5 files changed, 195 insertions, 0 deletions
diff --git a/kernel/src/kapi/cio.cpp b/kernel/src/kapi/cio.cpp
new file mode 100644
index 0000000..66493b6
--- /dev/null
+++ b/kernel/src/kapi/cio.cpp
@@ -0,0 +1,57 @@
+#include "kapi/cio.hpp"
+
+#include <optional>
+#include <string_view>
+#include <utility>
+
+namespace teachos::cio
+{
+  namespace
+  {
+    struct null_device final : public output_device
+    {
+      null_device static instance;
+
+      auto write(std::string_view) -> void override {}
+      auto writeln(std::string_view) -> void override {}
+
+      auto write_error(std::string_view) -> void override {}
+      auto writeln_error(std::string_view) -> void override {}
+    };
+
+    constinit null_device null_device::instance;
+  }  // namespace
+
+  // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+  constinit auto active_device = static_cast<output_device *>(&null_device::instance);
+
+  auto set_output_device(output_device & device) -> std::optional<output_device *>
+  {
+    if (&device == active_device)
+    {
+      return {};
+    }
+    return std::exchange(active_device, &device);
+  }
+
+  auto print(std::string_view text) -> void
+  {
+    active_device->write(text);
+  }
+
+  auto println(std::string_view text) -> void
+  {
+    active_device->writeln(text);
+  }
+
+  auto print_error(std::string_view text) -> void
+  {
+    active_device->write_error(text);
+  }
+
+  auto println_error(std::string_view text) -> void
+  {
+    active_device->writeln_error(text);
+  }
+
+}  // namespace teachos::cio
+\ No newline at end of file
diff --git a/kernel/src/kapi/memory.cpp b/kernel/src/kapi/memory.cpp
new file mode 100644
index 0000000..d6c84e1
--- /dev/null
+++ b/kernel/src/kapi/memory.cpp
@@ -0,0 +1,91 @@
+#include "kapi/memory.hpp"
+
+#include "kapi/system.hpp"
+
+#include <cstddef>
+#include <optional>
+#include <utility>
+
+namespace teachos::memory
+{
+
+  namespace
+  {
+    struct bad_frame_allocator final : public frame_allocator
+    {
+      bad_frame_allocator static instance;
+
+      auto allocate() noexcept -> std::optional<frame> override
+      {
+        system::panic("Tried to allocate a frame without an active allocator.");
+      }
+
+      auto release(frame) -> void override
+      {
+        system::panic("Tried to release a frame without an active allocator.");
+      }
+    };
+
+    struct bad_page_mapper final : public page_mapper
+    {
+      bad_page_mapper static instance;
+
+      auto map(page, frame, flags) -> std::byte * override
+      {
+        system::panic("Tried to map a page without an active mapper.");
+      }
+
+      auto unmap(page) -> void override
+      {
+        system::panic("Tried to unmap a page without an active mapper.");
+      }
+
+      auto try_unmap(page) noexcept -> bool override
+      {
+        return false;
+      }
+    };
+
+    constinit bad_frame_allocator bad_frame_allocator::instance{};
+    constinit bad_page_mapper bad_page_mapper::instance{};
+  }  // namespace
+
+  // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+  constinit auto active_frame_allocator = static_cast<frame_allocator *>(&bad_frame_allocator::instance);
+  // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+  constinit auto active_page_mapper = static_cast<page_mapper *>(&bad_page_mapper::instance);
+
+  auto set_frame_allocator(frame_allocator & allocator) -> std::optional<frame_allocator *>
+  {
+    if (&allocator == active_frame_allocator)
+    {
+      return {};
+    }
+    return std::exchange(active_frame_allocator, &allocator);
+  }
+
+  auto set_page_mapper(page_mapper & mapper) -> std::optional<page_mapper *>
+  {
+    if (&mapper == active_page_mapper)
+    {
+      return {};
+    }
+    return std::exchange(active_page_mapper, &mapper);
+  }
+
+  auto allocate_frame() -> std::optional<frame>
+  {
+    return active_frame_allocator->allocate();
+  }
+
+  auto map(page page, frame frame) -> std::byte *
+  {
+    return active_page_mapper->map(page, frame, page_mapper::flags::empty);
+  }
+
+  auto unmap(page page) -> void
+  {
+    return active_page_mapper->unmap(page);
+  }
+
+}  // namespace teachos::memory
+\ No newline at end of file
diff --git a/kernel/src/kapi/system.cpp b/kernel/src/kapi/system.cpp
new file mode 100644
index 0000000..3ae3f29
--- /dev/null
+++ b/kernel/src/kapi/system.cpp
@@ -0,0 +1,20 @@
+#include "kapi/system.hpp"
+
+#include "kapi/cio.hpp"
+#include "kapi/cpu.hpp"
+
+namespace teachos::system
+{
+
+  [[gnu::weak]]
+  auto panic(std::string_view message, std::source_location location) -> void
+  {
+    cio::println_error("!!!Kernel Panic!!! ");
+    cio::println_error(message);
+    cio::println_error(location.file_name());
+    cio::println_error(location.function_name());
+
+    cpu::halt();
+  }
+
+}  // namespace teachos::system
diff --git a/kernel/src/kstd.cpp b/kernel/src/kstd.cpp
new file mode 100644
index 0000000..2149c12
--- /dev/null
+++ b/kernel/src/kstd.cpp
@@ -0,0 +1,13 @@
+#include "kapi/system.hpp"
+
+#include <kstd/bits/os.hpp>
+
+namespace kstd::os
+{
+
+  auto panic(std::string_view message, std::source_location location) -> void
+  {
+    teachos::system::panic(message, location);
+  }
+
+}  // namespace kstd::os
+\ No newline at end of file
diff --git a/kernel/src/main.cpp b/kernel/src/main.cpp
new file mode 100644
index 0000000..3394275
--- /dev/null
+++ b/kernel/src/main.cpp
@@ -0,0 +1,14 @@
+#include "kapi/cio.hpp"
+#include "kapi/memory.hpp"
+#include "kapi/system.hpp"
+
+auto main() -> int
+{
+  teachos::cio::init();
+  teachos::cio::println("[OS] IO subsystem initialized.");
+
+  teachos::memory::init();
+  teachos::cio::println("[OS] Memory subsystem initialized.");
+
+  teachos::system::panic("Returning from kernel main!");
+}