From 9dad8ab2c72b9696ddd1324557eb5373f4f56b0a Mon Sep 17 00:00:00 2001
From: manuel <manuel@mausz.at>
Date: Tue, 27 Mar 2012 17:41:50 +0200
Subject: parse the arguments and populate the argv entries accordingly

---
 userprog/process.c | 86 ++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 70 insertions(+), 16 deletions(-)

diff --git a/userprog/process.c b/userprog/process.c
index bd4f6b0..bc8a1a9 100644
--- a/userprog/process.c
+++ b/userprog/process.c
@@ -591,8 +591,11 @@ load_segment (struct file *file, off_t ofs, uint8_t *upage,
 static bool
 setup_stack (void **esp, const char *args)
 {
-  uint8_t *kpage = NULL, stack_total;
+  uint8_t *kpage = NULL;
   const char *name = thread_current ()->name;
+  uint8_t *argv_cur, *argv_end = PHYS_BASE;
+  int argc = 0;
+  unsigned argslen = strlen(args);
 
   kpage = palloc_get_page (PAL_USER | PAL_ZERO);
   if (kpage == NULL)
@@ -602,31 +605,82 @@ setup_stack (void **esp, const char *args)
       palloc_free_page (kpage);
       return false;
   }
-  printf("cmd=%s\n", name);
-  printf("args=%s\n", args);
 
   *esp = PHYS_BASE;
-  printf("esp=%p\n", *esp);
 
   /* copy arguments to stack */
-  *esp -= strlen(args) + 1;
-  memcpy(*esp, args, strlen(args) + 1);
-  printf("esp=%p, off=%d\n", *esp, strlen(args) + 1);
+  if (argslen > 0)
+    {
+      argslen += 1; /* add the trailing \0 */
+      *esp -= argslen;
+      memcpy(*esp, args, argslen);
+      argv_end = *esp;
+    }
 
   /* copy executable name to stack */
   *esp -= strlen(name) + 1;
   memcpy(*esp, name, strlen(name) + 1);
-  printf("esp=%p, off=%d\n", *esp, strlen(name) + 1);
 
-  /* word align our stack so far */
-  stack_total = PHYS_BASE - *esp;
-  printf("stack_total=%u\n", stack_total);
-  printf("unaligned=%p off=%d\n", *esp, PHYS_BASE - *esp);
-  *esp -= (4 - stack_total % sizeof(char *)); /* thanks to thomas */
-  printf("aligned=%p off=%d\n", *esp, PHYS_BASE - *esp);
+  /* align our stack so far by word-size */
+  *esp -= (sizeof(uint32_t) - (PHYS_BASE - *esp) % sizeof(uint32_t)); /* thanks to thomas & edy */
+
+  /* terminate argv[] array by NULL ptr */
+  *esp -= sizeof(uint32_t);
+  *(uint32_t *) *esp = '\0';
+
+  /* push the argv[] entries */
+  if (argslen > 0)
+    {
+      /* we walk through our already pushed arguments in reverse order and
+         replace every occurrence of the space-character with '\0'-character
+         due to the fact we we walk in reverse order we can easily populate
+         the pointers to the elements of argv[] too */
+      for(argv_cur = PHYS_BASE - 1; argv_cur >= argv_end; argv_cur--)
+        {
+          /* check for space-character and replace if necessary */
+          if (*argv_cur == ' ')
+            {
+              *argv_cur = '\0';
+
+              /* since we walk in reverse order and already have replaced a
+                 character we simply check the preceding character. if it's
+                 a non-'\0'-character we know an argument starts here */
+              if (*(argv_cur + 1) != '\0')
+                {
+                  /* push pointer to argument */
+                  *esp -= sizeof(uint32_t);
+                  *(uint32_t *) *esp = (uint32_t) argv_cur + 1;
+                  argc++;
+                }
+            }
+        }
+
+      /* our loop above doesn't check/push the first argument as it's the
+         end of the loop. so let's do that */
+      if (*(argv_cur + 1) != '\0')
+        {
+          *esp -= sizeof(uint32_t);
+          *(uint32_t *) *esp = (uint32_t) argv_cur + 1;
+          argc++;
+        }
+    }
+
+  /* push argv[0] (executable name) */
+  *esp -= sizeof(uint32_t);
+  *(uint32_t *) *esp = (uint32_t) (PHYS_BASE - (argslen + strlen(name) + 1));
+  argc++;
+
+  /* push pointer to argv[]. this is simple as it's our current address */
+  *(uint32_t *) (*esp - 4) = *(uint32_t *) esp;
+  *esp -= sizeof(uint32_t);
+
+  /* push argc */
+  *esp -= sizeof(uint32_t);
+  *(uint32_t *) *esp = argc;
 
-  /* Currently we assume that 'argc = 0' */
-  *esp = PHYS_BASE - 12;
+  /* push fake return address */
+  *esp -= sizeof(uint32_t);
+  *(uint32_t *) *esp = 0;
 
   return true;
 }
-- 
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