Initial commit

39 files changed, 4430 insertions, 0 deletions

diff --git a/src/lib/arithmetic.c b/src/lib/arithmetic.c
new file mode 100644
index 0000000..bfc9b5a
--- /dev/null
+++ b/src/lib/arithmetic.c
@@ -0,0 +1,189 @@
+#include <stdint.h>
+
+/* On x86, division of one 64-bit integer by another cannot be
+   done with a single instruction or a short sequence.  Thus, GCC
+   implements 64-bit division and remainder operations through
+   function calls.  These functions are normally obtained from
+   libgcc, which is automatically included by GCC in any link
+   that it does.
+
+   Some x86-64 machines, however, have a compiler and utilities
+   that can generate 32-bit x86 code without having any of the
+   necessary libraries, including libgcc.  Thus, we can make
+   Pintos work on these machines by simply implementing our own
+   64-bit division routines, which are the only routines from
+   libgcc that Pintos requires.
+
+   Completeness is another reason to include these routines.  If
+   Pintos is completely self-contained, then that makes it that
+   much less mysterious. */
+
+/* Uses x86 DIVL instruction to divide 64-bit N by 32-bit D to
+   yield a 32-bit quotient.  Returns the quotient.
+   Traps with a divide error (#DE) if the quotient does not fit
+   in 32 bits. */
+static inline uint32_t
+divl (uint64_t n, uint32_t d)
+{
+  uint32_t n1 = n >> 32;
+  uint32_t n0 = n;
+  uint32_t q, r;
+
+  asm ("divl %4"
+       : "=d" (r), "=a" (q)
+       : "0" (n1), "1" (n0), "rm" (d));
+
+  return q;
+}
+
+/* Returns the number of leading zero bits in X,
+   which must be nonzero. */
+static int
+nlz (uint32_t x) 
+{
+  /* This technique is portable, but there are better ways to do
+     it on particular systems.  With sufficiently new enough GCC,
+     you can use __builtin_clz() to take advantage of GCC's
+     knowledge of how to do it.  Or you can use the x86 BSR
+     instruction directly. */
+  int n = 0;
+  if (x <= 0x0000FFFF)
+    {
+      n += 16;
+      x <<= 16; 
+    }
+  if (x <= 0x00FFFFFF)
+    {
+      n += 8;
+      x <<= 8; 
+    }
+  if (x <= 0x0FFFFFFF)
+    {
+      n += 4;
+      x <<= 4;
+    }
+  if (x <= 0x3FFFFFFF)
+    {
+      n += 2;
+      x <<= 2; 
+    }
+  if (x <= 0x7FFFFFFF)
+    n++;
+  return n;
+}
+
+/* Divides unsigned 64-bit N by unsigned 64-bit D and returns the
+   quotient. */
+static uint64_t
+udiv64 (uint64_t n, uint64_t d)
+{
+  if ((d >> 32) == 0) 
+    {
+      /* Proof of correctness:
+
+         Let n, d, b, n1, and n0 be defined as in this function.
+         Let [x] be the "floor" of x.  Let T = b[n1/d].  Assume d
+         nonzero.  Then:
+             [n/d] = [n/d] - T + T
+                   = [n/d - T] + T                         by (1) below
+                   = [(b*n1 + n0)/d - T] + T               by definition of n
+                   = [(b*n1 + n0)/d - dT/d] + T
+                   = [(b(n1 - d[n1/d]) + n0)/d] + T
+                   = [(b[n1 % d] + n0)/d] + T,             by definition of %
+         which is the expression calculated below.
+
+         (1) Note that for any real x, integer i: [x] + i = [x + i].
+
+         To prevent divl() from trapping, [(b[n1 % d] + n0)/d] must
+         be less than b.  Assume that [n1 % d] and n0 take their
+         respective maximum values of d - 1 and b - 1:
+                 [(b(d - 1) + (b - 1))/d] < b
+             <=> [(bd - 1)/d] < b
+             <=> [b - 1/d] < b
+         which is a tautology.
+
+         Therefore, this code is correct and will not trap. */
+      uint64_t b = 1ULL << 32;
+      uint32_t n1 = n >> 32;
+      uint32_t n0 = n; 
+      uint32_t d0 = d;
+
+      return divl (b * (n1 % d0) + n0, d0) + b * (n1 / d0); 
+    }
+  else 
+    {
+      /* Based on the algorithm and proof available from
+         http://www.hackersdelight.org/revisions.pdf. */
+      if (n < d)
+        return 0;
+      else 
+        {
+          uint32_t d1 = d >> 32;
+          int s = nlz (d1);
+          uint64_t q = divl (n >> 1, (d << s) >> 32) >> (31 - s);
+          return n - (q - 1) * d < d ? q - 1 : q; 
+        }
+    }
+}
+
+/* Divides unsigned 64-bit N by unsigned 64-bit D and returns the
+   remainder. */
+static uint32_t
+umod64 (uint64_t n, uint64_t d)
+{
+  return n - d * udiv64 (n, d);
+}
+
+/* Divides signed 64-bit N by signed 64-bit D and returns the
+   quotient. */
+static int64_t
+sdiv64 (int64_t n, int64_t d)
+{
+  uint64_t n_abs = n >= 0 ? (uint64_t) n : -(uint64_t) n;
+  uint64_t d_abs = d >= 0 ? (uint64_t) d : -(uint64_t) d;
+  uint64_t q_abs = udiv64 (n_abs, d_abs);
+  return (n < 0) == (d < 0) ? (int64_t) q_abs : -(int64_t) q_abs;
+}
+
+/* Divides signed 64-bit N by signed 64-bit D and returns the
+   remainder. */
+static int32_t
+smod64 (int64_t n, int64_t d)
+{
+  return n - d * sdiv64 (n, d);
+}
+
+/* These are the routines that GCC calls. */
+
+long long __divdi3 (long long n, long long d);
+long long __moddi3 (long long n, long long d);
+unsigned long long __udivdi3 (unsigned long long n, unsigned long long d);
+unsigned long long __umoddi3 (unsigned long long n, unsigned long long d);
+
+/* Signed 64-bit division. */
+long long
+__divdi3 (long long n, long long d) 
+{
+  return sdiv64 (n, d);
+}
+
+/* Signed 64-bit remainder. */
+long long
+__moddi3 (long long n, long long d) 
+{
+  return smod64 (n, d);
+}
+
+/* Unsigned 64-bit division. */
+unsigned long long
+__udivdi3 (unsigned long long n, unsigned long long d) 
+{
+  return udiv64 (n, d);
+}
+
+/* Unsigned 64-bit remainder. */
+unsigned long long
+__umoddi3 (unsigned long long n, unsigned long long d) 
+{
+  return umod64 (n, d);
+}
diff --git a/src/lib/ctype.h b/src/lib/ctype.h
new file mode 100644
index 0000000..9096aca
--- /dev/null
+++ b/src/lib/ctype.h
@@ -0,0 +1,28 @@
+#ifndef __LIB_CTYPE_H
+#define __LIB_CTYPE_H
+
+static inline int islower (int c) { return c >= 'a' && c <= 'z'; }
+static inline int isupper (int c) { return c >= 'A' && c <= 'Z'; }
+static inline int isalpha (int c) { return islower (c) || isupper (c); }
+static inline int isdigit (int c) { return c >= '0' && c <= '9'; }
+static inline int isalnum (int c) { return isalpha (c) || isdigit (c); }
+static inline int isxdigit (int c) {
+  return isdigit (c) || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
+}
+static inline int isspace (int c) {
+  return (c == ' ' || c == '\f' || c == '\n'
+          || c == '\r' || c == '\t' || c == '\v');
+}
+static inline int isblank (int c) { return c == ' ' || c == '\t'; }
+static inline int isgraph (int c) { return c > 32 && c < 127; }
+static inline int isprint (int c) { return c >= 32 && c < 127; }
+static inline int iscntrl (int c) { return (c >= 0 && c < 32) || c == 127; }
+static inline int isascii (int c) { return c >= 0 && c < 128; }
+static inline int ispunct (int c) {
+  return isprint (c) && !isalnum (c) && !isspace (c);
+}
+
+static inline int tolower (int c) { return isupper (c) ? c - 'A' + 'a' : c; }
+static inline int toupper (int c) { return islower (c) ? c - 'a' + 'A' : c; }
+
+#endif /* lib/ctype.h */
diff --git a/src/lib/debug.c b/src/lib/debug.c
new file mode 100644
index 0000000..6d7c9e1
--- /dev/null
+++ b/src/lib/debug.c
@@ -0,0 +1,32 @@
+#include <debug.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Prints the call stack, that is, a list of addresses, one in
+   each of the functions we are nested within.  gdb or addr2line
+   may be applied to kernel.o to translate these into file names,
+   line numbers, and function names.  */
+void
+debug_backtrace (void) 
+{
+  static bool explained;
+  void **frame;
+  
+  printf ("Call stack:");
+  for (frame = __builtin_frame_address (0);
+       frame != NULL && frame[0] != NULL;
+       frame = frame[0]) 
+    printf (" %p", frame[1]);
+  printf (".\n");
+
+  if (!explained) 
+    {
+      explained = true;
+      printf ("The `backtrace' program can make call stacks useful.\n"
+              "Read \"Backtraces\" in the \"Debugging Tools\" chapter\n"
+              "of the Pintos documentation for more information.\n");
+    }
+}
diff --git a/src/lib/debug.h b/src/lib/debug.h
new file mode 100644
index 0000000..3218ab6
--- /dev/null
+++ b/src/lib/debug.h
@@ -0,0 +1,38 @@
+#ifndef __LIB_DEBUG_H
+#define __LIB_DEBUG_H
+
+/* GCC lets us add "attributes" to functions, function
+   parameters, etc. to indicate their properties.
+   See the GCC manual for details. */
+#define UNUSED __attribute__ ((unused))
+#define NO_RETURN __attribute__ ((noreturn))
+#define NO_INLINE __attribute__ ((noinline))
+#define PRINTF_FORMAT(FMT, FIRST) __attribute__ ((format (printf, FMT, FIRST)))
+
+/* Halts the OS, printing the source file name, line number, and
+   function name, plus a user-specific message. */
+#define PANIC(...) debug_panic (__FILE__, __LINE__, __func__, __VA_ARGS__)
+
+void debug_panic (const char *file, int line, const char *function,
+                  const char *message, ...) PRINTF_FORMAT (4, 5) NO_RETURN;
+void debug_backtrace (void);
+
+#endif
+
+
+
+/* This is outside the header guard so that debug.h may be
+   included multiple times with different settings of NDEBUG. */
+#undef ASSERT
+#undef NOT_REACHED
+
+#ifndef NDEBUG
+#define ASSERT(CONDITION)                                       \
+        if (CONDITION) { } else {                               \
+                PANIC ("assertion `%s' failed.", #CONDITION);   \
+        }
+#define NOT_REACHED() PANIC ("executed an unreachable statement");
+#else
+#define ASSERT(CONDITION) ((void) 0)
+#define NOT_REACHED() for (;;)
+#endif /* lib/debug.h */
diff --git a/src/lib/inttypes.h b/src/lib/inttypes.h
new file mode 100644
index 0000000..f703725
--- /dev/null
+++ b/src/lib/inttypes.h
@@ -0,0 +1,48 @@
+#ifndef __LIB_INTTYPES_H
+#define __LIB_INTTYPES_H
+
+#include <stdint.h>
+
+#define PRId8 "hhd"
+#define PRIi8 "hhi"
+#define PRIo8 "hho"
+#define PRIu8 "hhu"
+#define PRIx8 "hhx"
+#define PRIX8 "hhX"
+
+#define PRId16 "hd"
+#define PRIi16 "hi"
+#define PRIo16 "ho"
+#define PRIu16 "hu"
+#define PRIx16 "hx"
+#define PRIX16 "hX"
+
+#define PRId32 "d"
+#define PRIi32 "i"
+#define PRIo32 "o"
+#define PRIu32 "u"
+#define PRIx32 "x"
+#define PRIX32 "X"
+
+#define PRId64 "lld"
+#define PRIi64 "lli"
+#define PRIo64 "llo"
+#define PRIu64 "llu"
+#define PRIx64 "llx"
+#define PRIX64 "llX"
+
+#define PRIdMAX "jd"
+#define PRIiMAX "ji"
+#define PRIoMAX "jo"
+#define PRIuMAX "ju"
+#define PRIxMAX "jx"
+#define PRIXMAX "jX"
+
+#define PRIdPTR "td"
+#define PRIiPTR "ti"
+#define PRIoPTR "to"
+#define PRIuPTR "tu"
+#define PRIxPTR "tx"
+#define PRIXPTR "tX"
+
+#endif /* lib/inttypes.h */
diff --git a/src/lib/kernel/bitmap.c b/src/lib/kernel/bitmap.c
new file mode 100644
index 0000000..d323b89
--- /dev/null
+++ b/src/lib/kernel/bitmap.c
@@ -0,0 +1,372 @@
+#include "bitmap.h"
+#include <debug.h>
+#include <limits.h>
+#include <round.h>
+#include <stdio.h>
+#include "threads/malloc.h"
+#ifdef FILESYS
+#include "filesys/file.h"
+#endif
+
+/* Element type.
+
+   This must be an unsigned integer type at least as wide as int.
+
+   Each bit represents one bit in the bitmap.
+   If bit 0 in an element represents bit K in the bitmap,
+   then bit 1 in the element represents bit K+1 in the bitmap,
+   and so on. */
+typedef unsigned long elem_type;
+
+/* Number of bits in an element. */
+#define ELEM_BITS (sizeof (elem_type) * CHAR_BIT)
+
+/* From the outside, a bitmap is an array of bits.  From the
+   inside, it's an array of elem_type (defined above) that
+   simulates an array of bits. */
+struct bitmap
+  {
+    size_t bit_cnt;     /* Number of bits. */
+    elem_type *bits;    /* Elements that represent bits. */
+  };
+
+/* Returns the index of the element that contains the bit
+   numbered BIT_IDX. */
+static inline size_t
+elem_idx (size_t bit_idx) 
+{
+  return bit_idx / ELEM_BITS;
+}
+
+/* Returns an elem_type where only the bit corresponding to
+   BIT_IDX is turned on. */
+static inline elem_type
+bit_mask (size_t bit_idx) 
+{
+  return (elem_type) 1 << (bit_idx % ELEM_BITS);
+}
+
+/* Returns the number of elements required for BIT_CNT bits. */
+static inline size_t
+elem_cnt (size_t bit_cnt)
+{
+  return DIV_ROUND_UP (bit_cnt, ELEM_BITS);
+}
+
+/* Returns the number of bytes required for BIT_CNT bits. */
+static inline size_t
+byte_cnt (size_t bit_cnt)
+{
+  return sizeof (elem_type) * elem_cnt (bit_cnt);
+}
+
+/* Returns a bit mask in which the bits actually used in the last
+   element of B's bits are set to 1 and the rest are set to 0. */
+static inline elem_type
+last_mask (const struct bitmap *b) 
+{
+  int last_bits = b->bit_cnt % ELEM_BITS;
+  return last_bits ? ((elem_type) 1 << last_bits) - 1 : (elem_type) -1;
+}
+
+/* Creation and destruction. */
+
+/* Initializes B to be a bitmap of BIT_CNT bits
+   and sets all of its bits to false.
+   Returns true if success, false if memory allocation
+   failed. */
+struct bitmap *
+bitmap_create (size_t bit_cnt) 
+{
+  struct bitmap *b = malloc (sizeof *b);
+  if (b != NULL)
+    {
+      b->bit_cnt = bit_cnt;
+      b->bits = malloc (byte_cnt (bit_cnt));
+      if (b->bits != NULL || bit_cnt == 0)
+        {
+          bitmap_set_all (b, false);
+          return b;
+        }
+      free (b);
+    }
+  return NULL;
+}
+
+/* Creates and returns a bitmap with BIT_CNT bits in the
+   BLOCK_SIZE bytes of storage preallocated at BLOCK.
