Attempt to add calls that Reload code segment and data segment register

1 files changed, 31 insertions, 0 deletions

diff --git a/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp b/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
index 578e264..dccce6b 100644
--- a/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
@@ -94,4 +94,35 @@ namespace teachos::arch::context_switching::descriptor_table
                                      "[Global Descriptor Table] Loaded TR value is not the same as the stored value.");
     return gdt;
   }
+
+  auto reload_cs_register(uint16_t gdt_data_offset) -> void
+  {
+    asm volatile("mov %[input], %%ax\n"
+                 "mov %%ax %%ds\n"  // Data Segment
+                 "mov %%ax %%es\n"  // Extra Segment (used for string operations)
+                 "mov %%ax %%fs\n"  // General-purpose Segment
+                 "mov %%ax %%gs\n"  // General-purpose Segment
+                 "mov %%ax %%ss\n"  // Stack Segment
+                 :                  /* no output from call */
+                 : [input] "r"(gdt_data_offset)
+                 : "ax");
+  }
+
+  auto reload_segment_register(uint16_t gdt_code_offset, uint16_t gdt_data_offset) -> void
+  {
+    /*
+      Whatever you do with the GDT has no effect on the CPU until you load new Segment Selectors into Segment Registers.
+      For most of these registers, the process is as simple as using MOV instructions, but changing the CS register
+      requires code resembling a jump or call to elsewhere, as this is the only way its value is meant to be changed.
+    */
+    auto function = [gdt_data_offset] { reload_cs_register(gdt_data_offset); };
+
+    asm volatile("push %[input]\n"
+                 "lea %[func], %%rax\n"
+                 "push %%rax\n"
+                 "retfq\n"
+                 : /* no output from call */
+                 : [input] "r"(gdt_code_offset), [func] "r"(&function)
+                 : "rax");
+  }
 }  // namespace teachos::arch::context_switching::descriptor_table