[CPU] Null backend enough for GPU trace viewing

src/xenia/app/xenia_main.cc

@@ -477,7 +477,7 @@ void EmulatorApp::EmulatorThread() {
   // Setup and initialize all subsystems. If we can't do something
   // (unsupported system, memory issues, etc) this will fail early.
   X_STATUS result = emulator_->Setup(
-      emulator_window_->window(), emulator_window_->imgui_drawer(),
+      emulator_window_->window(), emulator_window_->imgui_drawer(), true,
       CreateAudioSystem, CreateGraphicsSystem, CreateInputDrivers);
   if (XFAILED(result)) {
     XELOGE("Failed to setup emulator: {:08X}", result);

src/xenia/cpu/backend/null_backend.cc

@@ -0,0 +1,36 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2022 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#include "xenia/cpu/backend/null_backend.h"
+
+#include "xenia/cpu/backend/assembler.h"
+#include "xenia/cpu/function.h"
+
+namespace xe {
+namespace cpu {
+namespace backend {
+
+void NullBackend::CommitExecutableRange(uint32_t guest_low,
+                                        uint32_t guest_high) {}
+
+std::unique_ptr<Assembler> NullBackend::CreateAssembler() { return nullptr; }
+
+std::unique_ptr<GuestFunction> NullBackend::CreateGuestFunction(
+    Module* module, uint32_t address) {
+  return nullptr;
+}
+
+uint64_t NullBackend::CalculateNextHostInstruction(ThreadDebugInfo* thread_info,
+                                                   uint64_t current_pc) {
+  return current_pc;
+}
+
+}  // namespace backend
+}  // namespace cpu
+}  // namespace xe

src/xenia/cpu/backend/null_backend.h

@@ -0,0 +1,36 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2022 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_CPU_BACKEND_NULL_BACKEND_H_
+#define XENIA_CPU_BACKEND_NULL_BACKEND_H_
+
+#include "xenia/cpu/backend/backend.h"
+
+namespace xe {
+namespace cpu {
+namespace backend {
+
+class NullBackend : public Backend {
+ public:
+  void CommitExecutableRange(uint32_t guest_low, uint32_t guest_high) override;
+
+  std::unique_ptr<Assembler> CreateAssembler() override;
+
+  std::unique_ptr<GuestFunction> CreateGuestFunction(Module* module,
+                                                     uint32_t address) override;
+
+  uint64_t CalculateNextHostInstruction(ThreadDebugInfo* thread_info,
+                                        uint64_t current_pc) override;
+};
+
+}  // namespace backend
+}  // namespace cpu
+}  // namespace xe
+
+#endif  // XENIA_CPU_BACKEND_NULL_BACKEND_H_

src/xenia/cpu/processor.cc

@@ -134,7 +134,11 @@ bool Processor::Setup(std::unique_ptr<backend::Backend> backend) {
   // Stack walker is used when profiling, debugging, and dumping.
   // Note that creation may fail, in which case we'll have to disable those
   // features.
-  stack_walker_ = StackWalker::Create(backend_->code_cache());
+  // The code cache may be unavailable in case of a "null" backend.
+  cpu::backend::CodeCache* code_cache = backend_->code_cache();
+  if (code_cache) {
+    stack_walker_ = StackWalker::Create(code_cache);
+  }
   if (!stack_walker_) {
     // TODO(benvanik): disable features.
     if (cvars::debug) {

src/xenia/emulator.cc

@@ -27,6 +27,7 @@
 #include "xenia/base/platform.h"
 #include "xenia/base/string.h"
 #include "xenia/cpu/backend/code_cache.h"
+#include "xenia/cpu/backend/null_backend.h"
 #include "xenia/cpu/cpu_flags.h"
 #include "xenia/cpu/thread_state.h"
 #include "xenia/gpu/graphics_system.h"
@@ -131,6 +132,7 @@ Emulator::~Emulator() {
 
 X_STATUS Emulator::Setup(
     ui::Window* display_window, ui::ImGuiDrawer* imgui_drawer,
+    bool require_cpu_backend,
     std::function<std::unique_ptr<apu::AudioSystem>(cpu::Processor*)>
         audio_system_factory,
     std::function<std::unique_ptr<gpu::GraphicsSystem>()>
@@ -164,20 +166,21 @@ X_STATUS Emulator::Setup(
   export_resolver_ = std::make_unique<xe::cpu::ExportResolver>();
 
   std::unique_ptr<xe::cpu::backend::Backend> backend;
-  if (!backend) {
 #if XE_ARCH_AMD64
-    if (cvars::cpu == "x64") {
+  if (cvars::cpu == "x64") {
+    backend.reset(new xe::cpu::backend::x64::X64Backend());
+  }
+#endif  // XE_ARCH
+  if (cvars::cpu == "any") {
+    if (!backend) {
+#if XE_ARCH_AMD64
       backend.reset(new xe::cpu::backend::x64::X64Backend());
-    }
 #endif  // XE_ARCH
-    if (cvars::cpu == "any") {
-      if (!backend) {
-#if XE_ARCH_AMD64
-        backend.reset(new xe::cpu::backend::x64::X64Backend());
-#endif  // XE_ARCH
-      }
     }
   }
+  if (!backend && !require_cpu_backend) {
+    backend.reset(new xe::cpu::backend::NullBackend());
+  }
 
   // Initialize the CPU.
   processor_ = std::make_unique<xe::cpu::Processor>(memory_.get(),

src/xenia/emulator.h

@@ -161,6 +161,7 @@ class Emulator {
   // functions.
   X_STATUS Setup(
       ui::Window* display_window, ui::ImGuiDrawer* imgui_drawer,
+      bool require_cpu_backend,
       std::function<std::unique_ptr<apu::AudioSystem>(cpu::Processor*)>
           audio_system_factory,
       std::function<std::unique_ptr<gpu::GraphicsSystem>()>

src/xenia/gpu/trace_dump.cc

@@ -95,8 +95,8 @@ bool TraceDump::Setup() {
   // Create the emulator but don't initialize so we can setup the window.
   emulator_ = std::make_unique<Emulator>("", "", "", "");
   X_STATUS result = emulator_->Setup(
-      nullptr, nullptr, nullptr, [this]() { return CreateGraphicsSystem(); },
-      nullptr);
+      nullptr, nullptr, false, nullptr,
+      [this]() { return CreateGraphicsSystem(); }, nullptr);
   if (XFAILED(result)) {
     XELOGE("Failed to setup emulator: {:08X}", result);
     return false;

src/xenia/gpu/trace_viewer.cc

@@ -125,7 +125,7 @@ bool TraceViewer::Setup() {
   // Create the emulator but don't initialize so we can setup the window.
   emulator_ = std::make_unique<Emulator>("", "", "", "");
   X_STATUS result = emulator_->Setup(
-      window_.get(), nullptr, nullptr,
+      window_.get(), nullptr, false, nullptr,
       [this]() { return CreateGraphicsSystem(); }, nullptr);
   if (XFAILED(result)) {
     XELOGE("Failed to setup emulator: {:08X}", result);