Reland "[wasm] Prevent breakpoints on nonbreakable positions"

This is an unmodified reland of 3c98a2a3.
The actual issue was fixed in https://crrev.com/c/1926769.

Original change's description:
> [wasm] Prevent breakpoints on nonbreakable positions
>
> If a breakpoint is set on a non-breakable position, the wasm interpreter
> just stores the value 0xFF (kInternalBreakpoint) in the function body
> (actually, a copy of the function body). This might overwrite immediates
> and cause subsequent failures in the wasm interpreter.
>
> In JavaScript, breakpoints are just forwarded to the next breakable
> position. This CL implements the same for WebAssembly.
> A cctest tests this behavior, and the existing
> wasm-stepping-byte-offsets.js inspector test is extended to also set the
> breakpoint within an i32 constant immediate.
>
> R=leese@chromium.org, mstarzinger@chromium.org
> CC=​bmeurer@chromium.org
>
> Bug: chromium:1025184
> Change-Id: Ia2706f8f1c3d686cbbe8e1e7339d9ee86247bb4a
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1925152
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#65070}

Bug: chromium:1025184
Change-Id: I5e16df645bbacf039b7a5e55a0c2a64cdb4c6a32
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1926152
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65093}

src/wasm/wasm-debug.cc

@@ -674,9 +674,12 @@ Handle<Code> WasmDebugInfo::GetCWasmEntry(Handle<WasmDebugInfo> debug_info,
 
 namespace {
 
-#ifdef DEBUG
-bool IsBreakablePosition(wasm::NativeModule* native_module, int func_index,
-                         int offset_in_func) {
+// Return the next breakable position after {offset_in_func} in function
+// {func_index}, or 0 if there is none.
+// Note that 0 is never a breakable position in wasm, since the first byte
+// contains the locals count for the function.
+int FindNextBreakablePosition(wasm::NativeModule* native_module, int func_index,
+                              int offset_in_func) {
   AccountingAllocator alloc;
   Zone tmp(&alloc, ZONE_NAME);
   wasm::BodyLocalDecls locals(&tmp);
@@ -687,13 +690,12 @@ bool IsBreakablePosition(wasm::NativeModule* native_module, int func_index,
                                   module_start + func.code.end_offset(),
                                   &locals);
   DCHECK_LT(0, locals.encoded_size);
+  if (offset_in_func < 0) return 0;
   for (uint32_t offset : iterator.offsets()) {
-    if (offset > static_cast<uint32_t>(offset_in_func)) break;
-    if (offset == static_cast<uint32_t>(offset_in_func)) return true;
+    if (offset >= static_cast<uint32_t>(offset_in_func)) return offset;
   }
-  return false;
+  return 0;
 }
-#endif  // DEBUG
 
 }  // namespace
 
@@ -709,10 +711,10 @@ bool WasmScript::SetBreakPoint(Handle<Script> script, int* position,
   const wasm::WasmFunction& func = module->functions[func_index];
   int offset_in_func = *position - func.code.offset();
 
-  // According to the current design, we should only be called with valid
-  // breakable positions.
-  DCHECK(IsBreakablePosition(script->wasm_native_module(), func_index,
-                             offset_in_func));
+  int breakable_offset = FindNextBreakablePosition(script->wasm_native_module(),
+                                                   func_index, offset_in_func);
+  if (breakable_offset == 0) return false;
+  *position = func.code.offset() + breakable_offset;
 
   // Insert new break point into break_positions of module object.
   WasmScript::AddBreakpointToInfo(script, *position, break_point);
@@ -729,7 +731,7 @@ bool WasmScript::SetBreakPoint(Handle<Script> script, int* position,
           isolate);
       Handle<WasmDebugInfo> debug_info =
           WasmInstanceObject::GetOrCreateDebugInfo(instance);
-      WasmDebugInfo::SetBreakpoint(debug_info, func_index, offset_in_func);
+      WasmDebugInfo::SetBreakpoint(debug_info, func_index, breakable_offset);
     }
   }
 

test/cctest/wasm/test-wasm-breakpoints.cc

@@ -280,6 +280,13 @@ std::vector<WasmValue> wasmVec(Args... args) {
   return std::vector<WasmValue>{arr.begin(), arr.end()};
 }
 
