From 6c6ce77824b5a9338e59d2fcf24c9bc3e2059146 Mon Sep 17 00:00:00 2001
From: Themis Demetriades <td1223@ic.ac.uk>
Date: Mon, 4 Nov 2024 01:11:19 +0000
Subject: [PATCH] Implement complete stack initialization for user processes,
 without accounting for overflow

---
 src/userprog/process.c | 44 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/src/userprog/process.c b/src/userprog/process.c
index 452f020..7b6ebe9 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -58,6 +58,14 @@ process_execute (const char *file_name)
   return tid;
 }
 
+static void *
+push_to_stack (void **esp, void *data, size_t data_size)
+{
+  *esp -= data_size;
+  memcpy (*esp, data, data_size);
+  return *esp;
+}
+
 /* A thread function that loads a user process and starts it
    running. */
 static void
@@ -70,27 +78,32 @@ start_process (void *file_name_)
      of the process. */
   char *saveptr;
   char *arg = strtok_r (file_name_, " ", &saveptr);
+  
+  char file_name[15];
+  strlcpy (file_name, arg, 15);
 
   /* Initialize interrupt frame and load executable. */
   memset (&if_, 0, sizeof if_);
   if_.gs = if_.fs = if_.es = if_.ds = if_.ss = SEL_UDSEG;
   if_.cs = SEL_UCSEG;
   if_.eflags = FLAG_IF | FLAG_MBS;
-  success = load (arg, &if_.eip, &if_.esp);
+  success = load (file_name, &if_.eip, &if_.esp);
 
   /* Load command line argument *data* to user process stack.
      This can't cause overflow due to enforcing that the size of
      command line input must fit in a page. Also keep track
      of pointers to the argument data within a linked list. */
+  char *file_name_ptr = push_to_stack (&if_.esp, file_name,
+                                       (strlen (file_name) + 1)
+                                        * sizeof (char));
+
   struct list arg_list;
   list_init (&arg_list);
 
-  unsigned int arg_count = 1;
+  int arg_count = 1;
   while (arg != NULL)
     {
-      size_t arg_size = (strlen (arg) + 1) * sizeof (char);
-      if_.esp -= arg_size;
-      memcpy (if_.esp, arg, arg_size);
+      push_to_stack (&if_.esp, arg, (strlen (arg) + 1) * sizeof (char));
       
       struct arg_elem *arg_elem = malloc (sizeof (struct arg_elem));
       ASSERT (arg_elem != NULL);
@@ -122,6 +135,10 @@ start_process (void *file_name_)
      performance. */
   if_.esp -= align_size * sizeof (uint8_t);
   
+  /* Push a null pointer sentinel inside argv. */
+  if_.esp -= sizeof (char *);
+  *(char *) if_.esp = NULL;
+
   /* Push pointers to process arguments from argument linked list */
   struct list_elem *e = list_begin (&arg_list);
   struct list_elem *tail = list_tail (&arg_list);
@@ -129,13 +146,26 @@ start_process (void *file_name_)
     {
       struct arg_elem *arg_elem = list_entry (e, struct arg_elem, elem);
       
-      if_.esp -= sizeof (char *);
-      memcpy (if_.esp, arg_elem->arg, sizeof (char *));
+      push_to_stack (&if_.esp, &arg_elem->arg, sizeof (arg_elem->arg));
       
       e = list_next (e);
       free (arg_elem);
     }
 
+  /* Push pointer to the process file name to the stack. */
+  char **argv = push_to_stack (&if_.esp, &file_name_ptr,
+                               sizeof (file_name_ptr));
+
+  /* Push pointer to the start of argv array. */
+  push_to_stack (&if_.esp, &argv, sizeof(argv));
+
+  /* Push the number of arguments to the stack. */
+  push_to_stack (&if_.esp, &arg_count, sizeof (arg_count));
+
+  /* Push fake return address (null pointer). */
+  if_.esp -= sizeof (char *);
+  *(char *) if_.esp = NULL;
+
   /* If load failed, quit. */
   palloc_free_page (file_name_);
   if (!success)