[liftoff][debug] Implement StepIn

Update the "hook on function call" flag also in the wasm case, and
slightly change the {IsStepping} logic to stop in any frame if the last
step action was anything other than StepNext.
In future CLs, this has to be extended further for StepOut and for
StepOver at a return location.
When that is done, we can also reenable more stepping in the test.

R=thibaudm@chromium.org

Bug: v8:10321
Change-Id: Ib3aa8c2c2e137690140e5879a33e2bcc340821e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2108035
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66789}

src/debug/debug.cc

@@ -996,29 +996,6 @@ void Debug::PrepareStep(StepAction step_action) {
   StackTraceFrameIterator frames_it(isolate_, frame_id);
   StandardFrame* frame = frames_it.frame();
 
-  // Handle stepping in wasm functions via the wasm interpreter.
-  if (frame->is_wasm_interpreter_entry()) {
-    WasmInterpreterEntryFrame* wasm_frame =
-        WasmInterpreterEntryFrame::cast(frame);
-    if (wasm_frame->NumberOfActiveFrames() > 0) {
-      wasm_frame->debug_info().PrepareStep(step_action);
-      return;
-    }
-  }
-  // Handle stepping in Liftoff code.
-  if (FLAG_debug_in_liftoff && frame->is_wasm_compiled()) {
-    WasmCompiledFrame* wasm_frame = WasmCompiledFrame::cast(frame);
-    wasm::WasmCodeRefScope code_ref_scope;
-    wasm::WasmCode* code = wasm_frame->wasm_code();
-    if (code->is_liftoff()) {
-      wasm_frame->native_module()->GetDebugInfo()->PrepareStep(isolate_);
-      return;
-    }
-  }
-  // If this is wasm, but there are no interpreted frames on top, all we can do
-  // is step out.
-  if (frame->is_wasm()) step_action = StepOut;
-
   BreakLocation location = BreakLocation::Invalid();
   Handle<SharedFunctionInfo> shared;
   int current_frame_count = CurrentFrameCount();
@@ -1062,6 +1039,25 @@ void Debug::PrepareStep(StepAction step_action) {
     thread_local_.last_frame_count_ = current_frame_count;
     // No longer perform the current async step.
     clear_suspended_generator();
+  } else if (frame->is_wasm_interpreter_entry()) {
+    // Handle stepping in wasm functions via the wasm interpreter.
+    WasmInterpreterEntryFrame* wasm_frame =
+        WasmInterpreterEntryFrame::cast(frame);
+    if (wasm_frame->NumberOfActiveFrames() > 0) {
+      wasm_frame->debug_info().PrepareStep(step_action);
+      return;
+    }
+  } else if (FLAG_debug_in_liftoff && frame->is_wasm_compiled()) {
+    // Handle stepping in Liftoff code.
+    WasmCompiledFrame* wasm_frame = WasmCompiledFrame::cast(frame);
+    wasm::WasmCodeRefScope code_ref_scope;
+    wasm::WasmCode* code = wasm_frame->wasm_code();
+    if (code->is_liftoff()) {
+      wasm_frame->native_module()->GetDebugInfo()->PrepareStep(isolate_);
+    }
+    // In case the wasm code returns, prepare the next frame (if JS) to break.
+    step_action = StepOut;
+    UpdateHookOnFunctionCall();
   }
 
   switch (step_action) {

src/wasm/wasm-debug.cc

@@ -698,7 +698,9 @@ class DebugInfoImpl {
 
   bool IsStepping(WasmCompiledFrame* frame) {
     DCHECK_IMPLIES(stepping_frame_ != NO_ID, flooded_function_index_ != -1);
-    return stepping_frame_ == frame->id();
+    Isolate* isolate = frame->wasm_instance().GetIsolate();
+    StepAction last_step_action = isolate->debug()->last_step_action();
+    return last_step_action == StepIn || stepping_frame_ == frame->id();
   }
 
   void RemoveDebugSideTables(Vector<WasmCode* const> codes) {

test/inspector/debugger/wasm-stepping-liftoff-expected.txt

@@ -18,28 +18,18 @@ Debugger.stepOver called
 Paused at wasm://wasm/42af3c82:0:59
 Debugger.resume called
 Paused at wasm://wasm/42af3c82:0:73
+Debugger.stepInto called
+Paused at wasm://wasm/42af3c82:0:52
 Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:75
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:59
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:61
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:63
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:65
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:67
+Paused at wasm://wasm/42af3c82:0:53
 Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:68
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:70
+Paused at wasm://wasm/42af3c82:0:54
 Debugger.stepOver called
 Paused at wasm://wasm/42af3c82:0:73
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:75
-Debugger.stepOver called
-Paused at wasm://wasm/42af3c82:0:59
+Debugger.resume called
+Paused at wasm://wasm/42af3c82:0:52
+Debugger.resume called
+Paused at :0:24
 Debugger.resume called
 exports.main returned!
 Test stepping over a recursive call

test/inspector/debugger/wasm-stepping-liftoff.js

@@ -98,11 +98,15 @@ function instantiate(bytes) {
   await waitForPauseAndStep('stepOver');  // over call
   await waitForPauseAndStep('stepOver');  // over br
   await waitForPauseAndStep('resume');    // to next breakpoint (3rd iteration)
-  await waitForPauseAndStep('stepOver');  // over wasm_A
+  await waitForPauseAndStep('stepInto');  // into wasm_A
+  // Step out of wasm_A, back to wasm_B.
+  // TODO(clemensb/thibaudm): Replace by an actual 'stepOut'.
+  for (let i = 0; i < 3; ++i) await waitForPauseAndStep('stepOver');
   // Step over 10 times.
-  for (let i = 0; i < 10; ++i) await waitForPauseAndStep('stepOver');
-  // Then just resume.
-  await waitForPauseAndStep('resume');
+  // TODO(clemensb/thibaudm): Reenable once stepping over return works.
+  //for (let i = 0; i < 10; ++i) await waitForPauseAndStep('stepOver');
+  // Resume three more times to continue over other breakpoints.
+  for (let i = 0; i < 3; ++i) await waitForPauseAndStep('resume');
   InspectorTest.log('exports.main returned!');
 
   InspectorTest.log('Test stepping over a recursive call');