+int GetIntReturnValue(MaybeHandle<Object> retval) {
+  CHECK(!retval.is_null());
+  int result;
+  CHECK(retval.ToHandleChecked()->ToInt32(&result));
+  return result;
+}
+
 }  // namespace
 
 WASM_COMPILED_EXEC_TEST(WasmCollectPossibleBreakpoints) {
@@ -324,10 +331,25 @@ WASM_COMPILED_EXEC_TEST(WasmSimpleBreak) {
   Handle<Object> global(isolate->context().global_object(), isolate);
   MaybeHandle<Object> retval =
       Execution::Call(isolate, main_fun_wrapper, global, 0, nullptr);
-  CHECK(!retval.is_null());
-  int result;
-  CHECK(retval.ToHandleChecked()->ToInt32(&result));
-  CHECK_EQ(14, result);
+  CHECK_EQ(14, GetIntReturnValue(retval));
+}
+
+WASM_COMPILED_EXEC_TEST(WasmNonBreakablePosition) {
+  WasmRunner<int> runner(execution_tier);
+  Isolate* isolate = runner.main_isolate();
+
+  BUILD(runner, WASM_RETURN1(WASM_I32V_2(1024)));
+
+  Handle<JSFunction> main_fun_wrapper =
+      runner.builder().WrapCode(runner.function_index());
+  SetBreakpoint(&runner, runner.function_index(), 2, 4);
+
+  BreakHandler count_breaks(isolate, {{4, BreakHandler::Continue}});
+
+  Handle<Object> global(isolate->context().global_object(), isolate);
+  MaybeHandle<Object> retval =
+      Execution::Call(isolate, main_fun_wrapper, global, 0, nullptr);
+  CHECK_EQ(1024, GetIntReturnValue(retval));
 }
 
 WASM_COMPILED_EXEC_TEST(WasmSimpleStepping) {
@@ -351,10 +373,7 @@ WASM_COMPILED_EXEC_TEST(WasmSimpleStepping) {
   Handle<Object> global(isolate->context().global_object(), isolate);
   MaybeHandle<Object> retval =
       Execution::Call(isolate, main_fun_wrapper, global, 0, nullptr);
-  CHECK(!retval.is_null());
-  int result;
-  CHECK(retval.ToHandleChecked()->ToInt32(&result));
-  CHECK_EQ(14, result);
+  CHECK_EQ(14, GetIntReturnValue(retval));
 }
 
 WASM_COMPILED_EXEC_TEST(WasmStepInAndOut) {
@@ -470,10 +489,7 @@ WASM_COMPILED_EXEC_TEST(WasmRemoveBreakPoint) {
   Handle<Object> global(isolate->context().global_object(), isolate);
   MaybeHandle<Object> retval =
       Execution::Call(isolate, main_fun_wrapper, global, 0, nullptr);
-  CHECK(!retval.is_null());
-  int result;
-  CHECK(retval.ToHandleChecked()->ToInt32(&result));
-  CHECK_EQ(14, result);
+  CHECK_EQ(14, GetIntReturnValue(retval));
 }
 
 WASM_COMPILED_EXEC_TEST(WasmRemoveLastBreakPoint) {
@@ -501,10 +517,7 @@ WASM_COMPILED_EXEC_TEST(WasmRemoveLastBreakPoint) {
   Handle<Object> global(isolate->context().global_object(), isolate);
   MaybeHandle<Object> retval =
       Execution::Call(isolate, main_fun_wrapper, global, 0, nullptr);
-  CHECK(!retval.is_null());
-  int result;
-  CHECK(retval.ToHandleChecked()->ToInt32(&result));
-  CHECK_EQ(14, result);
+  CHECK_EQ(14, GetIntReturnValue(retval));
 }
 
 WASM_COMPILED_EXEC_TEST(WasmRemoveAllBreakPoint) {
@@ -534,10 +547,7 @@ WASM_COMPILED_EXEC_TEST(WasmRemoveAllBreakPoint) {
   Handle<Object> global(isolate->context().global_object(), isolate);
   MaybeHandle<Object> retval =
       Execution::Call(isolate, main_fun_wrapper, global, 0, nullptr);
-  CHECK(!retval.is_null());
-  int result;
-  CHECK(retval.ToHandleChecked()->ToInt32(&result));
-  CHECK_EQ(14, result);
+  CHECK_EQ(14, GetIntReturnValue(retval));
 }
 
