From d626b7a392aca74c5327daf493d5183a24571106 Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Sun, 3 Nov 2024 23:47:22 +0000
Subject: [PATCH] Implement basic syscall_handler using the lookup table, w/ E

---
 src/userprog/syscall.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 9164142..5e53cd3 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -17,6 +17,8 @@ typedef uintptr_t (*syscall_function) (uintptr_t, uintptr_t, uintptr_t);
 static void halt (void);
 static void exit (int status);
 
+static void *validate_user_pointer(void *ptr, size_t size);
+
 /* A struct defining a pair of a syscall_function along with its arity. */
 typedef struct {
   syscall_function function;
@@ -29,6 +31,9 @@ static const syscall_arguments syscall_lookup[] = {
   [SYS_EXIT] = {(syscall_function) exit, 1},
 };
 
+static const int lookup_size
+  = sizeof (syscall_lookup) / sizeof (syscall_arguments);
+
 void
 syscall_init (void) 
 {
@@ -36,10 +41,23 @@ syscall_init (void)
 }
 
 static void
-syscall_handler (struct intr_frame *f UNUSED) 
+syscall_handler (struct intr_frame *f)
 {
-  printf ("system call!\n");
-  thread_exit ();
+  validate_user_pointer(f->esp, 1);
+  int syscall_number = *(int *) f->esp;
+
+  if (syscall_number < 0 || syscall_number >= lookup_size)
+    thread_exit ();
+
+  syscall_arguments syscall = syscall_lookup[syscall_number];
+
+  validate_user_pointer (f->esp, syscall.arity);
+  uintptr_t args[3];
+
+  for (int i=0; i < syscall.arity; i++)
+      args[i] = *(uintptr_t *) (f->esp + 1 + i);
+
+  f->eax = syscall.function(args[0], args[1], args[2]);
 }
 
 static void