver ! 'receive',
+    %% let the other process receive the message:
+    receive after 10 -> ok end,
+    Self = self(),
+    seq_trace:reset_trace(),
+    Result = rpc:call(Node,?MODULE,stop_tracer,[1]),
+    stop_node(Node),
+    ok = io:format("~p~n",[Result]),
+    [{Label,{'receive',_,Self,Receiver,'receive'}, _}] = Result,
+    ok.
+
 call(doc) -> 
     "Tests special forms {is_seq_trace} and {get_seq_token} "
 	"in trace match specs.";