 }  // namespace wasm

test/inspector/debugger/wasm-stepping-byte-offsets-expected.txt

-Tests stepping through wasm scripts with source maps
-Installing code an global variable and instantiate.
-Got wasm script: wasm://wasm/18214bfe
-Requesting source for wasm://wasm/18214bfe...
+Tests stepping through wasm scripts by byte offsets
+Setting up global instance variable.
+Got wasm script: wasm://wasm/41f464ee
+Requesting source for wasm://wasm/41f464ee...
 Source retrieved without error: true
-Setting breakpoint on offset 54 (on the setlocal before the call), url wasm://wasm/18214bfe
-Result: {"id":4,"result":{"breakpointId":"4:0:54:4","actualLocation":{"scriptId":"4","lineNumber":0,"columnNumber":54}}}
+Setting breakpoint on offset 59 (should be propagated to 60, the offset of the call), url wasm://wasm/41f464ee
 {
-    columnNumber : 54
+    columnNumber : 60
     lineNumber : 0
     scriptId : <scriptId>
 }
-Paused at wasm://wasm/18214bfe/18214bfe-1:7:6
-at wasm_B (7:6):
- - scope (global):
-   -- skipped
- - scope (local):
-   locals: {"arg#0":4}
-   stack: {"0":3}
-at (anonymous) (0:17):
- - scope (global):
-   -- skipped
-Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:8:6
-at wasm_B (8:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:9:6
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
    locals: {"arg#0":3}
-   stack: {}
+   stack: {"0":1024}
 at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-0:1:2
+Paused at wasm://wasm/41f464ee/41f464ee-0:1:2
 at wasm_A (1:2):
  - scope (global):
    -- skipped
  - scope (local):
+   locals: {"arg#0":1024}
    stack: {}
-at wasm_B (8:6):
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -48,13 +37,14 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepOver called
-Paused at wasm://wasm/18214bfe/18214bfe-0:2:2
+Paused at wasm://wasm/41f464ee/41f464ee-0:2:2
 at wasm_A (2:2):
  - scope (global):
    -- skipped
  - scope (local):
+   locals: {"arg#0":1024}
    stack: {}
-at wasm_B (8:6):
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -64,8 +54,8 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepOut called
-Paused at wasm://wasm/18214bfe/18214bfe-1:9:6
-at wasm_B (9:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:10:6
+at wasm_B (10:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -75,19 +65,19 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepOut called
-Paused at wasm://wasm/18214bfe/18214bfe-1:7:6
-at wasm_B (7:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:9:6
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
-   locals: {"arg#0":3}
-   stack: {"0":2}
+   locals: {"arg#0":2}
+   stack: {"0":1024}
 at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepOver called
-Paused at wasm://wasm/18214bfe/18214bfe-1:8:6
-at wasm_B (8:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:10:6
+at wasm_B (10:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -96,9 +86,9 @@ at wasm_B (8:6):
 at (anonymous) (0:17):
  - scope (global):
    -- skipped
-Debugger.stepOver called
-Paused at wasm://wasm/18214bfe/18214bfe-1:9:6
-at wasm_B (9:6):
+Debugger.stepInto called
+Paused at wasm://wasm/41f464ee/41f464ee-1:1:2
+at wasm_B (1:2):
  - scope (global):
    -- skipped
  - scope (local):
@@ -108,35 +98,25 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.resume called
-Paused at wasm://wasm/18214bfe/18214bfe-1:7:6
-at wasm_B (7:6):
- - scope (global):
-   -- skipped
- - scope (local):
-   locals: {"arg#0":2}
-   stack: {"0":1}
-at (anonymous) (0:17):
- - scope (global):
-   -- skipped
-Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:8:6
