From e2514b22b2bd4be907094fb3a6223fa61c558620 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gustav=20S=C3=B6rn=C3=A4s?= <gustav@sornas.net>
Date: Thu, 4 Feb 2021 14:17:52 +0100
Subject: syscall_handler(): macro to read user process arguments

---
 src/userprog/syscall.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

(limited to 'src/userprog')

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 49e61e8..1287d98 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -13,10 +13,13 @@ syscall_init (void)
   intr_register_int (0x30, 3, INTR_ON, syscall_handler, "syscall");
 }
 
+// cast to TYPE and deref argument N from f->esp
+#define INTR_ESP(N, TYPE) *(TYPE *)(f->esp+(4*(N)))
+
 static void
 syscall_handler (struct intr_frame *f UNUSED) 
 {
-  int syscall_number = *((int *)f->esp);
+  int syscall_number = INTR_ESP(0, int);
   switch (syscall_number) {
     case 0:
       // halt
@@ -24,7 +27,7 @@ syscall_handler (struct intr_frame *f UNUSED)
       break;
     case 9:
       // printf
-      printf ("printf: %s", *((char **)(f->esp+8)));
+      printf ("printf: %s", INTR_ESP(2, char *));
       break;
     default:
       printf ("kernel: unknown syscall '%d'\n", syscall_number);
-- 
cgit v1.2.1