implement argument parsing

1 files changed, 55 insertions, 1 deletions

diff --git a/src/userprog/process.c b/src/userprog/process.c
index 0be6e30..2b50edd 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -295,10 +295,64 @@ load (const char *file_name, void (**eip) (void), void **esp)
     goto done;
   }
 
+  /* Copy passed command to start of user stack. */
+  size_t cmd_len = strlen (file_name);
+  char *esp_cmd = *esp;
+  esp_cmd -= cmd_len + 1;  // +1 makes room for '\0'
+  for (size_t i = 0; i < cmd_len; i++) {
+    esp_cmd[i] = file_name[i];
+  }
+  esp_cmd[cmd_len] = '\0';
+
+  unsigned argc = 0;
+
+  /* Tokenize passed command in-place. */
+  // esp_c still points to first character of passed command
+  char *token, *save_ptr;
+  for (token = strtok_r (esp_cmd, " ", &save_ptr); token != NULL;
+       token = strtok_r (NULL, " ", &save_ptr))
+  {
+    argc++;
+  }
+
+  file_name = esp_cmd;
+
+  /* Alignment for entries of argv. */
+  size_t psize = sizeof (char *);
+  size_t word_alignment = (cmd_len + psize) / psize;  // next address to place pointer
+
+  /* Write argv entries. */
+  char **esp_argv_entry = *esp;
+  esp_argv_entry -= word_alignment + argc + 1;  // +1 makes room for argv[argc] = NULL
+
+  char **esp_argv_first = esp_argv_entry;
+
+  // esp_cmd points to first entry so write directly
+  *esp_argv_entry = esp_cmd;
+  esp_argv_entry++;
+
+  for (unsigned i = 0; i < argc - 1; i++) {
+    // find next \0 in cmd
+    while (*(++esp_cmd) != '\0') {}
+    *esp_argv_entry = esp_cmd + 1;
+    esp_argv_entry++;
+  }
+
+  char *** esp_argv = esp_argv_first;
+  esp_argv--;
+
+  *esp_argv = esp_argv_first;
+
+  int *esp_argc = esp_argv;
+  esp_argc--;
+  *esp_argc = argc;
+
+  *esp = esp_argc - 1; // return address
+
    /* Uncomment the following line to print some debug
      information. This will be useful when you debug the program
      stack.*/
-/*#define STACK_DEBUG*/
+// #define STACK_DEBUG
 
 #ifdef STACK_DEBUG
   printf("*esp is %p\nstack contents:\n", *esp);