From d82476d59fb1076542a163bb2e6534023be43720 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gustav=20S=C3=B6rn=C3=A4s?= <gustav@sornas.net>
Date: Sun, 14 Mar 2021 13:09:18 +0100
Subject: intr_esp doesn't deref

---
 src/userprog/syscall.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

(limited to 'src/userprog')

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index a699784..0e0d97e 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -179,8 +179,8 @@ ptr_is_valid (const void *ptr)
   return true;
 }
 
-// cast to TYPE and deref argument N from f->esp
-#define INTR_ESP(N, TYPE) *(TYPE *)(f->esp+(4*(N)))
+// cast argument N from f->esp to TYPE without dereferencing
+#define INTR_ESP(N, TYPE) (TYPE *)(f->esp+(4*(N)))
 
 #define CHECK_ESP_AND_MAYBE_EXIT(N)          \
   do {                                       \
@@ -196,7 +196,7 @@ syscall_handler (struct intr_frame *f UNUSED)
 {
   // check esp
   CHECK_ESP_AND_MAYBE_EXIT (0);
-  int syscall_number = INTR_ESP (0, int);
+  int syscall_number = *INTR_ESP (0, int);
 
   switch (syscall_number) {
     case 0:
@@ -205,35 +205,35 @@ syscall_handler (struct intr_frame *f UNUSED)
       break;
     case 1:
       // exit
-      exit (INTR_ESP (1, int));
+      exit (*INTR_ESP (1, int));
       break;
     case 2:
       // exec
-      f->eax = exec (INTR_ESP (1, char *));
+      f->eax = exec (*INTR_ESP (1, char *));
       break;
     case 3:
       // wait
-      f->eax = wait (INTR_ESP (1, tid_t));
+      f->eax = wait (*INTR_ESP (1, tid_t));
       break;
     case 4:
       // create
-      f->eax = create (INTR_ESP (1, char *), INTR_ESP (2, off_t));
+      f->eax = create (*INTR_ESP (1, char *), *INTR_ESP (2, off_t));
       break;
     case 6:
       // open
-      f->eax = open (INTR_ESP (1, char *));
+      f->eax = open (*INTR_ESP (1, char *));
       break;
     case 8:
       // read
-      f->eax = read (INTR_ESP (1, int), INTR_ESP (2, void *), INTR_ESP (3, unsigned));
+      f->eax = read (*INTR_ESP (1, int), *INTR_ESP (2, void *), *INTR_ESP (3, unsigned));
       break;
     case 9:
       // write
-      f->eax = write (INTR_ESP (1, int), INTR_ESP (2, const void *), INTR_ESP (3, unsigned));
+      f->eax = write (*INTR_ESP (1, int), *INTR_ESP (2, const void *), *INTR_ESP (3, unsigned));
       break;
     case 12:
       // close
-      close (INTR_ESP (1, int));
+      close (*INTR_ESP (1, int));
       break;
     default:
       printf ("kernel: unknown syscall '%d'\n", syscall_number);
-- 
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