wip enable syscall

1 files changed, 12 insertions, 16 deletions

diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 33af765..21299da 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -33,22 +33,16 @@ namespace teachos::arch::context_switching
 
     auto user_mode_main() -> void
     {
-      kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
-
       video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
 
       asm volatile("syscall");
 
-      kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
-
-      video::vga::text::write("Successfully made a SYSCALL and returned back with SYSRET!",
+      video::vga::text::write("Successfully made a SYSCALL and returned back with SYSRETQ!",
                               video::vga::text::common_attributes::green_on_black);
     }
 
     auto syscall_handler() -> void
     {
-      kernel::cpu::validate_segment_registers(KERNEL_CODE_SEGMENT_SELECTOR, KERNEL_DATA_SEGMENT_SELECTOR);
-
       uint64_t dummy{};
       switch (dummy)
       {
@@ -65,17 +59,19 @@ namespace teachos::arch::context_switching
     {
       uint64_t const syscall_function = reinterpret_cast<uint64_t>(syscall_handler);
       kernel::cpu::write_msr(IA32_LSTAR_ADDRESS, syscall_function);
-      kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
-
-      uint64_t kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;    // Your 64-bit kernel code segment selector
-      uint64_t user_cs = USER_CODE_SEGMENT_SELECTOR + 0x3;  // User mode code segment selector (RPL=3)
-
-      uint64_t star_value = (user_cs << 48) | (kernel_cs << 32);
-
+      kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 1 << 9U);  // Disable interrupt flag during syscall
+
+      // @MTO: This produces following values:
+      // After SYSCALL: CS = 0x10, SS = 0x18
+      // After SYSRETQ: CS = 0x43, SS = 0x3b
+      //
+      // We probably need to modify our GDT, because the cs+8 = ss is an issue we cannot solve.
+      // Also, CS = 0x43 is weird. I expected it to be 0x33.
+      uint64_t kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
+      uint64_t user_cs = USER_CODE_SEGMENT_SELECTOR;
+      uint64_t star_value = (kernel_cs << 32) | (user_cs << 48);
       kernel::cpu::write_msr(IA32_STAR_ADDRESS, star_value);
-      kernel::cpu::write_msr(IA32_STAR_ADDRESS, KERNEL_CODE_SEGMENT_SELECTOR);
 
-      // kernel::cpu::write_msr(IA32_STAR_ADDRESS, KERNEL_CODE_SEGMENT_SELECTOR);
       kernel::cpu::set_efer_bit(kernel::cpu::efer_flags::SCE);
     }