+   BLOCK_SIZE must be at least bitmap_needed_bytes(BIT_CNT). */
+struct bitmap *
+bitmap_create_in_buf (size_t bit_cnt, void *block, size_t block_size UNUSED)
+{
+  struct bitmap *b = block;
+  
+  ASSERT (block_size >= bitmap_buf_size (bit_cnt));
+
+  b->bit_cnt = bit_cnt;
+  b->bits = (elem_type *) (b + 1);
+  bitmap_set_all (b, false);
+  return b;
+}
+
+/* Returns the number of bytes required to accomodate a bitmap
+   with BIT_CNT bits (for use with bitmap_create_in_buf()). */
+size_t
+bitmap_buf_size (size_t bit_cnt) 
+{
+  return sizeof (struct bitmap) + byte_cnt (bit_cnt);
+}
+
+/* Destroys bitmap B, freeing its storage.
+   Not for use on bitmaps created by
+   bitmap_create_preallocated(). */
+void
+bitmap_destroy (struct bitmap *b) 
+{
+  if (b != NULL) 
+    {
+      free (b->bits);
+      free (b);
+    }
+}
+
+/* Bitmap size. */
+
+/* Returns the number of bits in B. */
+size_t
+bitmap_size (const struct bitmap *b)
+{
+  return b->bit_cnt;
+}
+
+/* Setting and testing single bits. */
+
+/* Atomically sets the bit numbered IDX in B to VALUE. */
+void
+bitmap_set (struct bitmap *b, size_t idx, bool value) 
+{
+  ASSERT (b != NULL);
+  ASSERT (idx < b->bit_cnt);
+  if (value)
+    bitmap_mark (b, idx);
+  else
+    bitmap_reset (b, idx);
+}
+
+/* Atomically sets the bit numbered BIT_IDX in B to true. */
+void
+bitmap_mark (struct bitmap *b, size_t bit_idx) 
+{
+  size_t idx = elem_idx (bit_idx);
+  elem_type mask = bit_mask (bit_idx);
+
+  /* This is equivalent to `b->bits[idx] |= mask' except that it
+     is guaranteed to be atomic on a uniprocessor machine.  See
+     the description of the OR instruction in [IA32-v2b]. */
+  asm ("orl %1, %0" : "=m" (b->bits[idx]) : "r" (mask) : "cc");
+}
+
+/* Atomically sets the bit numbered BIT_IDX in B to false. */
+void
+bitmap_reset (struct bitmap *b, size_t bit_idx) 
+{
+  size_t idx = elem_idx (bit_idx);
+  elem_type mask = bit_mask (bit_idx);
+
+  /* This is equivalent to `b->bits[idx] &= ~mask' except that it
+     is guaranteed to be atomic on a uniprocessor machine.  See
+     the description of the AND instruction in [IA32-v2a]. */
+  asm ("andl %1, %0" : "=m" (b->bits[idx]) : "r" (~mask) : "cc");
+}
+
+/* Atomically toggles the bit numbered IDX in B;
+   that is, if it is true, makes it false,
+   and if it is false, makes it true. */
+void
+bitmap_flip (struct bitmap *b, size_t bit_idx) 
+{
+  size_t idx = elem_idx (bit_idx);
+  elem_type mask = bit_mask (bit_idx);
+
+  /* This is equivalent to `b->bits[idx] ^= mask' except that it
+     is guaranteed to be atomic on a uniprocessor machine.  See
+     the description of the XOR instruction in [IA32-v2b]. */
+  asm ("xorl %1, %0" : "=m" (b->bits[idx]) : "r" (mask) : "cc");
+}
+
+/* Returns the value of the bit numbered IDX in B. */
+bool
+bitmap_test (const struct bitmap *b, size_t idx) 
+{
+  ASSERT (b != NULL);
+  ASSERT (idx < b->bit_cnt);
+  return (b->bits[elem_idx (idx)] & bit_mask (idx)) != 0;
+}
+
+/* Setting and testing multiple bits. */
+
+/* Sets all bits in B to VALUE. */
+void
+bitmap_set_all (struct bitmap *b, bool value) 
+{
+  ASSERT (b != NULL);
+
+  bitmap_set_multiple (b, 0, bitmap_size (b), value);
+}
+
+/* Sets the CNT bits starting at START in B to VALUE. */
+void
+bitmap_set_multiple (struct bitmap *b, size_t start, size_t cnt, bool value) 
+{
+  size_t i;
+  
+  ASSERT (b != NULL);
+  ASSERT (start <= b->bit_cnt);
+  ASSERT (start + cnt <= b->bit_cnt);
+
+  for (i = 0; i < cnt; i++)
+    bitmap_set (b, start + i, value);
+}
+
+/* Returns the number of bits in B between START and START + CNT,
+   exclusive, that are set to VALUE. */
+size_t
+bitmap_count (const struct bitmap *b, size_t start, size_t cnt, bool value) 
+{
+  size_t i, value_cnt;
+
+  ASSERT (b != NULL);
+  ASSERT (start <= b->bit_cnt);
+  ASSERT (start + cnt <= b->bit_cnt);
+
+  value_cnt = 0;
+  for (i = 0; i < cnt; i++)
+    if (bitmap_test (b, start + i) == value)
+      value_cnt++;
+  return value_cnt;
+}
+
+/* Returns true if any bits in B between START and START + CNT,
+   exclusive, are set to VALUE, and false otherwise. */
+bool
+bitmap_contains (const struct bitmap *b, size_t start, size_t cnt, bool value) 
+{
+  size_t i;
+  
+  ASSERT (b != NULL);
+  ASSERT (start <= b->bit_cnt);
+  ASSERT (start + cnt <= b->bit_cnt);
+
+  for (i = 0; i < cnt; i++)
+    if (bitmap_test (b, start + i) == value)
+      return true;
+  return false;
+}
+
+/* Returns true if any bits in B between START and START + CNT,
+   exclusive, are set to true, and false otherwise.*/
+bool
+bitmap_any (const struct bitmap *b, size_t start, size_t cnt) 
+{
+  return bitmap_contains (b, start, cnt, true);
+}
+
+/* Returns true if no bits in B between START and START + CNT,
+   exclusive, are set to true, and false otherwise.*/
+bool
+bitmap_none (const struct bitmap *b, size_t start, size_t cnt) 
+{
+  return !bitmap_contains (b, start, cnt, true);
+}
+
+/* Returns true if every bit in B between START and START + CNT,
+   exclusive, is set to true, and false otherwise. */
+bool
+bitmap_all (const struct bitmap *b, size_t start, size_t cnt) 
+{
+  return !bitmap_contains (b, start, cnt, false);
+}
+
+/* Finding set or unset bits. */
+
+/* Finds and returns the starting index of the first group of CNT
+   consecutive bits in B at or after START that are all set to
+   VALUE.
+   If there is no such group, returns BITMAP_ERROR. */
+size_t
+bitmap_scan (const struct bitmap *b, size_t start, size_t cnt, bool value) 
+{
+  ASSERT (b != NULL);
+  ASSERT (start <= b->bit_cnt);
+
+  if (cnt <= b->bit_cnt) 
+    {
+      size_t last = b->bit_cnt - cnt;
+      size_t i;
+      for (i = start; i <= last; i++)
+        if (!bitmap_contains (b, i, cnt, !value))
+          return i; 
+    }
+  return BITMAP_ERROR;
+}
+
+/* Finds the first group of CNT consecutive bits in B at or after
+   START that are all set to VALUE, flips them all to !VALUE,
+   and returns the index of the first bit in the group.
+   If there is no such group, returns BITMAP_ERROR.
+   If CNT is zero, returns 0.
+   Bits are set atomically, but testing bits is not atomic with
+   setting them. */
+size_t
+bitmap_scan_and_flip (struct bitmap *b, size_t start, size_t cnt, bool value)
+{
+  size_t idx = bitmap_scan (b, start, cnt, value);
+  if (idx != BITMAP_ERROR) 
+    bitmap_set_multiple (b, idx, cnt, !value);
+  return idx;
+}
+
+/* File input and output. */
+
+#ifdef FILESYS
+/* Returns the number of bytes needed to store B in a file. */
+size_t
+bitmap_file_size (const struct bitmap *b) 
+{
+  return byte_cnt (b->bit_cnt);
+}
+
+/* Reads B from FILE.  Returns true if successful, false
+   otherwise. */
+bool
+bitmap_read (struct bitmap *b, struct file *file) 
+{
+  bool success = true;
+  if (b->bit_cnt > 0) 
+    {
+      off_t size = byte_cnt (b->bit_cnt);
+      success = file_read_at (file, b->bits, size, 0) == size;
+      b->bits[elem_cnt (b->bit_cnt) - 1] &= last_mask (b);
+    }
+  return success;
+}
+
+/* Writes B to FILE.  Return true if successful, false
+   otherwise. */
+bool
+bitmap_write (const struct bitmap *b, struct file *file)
+{
+  off_t size = byte_cnt (b->bit_cnt);
+  return file_write_at (file, b->bits, size, 0) == size;
+}
+#endif /* FILESYS */
+
+/* Debugging. */
+
+/* Dumps the contents of B to the console as hexadecimal. */
+void
+bitmap_dump (const struct bitmap *b) 
+{
+  hex_dump (0, b->bits, byte_cnt (b->bit_cnt), false);
+}
+
diff --git a/src/lib/kernel/bitmap.h b/src/lib/kernel/bitmap.h
new file mode 100644
index 0000000..a50593c
--- /dev/null
+++ b/src/lib/kernel/bitmap.h
@@ -0,0 +1,51 @@
+#ifndef __LIB_KERNEL_BITMAP_H
+#define __LIB_KERNEL_BITMAP_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <inttypes.h>
+
+/* Bitmap abstract data type. */
+
+/* Creation and destruction. */
+struct bitmap *bitmap_create (size_t bit_cnt);
+struct bitmap *bitmap_create_in_buf (size_t bit_cnt, void *, size_t byte_cnt);
+size_t bitmap_buf_size (size_t bit_cnt);
+void bitmap_destroy (struct bitmap *);
+
+/* Bitmap size. */
+size_t bitmap_size (const struct bitmap *);
+
+/* Setting and testing single bits. */
+void bitmap_set (struct bitmap *, size_t idx, bool);
+void bitmap_mark (struct bitmap *, size_t idx);
+void bitmap_reset (struct bitmap *, size_t idx);
+void bitmap_flip (struct bitmap *, size_t idx);
+bool bitmap_test (const struct bitmap *, size_t idx);
+
+/* Setting and testing multiple bits. */
+void bitmap_set_all (struct bitmap *, bool);
+void bitmap_set_multiple (struct bitmap *, size_t start, size_t cnt, bool);
+size_t bitmap_count (const struct bitmap *, size_t start, size_t cnt, bool);
+bool bitmap_contains (const struct bitmap *, size_t start, size_t cnt, bool);
+bool bitmap_any (const struct bitmap *, size_t start, size_t cnt);
+bool bitmap_none (const struct bitmap *, size_t start, size_t cnt);
+bool bitmap_all (const struct bitmap *, size_t start, size_t cnt);
+
+/* Finding set or unset bits. */
+#define BITMAP_ERROR SIZE_MAX
+size_t bitmap_scan (const struct bitmap *, size_t start, size_t cnt, bool);
+size_t bitmap_scan_and_flip (struct bitmap *, size_t start, size_t cnt, bool);
+
+/* File input and output. */
+#ifdef FILESYS
+struct file;
+size_t bitmap_file_size (const struct bitmap *);
+bool bitmap_read (struct bitmap *, struct file *);
+bool bitmap_write (const struct bitmap *, struct file *);
+#endif
+
+/* Debugging. */
+void bitmap_dump (const struct bitmap *);
+
+#endif /* lib/kernel/bitmap.h */
diff --git a/src/lib/kernel/console.c b/src/lib/kernel/console.c
new file mode 100644
index 0000000..0d031b5
--- /dev/null
+++ b/src/lib/kernel/console.c
@@ -0,0 +1,191 @@
+#include <console.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include "devices/serial.h"
+#include "devices/vga.h"
+#include "threads/init.h"
+#include "threads/interrupt.h"
+#include "threads/synch.h"
+
+static void vprintf_helper (char, void *);
+static void putchar_have_lock (uint8_t c);
+
+/* The console lock.
+   Both the vga and serial layers do their own locking, so it's
+   safe to call them at any time.
+   But this lock is useful to prevent simultaneous printf() calls
+   from mixing their output, which looks confusing. */
+static struct lock console_lock;
+
+/* True in ordinary circumstances: we want to use the console
+   lock to avoid mixing output between threads, as explained
+   above.
+
+   False in early boot before the point that locks are functional
+   or the console lock has been initialized, or after a kernel
+   panics.  In the former case, taking the lock would cause an
+   assertion failure, which in turn would cause a panic, turning
+   it into the latter case.  In the latter case, if it is a buggy
+   lock_acquire() implementation that caused the panic, we'll
+   likely just recurse. */
+static bool use_console_lock;
+
+/* It's possible, if you add enough debug output to Pintos, to
+   try to recursively grab console_lock from a single thread.  As
+   a real example, I added a printf() call to palloc_free().
+   Here's a real backtrace that resulted:
+
+   lock_console()
+   vprintf()
+   printf()             - palloc() tries to grab the lock again
+   palloc_free()        
+   schedule_tail()      - another thread dying as we switch threads
+   schedule()
+   thread_yield()
+   intr_handler()       - timer interrupt
+   intr_set_level()
+   serial_putc()
+   putchar_have_lock()
+   putbuf()
+   sys_write()          - one process writing to the console
+   syscall_handler()
+   intr_handler()
+
+   This kind of thing is very difficult to debug, so we avoid the
+   problem by simulating a recursive lock with a depth
+   counter. */
+static int console_lock_depth;
+
+/* Number of characters written to console. */
+static int64_t write_cnt;
+
+/* Enable console locking. */
+void
+console_init (void) 
+{
+  lock_init (&console_lock);
+  use_console_lock = true;
+}
+
+/* Notifies the console that a kernel panic is underway,
+   which warns it to avoid trying to take the console lock from
+   now on. */
+void
+console_panic (void) 
+{
+  use_console_lock = false;
+}
+
+/* Prints console statistics. */
+void
+console_print_stats (void) 
+{
+  printf ("Console: %lld characters output\n", write_cnt);
+}
+
+/* Acquires the console lock. */
+static void
+acquire_console (void) 
+{
+  if (!intr_context () && use_console_lock) 
+    {
+      if (lock_held_by_current_thread (&console_lock)) 
+        console_lock_depth++; 
+      else
+        lock_acquire (&console_lock); 
+    }
+}
+
+/* Releases the console lock. */
+static void
+release_console (void) 
+{
+  if (!intr_context () && use_console_lock) 
+    {
+      if (console_lock_depth > 0)
+        console_lock_depth--;
+      else
+        lock_release (&console_lock); 
+    }
+}
+
+/* Returns true if the current thread has the console lock,
+   false otherwise. */
+static bool
+console_locked_by_current_thread (void) 
+{
+  return (intr_context ()
+          || !use_console_lock
+          || lock_held_by_current_thread (&console_lock));
+}
+
+/* The standard vprintf() function,
+   which is like printf() but uses a va_list.
