[CPU] Null backend enough for GPU trace viewing

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) {