-at wasm_B (8:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:9:6
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
    locals: {"arg#0":1}
-   stack: {}
+   stack: {"0":1024}
 at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-0:1:2
+Paused at wasm://wasm/41f464ee/41f464ee-0:1:2
 at wasm_A (1:2):
  - scope (global):
    -- skipped
  - scope (local):
+   locals: {"arg#0":1024}
    stack: {}
-at wasm_B (8:6):
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -146,8 +126,8 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepOut called
-Paused at wasm://wasm/18214bfe/18214bfe-1:9:6
-at wasm_B (9:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:10:6
+at wasm_B (10:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -157,7 +137,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:1:2
+Paused at wasm://wasm/41f464ee/41f464ee-1:1:2
 at wasm_B (1:2):
  - scope (global):
    -- skipped
@@ -168,7 +148,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:2:4
+Paused at wasm://wasm/41f464ee/41f464ee-1:2:4
 at wasm_B (2:4):
  - scope (global):
    -- skipped
@@ -179,7 +159,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:3:4
+Paused at wasm://wasm/41f464ee/41f464ee-1:3:4
 at wasm_B (3:4):
  - scope (global):
    -- skipped
@@ -190,7 +170,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:4:6
+Paused at wasm://wasm/41f464ee/41f464ee-1:4:6
 at wasm_B (4:6):
  - scope (global):
    -- skipped
@@ -201,7 +181,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:5:6
+Paused at wasm://wasm/41f464ee/41f464ee-1:5:6
 at wasm_B (5:6):
  - scope (global):
    -- skipped
@@ -212,7 +192,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:6:6
+Paused at wasm://wasm/41f464ee/41f464ee-1:6:6
 at wasm_B (6:6):
  - scope (global):
    -- skipped
@@ -223,7 +203,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:7:6
+Paused at wasm://wasm/41f464ee/41f464ee-1:7:6
 at wasm_B (7:6):
  - scope (global):
    -- skipped
@@ -234,7 +214,7 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:8:6
+Paused at wasm://wasm/41f464ee/41f464ee-1:8:6
 at wasm_B (8:6):
  - scope (global):
    -- skipped
@@ -245,13 +225,25 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-0:1:2
+Paused at wasm://wasm/41f464ee/41f464ee-1:9:6
+at wasm_B (9:6):
+ - scope (global):
+   -- skipped
+ - scope (local):
+   locals: {"arg#0":0}
+   stack: {"0":1024}
+at (anonymous) (0:17):
+ - scope (global):
+   -- skipped
+Debugger.stepInto called
+Paused at wasm://wasm/41f464ee/41f464ee-0:1:2
 at wasm_A (1:2):
  - scope (global):
    -- skipped
  - scope (local):
+   locals: {"arg#0":1024}
    stack: {}
-at wasm_B (8:6):
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -261,13 +253,14 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-0:2:2
+Paused at wasm://wasm/41f464ee/41f464ee-0:2:2
 at wasm_A (2:2):
  - scope (global):
    -- skipped
  - scope (local):
+   locals: {"arg#0":1024}
    stack: {}
-at wasm_B (8:6):
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -277,13 +270,14 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-0:3:0
+Paused at wasm://wasm/41f464ee/41f464ee-0:3:0
 at wasm_A (3:0):
  - scope (global):
    -- skipped
  - scope (local):
+   locals: {"arg#0":1024}
    stack: {}
-at wasm_B (8:6):
+at wasm_B (9:6):
  - scope (global):
    -- skipped
  - scope (local):
@@ -293,8 +287,8 @@ at (anonymous) (0:17):
  - scope (global):
    -- skipped
 Debugger.stepInto called
-Paused at wasm://wasm/18214bfe/18214bfe-1:9:6
-at wasm_B (9:6):
+Paused at wasm://wasm/41f464ee/41f464ee-1:10:6
+at wasm_B (10:6):
  - scope (global):
    -- skipped
  - scope (local):