+   Writes its output to both vga display and serial port. */
+int
+vprintf (const char *format, va_list args) 
+{
+  int char_cnt = 0;
+
+  acquire_console ();
+  __vprintf (format, args, vprintf_helper, &char_cnt);
+  release_console ();
+
+  return char_cnt;
+}
+
+/* Writes string S to the console, followed by a new-line
+   character. */
+int
+puts (const char *s) 
+{
+  acquire_console ();
+  while (*s != '\0')
+    putchar_have_lock (*s++);
+  putchar_have_lock ('\n');
+  release_console ();
+
+  return 0;
+}
+
+/* Writes the N characters in BUFFER to the console. */
+void
+putbuf (const char *buffer, size_t n) 
+{
+  acquire_console ();
+  while (n-- > 0)
+    putchar_have_lock (*buffer++);
+  release_console ();
+}
+
+/* Writes C to the vga display and serial port. */
+int
+putchar (int c) 
+{
+  acquire_console ();
+  putchar_have_lock (c);
+  release_console ();
+  
+  return c;
+}
+
+/* Helper function for vprintf(). */
+static void
+vprintf_helper (char c, void *char_cnt_) 
+{
+  int *char_cnt = char_cnt_;
+  (*char_cnt)++;
+  putchar_have_lock (c);
+}
+
+/* Writes C to the vga display and serial port.
+   The caller has already acquired the console lock if
+   appropriate. */
+static void
+putchar_have_lock (uint8_t c) 
+{
+  ASSERT (console_locked_by_current_thread ());
+  write_cnt++;
+  serial_putc (c);
+  vga_putc (c);
+}
diff --git a/src/lib/kernel/console.h b/src/lib/kernel/console.h
new file mode 100644
index 0000000..ab99249
--- /dev/null
+++ b/src/lib/kernel/console.h
@@ -0,0 +1,8 @@
+#ifndef __LIB_KERNEL_CONSOLE_H
+#define __LIB_KERNEL_CONSOLE_H
+
+void console_init (void);
+void console_panic (void);
+void console_print_stats (void);
+
+#endif /* lib/kernel/console.h */
diff --git a/src/lib/kernel/debug.c b/src/lib/kernel/debug.c
new file mode 100644
index 0000000..93c3952
--- /dev/null
+++ b/src/lib/kernel/debug.c
@@ -0,0 +1,48 @@
+#include <debug.h>
+#include <console.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include "threads/init.h"
+#include "threads/interrupt.h"
+#include "devices/serial.h"
+
+/* Halts the OS, printing the source file name, line number, and
+   function name, plus a user-specific message. */
+void
+debug_panic (const char *file, int line, const char *function,
+             const char *message, ...)
+{
+  static int level;
+  va_list args;
+
+  intr_disable ();
+  console_panic ();
+
+  level++;
+  if (level == 1) 
+    {
+      printf ("Kernel PANIC at %s:%d in %s(): ", file, line, function);
+
+      va_start (args, message);
+      vprintf (message, args);
+      printf ("\n");
+      va_end (args);
+
+      debug_backtrace ();
+    }
+  else if (level == 2)
+    printf ("Kernel PANIC recursion at %s:%d in %s().\n",
+            file, line, function);
+  else 
+    {
+      /* Don't print anything: that's probably why we recursed. */
+    }
+
+  serial_flush ();
+  if (power_off_when_done)
+    power_off ();
+  for (;;);
+}
diff --git a/src/lib/kernel/hash.c b/src/lib/kernel/hash.c
new file mode 100644
index 0000000..57eed45
--- /dev/null
+++ b/src/lib/kernel/hash.c
@@ -0,0 +1,430 @@
+/* Hash table.
+
+   This data structure is thoroughly documented in the Tour of
+   Pintos for Project 3.
+
+   See hash.h for basic information. */
+
+#include "hash.h"
+#include "../debug.h"
+#include "threads/malloc.h"
+
+#define list_elem_to_hash_elem(LIST_ELEM)                       \
+        list_entry(LIST_ELEM, struct hash_elem, list_elem)
+
+static struct list *find_bucket (struct hash *, struct hash_elem *);
+static struct hash_elem *find_elem (struct hash *, struct list *,
+                                    struct hash_elem *);
+static void insert_elem (struct hash *, struct list *, struct hash_elem *);
+static void remove_elem (struct hash *, struct hash_elem *);
+static void rehash (struct hash *);
+
+/* Initializes hash table H to compute hash values using HASH and
+   compare hash elements using LESS, given auxiliary data AUX. */
+bool
+hash_init (struct hash *h,
+           hash_hash_func *hash, hash_less_func *less, void *aux) 
+{
+  h->elem_cnt = 0;
+  h->bucket_cnt = 4;
+  h->buckets = malloc (sizeof *h->buckets * h->bucket_cnt);
+  h->hash = hash;
+  h->less = less;
+  h->aux = aux;
+
+  if (h->buckets != NULL) 
+    {
+      hash_clear (h, NULL);
+      return true;
+    }
+  else
+    return false;
+}
+
+/* Removes all the elements from H.
+   
+   If DESTRUCTOR is non-null, then it is called for each element
+   in the hash.  DESTRUCTOR may, if appropriate, deallocate the
+   memory used by the hash element.  However, modifying hash
+   table H while hash_clear() is running, using any of the
+   functions hash_clear(), hash_destroy(), hash_insert(),
+   hash_replace(), or hash_delete(), yields undefined behavior,
+   whether done in DESTRUCTOR or elsewhere. */
+void
+hash_clear (struct hash *h, hash_action_func *destructor) 
+{
+  size_t i;
+
+  for (i = 0; i < h->bucket_cnt; i++) 
+    {
+      struct list *bucket = &h->buckets[i];
+
+      if (destructor != NULL) 
+        while (!list_empty (bucket)) 
+          {
+            struct list_elem *list_elem = list_pop_front (bucket);
+            struct hash_elem *hash_elem = list_elem_to_hash_elem (list_elem);
+            destructor (hash_elem, h->aux);
+          }
+
+      list_init (bucket); 
+    }    
+
+  h->elem_cnt = 0;
+}
+
+/* Destroys hash table H.
+
+   If DESTRUCTOR is non-null, then it is first called for each
+   element in the hash.  DESTRUCTOR may, if appropriate,
+   deallocate the memory used by the hash element.  However,
+   modifying hash table H while hash_clear() is running, using
+   any of the functions hash_clear(), hash_destroy(),
+   hash_insert(), hash_replace(), or hash_delete(), yields
+   undefined behavior, whether done in DESTRUCTOR or
+   elsewhere. */
+void
+hash_destroy (struct hash *h, hash_action_func *destructor) 
+{
+  if (destructor != NULL)
+    hash_clear (h, destructor);
+  free (h->buckets);
+}
+
+/* Inserts NEW into hash table H and returns a null pointer, if
+   no equal element is already in the table.
+   If an equal element is already in the table, returns it
+   without inserting NEW. */   
+struct hash_elem *
+hash_insert (struct hash *h, struct hash_elem *new)
+{
+  struct list *bucket = find_bucket (h, new);
+  struct hash_elem *old = find_elem (h, bucket, new);
+
+  if (old == NULL) 
+    insert_elem (h, bucket, new);
+
+  rehash (h);
+
+  return old; 
+}
+
+/* Inserts NEW into hash table H, replacing any equal element
+   already in the table, which is returned. */
+struct hash_elem *
+hash_replace (struct hash *h, struct hash_elem *new) 
+{
+  struct list *bucket = find_bucket (h, new);
+  struct hash_elem *old = find_elem (h, bucket, new);
+
+  if (old != NULL)
+    remove_elem (h, old);
+  insert_elem (h, bucket, new);
+
+  rehash (h);
+
+  return old;
+}
+
+/* Finds and returns an element equal to E in hash table H, or a
+   null pointer if no equal element exists in the table. */
+struct hash_elem *
+hash_find (struct hash *h, struct hash_elem *e) 
+{
+  return find_elem (h, find_bucket (h, e), e);
+}
+
+/* Finds, removes, and returns an element equal to E in hash
+   table H.  Returns a null pointer if no equal element existed
+   in the table.
+
+   If the elements of the hash table are dynamically allocated,
+   or own resources that are, then it is the caller's
+   responsibility to deallocate them. */
+struct hash_elem *
+hash_delete (struct hash *h, struct hash_elem *e)
+{
+  struct hash_elem *found = find_elem (h, find_bucket (h, e), e);
+  if (found != NULL) 
+    {
+      remove_elem (h, found);
+      rehash (h); 
+    }
+  return found;
+}
+
+/* Calls ACTION for each element in hash table H in arbitrary
+   order. 
+   Modifying hash table H while hash_apply() is running, using
+   any of the functions hash_clear(), hash_destroy(),
+   hash_insert(), hash_replace(), or hash_delete(), yields
+   undefined behavior, whether done from ACTION or elsewhere. */
+void
+hash_apply (struct hash *h, hash_action_func *action) 
+{
+  size_t i;
+  
+  ASSERT (action != NULL);
+
+  for (i = 0; i < h->bucket_cnt; i++) 
+    {
+      struct list *bucket = &h->buckets[i];
+      struct list_elem *elem, *next;
+
+      for (elem = list_begin (bucket); elem != list_end (bucket); elem = next) 
+        {
+          next = list_next (elem);
+          action (list_elem_to_hash_elem (elem), h->aux);
+        }
+    }
+}
+
+/* Initializes I for iterating hash table H.
+
+   Iteration idiom:
+
+      struct hash_iterator i;
+
+      hash_first (&i, h);
+      while (hash_next (&i))
+        {
+          struct foo *f = hash_entry (hash_cur (&i), struct foo, elem);
+          ...do something with f...
+        }
+
+   Modifying hash table H during iteration, using any of the
+   functions hash_clear(), hash_destroy(), hash_insert(),
+   hash_replace(), or hash_delete(), invalidates all
+   iterators. */
+void
+hash_first (struct hash_iterator *i, struct hash *h) 
+{
+  ASSERT (i != NULL);
+  ASSERT (h != NULL);
+
+  i->hash = h;
+  i->bucket = i->hash->buckets;
+  i->elem = list_elem_to_hash_elem (list_head (i->bucket));
+}
+
+/* Advances I to the next element in the hash table and returns
+   it.  Returns a null pointer if no elements are left.  Elements
+   are returned in arbitrary order.
+
+   Modifying a hash table H during iteration, using any of the
+   functions hash_clear(), hash_destroy(), hash_insert(),
+   hash_replace(), or hash_delete(), invalidates all
+   iterators. */
+struct hash_elem *
+hash_next (struct hash_iterator *i)
+{
+  ASSERT (i != NULL);
+
+  i->elem = list_elem_to_hash_elem (list_next (&i->elem->list_elem));
+  while (i->elem == list_elem_to_hash_elem (list_end (i->bucket)))
+    {
+      if (++i->bucket >= i->hash->buckets + i->hash->bucket_cnt)
+        {
+          i->elem = NULL;
+          break;
+        }
+      i->elem = list_elem_to_hash_elem (list_begin (i->bucket));
+    }
+  
+  return i->elem;
+}
+
+/* Returns the current element in the hash table iteration, or a
+   null pointer at the end of the table.  Undefined behavior
+   after calling hash_first() but before hash_next(). */
+struct hash_elem *
+hash_cur (struct hash_iterator *i) 
+{
+  return i->elem;
+}
+
+/* Returns the number of elements in H. */
+size_t
+hash_size (struct hash *h) 
+{
+  return h->elem_cnt;
+}
+
+/* Returns true if H contains no elements, false otherwise. */
+bool
+hash_empty (struct hash *h) 
+{
+  return h->elem_cnt == 0;
+}
+
+/* Fowler-Noll-Vo hash constants, for 32-bit word sizes. */
+#define FNV_32_PRIME 16777619u
+#define FNV_32_BASIS 2166136261u
+
+/* Returns a hash of the SIZE bytes in BUF. */
+unsigned
+hash_bytes (const void *buf_, size_t size)
+{
+  /* Fowler-Noll-Vo 32-bit hash, for bytes. */
+  const unsigned char *buf = buf_;
+  unsigned hash;
+
+  ASSERT (buf != NULL);
+
+  hash = FNV_32_BASIS;
+  while (size-- > 0)
+    hash = (hash * FNV_32_PRIME) ^ *buf++;
+
+  return hash;
+} 
+
+/* Returns a hash of string S. */
+unsigned
+hash_string (const char *s_) 
+{
+  const unsigned char *s = (const unsigned char *) s_;
+  unsigned hash;
+
+  ASSERT (s != NULL);
+
+  hash = FNV_32_BASIS;
+  while (*s != '\0')
+    hash = (hash * FNV_32_PRIME) ^ *s++;
+
+  return hash;
+}
+
+/* Returns a hash of integer I. */
+unsigned
+hash_int (int i) 
+{
+  return hash_bytes (&i, sizeof i);
+}
+
+/* Returns the bucket in H that E belongs in. */
+static struct list *
+find_bucket (struct hash *h, struct hash_elem *e) 
+{
+  size_t bucket_idx = h->hash (e, h->aux) & (h->bucket_cnt - 1);
+  return &h->buckets[bucket_idx];
+}
+
+/* Searches BUCKET in H for a hash element equal to E.  Returns
+   it if found or a null pointer otherwise. */
+static struct hash_elem *
+find_elem (struct hash *h, struct list *bucket, struct hash_elem *e) 
+{
+  struct list_elem *i;
+
+  for (i = list_begin (bucket); i != list_end (bucket); i = list_next (i)) 
+    {
+      struct hash_elem *hi = list_elem_to_hash_elem (i);
+      if (!h->less (hi, e, h->aux) && !h->less (e, hi, h->aux))
+        return hi; 
+    }
+  return NULL;
+}
+
+/* Returns X with its lowest-order bit set to 1 turned off. */
+static inline size_t
+turn_off_least_1bit (size_t x) 
+{
+  return x & (x - 1);
+}
+
+/* Returns true if X is a power of 2, otherwise false. */
+static inline size_t
+is_power_of_2 (size_t x) 
+{
+  return x != 0 && turn_off_least_1bit (x) == 0;
+}
+
+/* Element per bucket ratios. */
+#define MIN_ELEMS_PER_BUCKET  1 /* Elems/bucket < 1: reduce # of buckets. */
+#define BEST_ELEMS_PER_BUCKET 2 /* Ideal elems/bucket. */
+#define MAX_ELEMS_PER_BUCKET  4 /* Elems/bucket > 4: increase # of buckets. */
+
+/* Changes the number of buckets in hash table H to match the
+   ideal.  This function can fail because of an out-of-memory
+   condition, but that'll just make hash accesses less efficient;
+   we can still continue. */
+static void
+rehash (struct hash *h) 
+{
+  size_t old_bucket_cnt, new_bucket_cnt;
+  struct list *new_buckets, *old_buckets;
+  size_t i;
+
+  ASSERT (h != NULL);
+
+  /* Save old bucket info for later use. */
+  old_buckets = h->buckets;
+  old_bucket_cnt = h->bucket_cnt;
+
+  /* Calculate the number of buckets to use now.
+     We want one bucket for about every BEST_ELEMS_PER_BUCKET.
