kernel: add a temporary syscall dispatch system

arch/x86_64/irq.c

@@ -7,6 +7,7 @@
 #include <mango/machine/irq.h>
 #include <mango/panic.h>
 #include <mango/sched.h>
+#include <mango/syscall.h>
 #include <stddef.h>
 
 #define MAX_ISR_HANDLERS  16
@@ -151,6 +152,8 @@ int idt_init(struct idt_ptr *ptr)
 		init_global_idt();
 	}
 
+	set_syscall_gate((uintptr_t)syscall_gate);
+
 	ptr->i_limit = sizeof(idt) - 1;
 	ptr->i_base = (uintptr_t)&idt;
 
@@ -203,7 +206,7 @@ void irq_dispatch(struct ml_cpu_context *regs)
 void syscall_dispatch(struct ml_cpu_context *regs)
 {
 	unsigned int sysid = regs->rax;
-	virt_addr_t syscall_impl = 0;   // TODO
+	virt_addr_t syscall_impl = syscall_get_func(sysid);
 
 	if (syscall_impl == 0) {
 		regs->rax = KERN_UNSUPPORTED;