3 files changed, 34 insertions, 4 deletions
diff --git a/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp b/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp
index fd5a972..d495ce6 100644
--- a/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp
+++ b/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp
@@ -25,6 +25,12 @@ namespace teachos::arch::kernel::cpu
    */
   auto read_code_segment_register() -> context_switching::interrupt_descriptor_table::segment_selector;
 
+  /**
+   * @brief TODO
+   *
+   */
+  auto validate_data_segment_registers() -> context_switching::interrupt_descriptor_table::segment_selector;
+
 }  // namespace teachos::arch::kernel::cpu
 
 #endif  // TEACHOS_ARCH_X86_64_KERNEL_CPU_SEGMENT_REGISTER_HPP
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 3efba45..0f2ec93 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -2,6 +2,7 @@
 
 #include "arch/exception_handling/assert.hpp"
 #include "arch/kernel/cpu/call.hpp"
+#include "arch/kernel/cpu/control_register.hpp"
 #include "arch/kernel/cpu/if.hpp"
 #include "arch/kernel/cpu/segment_register.hpp"
 #include "arch/kernel/cpu/tr.hpp"
@@ -82,10 +83,12 @@ namespace teachos::arch::context_switching
   auto user_mode_main() -> void
   {
     auto current_segment = kernel::cpu::read_code_segment_register();
-    arch::exception_handling::assert(USER_CODE_SEGMENT_SELECTOR == current_segment,
-                                     "[Context Switching] Context switch into user mode not successful");
+    exception_handling::assert(USER_CODE_SEGMENT_SELECTOR == current_segment,
+                               "[Context Switching] Context switch into user mode not successful");
+    exception_handling::assert(USER_DATA_SEGMENT_SELECTOR == kernel::cpu::validate_data_segment_registers(),
+                               "[Context Switching] Context switch into user mode not successful");
 
-    video::vga::text::write("User Mode!!!", video::vga::text::common_attributes::green_on_black);
+    video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
   }
 
   auto switch_to_user_mode() -> void
diff --git a/arch/x86_64/src/kernel/cpu/segment_register.cpp b/arch/x86_64/src/kernel/cpu/segment_register.cpp
index 9fb7433..cb367b6 100644
--- a/arch/x86_64/src/kernel/cpu/segment_register.cpp
+++ b/arch/x86_64/src/kernel/cpu/segment_register.cpp
@@ -1,6 +1,7 @@
 #include "arch/kernel/cpu/segment_register.hpp"
 
 #include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
+#include "arch/exception_handling/assert.hpp"
 
 namespace teachos::arch::kernel::cpu
 {
@@ -37,6 +38,26 @@ namespace teachos::arch::kernel::cpu
     return current_value;
   }
 
-  auto validate_segment_registers() -> context_switching::interrupt_descriptor_table::segment_selector {}
+  auto validate_data_segment_registers() -> context_switching::interrupt_descriptor_table::segment_selector
+  {
+    context_switching::interrupt_descriptor_table::segment_selector ss;
+    context_switching::interrupt_descriptor_table::segment_selector ds;
+    context_switching::interrupt_descriptor_table::segment_selector es;
+    context_switching::interrupt_descriptor_table::segment_selector fs;
+    context_switching::interrupt_descriptor_table::segment_selector gs;
+
+    asm volatile(
+        "mov %%ss, %[ss_output]\n"
+        "mov %%ds, %[ds_output]\n"
+        "mov %%es, %[es_output]\n"
+        "mov %%fs, %[fs_output]\n"
+        "mov %%gs, %[gs_output]\n"
+        : [ss_output] "=r"(ss), [ds_output] "=r"(ds), [es_output] "=r"(es), [fs_output] "=r"(fs), [gs_output] "=r"(gs));
+
+    auto result = ss == ds && ss == es && ss == fs && ss == gs;
+    exception_handling::assert(result, "[Segment Register] Values in data register are not the same.");
+
+    return ss;
+  }
 
 }  // namespace teachos::arch::kernel::cpu