test/inspector/debugger/wasm-stepping-byte-offsets.js

-// Copyright 2018 the V8 project authors. All rights reserved.
+// Copyright 2019 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 let {session, contextGroup, Protocol} =
-    InspectorTest.start('Tests stepping through wasm scripts with source maps');
+    InspectorTest.start('Tests stepping through wasm scripts by byte offsets');
 
 utils.load('test/mjsunit/wasm/wasm-module-builder.js');
 
 var builder = new WasmModuleBuilder();
 
 var func_a_idx =
-    builder.addFunction('wasm_A', kSig_v_v).addBody([kExprNop, kExprNop]).index;
+    builder.addFunction('wasm_A', kSig_v_i).addBody([kExprNop, kExprNop]).index;
 
 // wasm_B calls wasm_A <param0> times.
 builder.addFunction('wasm_B', kSig_v_i)
@@ -23,6 +23,7 @@ builder.addFunction('wasm_B', kSig_v_i)
           kExprI32Const, 1,               // -
           kExprI32Sub,                    // -
           kExprLocalSet, 0,               // decrease <param0>
+          ...wasmI32Const(1024),          // some longer i32 const (2 byte imm)
           kExprCallFunction, func_a_idx,  // -
           kExprBr, 1,                     // continue
           kExprEnd,                       // -
@@ -51,9 +52,10 @@ function instantiate(bytes) {
     InspectorTest.logProtocolCommandCalls('Debugger.' + action);
 
   await Protocol.Debugger.enable();
-  InspectorTest.log('Installing code an global variable and instantiate.');
+  InspectorTest.log('Setting up global instance variable.');
   Protocol.Runtime.evaluate({
-    expression: `var instance;(${instantiate.toString()})(${JSON.stringify(module_bytes)})`
+    expression: `var instance;` +
+        `(${instantiate.toString()})(${JSON.stringify(module_bytes)})`
   });
   const [, {params: wasmScript}, ,] = await Protocol.Debugger.onceScriptParsed(4);
 
@@ -62,39 +64,39 @@ function instantiate(bytes) {
   const msg =
       await Protocol.Debugger.getScriptSource({scriptId: wasmScript.scriptId});
   InspectorTest.log(`Source retrieved without error: ${!msg.error}`);
-  // TODO: Add check that source text is empty but bytecode is present.
+  // TODO(leese): Add check that source text is empty but bytecode is present.
 
+  // Set the breakpoint on a non-breakable position. This should resolve to the
+  // next instruction.
   InspectorTest.log(
-      `Setting breakpoint on offset 54 (on the setlocal before the call), url ${wasmScript.url}`);
+      `Setting breakpoint on offset 59 (should be propagated to 60, the ` +
+      `offset of the call), url ${wasmScript.url}`);
   const bpmsg = await Protocol.Debugger.setBreakpoint({
-    location: {scriptId: wasmScript.scriptId, lineNumber: 0, columnNumber: 54}
+    location: {scriptId: wasmScript.scriptId, lineNumber: 0, columnNumber: 59}
   });
 
-  InspectorTest.log(`Result: ${JSON.stringify(bpmsg)}`);
   const actualLocation = bpmsg.result.actualLocation;
   InspectorTest.logMessage(actualLocation);
   Protocol.Runtime.evaluate({ expression: 'instance.exports.main(4)' });
-  await waitForPauseAndStep('stepInto');  // == stepOver, to call instruction
   await waitForPauseAndStep('stepInto');  // into call to wasm_A
   await waitForPauseAndStep('stepOver');  // over first nop
   await waitForPauseAndStep('stepOut');   // out of wasm_A
-  await waitForPauseAndStep('stepOut');  // out of wasm_B, stop on breakpoint again
-  await waitForPauseAndStep('stepOver');  // to call
+  await waitForPauseAndStep('stepOut');   // out of wasm_B, stop on breakpoint
   await waitForPauseAndStep('stepOver');  // over call
-  await waitForPauseAndStep('resume');  // to next breakpoint (third iteration)
-  await waitForPauseAndStep('stepInto');  // to call
+  await waitForPauseAndStep('stepInto');  // == stepOver br
+  await waitForPauseAndStep('resume');    // to next breakpoint (3rd iteration)
   await waitForPauseAndStep('stepInto');  // into wasm_A
   await waitForPauseAndStep('stepOut');   // out to wasm_B
-  // now step 9 times, until we are in wasm_A again.
-  for (let i = 0; i < 9; ++i) await waitForPauseAndStep('stepInto');
+  // Now step 10 times, until we are in wasm_A again.
+  for (let i = 0; i < 10; ++i) await waitForPauseAndStep('stepInto');
   // 3 more times, back to wasm_B.
   for (let i = 0; i < 3; ++i) await waitForPauseAndStep('stepInto');
-  // then just resume.
+  // Then just resume.
   await waitForPauseAndStep('resume');
   InspectorTest.log('exports.main returned!');
   InspectorTest.log('Finished!');
-  //InspectorTest.completeTest();
-})().catch(reason => InspectorTest.log(`Failed: ${reason}`)).finally(InspectorTest.completeTest);
+})().catch(reason => InspectorTest.log(`Failed: ${reason}`))
+    .finally(InspectorTest.completeTest);
 
 async function waitForPauseAndStep(stepAction) {
   const {params: {callFrames}} = await Protocol.Debugger.oncePaused();