Rework tracing for blocks running as methods

The main impetus for this change is to fix [Bug #13392]. Previously, we
fired the "return" TracePoint event after popping the stack frame for
the block running as method (BMETHOD). This gave undesirable source
location outputs as the return event normally fires right before the
frame going away.

The iseq for each block can run both as a block and as a method. To
accommodate that, this commit makes vm_trace() fire call/return events for
instructions that have b_call/b_return events attached when the iseq is
running as a BMETHOD. The logic for rewriting to "trace_*" instruction
is tweaked so that when the user listens to call/return events,
instructions with b_call/b_return become trace variants.

To continue to provide the return value for non-local returns done using
the "return" or "break" keyword inside BMETHODs, the stack unwinding
code is tweaked. b_return events now provide the same return value as
return events for these non-local cases. A pre-existing test deemed not
providing a return value for these b_return events as a limitation.

This commit removes the checks for call/return TracePoint events that
happen when calling into BMETHODs when no TracePoints are active.
Technically, migrating just the return event is enough to fix the bug,
but migrating both call and return removes our reliance on
`VM_FRAME_FLAG_FINISH` and re-entering the interpreter when the caller
is already in the interpreter.

1 files changed, 23 insertions, 2 deletions

diff --git a/iseq.c b/iseq.c
index f0117d94ce..e42525cb9f 100644
--- a/iseq.c
+++ b/iseq.c
@@ -3310,6 +3310,23 @@ rb_iseq_trace_flag_cleared(const rb_iseq_t *iseq, size_t pos)
     encoded_iseq_trace_instrument(&iseq_encoded[pos], 0, false);
 }
 
+// We need to fire call events on instructions with b_call events if the block
+// is running as a method. So, if we are listening for call events, then
+// instructions that have b_call events need to become trace variants.
+// Use this function when making decisions about recompiling to trace variants.
+static inline rb_event_flag_t
+add_bmethod_events(rb_event_flag_t events)
+{
+    if (events & RUBY_EVENT_CALL) {
+        events |= RUBY_EVENT_B_CALL;
+    }
+    if (events & RUBY_EVENT_RETURN) {
+        events |= RUBY_EVENT_B_RETURN;
+    }
+    return events;
+}
+
+// Note, to support call/return events for bmethods, turnon_event can have more events than tpval.
 static int
 iseq_add_local_tracepoint(const rb_iseq_t *iseq, rb_event_flag_t turnon_events, VALUE tpval, unsigned int target_line)
 {
@@ -3365,9 +3382,12 @@ iseq_add_local_tracepoint_i(const rb_iseq_t *iseq, void *p)
 }
 
 int
-rb_iseq_add_local_tracepoint_recursively(const rb_iseq_t *iseq, rb_event_flag_t turnon_events, VALUE tpval, unsigned int target_line)
+rb_iseq_add_local_tracepoint_recursively(const rb_iseq_t *iseq, rb_event_flag_t turnon_events, VALUE tpval, unsigned int target_line, bool target_bmethod)
 {
     struct trace_set_local_events_struct data;
+    if (target_bmethod) {
+        turnon_events = add_bmethod_events(turnon_events);
+    }
     data.turnon_events = turnon_events;
     data.tpval = tpval;
     data.target_line = target_line;
@@ -3399,6 +3419,7 @@ iseq_remove_local_tracepoint(const rb_iseq_t *iseq, VALUE tpval)
             ((rb_iseq_t *)iseq)->aux.exec.local_hooks = NULL;
         }
 
+        local_events = add_bmethod_events(local_events);
         for (pc = 0; pc<body->iseq_size;) {
             rb_event_flag_t pc_events = rb_iseq_event_flags(iseq, pc);
             pc += encoded_iseq_trace_instrument(&iseq_encoded[pc], pc_events & (local_events | iseq->aux.exec.global_trace_events), false);
@@ -3449,7 +3470,7 @@ rb_iseq_trace_set(const rb_iseq_t *iseq, rb_event_flag_t turnon_events)
         rb_event_flag_t enabled_events;
         rb_event_flag_t local_events = iseq->aux.exec.local_hooks ? iseq->aux.exec.local_hooks->events : 0;
         ((rb_iseq_t *)iseq)->aux.exec.global_trace_events = turnon_events;
-        enabled_events = turnon_events | local_events;
+        enabled_events = add_bmethod_events(turnon_events | local_events);
 
         for (pc=0; pc<body->iseq_size;) {
             rb_event_flag_t pc_events = rb_iseq_event_flags(iseq, pc);