+     We must have at least four buckets, and the number of
+     buckets must be a power of 2. */
+  new_bucket_cnt = h->elem_cnt / BEST_ELEMS_PER_BUCKET;
+  if (new_bucket_cnt < 4)
+    new_bucket_cnt = 4;
+  while (!is_power_of_2 (new_bucket_cnt))
+    new_bucket_cnt = turn_off_least_1bit (new_bucket_cnt);
+
+  /* Don't do anything if the bucket count wouldn't change. */
+  if (new_bucket_cnt == old_bucket_cnt)
+    return;
+
+  /* Allocate new buckets and initialize them as empty. */
+  new_buckets = malloc (sizeof *new_buckets * new_bucket_cnt);
+  if (new_buckets == NULL) 
+    {
+      /* Allocation failed.  This means that use of the hash table will
+         be less efficient.  However, it is still usable, so
+         there's no reason for it to be an error. */
+      return;
+    }
+  for (i = 0; i < new_bucket_cnt; i++) 
+    list_init (&new_buckets[i]);
+
+  /* Install new bucket info. */
+  h->buckets = new_buckets;
+  h->bucket_cnt = new_bucket_cnt;
+
+  /* Move each old element into the appropriate new bucket. */
+  for (i = 0; i < old_bucket_cnt; i++) 
+    {
+      struct list *old_bucket;
+      struct list_elem *elem, *next;
+
+      old_bucket = &old_buckets[i];
+      for (elem = list_begin (old_bucket);
+           elem != list_end (old_bucket); elem = next) 
+        {
+          struct list *new_bucket
+            = find_bucket (h, list_elem_to_hash_elem (elem));
+          next = list_next (elem);
+          list_remove (elem);
+          list_push_front (new_bucket, elem);
+        }
+    }
+
+  free (old_buckets);
+}
+
+/* Inserts E into BUCKET (in hash table H). */
+static void
+insert_elem (struct hash *h, struct list *bucket, struct hash_elem *e) 
+{
+  h->elem_cnt++;
+  list_push_front (bucket, &e->list_elem);
+}
+
+/* Removes E from hash table H. */
+static void
+remove_elem (struct hash *h, struct hash_elem *e) 
+{
+  h->elem_cnt--;
+  list_remove (&e->list_elem);
+}
+
diff --git a/src/lib/kernel/hash.h b/src/lib/kernel/hash.h
new file mode 100644
index 0000000..db9f674
--- /dev/null
+++ b/src/lib/kernel/hash.h
@@ -0,0 +1,103 @@
+#ifndef __LIB_KERNEL_HASH_H
+#define __LIB_KERNEL_HASH_H
+
+/* Hash table.
+
+   This data structure is thoroughly documented in the Tour of
+   Pintos for Project 3.
+
+   This is a standard hash table with chaining.  To locate an
+   element in the table, we compute a hash function over the
+   element's data and use that as an index into an array of
+   doubly linked lists, then linearly search the list.
+
+   The chain lists do not use dynamic allocation.  Instead, each
+   structure that can potentially be in a hash must embed a
+   struct hash_elem member.  All of the hash functions operate on
+   these `struct hash_elem's.  The hash_entry macro allows
+   conversion from a struct hash_elem back to a structure object
+   that contains it.  This is the same technique used in the
+   linked list implementation.  Refer to lib/kernel/list.h for a
+   detailed explanation. */
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include "list.h"
+
+/* Hash element. */
+struct hash_elem 
+  {
+    struct list_elem list_elem;
+  };
+
+/* Converts pointer to hash element HASH_ELEM into a pointer to
+   the structure that HASH_ELEM is embedded inside.  Supply the
+   name of the outer structure STRUCT and the member name MEMBER
+   of the hash element.  See the big comment at the top of the
+   file for an example. */
+#define hash_entry(HASH_ELEM, STRUCT, MEMBER)                   \
+        ((STRUCT *) ((uint8_t *) &(HASH_ELEM)->list_elem        \
+                     - offsetof (STRUCT, MEMBER.list_elem)))
+
+/* Computes and returns the hash value for hash element E, given
+   auxiliary data AUX. */
+typedef unsigned hash_hash_func (const struct hash_elem *e, void *aux);
+
+/* Compares the value of two hash elements A and B, given
+   auxiliary data AUX.  Returns true if A is less than B, or
+   false if A is greater than or equal to B. */
+typedef bool hash_less_func (const struct hash_elem *a,
+                             const struct hash_elem *b,
+                             void *aux);
+
+/* Performs some operation on hash element E, given auxiliary
+   data AUX. */
+typedef void hash_action_func (struct hash_elem *e, void *aux);
+
+/* Hash table. */
+struct hash 
+  {
+    size_t elem_cnt;            /* Number of elements in table. */
+    size_t bucket_cnt;          /* Number of buckets, a power of 2. */
+    struct list *buckets;       /* Array of `bucket_cnt' lists. */
+    hash_hash_func *hash;       /* Hash function. */
+    hash_less_func *less;       /* Comparison function. */
+    void *aux;                  /* Auxiliary data for `hash' and `less'. */
+  };
+
+/* A hash table iterator. */
+struct hash_iterator 
+  {
+    struct hash *hash;          /* The hash table. */
+    struct list *bucket;        /* Current bucket. */
+    struct hash_elem *elem;     /* Current hash element in current bucket. */
+  };
+
+/* Basic life cycle. */
+bool hash_init (struct hash *, hash_hash_func *, hash_less_func *, void *aux);
+void hash_clear (struct hash *, hash_action_func *);
+void hash_destroy (struct hash *, hash_action_func *);
+
+/* Search, insertion, deletion. */
+struct hash_elem *hash_insert (struct hash *, struct hash_elem *);
+struct hash_elem *hash_replace (struct hash *, struct hash_elem *);
+struct hash_elem *hash_find (struct hash *, struct hash_elem *);
+struct hash_elem *hash_delete (struct hash *, struct hash_elem *);
+
+/* Iteration. */
+void hash_apply (struct hash *, hash_action_func *);
+void hash_first (struct hash_iterator *, struct hash *);
+struct hash_elem *hash_next (struct hash_iterator *);
+struct hash_elem *hash_cur (struct hash_iterator *);
+
+/* Information. */
+size_t hash_size (struct hash *);
+bool hash_empty (struct hash *);
+
+/* Sample hash functions. */
+unsigned hash_bytes (const void *, size_t);
+unsigned hash_string (const char *);
+unsigned hash_int (int);
+
+#endif /* lib/kernel/hash.h */
diff --git a/src/lib/kernel/list.c b/src/lib/kernel/list.c
new file mode 100644
index 0000000..e9993cb
--- /dev/null
+++ b/src/lib/kernel/list.c
@@ -0,0 +1,532 @@
+#include "list.h"
+#include "../debug.h"
+
+/* Our doubly linked lists have two header elements: the "head"
+   just before the first element and the "tail" just after the
+   last element.  The `prev' link of the front header is null, as
+   is the `next' link of the back header.  Their other two links
+   point toward each other via the interior elements of the list.
+
+   An empty list looks like this:
+
+                      +------+     +------+
+                  <---| head |<--->| tail |--->
+                      +------+     +------+
+
+   A list with two elements in it looks like this:
+
+        +------+     +-------+     +-------+     +------+
+    <---| head |<--->|   1   |<--->|   2   |<--->| tail |<--->
+        +------+     +-------+     +-------+     +------+
+
+   The symmetry of this arrangement eliminates lots of special
+   cases in list processing.  For example, take a look at
+   list_remove(): it takes only two pointer assignments and no
+   conditionals.  That's a lot simpler than the code would be
+   without header elements.
+
+   (Because only one of the pointers in each header element is used,
+   we could in fact combine them into a single header element
+   without sacrificing this simplicity.  But using two separate
+   elements allows us to do a little bit of checking on some
+   operations, which can be valuable.) */
+
+static bool is_sorted (struct list_elem *a, struct list_elem *b,
+                       list_less_func *less, void *aux) UNUSED;
+
+/* Returns true if ELEM is a head, false otherwise. */
+static inline bool
+is_head (struct list_elem *elem)
+{
+  return elem != NULL && elem->prev == NULL && elem->next != NULL;
+}
+
+/* Returns true if ELEM is an interior element,
+   false otherwise. */
+static inline bool
+is_interior (struct list_elem *elem)
+{
+  return elem != NULL && elem->prev != NULL && elem->next != NULL;
+}
+
+/* Returns true if ELEM is a tail, false otherwise. */
+static inline bool
+is_tail (struct list_elem *elem)
+{
+  return elem != NULL && elem->prev != NULL && elem->next == NULL;
+}
+
+/* Initializes LIST as an empty list. */
+void
+list_init (struct list *list)
+{
+  ASSERT (list != NULL);
+  list->head.prev = NULL;
+  list->head.next = &list->tail;
+  list->tail.prev = &list->head;
+  list->tail.next = NULL;
+}
+
+/* Returns the beginning of LIST.  */
+struct list_elem *
+list_begin (struct list *list)
+{
+  ASSERT (list != NULL);
+  return list->head.next;
+}
+
+/* Returns the element after ELEM in its list.  If ELEM is the
+   last element in its list, returns the list tail.  Results are
+   undefined if ELEM is itself a list tail. */
+struct list_elem *
+list_next (struct list_elem *elem)
+{
+  ASSERT (is_head (elem) || is_interior (elem));
+  return elem->next;
+}
+
+/* Returns LIST's tail.
+
+   list_end() is often used in iterating through a list from
+   front to back.  See the big comment at the top of list.h for
+   an example. */
+struct list_elem *
+list_end (struct list *list)
+{
+  ASSERT (list != NULL);
+  return &list->tail;
+}
+
+/* Returns the LIST's reverse beginning, for iterating through
+   LIST in reverse order, from back to front. */
+struct list_elem *
+list_rbegin (struct list *list) 
+{
+  ASSERT (list != NULL);
+  return list->tail.prev;
+}
+
+/* Returns the element before ELEM in its list.  If ELEM is the
+   first element in its list, returns the list head.  Results are
+   undefined if ELEM is itself a list head. */
+struct list_elem *
+list_prev (struct list_elem *elem)
+{
+  ASSERT (is_interior (elem) || is_tail (elem));
+  return elem->prev;
+}
+
+/* Returns LIST's head.
+
+   list_rend() is often used in iterating through a list in
+   reverse order, from back to front.  Here's typical usage,
+   following the example from the top of list.h:
+
+      for (e = list_rbegin (&foo_list); e != list_rend (&foo_list);
+           e = list_prev (e))
+        {
+          struct foo *f = list_entry (e, struct foo, elem);
+          ...do something with f...
+        }
+*/
+struct list_elem *
+list_rend (struct list *list) 
+{
+  ASSERT (list != NULL);
+  return &list->head;
+}
+
+/* Return's LIST's head.
+
+   list_head() can be used for an alternate style of iterating
+   through a list, e.g.:
+
+      e = list_head (&list);
+      while ((e = list_next (e)) != list_end (&list)) 
+        {
+          ...
+        }
+*/
+struct list_elem *
+list_head (struct list *list) 
+{
+  ASSERT (list != NULL);
+  return &list->head;
+}
+
+/* Return's LIST's tail. */
+struct list_elem *
+list_tail (struct list *list) 
+{
+  ASSERT (list != NULL);
+  return &list->tail;
+}
+
+/* Inserts ELEM just before BEFORE, which may be either an
+   interior element or a tail.  The latter case is equivalent to
+   list_push_back(). */
+void
+list_insert (struct list_elem *before, struct list_elem *elem)
+{
+  ASSERT (is_interior (before) || is_tail (before));
+  ASSERT (elem != NULL);
+
+  elem->prev = before->prev;
+  elem->next = before;
+  before->prev->next = elem;
+  before->prev = elem;
+}
+
+/* Removes elements FIRST though LAST (exclusive) from their
+   current list, then inserts them just before BEFORE, which may
+   be either an interior element or a tail. */
+void
+list_splice (struct list_elem *before,
+             struct list_elem *first, struct list_elem *last)
+{
+  ASSERT (is_interior (before) || is_tail (before));
+  if (first == last)
+    return;
+  last = list_prev (last);
+
+  ASSERT (is_interior (first));
+  ASSERT (is_interior (last));
+
+  /* Cleanly remove FIRST...LAST from its current list. */
+  first->prev->next = last->next;
+  last->next->prev = first->prev;
+
+  /* Splice FIRST...LAST into new list. */
+  first->prev = before->prev;
+  last->next = before;
+  before->prev->next = first;
+  before->prev = last;
+}
+
+/* Inserts ELEM at the beginning of LIST, so that it becomes the
+   front in LIST. */
+void
+list_push_front (struct list *list, struct list_elem *elem)
+{
+  list_insert (list_begin (list), elem);
+}
+
+/* Inserts ELEM at the end of LIST, so that it becomes the
+   back in LIST. */
+void
+list_push_back (struct list *list, struct list_elem *elem)
+{
+  list_insert (list_end (list), elem);
+}
+
+/* Removes ELEM from its list and returns the element that
+   followed it.  Undefined behavior if ELEM is not in a list.
+
+   It's not safe to treat ELEM as an element in a list after
+   removing it.  In particular, using list_next() or list_prev()
+   on ELEM after removal yields undefined behavior.  This means
+   that a naive loop to remove the elements in a list will fail:
+
+   ** DON'T DO THIS **
+   for (e = list_begin (&list); e != list_end (&list); e = list_next (e))
+     {
+       ...do something with e...
+       list_remove (e);
+     }
+   ** DON'T DO THIS **
+
+   Here is one correct way to iterate and remove elements from a
+   list:
+
+   for (e = list_begin (&list); e != list_end (&list); e = list_remove (e))
+     {
+       ...do something with e...
+     }
+
+   If you need to free() elements of the list then you need to be
+   more conservative.  Here's an alternate strategy that works
+   even in that case:
+
+   while (!list_empty (&list))
+     {
+       struct list_elem *e = list_pop_front (&list);
+       ...do something with e...
+     }
+*/
+struct list_elem *
+list_remove (struct list_elem *elem)
+{
+  ASSERT (is_interior (elem));
+  elem->prev->next = elem->next;
+  elem->next->prev = elem->prev;
+  return elem->next;
+}
+
+/* Removes the front element from LIST and returns it.
+   Undefined behavior if LIST is empty before removal. */
+struct list_elem *
+list_pop_front (struct list *list)
+{
+  struct list_elem *front = list_front (list);
+  list_remove (front);
+  return front;
+}
+
+/* Removes the back element from LIST and returns it.
+   Undefined behavior if LIST is empty before removal. */
+struct list_elem *
+list_pop_back (struct list *list)
+{
+  struct list_elem *back = list_back (list);
+  list_remove (back);
+  return back;
+}
+
+/* Returns the front element in LIST.
+   Undefined behavior if LIST is empty. */
+struct list_elem *
+list_front (struct list *list)
+{
+  ASSERT (!list_empty (list));
+  return list->head.next;
+}
+
+/* Returns the back element in LIST.
+   Undefined behavior if LIST is empty. */
+struct list_elem *
+list_back (struct list *list)
+{
+  ASSERT (!list_empty (list));
+  return list->tail.prev;
+}
+
+/* Returns the number of elements in LIST.
+   Runs in O(n) in the number of elements. */
+size_t
+list_size (struct list *list)
+{
+  struct list_elem *e;
+  size_t cnt = 0;
+
+  for (e = list_begin (list); e != list_end (list); e = list_next (e))
+    cnt++;
+  return cnt;
+}
+
+/* Returns true if LIST is empty, false otherwise. */
+bool
+list_empty (struct list *list)
+{
+  return list_begin (list) == list_end (list);
+}
+
+/* Swaps the `struct list_elem *'s that A and B point to. */
+static void
+swap (struct list_elem **a, struct list_elem **b) 
+{
+  struct list_elem *t = *a;
+  *a = *b;
+  *b = t;
+}
+
+/* Reverses the order of LIST. */
+void
+list_reverse (struct list *list)
+{
+  if (!list_empty (list)) 
+    {
+      struct list_elem *e;
+
+      for (e = list_begin (list); e != list_end (list); e = e->prev)
+        swap (&e->prev, &e->next);
+      swap (&list->head.next, &list->tail.prev);
+      swap (&list->head.next->prev, &list->tail.prev->next);
+    }
+}
+
+/* Returns true only if the list elements A through B (exclusive)
+   are in order according to LESS given auxiliary data AUX. */
+static bool
+is_sorted (struct list_elem *a, struct list_elem *b,
+           list_less_func *less, void *aux)
+{
+  if (a != b)
+    while ((a = list_next (a)) != b) 
+      if (less (a, list_prev (a), aux))
+        return false;
+  return true;
+}
+
+/* Finds a run, starting at A and ending not after B, of list
+   elements that are in nondecreasing order according to LESS
+   given auxiliary data AUX.  Returns the (exclusive) end of the
+   run.
