kvm: Add framework for machine types and MMIO dispatch

The core of the machine-type support is the new operations table,
kvm_ops_t. This acts as a standard C-style virtual table decoupling the
generic KVM core logic from target specific hardware emualtion. The
kvm_t VM instance now points to an ops table, which defines the
"personality" of the guest. A kvm_probe() factory function has been
added to initialize a kvm_t instance with the correct ops table for a
given machine type (eg, Switch 1).

The ops table's .mmio_read and .mmio_write function pointers are the
link between the armv8 CPU core and this new MMIO dispatcher. When a
physical memory access is determined to be MMIO, the VM will call the
appropriate function pointer, which in turn will use the MMIO dispatcher
to find and execute the correct device handler.

The initial implementation for the Switch 1 target
(targets/switch1/hardware/probe.cpp) is a stub. The bootstrapping
logic will be added in subsequent patches.

Signed-off-by: Ronald Caesar <github43132@proton.me>

src/main.cpp

@@ -0,0 +1,123 @@
+// Copyright 2025 Pound Emulator Project. All rights reserved.
+
+#include <chrono>
+#include <memory>
+#include <thread>
+
+#include "common/Config.h"
+#include "common/Logging/Backend.h"
+#include "common/Logging/Log.h"
+#include "frontend/gui.h"
+#include "host/memory/arena.h"
+
+#include <SDL3/SDL_opengl.h>
+#include "frontend/color.h"
+#include "frontend/panels.h"
+#include "imgui_impl_opengl3.h"
+#include "imgui_impl_sdl3.h"
+
+int main()
+{
+    Base::Log::Initialize();
+    Base::Log::Start();
+
+    const auto& config_dir = Base::FS::GetUserPath(Base::FS::PathType::BinaryDir);
+    Config::Load(config_dir / "config.toml");
+
+    // Create GUI manager
+    gui::window_t window = {.data = nullptr, .gl_context = nullptr};
+    (void)gui::window_init(&window, "Pound Emulator", Config::windowWidth(), Config::windowHeight());
+
+    if (bool return_code = gui::init_imgui(&window); false == return_code)
+    {
+        LOG_ERROR(Render, "Failed to initialize GUI");
+        return EXIT_FAILURE;
+    }
+
+    const size_t panels_capacity = 2;
+    const char* panel_names[panels_capacity] = {PANEL_NAME_CPU, PANEL_NAME_PERFORMANCE};
+    bool panels_visibility[panels_capacity] = {};
+    bool imgui_demo_visible = false;
+
+    gui::gui_t gui = {
+        .window = window,
+        .custom_panels = panel_names,
+        .custom_panels_visibility = panels_visibility,
+        .custom_panels_capacity = panels_capacity,
+    };
+
+    gui::panel::performance_panel_t performance_panel = {};
+    gui::panel::performance_data_t performance_data = {.frame_count = 1};
+    std::chrono::steady_clock::time_point performance_panel_last_render = std::chrono::steady_clock::now();
+
+    // Main loop
+    bool is_running = true;
+    bool show_cpu_result_popup = false;
+    while (true == is_running)
+    {
+        SDL_Event event = {};
+        while (::SDL_PollEvent(&event))
+        {
+            (void)::ImGui_ImplSDL3_ProcessEvent(&event);
+            if (event.type == SDL_EVENT_QUIT)
+            {
+                is_running = false;
+            }
+        }
+
+        ::ImGui_ImplOpenGL3_NewFrame();
+        ::ImGui_ImplSDL3_NewFrame();
+        ::ImGui::NewFrame();
+        if (int8_t return_code = gui::render_memu_bar(gui.custom_panels, gui.custom_panels_capacity,
+                                                      gui.custom_panels_visibility, &imgui_demo_visible);
+            WINDOW_SHOULD_CLOSE == return_code)
+        {
+            is_running = false;
+        }
+
+        for (size_t i = 0; i < panels_capacity; ++i)
+        {
+            if (false == gui.custom_panels_visibility[i])
+            {
+                continue;
+            }
+
+            if (0 == ::strcmp(gui.custom_panels[i], PANEL_NAME_PERFORMANCE))
+            {
+                int8_t return_code = gui::panel::render_performance_panel(&performance_panel, &performance_data,
+                                                                          &performance_panel_last_render);
+                if (ERROR_PANEL_IS_CLOSED == return_code)
+                {
+                    gui.custom_panels_visibility[i] = false;
+                }
+            }
+            if (0 == ::strcmp(gui.custom_panels[i], PANEL_NAME_CPU))
+            {
+                int8_t return_code = gui::panel::render_cpu_panel(&show_cpu_result_popup);
+                if (ERROR_PANEL_IS_CLOSED == return_code)
+                {
+                    gui.custom_panels_visibility[i] = false;
+                }
+            }
+        }
+
+        // End Frame.
+        ImGui::Render();
+        const ImGuiIO& io = ImGui::GetIO();
+        ::glViewport(0, 0, static_cast<GLint>(io.DisplaySize.x), static_cast<GLint>(io.DisplaySize.y));
+        ::glClearColor(0.08f, 0.08f, 0.10f, 1.0f);
+        ::glClear(GL_COLOR_BUFFER_BIT);
+
+        ::ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
+        if (bool sdl_ret_code = ::SDL_GL_SwapWindow(gui.window.data); false == sdl_ret_code)
+        {
+            LOG_ERROR(Render, "Failed to update window with OpenGL rendering: {}", SDL_GetError());
+            is_running = false;
+        }
+
+        // Small delay to prevent excessive CPU usage
+        std::this_thread::sleep_for(std::chrono::milliseconds(5));
+    }
+
+    gui::destroy();
+}