[diagnostics] Only conditionally enable ETWJITInterface

While testing the perf for v8-etw, I noticed that the runtime flag
didn't completely guard from event emission. This change fixes that.

Bug: v8:11043
Change-Id: Iee919e6030214e18173c93e4426d6437aed08235
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2757894Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Sara Tang <sartang@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#73424}

src/api/api.cc

@@ -8135,7 +8135,7 @@ void Isolate::Initialize(Isolate* isolate,
   }
 #endif  // ENABLE_GDB_JIT_INTERFACE
 #if defined(V8_TARGET_OS_WIN) && defined(V8_ENABLE_SYSTEM_INSTRUMENTATION)
-  if (code_event_handler == nullptr) {
+  if (code_event_handler == nullptr && i::FLAG_enable_system_instrumentation) {
     code_event_handler = i::ETWJITInterface::EventHandler;
   }
 #endif  // defined(V8_TARGET_OS_WIN)

src/d8/d8.cc

@@ -4536,13 +4536,16 @@ int Shell::Main(int argc, char* argv[]) {
   std::unique_ptr<platform::tracing::TracingController> tracing;
   if (options.trace_enabled && !i::FLAG_verify_predictable) {
     tracing = std::make_unique<platform::tracing::TracingController>();
-    const char* trace_path =
-        options.trace_path ? options.trace_path : "v8_trace.json";
-    trace_file.open(trace_path);
-    if (!trace_file.good()) {
-      printf("Cannot open trace file '%s' for writing: %s.\n", trace_path,
-             strerror(errno));
-      return 1;
+
+    if (!options.enable_system_instrumentation) {
+      const char* trace_path =
+          options.trace_path ? options.trace_path : "v8_trace.json";
+      trace_file.open(trace_path);
+      if (!trace_file.good()) {
+        printf("Cannot open trace file '%s' for writing: %s.\n", trace_path,
+               strerror(errno));
+        return 1;
+      }
     }
 
 #ifdef V8_USE_PERFETTO

src/flags/flag-definitions.h

@@ -1880,6 +1880,9 @@ DEFINE_BOOL(interpreted_frames_native_stack, false,
             "profilers).")
 #endif
 
+DEFINE_BOOL(enable_system_instrumentation, false,
+            "Enable platform-specific profiling.")
+
 //
 // Disassembler only flags
 //

src/init/v8.cc

@@ -176,15 +176,19 @@ void V8::InitializePlatform(v8::Platform* platform) {
   v8::base::SetPrintStackTrace(platform_->GetStackTracePrinter());
   v8::tracing::TracingCategoryObserver::SetUp();
 #if defined(V8_TARGET_OS_WIN) && defined(V8_ENABLE_SYSTEM_INSTRUMENTATION)
-  // TODO(sartang@microsoft.com): Move to platform specific diagnostics object
-  v8::internal::ETWJITInterface::Register();
+  if (FLAG_enable_system_instrumentation) {
+    // TODO(sartang@microsoft.com): Move to platform specific diagnostics object
+    v8::internal::ETWJITInterface::Register();
+  }
 #endif
 }
 
 void V8::ShutdownPlatform() {
   CHECK(platform_);
 #if defined(V8_TARGET_OS_WIN) && defined(V8_ENABLE_SYSTEM_INSTRUMENTATION)
-  v8::internal::ETWJITInterface::Unregister();
+  if (FLAG_enable_system_instrumentation) {
+    v8::internal::ETWJITInterface::Unregister();
+  }
 #endif
   v8::tracing::TracingCategoryObserver::TearDown();
   v8::base::SetPrintStackTrace(nullptr);