Refactor stack growth to be helper functions in exception for easier merging

# Conflicts:
#   src/Makefile.build

src/Makefile.build

@@ -65,6 +65,7 @@ userprog_SRC += userprog/tss.c		# TSS management.
 vm_SRC += vm/frame.c                    # Frame table manager.
 vm_SRC += vm/page.c                     # Page table manager.
 vm_SRC += devices/swap.c		# Swap block manager.
+#vm_SRC = vm/file.c			# Some other file.
 
 # Filesystem code.
 filesys_SRC  = filesys/filesys.c	# Filesystem core.

src/threads/thread.h

@@ -143,6 +143,8 @@ struct thread
     struct hash open_files;             /* Hash Table of FD -> Struct File. */
 #endif
 
+    void *curr_esp;
+
     /* Owned by thread.c. */
     unsigned magic;                     /* Detects stack overflow. */
   };

src/userprog/Make.vars

@@ -1,7 +1,7 @@
 # -*- makefile -*-
 
-kernel.bin: DEFINES = -DUSERPROG -DFILESYS
-KERNEL_SUBDIRS = threads devices lib lib/kernel userprog filesys
+kernel.bin: DEFINES = -DUSERPROG -DFILESYS -DVM
+KERNEL_SUBDIRS = threads devices lib lib/kernel userprog filesys vm
 TEST_SUBDIRS = tests/userprog tests/userprog/no-vm tests/filesys/base
 GRADING_FILE = $(SRCDIR)/tests/userprog/Grading
 SIMULATOR = --qemu

src/userprog/exception.c

@@ -2,8 +2,15 @@
 #include <inttypes.h>
 #include <stdio.h>
 #include "userprog/gdt.h"
+#include "userprog/pagedir.h"
+#include "userprog/process.h"
 #include "threads/interrupt.h"
+#include "threads/palloc.h"
 #include "threads/thread.h"
+#include "threads/vaddr.h"
+
+#define MAX_STACK_SIZE (8 * 1024 * 1024) // 8MB
+#define MAX_STACK_OFFSET 32 // 32 bytes offset below stack pointer (ESP)
 
 /* Number of page faults processed. */
 static long long page_fault_cnt;
@@ -11,6 +18,9 @@ static long long page_fault_cnt;
 static void kill (struct intr_frame *);
 static void page_fault (struct intr_frame *);
 
+static bool is_valid_stack_access (const void *fault_addr, const void *esp);
+static bool grow_stack (void *upage);
+
 /* Registers handlers for interrupts that can be caused by user
    programs.
 
@@ -145,6 +155,27 @@ page_fault (struct intr_frame *f)
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
+  if (!user || !not_present)
+  {
+    f->eip = (void *)f->eax;
+    f->eax = 0xffffffff;
+    return;
+  }
+
+  /* If the fault address is in a user page that is not present, then it might
+   be just that the stack needs to grow. So we attempt to grow the stack. */
+  void *upage = pg_round_down (fault_addr);
+  if (not_present && is_user_vaddr (upage) && upage != NULL)
+    {
+      if (is_valid_stack_access (fault_addr, f->esp))
+        {
+          if (grow_stack (upage))
+            return;
+        }
+
+      /* TODO: Check SPT for the page. */
+    }
+
   /* To implement virtual memory, delete the rest of the function
      body, and replace it with code that brings in the page to
      which fault_addr refers. */
@@ -156,3 +187,50 @@ page_fault (struct intr_frame *f)
   kill (f);
 }
 