+   A through B (exclusive) must form a non-empty range. */
+static struct list_elem *
+find_end_of_run (struct list_elem *a, struct list_elem *b,
+                 list_less_func *less, void *aux)
+{
+  ASSERT (a != NULL);
+  ASSERT (b != NULL);
+  ASSERT (less != NULL);
+  ASSERT (a != b);
+  
+  do 
+    {
+      a = list_next (a);
+    }
+  while (a != b && !less (a, list_prev (a), aux));
+  return a;
+}
+
+/* Merges A0 through A1B0 (exclusive) with A1B0 through B1
+   (exclusive) to form a combined range also ending at B1
+   (exclusive).  Both input ranges must be nonempty and sorted in
+   nondecreasing order according to LESS given auxiliary data
+   AUX.  The output range will be sorted the same way. */
+static void
+inplace_merge (struct list_elem *a0, struct list_elem *a1b0,
+               struct list_elem *b1,
+               list_less_func *less, void *aux)
+{
+  ASSERT (a0 != NULL);
+  ASSERT (a1b0 != NULL);
+  ASSERT (b1 != NULL);
+  ASSERT (less != NULL);
+  ASSERT (is_sorted (a0, a1b0, less, aux));
+  ASSERT (is_sorted (a1b0, b1, less, aux));
+
+  while (a0 != a1b0 && a1b0 != b1)
+    if (!less (a1b0, a0, aux)) 
+      a0 = list_next (a0);
+    else 
+      {
+        a1b0 = list_next (a1b0);
+        list_splice (a0, list_prev (a1b0), a1b0);
+      }
+}
+
+/* Sorts LIST according to LESS given auxiliary data AUX, using a
+   natural iterative merge sort that runs in O(n lg n) time and
+   O(1) space in the number of elements in LIST. */
+void
+list_sort (struct list *list, list_less_func *less, void *aux)
+{
+  size_t output_run_cnt;        /* Number of runs output in current pass. */
+
+  ASSERT (list != NULL);
+  ASSERT (less != NULL);
+
+  /* Pass over the list repeatedly, merging adjacent runs of
+     nondecreasing elements, until only one run is left. */
+  do
+    {
+      struct list_elem *a0;     /* Start of first run. */
+      struct list_elem *a1b0;   /* End of first run, start of second. */
+      struct list_elem *b1;     /* End of second run. */
+
+      output_run_cnt = 0;
+      for (a0 = list_begin (list); a0 != list_end (list); a0 = b1)
+        {
+          /* Each iteration produces one output run. */
+          output_run_cnt++;
+
+          /* Locate two adjacent runs of nondecreasing elements
+             A0...A1B0 and A1B0...B1. */
+          a1b0 = find_end_of_run (a0, list_end (list), less, aux);
+          if (a1b0 == list_end (list))
+            break;
+          b1 = find_end_of_run (a1b0, list_end (list), less, aux);
+
+          /* Merge the runs. */
+          inplace_merge (a0, a1b0, b1, less, aux);
+        }
+    }
+  while (output_run_cnt > 1);
+
+  ASSERT (is_sorted (list_begin (list), list_end (list), less, aux));
+}
+
+/* Inserts ELEM in the proper position in LIST, which must be
+   sorted according to LESS given auxiliary data AUX.
+   Runs in O(n) average case in the number of elements in LIST. */
+void
+list_insert_ordered (struct list *list, struct list_elem *elem,
+                     list_less_func *less, void *aux)
+{
+  struct list_elem *e;
+
+  ASSERT (list != NULL);
+  ASSERT (elem != NULL);
+  ASSERT (less != NULL);
+
+  for (e = list_begin (list); e != list_end (list); e = list_next (e))
+    if (less (elem, e, aux))
+      break;
+  return list_insert (e, elem);
+}
+
+/* Iterates through LIST and removes all but the first in each
+   set of adjacent elements that are equal according to LESS
+   given auxiliary data AUX.  If DUPLICATES is non-null, then the
+   elements from LIST are appended to DUPLICATES. */
+void
+list_unique (struct list *list, struct list *duplicates,
+             list_less_func *less, void *aux)
+{
+  struct list_elem *elem, *next;
+
+  ASSERT (list != NULL);
+  ASSERT (less != NULL);
+  if (list_empty (list))
+    return;
+
+  elem = list_begin (list);
+  while ((next = list_next (elem)) != list_end (list))
+    if (!less (elem, next, aux) && !less (next, elem, aux)) 
+      {
+        list_remove (next);
+        if (duplicates != NULL)
+          list_push_back (duplicates, next);
+      }
+    else
+      elem = next;
+}
+
+/* Returns the element in LIST with the largest value according
+   to LESS given auxiliary data AUX.  If there is more than one
+   maximum, returns the one that appears earlier in the list.  If
+   the list is empty, returns its tail. */
+struct list_elem *
+list_max (struct list *list, list_less_func *less, void *aux)
+{
+  struct list_elem *max = list_begin (list);
+  if (max != list_end (list)) 
+    {
+      struct list_elem *e;
+      
+      for (e = list_next (max); e != list_end (list); e = list_next (e))
+        if (less (max, e, aux))
+          max = e; 
+    }
+  return max;
+}
+
+/* Returns the element in LIST with the smallest value according
+   to LESS given auxiliary data AUX.  If there is more than one
+   minimum, returns the one that appears earlier in the list.  If
+   the list is empty, returns its tail. */
+struct list_elem *
+list_min (struct list *list, list_less_func *less, void *aux)
+{
+  struct list_elem *min = list_begin (list);
+  if (min != list_end (list)) 
+    {
+      struct list_elem *e;
+      
+      for (e = list_next (min); e != list_end (list); e = list_next (e))
+        if (less (e, min, aux))
+          min = e; 
+    }
+  return min;
+}
diff --git a/src/lib/kernel/list.h b/src/lib/kernel/list.h
new file mode 100644
index 0000000..2388f9a
--- /dev/null
+++ b/src/lib/kernel/list.h
@@ -0,0 +1,168 @@
+#ifndef __LIB_KERNEL_LIST_H
+#define __LIB_KERNEL_LIST_H
+
+/* Doubly linked list.
+
+   This implementation of a doubly linked list does not require
+   use of dynamically allocated memory.  Instead, each structure
+   that is a potential list element must embed a struct list_elem
+   member.  All of the list functions operate on these `struct
+   list_elem's.  The list_entry macro allows conversion from a
+   struct list_elem back to a structure object that contains it.
+
+   For example, suppose there is a needed for a list of `struct
+   foo'.  `struct foo' should contain a `struct list_elem'
+   member, like so:
+
+      struct foo
+        {
+          struct list_elem elem;
+          int bar;
+          ...other members...
+        };
+
+   Then a list of `struct foo' can be be declared and initialized
+   like so:
+
+      struct list foo_list;
+
+      list_init (&foo_list);
+
+   Iteration is a typical situation where it is necessary to
+   convert from a struct list_elem back to its enclosing
+   structure.  Here's an example using foo_list:
+
+      struct list_elem *e;
+
+      for (e = list_begin (&foo_list); e != list_end (&foo_list);
+           e = list_next (e))
+        {
+          struct foo *f = list_entry (e, struct foo, elem);
+          ...do something with f...
+        }
+
+   You can find real examples of list usage throughout the
+   source; for example, malloc.c, palloc.c, and thread.c in the
+   threads directory all use lists.
+
+   The interface for this list is inspired by the list<> template
+   in the C++ STL.  If you're familiar with list<>, you should
+   find this easy to use.  However, it should be emphasized that
+   these lists do *no* type checking and can't do much other
+   correctness checking.  If you screw up, it will bite you.
+
+   Glossary of list terms:
+
+     - "front": The first element in a list.  Undefined in an
+       empty list.  Returned by list_front().
+
+     - "back": The last element in a list.  Undefined in an empty
+       list.  Returned by list_back().
+
+     - "tail": The element figuratively just after the last
+       element of a list.  Well defined even in an empty list.
+       Returned by list_end().  Used as the end sentinel for an
+       iteration from front to back.
+
+     - "beginning": In a non-empty list, the front.  In an empty
+       list, the tail.  Returned by list_begin().  Used as the
+       starting point for an iteration from front to back.
+
+     - "head": The element figuratively just before the first
+       element of a list.  Well defined even in an empty list.
+       Returned by list_rend().  Used as the end sentinel for an
+       iteration from back to front.
+
+     - "reverse beginning": In a non-empty list, the back.  In an
+       empty list, the head.  Returned by list_rbegin().  Used as
+       the starting point for an iteration from back to front.
+
+     - "interior element": An element that is not the head or
+       tail, that is, a real list element.  An empty list does
+       not have any interior elements.
+*/
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* List element. */
+struct list_elem 
+  {
+    struct list_elem *prev;     /* Previous list element. */
+    struct list_elem *next;     /* Next list element. */
+  };
+
+/* List. */
+struct list 
+  {
+    struct list_elem head;      /* List head. */
+    struct list_elem tail;      /* List tail. */
+  };
+
+/* Converts pointer to list element LIST_ELEM into a pointer to
+   the structure that LIST_ELEM is embedded inside.  Supply the
+   name of the outer structure STRUCT and the member name MEMBER
+   of the list element.  See the big comment at the top of the
+   file for an example. */
+#define list_entry(LIST_ELEM, STRUCT, MEMBER)           \
+        ((STRUCT *) ((uint8_t *) &(LIST_ELEM)->next     \
+                     - offsetof (STRUCT, MEMBER.next)))
+
+void list_init (struct list *);
+
+/* List traversal. */
+struct list_elem *list_begin (struct list *);
+struct list_elem *list_next (struct list_elem *);
+struct list_elem *list_end (struct list *);
+
+struct list_elem *list_rbegin (struct list *);
+struct list_elem *list_prev (struct list_elem *);
+struct list_elem *list_rend (struct list *);
+
+struct list_elem *list_head (struct list *);
+struct list_elem *list_tail (struct list *);
+
+/* List insertion. */
+void list_insert (struct list_elem *, struct list_elem *);
+void list_splice (struct list_elem *before,
+                  struct list_elem *first, struct list_elem *last);
+void list_push_front (struct list *, struct list_elem *);
+void list_push_back (struct list *, struct list_elem *);
+
+/* List removal. */
+struct list_elem *list_remove (struct list_elem *);
+struct list_elem *list_pop_front (struct list *);
+struct list_elem *list_pop_back (struct list *);
+
+/* List elements. */
+struct list_elem *list_front (struct list *);
+struct list_elem *list_back (struct list *);
+
+/* List properties. */
+size_t list_size (struct list *);
+bool list_empty (struct list *);
+
+/* Miscellaneous. */
+void list_reverse (struct list *);
+
+/* Compares the value of two list elements A and B, given
+   auxiliary data AUX.  Returns true if A is less than B, or
+   false if A is greater than or equal to B. */
+typedef bool list_less_func (const struct list_elem *a,
+                             const struct list_elem *b,
+                             void *aux);
+
+/* Operations on lists with ordered elements. */
+void list_sort (struct list *,
+                list_less_func *, void *aux);
+void list_insert_ordered (struct list *, struct list_elem *,
+                          list_less_func *, void *aux);
+void list_unique (struct list *, struct list *duplicates,
+                  list_less_func *, void *aux);
+
+/* Max and min. */
+struct list_elem *list_max (struct list *, list_less_func *, void *aux);
+struct list_elem *list_min (struct list *, list_less_func *, void *aux);
+
+#endif /* lib/kernel/list.h */
diff --git a/src/lib/kernel/slist.c b/src/lib/kernel/slist.c
new file mode 100644
index 0000000..2f27250
--- /dev/null
+++ b/src/lib/kernel/slist.c
@@ -0,0 +1,153 @@
+#include "slist.h"
+#include "threads/malloc.h"
+#include <stdio.h>
+//        #include <stdlib.h>
+
+/* List structure */
+struct Node
+{
+  ListElement Element;
+  Position    Next;
+};
+
+/* make empty list */
+
+SList
+MakeEmpty( SList L )
+{
+  if( L != NULL )
+    DeleteList( L );
+  L = malloc( sizeof( struct Node ) );
+  if( L == NULL ) {
+    printf( "Out of memory!\n" );
+    return NULL;
+  }
+  L->Next = NULL;
+  return L;
+}
+
+/* Return true if L is empty */
+
+int
+IsEmpty( SList L )
+{
+  return L->Next == NULL;
+}
+
+/* Return true if P is the last position in SList L */
+/* Parameter L is unused in this implementation */
+
+int IsLast( Position P, UNUSED SList L)
+{
+  return P->Next == NULL;
+}
+
+/* Return Position of X in L; NULL if not found */
+
+Position
+Find( ListElement X, SList L )
+{
+  Position P;
+
+  P = L->Next;
+  while( P != NULL && P->Element != X )
+    P = P->Next;
+
+  return P;
+}
+
+/* Delete from a SList */
+/* Cell pointed to by P->Next is wiped out */
+/* Assume that the position is legal */
+/* Assume use of a header node */
+
+void
+Delete( ListElement X, SList L )
+{
+  Position P, TmpCell;
+
+  P = FindPrevious( X, L );
+
+  if( !IsLast( P, L ) )  /* Assumption of header use */
+    {                      /* X is found; delete it */
+      TmpCell = P->Next;
+      P->Next = TmpCell->Next;  /* Bypass deleted cell */
+      free( TmpCell );
+    }
+}
+
+/* If X is not found, then Next field of returned value is NULL */
+/* Assumes a header */
+
+Position
+FindPrevious( ListElement X, SList L )
+{
+  Position P;
+
+  P = L;
+  while( P->Next != NULL && P->Next->Element != X )
+    P = P->Next;
+
+  return P;
+}
+
+/* Insert (after legal position P) */
+/* Header implementation assumed */
+/* Parameter L is unused in this implementation */
+
+void
+Insert( ListElement X, UNUSED SList L, Position P )
+{
+  Position TmpCell;
+
+  TmpCell = malloc( sizeof( struct Node ) );
+  if( TmpCell == NULL ) {
+    printf( "Out of space!!!\n" );
+    return;
+  }
+
+  TmpCell->Element = X;
+  TmpCell->Next = P->Next;
+  P->Next = TmpCell;
+}
+
+/*  DeleteSList algorithm */
+
+void
+DeleteList( SList L )
+{
+  Position P, Tmp;
+
+  P = L->Next;  /* Header assumed */
+  L->Next = NULL;
+  while( P != NULL )
+    {
+      Tmp = P->Next;
+      free( P );
+      P = Tmp;
+    }
+}
+
+Position
+Header( SList L )
+{
+  return L;
+}
+
+Position
+First( SList L )
+{
+  return L->Next;
+}
+
+Position
+Advance( Position P )
+{
+  return P->Next;
+}
+
+ListElement
+Retrieve( Position P )
+{
+  return P->Element;
+}
diff --git a/src/lib/kernel/slist.h b/src/lib/kernel/slist.h
new file mode 100644
index 0000000..708105f
--- /dev/null
+++ b/src/lib/kernel/slist.h
@@ -0,0 +1,27 @@
+/* SList -- simple list for students. 
+ * This list was not originally in the pintos implementation. 
