3 files changed, 69 insertions, 16 deletions
diff --git a/arch/x86_64/src/kernel/cpu/segment_register.cpp b/arch/x86_64/src/kernel/cpu/segment_register.cpp
new file mode 100644
index 0000000..f70c558
--- /dev/null
+++ b/arch/x86_64/src/kernel/cpu/segment_register.cpp
@@ -0,0 +1,34 @@
+#include "arch/kernel/cpu/segment_register.hpp"
+
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
+
+namespace teachos::arch::kernel::cpu
+{
+  [[gnu::naked]]
+  auto reload_segment_registers() -> void
+  {
+    asm volatile("xor %rax, %rax\n"
+                 "mov %rax, %ss\n"
+                 "mov %rax, %ds\n"
+                 "mov %rax, %es\n"
+                 "mov %rax, %fs\n"
+                 "mov %rax, %gs\n"
+                 "ret");
+  }
+
+  [[gnu::naked]]
+  auto set_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void
+  {
+    asm volatile("xor %%rax, %%rax\n"
+                 "mov %[input], %%ax\n"
+                 "mov %%rax, %%ss\n"
+                 "mov %%rax, %%ds\n"
+                 "mov %%rax, %%es\n"
+                 "mov %%rax, %%fs\n"
+                 "mov %%rax, %%gs\n"
+                 "ret"
+                 : /* No output from call */
+                 : [input] "m"(segment_selector));
+  }
+
+}  // namespace teachos::arch::kernel::cpu
diff --git a/arch/x86_64/src/kernel/cpu/ss.cpp b/arch/x86_64/src/kernel/cpu/ss.cpp
deleted file mode 100644
index 0978eca..0000000
--- a/arch/x86_64/src/kernel/cpu/ss.cpp
+++ /dev/null
@@ -1,16 +0,0 @@
-#include "arch/kernel/cpu/ss.hpp"
-
-namespace teachos::arch::kernel::cpu
-{
-  auto read_ss() -> context_switching::interrupt_descriptor_table::segment_selector
-  {
-    context_switching::interrupt_descriptor_table::segment_selector segment_selector{};
-    asm volatile("mov %%ss, %[output]" : [output] "=m"(segment_selector));
-    return segment_selector;
-  }
-
-  auto write_ss(context_switching::interrupt_descriptor_table::segment_selector selector) -> void
-  {
-    asm volatile("mov %[input], %%ss" : /* no output from call */ : [input] "m"(selector));
-  }
-}  // namespace teachos::arch::kernel::cpu
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 7782d30..7d4173e 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -1,9 +1,11 @@
 #include "arch/kernel/main.hpp"
 
 #include "arch/boot/pointers.hpp"
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
 #include "arch/context_switching/main.hpp"
 #include "arch/kernel/cpu/if.hpp"
 #include "arch/kernel/cpu/jmp.hpp"
+#include "arch/kernel/cpu/segment_register.hpp"
 #include "arch/memory/heap/bump_allocator.hpp"
 #include "arch/memory/heap/global_heap_allocator.hpp"
 #include "arch/memory/main.hpp"
@@ -49,6 +51,23 @@ namespace teachos::arch::kernel
     delete test9;
   }
 
+  [[gnu::naked]]
+  auto push_code_segment(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void
+  {
+    asm volatile("push %%rbp\n"
+                 "push %[input]"
+                 : /* No output from call */
+                 : [input] "m"(segment_selector));
+  }
+
+  [[gnu::naked]]
+  auto iret() -> void
+  {
+    asm volatile("iret"
+                 : /* No output from call */
+                 : /* No input to call */);
+  }
+
   auto main() -> void
   {
     video::vga::text::clear();
@@ -64,6 +83,22 @@ namespace teachos::arch::kernel
     heap_test();
 
     decltype(auto) descriptor_tables = context_switching::initialize_descriptor_tables();
+
+    // - Clear NT flag in EFLAGS register (for far return)
+
+    // - Push return instruction pointer
+    // - Push return code segment selector
+    context_switching::interrupt_descriptor_table::segment_selector user_code_segment_selector{
+        3U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
+    push_code_segment(user_code_segment_selector);
+
+    context_switching::interrupt_descriptor_table::segment_selector user_data_segment_selector{
+        4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
+    kernel::cpu::set_segment_registers(user_data_segment_selector);
+
+    // IRET
+    iret();
+
     (void)descriptor_tables;
   }
 }  // namespace teachos::arch::kernel