From 7cd9aa21b31afaae1331d68d6caa14b901588003 Mon Sep 17 00:00:00 2001
From: "Herman S." <429230+has207@users.noreply.github.com>
Date: Mon, 16 Mar 2026 09:08:13 +0900
Subject: [PATCH] [Testing] Add SetGuestRoundingMode and trampoline creation
 backend tests

---
 .../cpu/testing/backend_integration_test.cc   | 125 ++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 src/xenia/cpu/testing/backend_integration_test.cc

diff --git a/src/xenia/cpu/testing/backend_integration_test.cc b/src/xenia/cpu/testing/backend_integration_test.cc
new file mode 100644
index 000000000..bd091a79f
--- /dev/null
+++ b/src/xenia/cpu/testing/backend_integration_test.cc
@@ -0,0 +1,125 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2026 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#include "xenia/cpu/testing/util.h"
+
+#include <atomic>
+#include <cmath>
+
+#include "xenia/base/platform.h"
+#if XE_ARCH_AMD64
+#include "xenia/cpu/backend/x64/x64_backend.h"
+#elif XE_ARCH_ARM64
+#include "xenia/cpu/backend/a64/a64_backend.h"
+#endif
+
+using namespace xe;
+using namespace xe::cpu;
+using namespace xe::cpu::hir;
+using namespace xe::cpu::testing;
+using xe::cpu::ppc::PPCContext;
+
+// =============================================================================
+// SetGuestRoundingMode (C++ path, not HIR opcode)
+// =============================================================================
+// This tests that calling SetGuestRoundingMode from C++ (as the kernel
+// emulation layer does) actually changes the hardware rounding mode, so that
+// subsequent JIT'd FP operations produce correctly rounded results.
+TEST_CASE("SET_GUEST_ROUNDING_MODE_CPP_PATH", "[backend]") {
+  // The HIR function just does an f32 add and returns the result.
+  // The rounding mode is set from C++ in pre_call, NOT via HIR opcode.
+  TestFunction test([](HIRBuilder& b) {
+    auto a = b.Convert(LoadFPR(b, 4), FLOAT32_TYPE);
+    auto c = b.Convert(LoadFPR(b, 5), FLOAT32_TYPE);
+    auto sum = b.Add(a, c);
+    StoreFPR(b, 3, b.Convert(sum, FLOAT64_TYPE));
+    b.Return();
+  });
+
+  // Mode 2 = toward +infinity.
+  test.Run(
+      [&test](PPCContext* ctx) {
+        ctx->f[4] = 1.0;
+        ctx->f[5] = std::ldexp(1.0, -24);
+        // Call the C++ SetGuestRoundingMode path.
+        test.processors[0]->backend()->SetGuestRoundingMode(ctx, 2);
+      },
+      [&test](PPCContext* ctx) {
+        auto result = static_cast<float>(ctx->f[3]);
+        float expected = std::nextafterf(1.0f, 2.0f);
+        REQUIRE(result == expected);
+        // Reset to nearest for subsequent tests.
+        test.processors[0]->backend()->SetGuestRoundingMode(ctx, 0);
+      });
+
+  // Mode 1 = toward zero.
+  test.Run(
+      [&test](PPCContext* ctx) {
+        ctx->f[4] = 1.0;
+        ctx->f[5] = std::ldexp(1.0, -24);
+        test.processors[0]->backend()->SetGuestRoundingMode(ctx, 1);
+      },
+      [&test](PPCContext* ctx) {
+        auto result = static_cast<float>(ctx->f[3]);
+        REQUIRE(result == 1.0f);
+        test.processors[0]->backend()->SetGuestRoundingMode(ctx, 0);
+      });
+}
+
+// =============================================================================
+// Guest Trampolines
+// =============================================================================
+// Test that CreateGuestTrampoline creates a callable trampoline that
+// transitions from guest JIT code back to a host C++ callback.
+static std::atomic<int> trampoline_call_count{0};
+static void* trampoline_received_arg1 = nullptr;
+static void* trampoline_received_arg2 = nullptr;
+
+static void TrampolineCallback(ppc::PPCContext* ctx, void* userarg1,
+                               void* userarg2) {
+  trampoline_call_count.fetch_add(1);
+  trampoline_received_arg1 = userarg1;
+  trampoline_received_arg2 = userarg2;
+  // Write a marker value so the test can verify the callback ran.
+  ctx->r[3] = 0xCAFEBABE;
+}
+
+TEST_CASE("GUEST_TRAMPOLINE_BASIC", "[backend]") {
+  // Reset global state.
+  trampoline_call_count = 0;
+  trampoline_received_arg1 = nullptr;
+  trampoline_received_arg2 = nullptr;
+
+  auto memory = std::make_unique<Memory>();
+  memory->Initialize();
+
+  std::unique_ptr<xe::cpu::backend::Backend> backend;
+#if XE_ARCH_AMD64
+  backend.reset(new xe::cpu::backend::x64::X64Backend());
+#elif XE_ARCH_ARM64
+  backend.reset(new xe::cpu::backend::a64::A64Backend());
+#endif
+  REQUIRE(backend);
+
+  auto processor = std::make_unique<Processor>(memory.get(), nullptr);
+  processor->Setup(std::move(backend));
+
+  // Create a trampoline with known userdata pointers.
+  void* tag1 = reinterpret_cast<void*>(static_cast<uintptr_t>(0x1111));
+  void* tag2 = reinterpret_cast<void*>(static_cast<uintptr_t>(0x2222));
+  uint32_t trampoline_addr = processor->backend()->CreateGuestTrampoline(
+      TrampolineCallback, tag1, tag2, false);
+
+  REQUIRE(trampoline_addr != 0);
+  REQUIRE(trampoline_addr >= 0x80000000);
+  REQUIRE(trampoline_addr < 0x80040000);
+
+  // Clean up the trampoline.
+  processor->backend()->FreeGuestTrampoline(trampoline_addr);
+}