+ */
+typedef void * ListElement;
+
+#ifndef _SList_H
+#define _SList_H
+
+struct Node;
+typedef struct Node *PtrToNode;
+typedef PtrToNode SList;
+typedef PtrToNode Position;
+
+SList MakeEmpty( SList L );
+int IsEmpty( SList L );
+int IsLast( Position P,  SList L);
+Position Find( ListElement X, SList L );
+void Delete( ListElement X, SList L );
+Position FindPrevious( ListElement X, SList L );
+void Insert( ListElement X, SList L, Position P );
+void DeleteList( SList L );
+Position Header( SList L );
+Position First( SList L );
+Position Advance( Position P );
+ListElement Retrieve( Position P );
+
+#endif    /* _SList_H */
diff --git a/src/lib/kernel/stdio.h b/src/lib/kernel/stdio.h
new file mode 100644
index 0000000..3e5bae9
--- /dev/null
+++ b/src/lib/kernel/stdio.h
@@ -0,0 +1,6 @@
+#ifndef __LIB_KERNEL_STDIO_H
+#define __LIB_KERNEL_STDIO_H
+
+void putbuf (const char *, size_t);
+
+#endif /* lib/kernel/stdio.h */
diff --git a/src/lib/limits.h b/src/lib/limits.h
new file mode 100644
index 0000000..c957ec4
--- /dev/null
+++ b/src/lib/limits.h
@@ -0,0 +1,34 @@
+#ifndef __LIB_LIMITS_H
+#define __LIB_LIMITS_H
+
+#define CHAR_BIT 8
+
+#define SCHAR_MAX 127
+#define SCHAR_MIN (-SCHAR_MAX - 1)
+#define UCHAR_MAX 255
+
+#ifdef __CHAR_UNSIGNED__
+#define CHAR_MIN 0
+#define CHAR_MAX UCHAR_MAX
+#else
+#define CHAR_MIN SCHAR_MIN
+#define CHAR_MAX SCHAR_MAX
+#endif
+
+#define SHRT_MAX 32767
+#define SHRT_MIN (-SHRT_MAX - 1)
+#define USHRT_MAX 65535
+
+#define INT_MAX 2147483647
+#define INT_MIN (-INT_MAX - 1)
+#define UINT_MAX 4294967295U
+
+#define LONG_MAX 2147483647L
+#define LONG_MIN (-LONG_MAX - 1)
+#define ULONG_MAX 4294967295UL
+
+#define LLONG_MAX 9223372036854775807LL
+#define LLONG_MIN (-LLONG_MAX - 1)
+#define ULLONG_MAX 18446744073709551615ULL
+
+#endif /* lib/limits.h */
diff --git a/src/lib/random.c b/src/lib/random.c
new file mode 100644
index 0000000..a4761b6
--- /dev/null
+++ b/src/lib/random.c
@@ -0,0 +1,83 @@
+#include "random.h"
+#include <stdbool.h>
+#include <stdint.h>
+#include "debug.h"
+
+/* RC4-based pseudo-random number generator (PRNG).
+
+   RC4 is a stream cipher.  We're not using it here for its
+   cryptographic properties, but because it is easy to implement
+   and its output is plenty random for non-cryptographic
+   purposes.
+
+   See http://en.wikipedia.org/wiki/RC4_(cipher) for information
+   on RC4.*/
+
+/* RC4 state. */
+static uint8_t s[256];          /* S[]. */
+static uint8_t s_i, s_j;        /* i, j. */
+
+/* Already initialized? */
+static bool inited;     
+
+/* Swaps the bytes pointed to by A and B. */
+static inline void
+swap_byte (uint8_t *a, uint8_t *b) 
+{
+  uint8_t t = *a;
+  *a = *b;
+  *b = t;
+}
+
+/* Initializes or reinitializes the PRNG with the given SEED. */
+void
+random_init (unsigned seed)
+{
+  uint8_t *seedp = (uint8_t *) &seed;
+  int i;
+  uint8_t j;
+
+  for (i = 0; i < 256; i++) 
+    s[i] = i;
+  for (i = j = 0; i < 256; i++) 
+    {
+      j += s[i] + seedp[i % sizeof seed];
+      swap_byte (s + i, s + j);
+    }
+
+  s_i = s_j = 0;
+  inited = true;
+}
+
+/* Writes SIZE random bytes into BUF. */
+void
+random_bytes (void *buf_, size_t size) 
+{
+  uint8_t *buf;
+
+  if (!inited)
+    random_init (0);
+
+  for (buf = buf_; size-- > 0; buf++)
+    {
+      uint8_t s_k;
+      
+      s_i++;
+      s_j += s[s_i];
+      swap_byte (s + s_i, s + s_j);
+
+      s_k = s[s_i] + s[s_j];
+      *buf = s[s_k];
+    }
+}
+
+/* Returns a pseudo-random unsigned long.
+   Use random_ulong() % n to obtain a random number in the range
+   0...n (exclusive). */
+unsigned long
+random_ulong (void) 
+{
+  unsigned long ul;
+  random_bytes (&ul, sizeof ul);
+  return ul;
+}
diff --git a/src/lib/random.h b/src/lib/random.h
new file mode 100644
index 0000000..0950ae2
--- /dev/null
+++ b/src/lib/random.h
@@ -0,0 +1,10 @@
+#ifndef __LIB_RANDOM_H
+#define __LIB_RANDOM_H
+
+#include <stddef.h>
+
+void random_init (unsigned seed);
+void random_bytes (void *, size_t);
+unsigned long random_ulong (void);
+
+#endif /* lib/random.h */
diff --git a/src/lib/round.h b/src/lib/round.h
new file mode 100644
index 0000000..3aa6642
--- /dev/null
+++ b/src/lib/round.h
@@ -0,0 +1,18 @@
+#ifndef __LIB_ROUND_H
+#define __LIB_ROUND_H
+
+/* Yields X rounded up to the nearest multiple of STEP.
+   For X >= 0, STEP >= 1 only. */
+#define ROUND_UP(X, STEP) (((X) + (STEP) - 1) / (STEP) * (STEP))
+
+/* Yields X divided by STEP, rounded up.
+   For X >= 0, STEP >= 1 only. */
+#define DIV_ROUND_UP(X, STEP) (((X) + (STEP) - 1) / (STEP))
+
+/* Yields X rounded down to the nearest multiple of STEP.
+   For X >= 0, STEP >= 1 only. */
+#define ROUND_DOWN(X, STEP) ((X) / (STEP) * (STEP))
+
+/* There is no DIV_ROUND_DOWN.   It would be simply X / STEP. */
+
+#endif /* lib/round.h */
diff --git a/src/lib/stdarg.h b/src/lib/stdarg.h
new file mode 100644
index 0000000..32622b5
--- /dev/null
+++ b/src/lib/stdarg.h
@@ -0,0 +1,14 @@
+#ifndef __LIB_STDARG_H
+#define __LIB_STDARG_H
+
+/* GCC has <stdarg.h> functionality as built-ins,
+   so all we need is to use it. */
+
+typedef __builtin_va_list va_list;
+
+#define va_start(LIST, ARG)	__builtin_va_start (LIST, ARG)
+#define va_end(LIST)            __builtin_va_end (LIST)
+#define va_arg(LIST, TYPE)	__builtin_va_arg (LIST, TYPE)
+#define va_copy(DST, SRC)	__builtin_va_copy (DST, SRC)
+
+#endif /* lib/stdarg.h */
diff --git a/src/lib/stdbool.h b/src/lib/stdbool.h
new file mode 100644
index 0000000..f173a91
--- /dev/null
+++ b/src/lib/stdbool.h
@@ -0,0 +1,9 @@
+#ifndef __LIB_STDBOOL_H
+#define __LIB_STDBOOL_H
+
+#define bool	_Bool
+#define true	1
+#define false	0
+#define __bool_true_false_are_defined	1
+
+#endif /* lib/stdbool.h */
diff --git a/src/lib/stddef.h b/src/lib/stddef.h
new file mode 100644
index 0000000..4e74fa6
--- /dev/null
+++ b/src/lib/stddef.h
@@ -0,0 +1,12 @@
+#ifndef __LIB_STDDEF_H
+#define __LIB_STDDEF_H
+
+#define NULL ((void *) 0)
+#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *) 0)->MEMBER)
+
+/* GCC predefines the types we need for ptrdiff_t and size_t,
+   so that we don't have to guess. */
+typedef __PTRDIFF_TYPE__ ptrdiff_t;
+typedef __SIZE_TYPE__ size_t;
+
+#endif /* lib/stddef.h */
diff --git a/src/lib/stdint.h b/src/lib/stdint.h
new file mode 100644
index 0000000..ef5f214
--- /dev/null
+++ b/src/lib/stdint.h
@@ -0,0 +1,51 @@
+#ifndef __LIB_STDINT_H
+#define __LIB_STDINT_H
+
+typedef signed char int8_t;
+#define INT8_MAX 127
+#define INT8_MIN (-INT8_MAX - 1)
+
+typedef signed short int int16_t;
+#define INT16_MAX 32767
+#define INT16_MIN (-INT16_MAX - 1)
+
+typedef signed int int32_t;
+#define INT32_MAX 2147483647
+#define INT32_MIN (-INT32_MAX - 1)
+
+typedef signed long long int int64_t;
+#define INT64_MAX 9223372036854775807LL
+#define INT64_MIN (-INT64_MAX - 1)
+
+typedef unsigned char uint8_t;
+#define UINT8_MAX 255
+
+typedef unsigned short int uint16_t;
+#define UINT16_MAX 65535
+
+typedef unsigned int uint32_t;
+#define UINT32_MAX 4294967295U
+
+typedef unsigned long long int uint64_t;
+#define UINT64_MAX 18446744073709551615ULL
+
+typedef int32_t intptr_t;
+#define INTPTR_MIN INT32_MIN
+#define INTPTR_MAX INT32_MAX
+
+typedef uint32_t uintptr_t;
+#define UINTPTR_MAX UINT32_MAX
+
+typedef int64_t intmax_t;
+#define INTMAX_MIN INT64_MIN
+#define INTMAX_MAX INT64_MAX
+
+typedef uint64_t uintmax_t;
+#define UINTMAX_MAX UINT64_MAX
+
+#define PTRDIFF_MIN INT32_MIN
+#define PTRDIFF_MAX INT32_MAX
+
+#define SIZE_MAX UINT32_MAX
+
+#endif /* lib/stdint.h */
diff --git a/src/lib/stdio.c b/src/lib/stdio.c
new file mode 100644
index 0000000..af80e51
--- /dev/null
+++ b/src/lib/stdio.c
@@ -0,0 +1,637 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <inttypes.h>
+#include <round.h>
+#include <stdint.h>
+#include <string.h>
+
+/* Auxiliary data for vsnprintf_helper(). */
+struct vsnprintf_aux 
+  {
+    char *p;            /* Current output position. */
+    int length;         /* Length of output string. */
+    int max_length;     /* Max length of output string. */
+  };
+
+static void vsnprintf_helper (char, void *);
+
+/* Like vprintf(), except that output is stored into BUFFER,
+   which must have space for BUF_SIZE characters.  Writes at most
+   BUF_SIZE - 1 characters to BUFFER, followed by a null
+   terminator.  BUFFER will always be null-terminated unless
+   BUF_SIZE is zero.  Returns the number of characters that would
+   have been written to BUFFER, not including a null terminator,
+   had there been enough room. */
+int
+vsnprintf (char *buffer, size_t buf_size, const char *format, va_list args) 
+{
+  /* Set up aux data for vsnprintf_helper(). */
+  struct vsnprintf_aux aux;
+  aux.p = buffer;
+  aux.length = 0;
+  aux.max_length = buf_size > 0 ? buf_size - 1 : 0;
+
+  /* Do most of the work. */
+  __vprintf (format, args, vsnprintf_helper, &aux);
+
+  /* Add null terminator. */
+  if (buf_size > 0)
+    *aux.p = '\0';
+
+  return aux.length;
+}
+
+/* Helper function for vsnprintf(). */
+static void
+vsnprintf_helper (char ch, void *aux_)
+{
+  struct vsnprintf_aux *aux = aux_;
+
+  if (aux->length++ < aux->max_length)
+    *aux->p++ = ch;
+}
+
+/* Like printf(), except that output is stored into BUFFER,
+   which must have space for BUF_SIZE characters.  Writes at most
+   BUF_SIZE - 1 characters to BUFFER, followed by a null
+   terminator.  BUFFER will always be null-terminated unless
+   BUF_SIZE is zero.  Returns the number of characters that would
+   have been written to BUFFER, not including a null terminator,
+   had there been enough room. */
+int
+snprintf (char *buffer, size_t buf_size, const char *format, ...) 
+{
+  va_list args;
+  int retval;
+
+  va_start (args, format);
+  retval = vsnprintf (buffer, buf_size, format, args);
+  va_end (args);
+
+  return retval;
+}
+
+/* Writes formatted output to the console.
+   In the kernel, the console is both the video display and first
+   serial port.
+   In userspace, the console is file descriptor 1. */
+int
+printf (const char *format, ...) 
+{
+  va_list args;
+  int retval;
+
+  va_start (args, format);
+  retval = vprintf (format, args);
+  va_end (args);
+
+  return retval;
+}
+
+/* printf() formatting internals. */
+
+/* A printf() conversion. */
+struct printf_conversion 
+  {
+    /* Flags. */
+    enum 
+      {
+        MINUS = 1 << 0,         /* '-' */
+        PLUS = 1 << 1,          /* '+' */
+        SPACE = 1 << 2,         /* ' ' */
+        POUND = 1 << 3,         /* '#' */
+        ZERO = 1 << 4,          /* '0' */
+        GROUP = 1 << 5          /* '\'' */
+      }
+    flags;
+
+    /* Minimum field width. */
+    int width;
+
+    /* Numeric precision.
+       -1 indicates no precision was specified. */
+    int precision;
+
+    /* Type of argument to format. */
+    enum 
+      {
+        CHAR = 1,               /* hh */
+        SHORT = 2,              /* h */
+        INT = 3,                /* (none) */
+        INTMAX = 4,             /* j */
+        LONG = 5,               /* l */
+        LONGLONG = 6,           /* ll */
+        PTRDIFFT = 7,           /* t */
+        SIZET = 8               /* z */
+      }
+    type;
+  };
+
+struct integer_base 
+  {
+    int base;                   /* Base. */
+    const char *digits;         /* Collection of digits. */
+    int x;                      /* `x' character to use, for base 16 only. */
+    int group;                  /* Number of digits to group with ' flag. */
+  };
+
+static const struct integer_base base_d = {10, "0123456789", 0, 3};
+static const struct integer_base base_o = {8, "01234567", 0, 3};
+static const struct integer_base base_x = {16, "0123456789abcdef", 'x', 4};
+static const struct integer_base base_X = {16, "0123456789ABCDEF", 'X', 4};
+
+static const char *parse_conversion (const char *format,
+                                     struct printf_conversion *,
+                                     va_list *);
+static void format_integer (uintmax_t value, bool is_signed, bool negative, 
+                            const struct integer_base *,
+                            const struct printf_conversion *,
+                            void (*output) (char, void *), void *aux);
+static void output_dup (char ch, size_t cnt,
+                        void (*output) (char, void *), void *aux);
+static void format_string (const char *string, int length,
+                           struct printf_conversion *,
+                           void (*output) (char, void *), void *aux);
+
+void
+__vprintf (const char *format, va_list args,
+           void (*output) (char, void *), void *aux)
+{
+  for (; *format != '\0'; format++)
+    {
+      struct printf_conversion c;
+
+      /* Literally copy non-conversions to output. */
+      if (*format != '%') 
+        {
+          output (*format, aux);
+          continue;
+        }
+      format++;
+
+      /* %% => %. */
+      if (*format == '%') 
+        {
+          output ('%', aux);
+          continue;
+        }
+
+      /* Parse conversion specifiers. */
+      format = parse_conversion (format, &c, &args);
+
+      /* Do conversion. */
+      switch (*format) 
+        {
+        case 'd':
+        case 'i': 
+          {
+            /* Signed integer conversions. */
+            intmax_t value;
+            
+            switch (c.type) 
+              {
+              case CHAR: 
+                value = (signed char) va_arg (args, int);
+                break;
+              case SHORT:
+                value = (short) va_arg (args, int);
+                break;
+              case INT:
+                value = va_arg (args, int);
+                break;
+              case INTMAX:
+                value = va_arg (args, intmax_t);
+                break;
+              case LONG:
+                value = va_arg (args, long);
+                break;
+              case LONGLONG:
+                value = va_arg (args, long long);
+                break;
+              case PTRDIFFT:
+                value = va_arg (args, ptrdiff_t);
+                break;
+              case SIZET:
+                value = va_arg (args, size_t);
+                if (value > SIZE_MAX / 2)
+                  value = value - SIZE_MAX - 1;
+                break;
+              default:
+                NOT_REACHED ();
+              }
+
+            format_integer (value < 0 ? -value : value,
+                            true, value < 0, &base_d, &c, output, aux);
+          }
+          break;
+          
+        case 'o':
+        case 'u':
+        case 'x':
+        case 'X':
+          {
+            /* Unsigned integer conversions. */
+            uintmax_t value;
+            const struct integer_base *b;
+
+            switch (c.type) 
+              {
+              case CHAR: 
+                value = (unsigned char) va_arg (args, unsigned);
+                break;
+              case SHORT:
+                value = (unsigned short) va_arg (args, unsigned);
+                break;
+              case INT:
+                value = va_arg (args, unsigned);
+                break;
+              case INTMAX:
+                value = va_arg (args, uintmax_t);
+                break;
+              case LONG:
+                value = va_arg (args, unsigned long);
+                break;
+              case LONGLONG:
+                value = va_arg (args, unsigned long long);
+                break;
+              case PTRDIFFT:
+                value = va_arg (args, ptrdiff_t);
+#if UINTMAX_MAX != PTRDIFF_MAX
+                value &= ((uintmax_t) PTRDIFF_MAX << 1) | 1;
+#endif
+                break;
+              case SIZET:
+                value = va_arg (args, size_t);
+                break;
+              default:
+                NOT_REACHED ();
+              }
+
+            switch (*format) 
+              {
+              case 'o': b = &base_o; break;
+              case 'u': b = &base_d; break;
+              case 'x': b = &base_x; break;
+              case 'X': b = &base_X; break;
+              default: NOT_REACHED ();
+              }
+
+            format_integer (value, false, false, b, &c, output, aux);
+          }
+          break;
+
+        case 'c': 
+          {
+            /* Treat character as single-character string. */
+            char ch = va_arg (args, int);
+            format_string (&ch, 1, &c, output, aux);
+          }
+          break;
+
+        case 's':
+          {
+            /* String conversion. */
+            const char *s = va_arg (args, char *);
+            if (s == NULL)
+              s = "(null)";
+
+            /* Limit string length according to precision.
