WIP syscall

3 files changed, 31 insertions, 4 deletions

diff --git a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
index c50ac1d..c041198 100644
--- a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
@@ -27,8 +27,8 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
       }
 
       interrupt_descriptor_table.at(0x80) = {
-          segment_selector{3U, segment_selector::REQUEST_LEVEL_USER}, ist_offset{0U},
-          idt_flags{idt_flags::DESCRIPTOR_LEVEL_USER | idt_flags::INTERRUPT_GATE | idt_flags::PRESENT},
+          segment_selector{1U, segment_selector::REQUEST_LEVEL_KERNEL}, ist_offset{0U},
+          idt_flags{idt_flags::DESCRIPTOR_LEVEL_USER | idt_flags::TRAP_GATE | idt_flags::PRESENT},
           uint64_t{reinterpret_cast<uint64_t>(interrupt_handling::syscall_interrupt_handler)}};
 
       return interrupt_descriptor_table;
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 7be286a..faaf831 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -52,7 +52,14 @@ namespace teachos::arch::context_switching
   {
     kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
 
-    asm volatile("INT $0x80");
+    // TODO/INFO:
+    // https://stackoverflow.com/questions/46022184/osdev-syscall-sysret-and-sysenter-sysexit-instructions-enabling
+    // https://stackoverflow.com/questions/12806584/what-is-better-int-0x80-or-syscall-in-32-bit-code-on-linux
+    //
+    // People claim that SYSENTER is for 32-Bit, while SYSCALL is for 64-Bit!
+
+    // asm volatile("INT $0x80");
+    asm volatile("SYSCALL");
 
     video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
   }
diff --git a/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp b/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
index 6075770..7afd87d 100644
--- a/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
+++ b/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
@@ -15,7 +15,27 @@ namespace teachos::arch::interrupt_handling
   [[gnu::interrupt]] [[gnu::section(".interrupt_text")]]
   auto syscall_interrupt_handler(interrupt_frame * frame) -> void
   {
+    // RDI, RSI, RDX, RCX, R8, R9
+    // RDI -> SYSCALL number
+    // Others are arguments
+
+    // TODO: The registers are not available here. We need to set them up on the stack
+    // and access them via argument.
+
+    uint64_t syscall_number{};
+    asm volatile("mov %%rdi, %0" : "=r"(syscall_number));
+
+    // Handle system call based on the number
+    switch (syscall_number)
+    {
+      case 1:
+        video::vga::text::write("SYSCALL 1.", video::vga::text::common_attributes::green_on_black);
+        break;
+      default:
+        // Handle unknown syscall
+        break;
+    }
+
     (void)frame;
-    video::vga::text::write("A SYSCALL interrupt occurred.", video::vga::text::common_attributes::green_on_black);
   }
 }  // namespace teachos::arch::interrupt_handling