1 files changed, 98 insertions, 0 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..b08c9c4
--- /dev/null
+++ b/arch/x86_64/src/kernel/cpu/segment_register.cpp
@@ -0,0 +1,98 @@
+#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
+{
+  auto reload_data_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"
+                 : /* no output from call */
+                 : /* no input to call */
+                 : "rax");
+  }
+
+  auto set_data_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment) -> void
+  {
+    asm volatile("xor %%rax, %%rax\n"
+                 "mov %[input], %%ax\n"
+                 "mov %%rax, %%ds\n"
+                 "mov %%rax, %%es\n"
+                 "mov %%rax, %%fs\n"
+                 "mov %%rax, %%gs\n"
+                 : /* no output from call */
+                 : [input] "m"(data_segment)
+                 : "rax");
+  }
+
+  auto read_code_segment_register() -> context_switching::interrupt_descriptor_table::segment_selector
+  {
+    context_switching::interrupt_descriptor_table::segment_selector current_value{};
+    asm volatile("mov %%cs, %[output]" : [output] "=r"(current_value));
+    return current_value;
+  }
+
+  auto validate_data_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment)
+      -> void
+  {
+    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.");
+    result = (ss == data_segment);
+    exception_handling::assert(
+        result, "[Segment Register] Expected Data Segment is not the same as the value in the Stack Segment register.");
+  }
+
+  auto validate_code_segment_register(context_switching::interrupt_descriptor_table::segment_selector code_segment)
+      -> void
+  {
+    auto const cs = read_code_segment_register();
+    exception_handling::assert(
+        cs == code_segment,
+        "[Segment Register] Expected Code Segment is not the same as the value in the Code Segment register.");
+  }
+
+  auto validate_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment,
+                                  context_switching::interrupt_descriptor_table::segment_selector code_segment) -> void
+  {
+    validate_data_segment_registers(data_segment);
+    validate_code_segment_register(code_segment);
+  }
+
+  auto set_code_segment_register(context_switching::interrupt_descriptor_table::segment_selector data_segment,
+                                 context_switching::interrupt_descriptor_table::segment_selector code_segment,
+                                 uint64_t address) -> void
+  {
+    asm volatile("mov %%rsp, %%rax\n"
+                 "push %[data_segment]\n"
+                 "push %%rax\n"
+                 "pushfq\n"
+                 "push %[code_segment]\n"
+                 "mov %[return_function], %%rax\n"
+                 "push %%rax\n"
+                 "iretq\n"
+                 : /* no output from call */
+                 : [data_segment] "m"(data_segment), [code_segment] "m"(code_segment), [return_function] "r"(address)
+                 : "rax");
+  }
+
+}  // namespace teachos::arch::kernel::cpu