WIP experiment with converting GDT to 8-Byte entries

1 files changed, 17 insertions, 7 deletions

diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 7db9583..5901998 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -29,7 +29,19 @@ namespace teachos::arch::context_switching
     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_global_descriptor_table_register() -> void { kernel::cpu::call(KERNEL_CODE_POINTER); }
+    auto reload_gdtr() -> void
+    {
+      // asm volatile("pushq $0x8\n\t"            // Push new CS
+      //              "lea 1f(%%rip), %%rax\n\t"  // Get address of label 1 into RAX
+      //              "pushq %%rax\n\t"           // Push return address
+      //              "lretq\n"                   // Far return (loads CS:RIP)
+      //              "1:\n\t"                    // Label to return to
+      //              :
+      //              :
+      //              : "rax", "memory");
+
+      kernel::cpu::call(KERNEL_CODE_POINTER);
+    }
 
     auto user_mode_main() -> void
     {
@@ -83,9 +95,7 @@ namespace teachos::arch::context_switching
       kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
 
       uint64_t kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
-      // We want to provide the user code segment, but the instruction calculates + 0x10 to fill the
-      // cs register (See https://www.felixcloutier.com/x86/sysret).
-      uint64_t user_cs = USER_CODE_SEGMENT_SELECTOR - 0x10;
+      uint64_t user_cs = KERNEL_CODE_SEGMENT_SELECTOR;
       uint64_t star_value = (kernel_cs << 32) | (user_cs << 48);
       kernel::cpu::write_msr(IA32_STAR_ADDRESS, star_value);
 
@@ -102,17 +112,17 @@ namespace teachos::arch::context_switching
     {
       kernel::cpu::clear_interrupt_flag();
 
-      segment_descriptor_table::update_global_descriptor_table_register();
+      segment_descriptor_table::update_gdtr();
       interrupt_descriptor_table::update_interrupt_descriptor_table_register();
 
-      reload_global_descriptor_table_register();
+      reload_gdtr();
       segment_descriptor_table::update_task_state_segment_register();
 
       kernel::cpu::set_interrupt_flag();
       initalized = true;
     }
 
-    descriptor_tables tables = {segment_descriptor_table::get_or_create_global_descriptor_table(),
+    descriptor_tables tables = {segment_descriptor_table::get_or_create_gdt(),
                                 interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()};
     return tables;
   }