+/* Validates whether the fault address is a valid stack access. Access is a
+   valid stack access under the following two conditions:
+     1. The fault address must be within MAX_STACK_OFFSET (32) bytes below
+      the current stack pointer. (Accounts for both PUSH and PUSHA instructions)
+     2. Growing this stack to this address does not cause it to exceed the
+      MAX_STACK_SIZE (8MB) limit.
+
+   Returns true if both conditions are met, false otherwise.
+
+   Pre: fault_addr is a valid user virtual address (so also not NULL). */
+static bool
+is_valid_stack_access (const void *fault_addr, const void *esp)
+{
+  uint32_t new_stack_size = PHYS_BASE - pg_round_down (fault_addr);
+
+  uint32_t *lowest_valid_push_addr = (uint32_t *)esp - MAX_STACK_OFFSET;
+  bool is_within_push_range = (uint32_t *)fault_addr >= lowest_valid_push_addr;
+
+  return is_within_push_range && new_stack_size <= MAX_STACK_SIZE;
+}
+
+/* Attempts to grow the stack by allocating and mapping a new page.
+  This involves:
+    1. Allocating a zeroed page from the user pool
+    2. Installing it into the page table with write permissions
+
+  Returns true if the stack was successfully grown, false if either
+  allocation or installation fails.
+
+  Pre: upage is a valid page-aligned address (so also not NULL). */
+static bool
+grow_stack (void *upage)
+{
+  /* Allocate new page for stack */
+  void *kpage = palloc_get_page (PAL_USER | PAL_ZERO);
+  if (kpage == NULL)
+    return false;
+
+  /* Install the page into user page table */
+  if (!install_page (upage, kpage, true))
+    {
+      palloc_free_page (kpage);
+      return false;
+    }
+
+  return true;
+}

src/userprog/process.c

@@ -118,7 +118,7 @@ process_execute (const char *cmd)
 
 static void *get_usr_kpage (enum palloc_flags flags, void *upage);
 static void free_usr_kpage (void *kpage);
-static bool install_page (void *upage, void *kpage, bool writable);
+bool install_page (void *upage, void *kpage, bool writable);
 
 static bool process_init_stack (char *cmd_saveptr, void **esp, char *file_name);
 static void *push_to_stack (void **esp, void *data, size_t data_size);
@@ -809,7 +809,7 @@ free_usr_kpage (void *kpage)
    with palloc_get_page().
    Returns true on success, false if UPAGE is already mapped or
    if memory allocation fails. */
-static bool
+bool
 install_page (void *upage, void *kpage, bool writable)
 {
   struct thread *t = thread_current ();

src/userprog/process.h

@@ -8,4 +8,6 @@ int process_wait (tid_t);
 void process_exit (void);
 void process_activate (void);
 
+bool install_page (void *upage, void *kpage, bool writable);
+
 #endif /* userprog/process.h */

src/userprog/syscall.c

@@ -11,6 +11,7 @@
 #include "userprog/process.h"
 #include "userprog/pagedir.h"
 #include <stdio.h>
+#include <stdbool.h>
 #include <syscall-nr.h>
 
 #define MAX_SYSCALL_ARGS 3
@@ -46,8 +47,11 @@ static unsigned syscall_tell (int fd);
 static void syscall_close (int fd);
 
 static struct open_file *fd_get_file (int fd);
-static void validate_user_pointer (const void *start, size_t size);
-static void validate_user_string (const char *str);
+static void validate_user_pointer (const void *ptr, size_t size,
+                                   bool check_write);
+static void validate_user_string (const char *str, bool check_write);
+static int get_user (const uint8_t *);
+static bool put_user (uint8_t *, uint8_t);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 struct syscall_arguments
@@ -96,8 +100,9 @@ static void
 syscall_handler (struct intr_frame *f)
 {
   /* First, read the system call number from the stack. */
-  validate_user_pointer (f->esp, sizeof (uintptr_t));
-  uintptr_t syscall_number = *(int *) f->esp;
+  validate_user_pointer (f->esp, sizeof (uintptr_t), false);
+  uintptr_t syscall_number = *(int *)f->esp;
+  thread_current ()->curr_esp = f->esp;
 
   /* Ensures the number corresponds to a system call that can be handled. */
   if (syscall_number >= LOOKUP_SIZE)
@@ -107,11 +112,10 @@ syscall_handler (struct intr_frame *f)
 