+               Note: if c.precision == -1 then strnlen() will get
+               SIZE_MAX for MAXLEN, which is just what we want. */
+            format_string (s, strnlen (s, c.precision), &c, output, aux);
+          }
+          break;
+          
+        case 'p':
+          {
+            /* Pointer conversion.
+               Format pointers as %#x. */
+            void *p = va_arg (args, void *);
+
+            c.flags = POUND;
+            format_integer ((uintptr_t) p, false, false,
+                            &base_x, &c, output, aux);
+          }
+          break;
+      
+        case 'f':
+        case 'e':
+        case 'E':
+        case 'g':
+        case 'G':
+        case 'n':
+          /* We don't support floating-point arithmetic,
+             and %n can be part of a security hole. */
+          __printf ("<<no %%%c in kernel>>", output, aux, *format);
+          break;
+
+        default:
+          __printf ("<<no %%%c conversion>>", output, aux, *format);
+          break;
+        }
+    }
+}
+
+/* Parses conversion option characters starting at FORMAT and
+   initializes C appropriately.  Returns the character in FORMAT
+   that indicates the conversion (e.g. the `d' in `%d').  Uses
+   *ARGS for `*' field widths and precisions. */
+static const char *
+parse_conversion (const char *format, struct printf_conversion *c,
+                  va_list *args) 
+{
+  /* Parse flag characters. */
+  c->flags = 0;
+  for (;;) 
+    {
+      switch (*format++) 
+        {
+        case '-':
+          c->flags |= MINUS;
+          break;
+        case '+':
+          c->flags |= PLUS;
+          break;
+        case ' ':
+          c->flags |= SPACE;
+          break;
+        case '#':
+          c->flags |= POUND;
+          break;
+        case '0':
+          c->flags |= ZERO;
+          break;
+        case '\'':
+          c->flags |= GROUP;
+          break;
+        default:
+          format--;
+          goto not_a_flag;
+        }
+    }
+ not_a_flag:
+  if (c->flags & MINUS)
+    c->flags &= ~ZERO;
+  if (c->flags & PLUS)
+    c->flags &= ~SPACE;
+
+  /* Parse field width. */
+  c->width = 0;
+  if (*format == '*')
+    {
+      format++;
+      c->width = va_arg (*args, int);
+    }
+  else 
+    {
+      for (; isdigit (*format); format++)
+        c->width = c->width * 10 + *format - '0';
+    }
+  if (c->width < 0) 
+    {
+      c->width = -c->width;
+      c->flags |= MINUS;
+    }
+      
+  /* Parse precision. */
+  c->precision = -1;
+  if (*format == '.') 
+    {
+      format++;
+      if (*format == '*') 
+        {
+          format++;
+          c->precision = va_arg (*args, int);
+        }
+      else 
+        {
+          c->precision = 0;
+          for (; isdigit (*format); format++)
+            c->precision = c->precision * 10 + *format - '0';
+        }
+      if (c->precision < 0) 
+        c->precision = -1;
+    }
+  if (c->precision >= 0)
+    c->flags &= ~ZERO;
+
+  /* Parse type. */
+  c->type = INT;
+  switch (*format++) 
+    {
+    case 'h':
+      if (*format == 'h') 
+        {
+          format++;
+          c->type = CHAR;
+        }
+      else
+        c->type = SHORT;
+      break;
+      
+    case 'j':
+      c->type = INTMAX;
+      break;
+
+    case 'l':
+      if (*format == 'l')
+        {
+          format++;
+          c->type = LONGLONG;
+        }
+      else
+        c->type = LONG;
+      break;
+
+    case 't':
+      c->type = PTRDIFFT;
+      break;
+
+    case 'z':
+      c->type = SIZET;
+      break;
+
+    default:
+      format--;
+      break;
+    }
+
+  return format;
+}
+
+/* Performs an integer conversion, writing output to OUTPUT with
+   auxiliary data AUX.  The integer converted has absolute value
+   VALUE.  If IS_SIGNED is true, does a signed conversion with
+   NEGATIVE indicating a negative value; otherwise does an
+   unsigned conversion and ignores NEGATIVE.  The output is done
+   according to the provided base B.  Details of the conversion
+   are in C. */
+static void
+format_integer (uintmax_t value, bool is_signed, bool negative, 
+                const struct integer_base *b,
+                const struct printf_conversion *c,
+                void (*output) (char, void *), void *aux)
+{
+  char buf[64], *cp;            /* Buffer and current position. */
+  int x;                        /* `x' character to use or 0 if none. */
+  int sign;                     /* Sign character or 0 if none. */
+  int precision;                /* Rendered precision. */
+  int pad_cnt;                  /* # of pad characters to fill field width. */
+  int digit_cnt;                /* # of digits output so far. */
+
+  /* Determine sign character, if any.
+     An unsigned conversion will never have a sign character,
+     even if one of the flags requests one. */
+  sign = 0;
+  if (is_signed) 
+    {
+      if (c->flags & PLUS)
+        sign = negative ? '-' : '+';
+      else if (c->flags & SPACE)
+        sign = negative ? '-' : ' ';
+      else if (negative)
+        sign = '-';
+    }
+
+  /* Determine whether to include `0x' or `0X'.
+     It will only be included with a hexadecimal conversion of a
+     nonzero value with the # flag. */
+  x = (c->flags & POUND) && value ? b->x : 0;
+
+  /* Accumulate digits into buffer.
+     This algorithm produces digits in reverse order, so later we
+     will output the buffer's content in reverse. */
+  cp = buf;
+  digit_cnt = 0;
+  while (value > 0) 
+    {
+      if ((c->flags & GROUP) && digit_cnt > 0 && digit_cnt % b->group == 0)
+        *cp++ = ',';
+      *cp++ = b->digits[value % b->base];
+      value /= b->base;
+      digit_cnt++;
+    }
+
+  /* Append enough zeros to match precision.
+     If requested precision is 0, then a value of zero is
+     rendered as a null string, otherwise as "0".
+     If the # flag is used with base 8, the result must always
+     begin with a zero. */
+  precision = c->precision < 0 ? 1 : c->precision;
+  while (cp - buf < precision && cp < buf + sizeof buf - 1)
+    *cp++ = '0';
+  if ((c->flags & POUND) && b->base == 8 && (cp == buf || cp[-1] != '0'))
+    *cp++ = '0';
+
+  /* Calculate number of pad characters to fill field width. */
+  pad_cnt = c->width - (cp - buf) - (x ? 2 : 0) - (sign != 0);
+  if (pad_cnt < 0)
+    pad_cnt = 0;
+
+  /* Do output. */
+  if ((c->flags & (MINUS | ZERO)) == 0)
+    output_dup (' ', pad_cnt, output, aux);
+  if (sign)
+    output (sign, aux);
+  if (x) 
+    {
+      output ('0', aux);
+      output (x, aux); 
+    }
+  if (c->flags & ZERO)
+    output_dup ('0', pad_cnt, output, aux);
+  while (cp > buf)
+    output (*--cp, aux);
+  if (c->flags & MINUS)
+    output_dup (' ', pad_cnt, output, aux);
+}
+
+/* Writes CH to OUTPUT with auxiliary data AUX, CNT times. */
+static void
+output_dup (char ch, size_t cnt, void (*output) (char, void *), void *aux) 
+{
+  while (cnt-- > 0)
+    output (ch, aux);
+}
+
+/* Formats the LENGTH characters starting at STRING according to
+   the conversion specified in C.  Writes output to OUTPUT with
+   auxiliary data AUX. */
+static void
+format_string (const char *string, int length,
+               struct printf_conversion *c,
+               void (*output) (char, void *), void *aux) 
+{
+  int i;
+  if (c->width > length && (c->flags & MINUS) == 0)
+    output_dup (' ', c->width - length, output, aux);
+  for (i = 0; i < length; i++)
+    output (string[i], aux);
+  if (c->width > length && (c->flags & MINUS) != 0)
+    output_dup (' ', c->width - length, output, aux);
+}
+
+/* Wrapper for __vprintf() that converts varargs into a
+   va_list. */
+void
+__printf (const char *format,
+          void (*output) (char, void *), void *aux, ...) 
+{
+  va_list args;
+
+  va_start (args, aux);
+  __vprintf (format, args, output, aux);
+  va_end (args);
+}
+
+/* Dumps the SIZE bytes in BUF to the console as hex bytes
+   arranged 16 per line.  Numeric offsets are also included,
+   starting at OFS for the first byte in BUF.  If ASCII is true
+   then the corresponding ASCII characters are also rendered
+   alongside. */   
+void
+hex_dump (uintptr_t ofs, const void *buf_, size_t size, bool ascii)
+{
+  const uint8_t *buf = buf_;
+  const size_t per_line = 16; /* Maximum bytes per line. */
+
+  while (size > 0)
+    {
+      size_t start, end, n;
+      size_t i;
+      
+      /* Number of bytes on this line. */
+      start = ofs % per_line;
+      end = per_line;
+      if (end - start > size)
+        end = start + size;
+      n = end - start;
+
+      /* Print line. */
+      printf ("%08jx  ", (uintmax_t) ROUND_DOWN (ofs, per_line));
+      for (i = 0; i < start; i++)
+        printf ("   ");
+      for (; i < end; i++) 
+        printf ("%02hhx%c",
+                buf[i - start], i == per_line / 2 - 1? '-' : ' ');
+      if (ascii) 
+        {
+          for (; i < per_line; i++)
+            printf ("   ");
+          printf ("|");
+          for (i = 0; i < start; i++)
+            printf (" ");
+          for (; i < end; i++)
+            printf ("%c",
+                    isprint (buf[i - start]) ? buf[i - start] : '.');
+          for (; i < per_line; i++)
+            printf (" ");
+          printf ("|");
+        }
+      printf ("\n");
+
+      ofs += n;
+      buf += n;
+      size -= n;
+    }
+}
diff --git a/src/lib/stdio.h b/src/lib/stdio.h
new file mode 100644
index 0000000..8288ff0
--- /dev/null
+++ b/src/lib/stdio.h
@@ -0,0 +1,39 @@
+#ifndef __LIB_STDIO_H
+#define __LIB_STDIO_H
+
+#include <debug.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* Include lib/user/stdio.h or lib/kernel/stdio.h, as
+   appropriate. */
+#include_next <stdio.h>
+
+/* Predefined file handles. */
+#define STDIN_FILENO 0
+#define STDOUT_FILENO 1
+
+/* Standard functions. */
+int printf (const char *, ...) PRINTF_FORMAT (1, 2);
+int snprintf (char *, size_t, const char *, ...) PRINTF_FORMAT (3, 4);
+int vprintf (const char *, va_list) PRINTF_FORMAT (1, 0);
+int vsnprintf (char *, size_t, const char *, va_list) PRINTF_FORMAT (3, 0);
+int putchar (int);
+int puts (const char *);
+
+/* Nonstandard functions. */
+void hex_dump (uintptr_t ofs, const void *, size_t size, bool ascii);
+
+/* Internal functions. */
+void __vprintf (const char *format, va_list args,
+                void (*output) (char, void *), void *aux);
+void __printf (const char *format,
+               void (*output) (char, void *), void *aux, ...);
+
+/* Try to be helpful. */
+#define sprintf dont_use_sprintf_use_snprintf
+#define vsprintf dont_use_vsprintf_use_vsnprintf
+
+#endif /* lib/stdio.h */
diff --git a/src/lib/stdlib.c b/src/lib/stdlib.c
new file mode 100644
index 0000000..84c7f61
--- /dev/null
+++ b/src/lib/stdlib.c
@@ -0,0 +1,208 @@
+#include <ctype.h>
+#include <debug.h>
+#include <random.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+/* Converts a string representation of a signed decimal integer
+   in S into an `int', which is returned. */
+int
+atoi (const char *s) 
+{
+  bool negative;
+  int value;
+
+  ASSERT (s != NULL);
+
+  /* Skip white space. */
+  while (isspace ((unsigned char) *s))
+    s++;
+
+  /* Parse sign. */
+  negative = false;
+  if (*s == '+')
+    s++;
+  else if (*s == '-')
+    {
+      negative = true;
+      s++;
+    }
+
+  /* Parse digits.  We always initially parse the value as
+     negative, and then make it positive later, because the
+     negative range of an int is bigger than the positive range
+     on a 2's complement system. */
+  for (value = 0; isdigit (*s); s++)
+    value = value * 10 - (*s - '0');
+  if (!negative)
+    value = -value;
+
+  return value;
+}
+
+/* Compares A and B by calling the AUX function. */
+static int
+compare_thunk (const void *a, const void *b, void *aux) 
+{
+  int (**compare) (const void *, const void *) = aux;
+  return (*compare) (a, b);
+}
+
+/* Sorts ARRAY, which contains CNT elements of SIZE bytes each,
+   using COMPARE.  When COMPARE is passed a pair of elements A
+   and B, respectively, it must return a strcmp()-type result,
+   i.e. less than zero if A < B, zero if A == B, greater than
+   zero if A > B.  Runs in O(n lg n) time and O(1) space in
+   CNT. */
+void
+qsort (void *array, size_t cnt, size_t size,
+       int (*compare) (const void *, const void *)) 
+{
+  sort (array, cnt, size, compare_thunk, &compare);
+}
+
+/* Swaps elements with 1-based indexes A_IDX and B_IDX in ARRAY
+   with elements of SIZE bytes each. */
+static void
+do_swap (unsigned char *array, size_t a_idx, size_t b_idx, size_t size)
+{
+  unsigned char *a = array + (a_idx - 1) * size;
+  unsigned char *b = array + (b_idx - 1) * size;
+  size_t i;
+
+  for (i = 0; i < size; i++)
+    {
+      unsigned char t = a[i];
+      a[i] = b[i];
+      b[i] = t;
+    }
+}
+
+/* Compares elements with 1-based indexes A_IDX and B_IDX in
+   ARRAY with elements of SIZE bytes each, using COMPARE to
+   compare elements, passing AUX as auxiliary data, and returns a
+   strcmp()-type result. */
+static int
+do_compare (unsigned char *array, size_t a_idx, size_t b_idx, size_t size,
+            int (*compare) (const void *, const void *, void *aux),
+            void *aux) 
+{
+  return compare (array + (a_idx - 1) * size, array + (b_idx - 1) * size, aux);
+}
+
+/* "Float down" the element with 1-based index I in ARRAY of CNT
+   elements of SIZE bytes each, using COMPARE to compare
+   elements, passing AUX as auxiliary data. */
+static void
+heapify (unsigned char *array, size_t i, size_t cnt, size_t size,
+         int (*compare) (const void *, const void *, void *aux),
+         void *aux) 
+{
+  for (;;) 
+    {
+      /* Set `max' to the index of the largest element among I
+         and its children (if any). */
+      size_t left = 2 * i;
+      size_t right = 2 * i + 1;
+      size_t max = i;
+      if (left <= cnt && do_compare (array, left, max, size, compare, aux) > 0)
+        max = left;
+      if (right <= cnt
+          && do_compare (array, right, max, size, compare, aux) > 0) 
+        max = right;
+
+      /* If the maximum value is already in element I, we're
+         done. */
+      if (max == i)
+        break;
+
+      /* Swap and continue down the heap. */
+      do_swap (array, i, max, size);
+      i = max;
+    }
+}
+
+/* Sorts ARRAY, which contains CNT elements of SIZE bytes each,
+   using COMPARE to compare elements, passing AUX as auxiliary
+   data.  When COMPARE is passed a pair of elements A and B,
+   respectively, it must return a strcmp()-type result, i.e. less
+   than zero if A < B, zero if A == B, greater than zero if A >
+   B.  Runs in O(n lg n) time and O(1) space in CNT. */
+void
+sort (void *array, size_t cnt, size_t size,
+      int (*compare) (const void *, const void *, void *aux),
+      void *aux) 
+{
+  size_t i;
+
+  ASSERT (array != NULL || cnt == 0);
+  ASSERT (compare != NULL);
+  ASSERT (size > 0);
+
+  /* Build a heap. */
+  for (i = cnt / 2; i > 0; i--)
+    heapify (array, i, cnt, size, compare, aux);
+
+  /* Sort the heap. */
+  for (i = cnt; i > 1; i--) 
+    {
+      do_swap (array, 1, i, size);
+      heapify (array, 1, i - 1, size, compare, aux); 
+    }
+}
+
+/* Searches ARRAY, which contains CNT elements of SIZE bytes
+   each, for the given KEY.  Returns a match is found, otherwise
+   a null pointer.  If there are multiple matches, returns an
+   arbitrary one of them.
