os: rework kernel architecture

Rework the code structure and architecture of the kernel by separating
platform-dependent and platform-independent code more cleanly. As of
this patchset, full feature parity has not been achieved. Nonetheless, a
sufficient subset of functionality has been ported to the new
architecture to demonstrate the feasibility of the new structure.

1 files changed, 66 insertions, 0 deletions

diff --git a/arch/x86_64/pre/src/context_switching/main.cpp b/arch/x86_64/pre/src/context_switching/main.cpp
new file mode 100644
index 0000000..3eb6dae
--- /dev/null
+++ b/arch/x86_64/pre/src/context_switching/main.cpp
@@ -0,0 +1,66 @@
+#include "arch/context_switching/main.hpp"
+
+#include "arch/boot/pointers.hpp"
+#include "arch/context_switching/syscall/syscall_enable.hpp"
+#include "arch/kernel/cpu/call.hpp"
+#include "arch/kernel/cpu/if.hpp"
+#include "arch/kernel/cpu/segment_register.hpp"
+#include "arch/kernel/cpu/tr.hpp"
+#include "arch/user/main.hpp"
+
+namespace teachos::arch::context_switching
+{
+  namespace
+  {
+    constexpr interrupt_descriptor_table::segment_selector KERNEL_CODE_SEGMENT_SELECTOR{
+      1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
+    constexpr kernel::cpu::far_pointer KERNEL_CODE_POINTER{&kernel::cpu::reload_data_segment_registers,
+                                                           KERNEL_CODE_SEGMENT_SELECTOR};
+    constexpr context_switching::interrupt_descriptor_table::segment_selector USER_CODE_SEGMENT_SELECTOR{
+      3U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
+    constexpr context_switching::interrupt_descriptor_table::segment_selector USER_DATA_SEGMENT_SELECTOR{
+      4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
+
+    auto reload_gdtr() -> void
+    {
+      kernel::cpu::call(KERNEL_CODE_POINTER);
+    }
+  }  // namespace
+
+  auto initialize_descriptor_tables() -> descriptor_tables
+  {
+    bool static initalized = false;
+
+    if (!initalized)
+    {
+      kernel::cpu::clear_interrupt_flag();
+
+      segment_descriptor_table::update_gdtr();
+      interrupt_descriptor_table::update_interrupt_descriptor_table_register();
+
+      reload_gdtr();
+      segment_descriptor_table::update_tss_register();
+
+      kernel::cpu::set_interrupt_flag();
+      initalized = true;
+    }
+
+    descriptor_tables tables = {segment_descriptor_table::get_or_create_gdt(),
+                                interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()};
+    return tables;
+  }
+
+  auto switch_to_user_mode() -> void
+  {
+    syscall::enable_syscall();
+    switch_context(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR, user::main);
+  }
+
+  auto switch_context(interrupt_descriptor_table::segment_selector data_segment,
+                      interrupt_descriptor_table::segment_selector code_segment, void (*return_function)()) -> void
+  {
+    (void)initialize_descriptor_tables();
+    kernel::cpu::set_data_segment_registers(data_segment);
+    kernel::cpu::set_code_segment_register(data_segment, code_segment, reinterpret_cast<uint64_t>(return_function));
+  }
+}  // namespace teachos::arch::context_switching