   /* Next, read and copy the arguments from the stack pointer. */
   validate_user_pointer (f->esp + sizeof (uintptr_t),
-                         syscall.arity * sizeof (uintptr_t));
-
-  uintptr_t args[MAX_SYSCALL_ARGS] = {0};
+                         syscall.arity * sizeof (uintptr_t), false);
+  uintptr_t args[MAX_SYSCALL_ARGS] = { 0 };
   for (int i = 0; i < syscall.arity && i < MAX_SYSCALL_ARGS; i++)
-    args[i] = *(uintptr_t *) (f->esp + sizeof (uintptr_t) * (i + 1));
+    args[i] = *(uintptr_t *)(f->esp + sizeof (uintptr_t) * (i + 1));
 
   /* Call the function that handles this system call with the arguments. When
      there is a return value it is stored in f->eax. */
@@ -140,8 +144,7 @@ syscall_exit (int status)
 static pid_t
 syscall_exec (const char *cmd_line)
 {
-  /* Validate the user string before executing the process. */
-  validate_user_string (cmd_line);
+  validate_user_string (cmd_line, false);
 
   return process_execute (cmd_line); /* Returns the PID of the new process */
 }
@@ -160,8 +163,7 @@ syscall_wait (pid_t pid)
 static bool
 syscall_create (const char *file, unsigned initial_size)
 {
-  /* Validate the user string before creating the file. */
-  validate_user_string (file);
+  validate_user_string (file, false);
 
   /* Acquire the file system lock to prevent race conditions. */
   lock_acquire (&filesys_lock);
@@ -178,8 +180,7 @@ syscall_create (const char *file, unsigned initial_size)
 static bool
 syscall_remove (const char *file)
 {
-  /* Validate the user string before removing the file. */
-  validate_user_string (file);
+  validate_user_string (file, false);
 
   /* Acquire the file system lock to prevent race conditions. */
   lock_acquire (&filesys_lock);
@@ -197,8 +198,7 @@ syscall_remove (const char *file)
 static int
 syscall_open (const char *file)
 {
-  /* Validate the user string before opening the file. */
-  validate_user_string (file);
+  validate_user_string (file, false);
 
   /* Acquire the file system lock to prevent race conditions. */
   lock_acquire (&filesys_lock);
@@ -264,8 +264,7 @@ syscall_read (int fd, void *buffer, unsigned size)
   if (fd < STDIN_FILENO || fd == STDOUT_FILENO)
     return EXIT_FAILURE;
 
-  /* Validate the user buffer for the provided size before reading. */
-  validate_user_pointer (buffer, size);
+  validate_user_pointer (buffer, size, true);
 
   if (fd == STDIN_FILENO)
     {
@@ -308,8 +307,7 @@ syscall_write (int fd, const void *buffer, unsigned size)
   if (fd <= 0)
     return 0;
 
-  /* Validate the user buffer for the provided size before writing. */
-  validate_user_pointer (buffer, size);
+  validate_user_pointer (buffer, size, false);
 
   if (fd == STDOUT_FILENO)
     {
@@ -451,63 +449,91 @@ fd_get_file (int fd)
   return hash_entry (e, struct open_file, elem);
 }
 
