Kernel/Userspace: Start initial work on userspace and syscalls

kernel/arch/i386/IDT.cpp

@@ -151,6 +151,29 @@ found:
 		"popa;"
 		"iret;"
 	);
+	
+	extern "C" void syscall_asm();
+	asm(
+	".global syscall_asm;"
+	"syscall_asm:"
+		"pusha;"
+		"pushw %ds;"
+		"pushw %es;"
+		"pushw %ss;"
+		"pushw %ss;"
+		"popw %ds;"
+		"popw %es;"
+		"pushl %edx;"
+		"pushl %ecx;"
+		"pushl %ebx;"
+		"pushl %eax;"
+		"call cpp_syscall_handler;"
+		"addl $16, %esp;"
+		"popw %es;"
+		"popw %ds;"
+		"popa;"
+		"iret;"
+	);
 
 	static void flush_idt()
 	{
@@ -175,6 +198,12 @@ found:
 		flush_idt();
 	}
 
+	void register_syscall_handler(uint8_t offset, void(*handler)())
+	{
+		register_interrupt_handler(offset, handler);
+		s_idt[offset].DPL = 3;
+	}
+
 	void initialize()
 	{
 		constexpr size_t idt_size = 0x100 * sizeof(GateDescriptor);
@@ -219,6 +248,8 @@ found:
 		REGISTER_HANDLER(0x1E);
 		REGISTER_HANDLER(0x1F);
 
+		register_syscall_handler(0x80, syscall_asm);
+
 		flush_idt();
 	}