-/* Validates if a block of memory starting at START and of size SIZE bytes is
-   fully contained within user virtual memory. Kills the thread (by exiting with
-   failure) if the memory is invalid. Otherwise, returns (nothing) normally.
-   If the size is 0, the function does no checks and returns the given ptr. */
+/* Validates if a block of memory starting at PTR and of size SIZE bytes is
+   fully contained within valid user virtual memory. thread_exit () if the
+   memory is invalid.
+   If the size is 0, the function does no checks and returns PTR. */
 static void
-validate_user_pointer (const void *start, size_t size)
+validate_user_pointer (const void *ptr, size_t size, bool check_write)
 {
-  /* If the size is 0, we do not need to check anything. */
   if (size == 0)
     return;
-
-  const void *end = start + size - 1;
-
-  /* Check if the start and end pointers are valid user virtual addresses. */
-  if (start == NULL || !is_user_vaddr (start) || !is_user_vaddr (end))
+  /* ptr < ptr + size - 1, so sufficient to check that (ptr + size -1) is a
+     valid user virtual memory address. */
+  void *last = ptr + size - 1;
+  if (!is_user_vaddr (last))
     syscall_exit (EXIT_FAILURE);
-
-  /* We now need to check if the entire memory block is mapped to physical
-     memory by the page table. */
-  for (const void *ptr = pg_round_down (start); ptr <= end; ptr += PGSIZE)
-    if (pagedir_get_page (thread_current ()->pagedir, ptr) == NULL)
+  ptr = pg_round_down (ptr);
+  while (ptr <= last)
+    {
+      int result;
+      /* Check read access to pointer. */
+      if ((result = get_user (ptr)) == -1)
         syscall_exit (EXIT_FAILURE);
+      /* Check write access to pointer (if required). */
+      if (check_write && !put_user (ptr, result))
+        syscall_exit (EXIT_FAILURE);
+      ptr += PGSIZE;
+    }
 }
 
-/* Validates if a string is fully contained within user virtual memory. Kills
-   the thread (by exiting with failure) if the memory is invalid. Otherwise,
-   returns (nothing) normally. */
+/* Validates of a C-string starting at ptr is fully contained within valid
+   user virtual memory. thread_exit () if the memory is invalid. */
 static void
-validate_user_string (const char *str)
+validate_user_string (const char *ptr, bool check_write)
 {
-  /* Check if the string pointer is a valid user virtual address. */
-  if (str == NULL || !is_user_vaddr (str))
-    syscall_exit (EXIT_FAILURE);
+  size_t offset = (uintptr_t) ptr % PGSIZE;
 
-  /* Calculate the offset of the string within the (first) page. */
-  size_t offset = (uintptr_t) str % PGSIZE;
-
-  /* We move page by page, checking if the page is mapped to physical memory. */
   for (;;)
     {
-    void *page = pg_round_down (str);
+      void *page = pg_round_down (ptr);
 
-    /* If we reach addresses that are not mapped to physical memory before the
-       end of the string, the thread is terminated. */
-    if (!is_user_vaddr(page) ||
-        pagedir_get_page (thread_current ()->pagedir, page) == NULL)
+      if (!is_user_vaddr (page))
+        syscall_exit (EXIT_FAILURE);
+      if (!is_user_vaddr (ptr))
+        syscall_exit (EXIT_FAILURE);
+      int result;
+      if ((result = get_user ((const uint8_t *)ptr)) == -1)
+        syscall_exit (EXIT_FAILURE);
+      if (check_write && !put_user ((uint8_t *)ptr, result))
         syscall_exit (EXIT_FAILURE);
 
       while (offset < PGSIZE)
       {
-        if (*str == '\0')
+        if (*ptr == '\0')
           return; /* We reached the end of the string without issues. */
 
-        str++;
+        ptr++;
         offset++;
       }
 
-    offset = 0; /* Next page will start at the beginning. */
+      offset = 0;
+
     }
 }
+
+/* PROVIDED BY SPEC.
+   Reads a byte at user virtual address UADDR.
+   UADDR must be below PHYS_BASE.
+   Returns the byte value if successful, -1 if a segfault occurred. */
+static int
+get_user (const uint8_t *uaddr)
+{
+  int result;
+  asm ("movl $1f, %0; movzbl %1, %0; 1:" : "=&a"(result) : "m"(*uaddr));
+  return result;
+}
+
+/* PROVIDED BY SPEC.
+   Writes BYTE to user address UDST.
+   UDST must be below PHYS_BASE.
+   Returns true if successful, false if a segfault occurred. */
+static bool
+put_user (uint8_t *udst, uint8_t byte)
+{
+  int error_code;
+  asm ("movl $1f, %0; movb %b2, %1; 1:"
+       : "=&a"(error_code), "=m"(*udst)
+       : "q"(byte));
+  return error_code != -1;
+}