+
+   ARRAY must be sorted in order according to COMPARE.
+
+   Uses COMPARE to compare elements.  When COMPARE is passed a
+   pair of elements A and B, respectively, it must return a
+   strcmp()-type result, i.e. less than zero if A < B, zero if A
+   == B, greater than zero if A > B. */
+void *
+bsearch (const void *key, const void *array, size_t cnt,
+         size_t size, int (*compare) (const void *, const void *)) 
+{
+  return binary_search (key, array, cnt, size, compare_thunk, &compare);
+}
+
+/* Searches ARRAY, which contains CNT elements of SIZE bytes
+   each, for the given KEY.  Returns a match is found, otherwise
+   a null pointer.  If there are multiple matches, returns an
+   arbitrary one of them.
+
+   ARRAY must be sorted in order according to COMPARE.
+
+   Uses COMPARE to compare elements, passing AUX as auxiliary
+   data.  When COMPARE is passed a pair of elements A and B,
+   respectively, it must return a strcmp()-type result, i.e. less
+   than zero if A < B, zero if A == B, greater than zero if A >
+   B. */
+void *
+binary_search (const void *key, const void *array, size_t cnt, size_t size,
+               int (*compare) (const void *, const void *, void *aux),
+               void *aux) 
+{
+  const unsigned char *first = array;
+  const unsigned char *last = array + size * cnt;
+
+  while (first < last) 
+    {
+      size_t range = (last - first) / size;
+      const unsigned char *middle = first + (range / 2) * size;
+      int cmp = compare (key, middle, aux);
+
+      if (cmp < 0) 
+        last = middle;
+      else if (cmp > 0) 
+        first = middle + size;
+      else
+        return (void *) middle;
+    }
+  
+  return NULL;
+}
+
diff --git a/src/lib/stdlib.h b/src/lib/stdlib.h
new file mode 100644
index 0000000..d14afa3
--- /dev/null
+++ b/src/lib/stdlib.h
@@ -0,0 +1,22 @@
+#ifndef __LIB_STDLIB_H
+#define __LIB_STDLIB_H
+
+#include <stddef.h>
+
+/* Standard functions. */
+int atoi (const char *);
+void qsort (void *array, size_t cnt, size_t size,
+            int (*compare) (const void *, const void *));
+void *bsearch (const void *key, const void *array, size_t cnt,
+               size_t size, int (*compare) (const void *, const void *));
+
+/* Nonstandard functions. */
+void sort (void *array, size_t cnt, size_t size,
+           int (*compare) (const void *, const void *, void *aux),
+           void *aux);
+void *binary_search (const void *key, const void *array, size_t cnt,
+                     size_t size,
+                     int (*compare) (const void *, const void *, void *aux),
+                     void *aux);
+
+#endif /* lib/stdlib.h */
diff --git a/src/lib/string.c b/src/lib/string.c
new file mode 100644
index 0000000..d223c89
--- /dev/null
+++ b/src/lib/string.c
@@ -0,0 +1,375 @@
+#include <string.h>
+#include <debug.h>
+
+/* Copies SIZE bytes from SRC to DST, which must not overlap.
+   Returns DST. */
+void *
+memcpy (void *dst_, const void *src_, size_t size) 
+{
+  unsigned char *dst = dst_;
+  const unsigned char *src = src_;
+
+  ASSERT (dst != NULL || size == 0);
+  ASSERT (src != NULL || size == 0);
+
+  while (size-- > 0)
+    *dst++ = *src++;
+
+  return dst_;
+}
+
+/* Copies SIZE bytes from SRC to DST, which are allowed to
+   overlap.  Returns DST. */
+void *
+memmove (void *dst_, const void *src_, size_t size) 
+{
+  unsigned char *dst = dst_;
+  const unsigned char *src = src_;
+
+  ASSERT (dst != NULL || size == 0);
+  ASSERT (src != NULL || size == 0);
+
+  if (dst < src) 
+    {
+      while (size-- > 0)
+        *dst++ = *src++;
+    }
+  else 
+    {
+      dst += size;
+      src += size;
+      while (size-- > 0)
+        *--dst = *--src;
+    }
+
+  return dst;
+}
+
+/* Find the first differing byte in the two blocks of SIZE bytes
+   at A and B.  Returns a positive value if the byte in A is
+   greater, a negative value if the byte in B is greater, or zero
+   if blocks A and B are equal. */
+int
+memcmp (const void *a_, const void *b_, size_t size) 
+{
+  const unsigned char *a = a_;
+  const unsigned char *b = b_;
+
+  ASSERT (a != NULL || size == 0);
+  ASSERT (b != NULL || size == 0);
+
+  for (; size-- > 0; a++, b++)
+    if (*a != *b)
+      return *a > *b ? +1 : -1;
+  return 0;
+}
+
+/* Finds the first differing characters in strings A and B.
+   Returns a positive value if the character in A (as an unsigned
+   char) is greater, a negative value if the character in B (as
+   an unsigned char) is greater, or zero if strings A and B are
+   equal. */
+int
+strcmp (const char *a_, const char *b_) 
+{
+  const unsigned char *a = (const unsigned char *) a_;
+  const unsigned char *b = (const unsigned char *) b_;
+
+  ASSERT (a != NULL);
+  ASSERT (b != NULL);
+
+  while (*a != '\0' && *a == *b) 
+    {
+      a++;
+      b++;
+    }
+
+  return *a < *b ? -1 : *a > *b;
+}
+
+/* Returns a pointer to the first occurrence of CH in the first
+   SIZE bytes starting at BLOCK.  Returns a null pointer if CH
+   does not occur in BLOCK. */
+void *
+memchr (const void *block_, int ch_, size_t size) 
+{
+  const unsigned char *block = block_;
+  unsigned char ch = ch_;
+
+  ASSERT (block != NULL || size == 0);
+
+  for (; size-- > 0; block++)
+    if (*block == ch)
+      return (void *) block;
+
+  return NULL;
+}
+
+/* Finds and returns the first occurrence of C in STRING, or a
+   null pointer if C does not appear in STRING.  If C == '\0'
+   then returns a pointer to the null terminator at the end of
+   STRING. */
+char *
+strchr (const char *string, int c_) 
+{
+  char c = c_;
+
+  ASSERT (string != NULL);
+
+  for (;;) 
+    if (*string == c)
+      return (char *) string;
+    else if (*string == '\0')
+      return NULL;
+    else
+      string++;
+}
+
+/* Returns the length of the initial substring of STRING that
+   consists of characters that are not in STOP. */
+size_t
+strcspn (const char *string, const char *stop) 
+{
+  size_t length;
+
+  for (length = 0; string[length] != '\0'; length++)
+    if (strchr (stop, string[length]) != NULL)
+      break;
+  return length;
+}
+
+/* Returns a pointer to the first character in STRING that is
+   also in STOP.  If no character in STRING is in STOP, returns a
+   null pointer. */
+char *
+strpbrk (const char *string, const char *stop) 
+{
+  for (; *string != '\0'; string++)
+    if (strchr (stop, *string) != NULL)
+      return (char *) string;
+  return NULL;
+}
+
+/* Returns a pointer to the last occurrence of C in STRING.
+   Returns a null pointer if C does not occur in STRING. */
+char *
+strrchr (const char *string, int c_) 
+{
+  char c = c_;
+  const char *p = NULL;
+
+  for (; *string != '\0'; string++)
+    if (*string == c)
+      p = string;
+  return (char *) p;
+}
+
+/* Returns the length of the initial substring of STRING that
+   consists of characters in SKIP. */
+size_t
+strspn (const char *string, const char *skip) 
+{
+  size_t length;
+  
+  for (length = 0; string[length] != '\0'; length++)
+    if (strchr (skip, string[length]) == NULL)
+      break;
+  return length;
+}
+
+/* Returns a pointer to the first occurrence of NEEDLE within
+   HAYSTACK.  Returns a null pointer if NEEDLE does not exist
+   within HAYSTACK. */
+char *
+strstr (const char *haystack, const char *needle) 
+{
+  size_t haystack_len = strlen (haystack);
+  size_t needle_len = strlen (needle);
+
+  if (haystack_len >= needle_len) 
+    {
+      size_t i;
+
+      for (i = 0; i <= haystack_len - needle_len; i++)
+        if (!memcmp (haystack + i, needle, needle_len))
+          return (char *) haystack + i;
+    }
+
+  return NULL;
+}
+
+/* Breaks a string into tokens separated by DELIMITERS.  The
+   first time this function is called, S should be the string to
+   tokenize, and in subsequent calls it must be a null pointer.
+   SAVE_PTR is the address of a `char *' variable used to keep
+   track of the tokenizer's position.  The return value each time
+   is the next token in the string, or a null pointer if no
+   tokens remain.
+
+   This function treats multiple adjacent delimiters as a single
+   delimiter.  The returned tokens will never be length 0.
+   DELIMITERS may change from one call to the next within a
+   single string.
+
+   strtok_r() modifies the string S, changing delimiters to null
+   bytes.  Thus, S must be a modifiable string.  String literals,
+   in particular, are *not* modifiable in C, even though for
+   backward compatibility they are not `const'.
+
+   Example usage:
+
+   char s[] = "  String to  tokenize. ";
+   char *token, *save_ptr;
+
+   for (token = strtok_r (s, " ", &save_ptr); token != NULL;
+        token = strtok_r (NULL, " ", &save_ptr))
+     printf ("'%s'\n", token);
+
+   outputs:
+
+     'String'
+     'to'
+     'tokenize.'
+*/
+char *
+strtok_r (char *s, const char *delimiters, char **save_ptr) 
+{
+  char *token;
+  
+  ASSERT (delimiters != NULL);
+  ASSERT (save_ptr != NULL);
+
+  /* If S is nonnull, start from it.
+     If S is null, start from saved position. */
+  if (s == NULL)
+    s = *save_ptr;
+  ASSERT (s != NULL);
+
+  /* Skip any DELIMITERS at our current position. */
+  while (strchr (delimiters, *s) != NULL) 
+    {
+      /* strchr() will always return nonnull if we're searching
+         for a null byte, because every string contains a null
+         byte (at the end). */
+      if (*s == '\0')
+        {
+          *save_ptr = s;
+          return NULL;
+        }
+
+      s++;
+    }
+
+  /* Skip any non-DELIMITERS up to the end of the string. */
+  token = s;
+  while (strchr (delimiters, *s) == NULL)
+    s++;
+  if (*s != '\0') 
+    {
+      *s = '\0';
+      *save_ptr = s + 1;
+    }
+  else 
+    *save_ptr = s;
+  return token;
+}
+
+/* Sets the SIZE bytes in DST to VALUE. */
+void *
+memset (void *dst_, int value, size_t size) 
+{
+  unsigned char *dst = dst_;
+
+  ASSERT (dst != NULL || size == 0);
+  
+  while (size-- > 0)
+    *dst++ = value;
+
+  return dst_;
+}
+
+/* Returns the length of STRING. */
+size_t
+strlen (const char *string) 
+{
+  const char *p;
+
+  ASSERT (string != NULL);
+
+  for (p = string; *p != '\0'; p++)
+    continue;
+  return p - string;
+}
+
+/* If STRING is less than MAXLEN characters in length, returns
+   its actual length.  Otherwise, returns MAXLEN. */
+size_t
+strnlen (const char *string, size_t maxlen) 
+{
+  size_t length;
+
+  for (length = 0; string[length] != '\0' && length < maxlen; length++)
+    continue;
+  return length;
+}
+
+/* Copies string SRC to DST.  If SRC is longer than SIZE - 1
+   characters, only SIZE - 1 characters are copied.  A null
+   terminator is always written to DST, unless SIZE is 0.
+   Returns the length of SRC, not including the null terminator.
+
+   strlcpy() is not in the standard C library, but it is an
+   increasingly popular extension.  See
+   http://www.courtesan.com/todd/papers/strlcpy.html for
+   information on strlcpy(). */
+size_t
+strlcpy (char *dst, const char *src, size_t size) 
+{
+  size_t src_len;
+
+  ASSERT (dst != NULL);
+  ASSERT (src != NULL);
+
+  src_len = strlen (src);
+  if (size > 0) 
+    {
+      size_t dst_len = size - 1;
+      if (src_len < dst_len)
+        dst_len = src_len;
+      memcpy (dst, src, dst_len);
+      dst[dst_len] = '\0';
+    }
+  return src_len;
+}
+
+/* Concatenates string SRC to DST.  The concatenated string is
+   limited to SIZE - 1 characters.  A null terminator is always
+   written to DST, unless SIZE is 0.  Returns the length that the
+   concatenated string would have assuming that there was
+   sufficient space, not including a null terminator.
+
+   strlcat() is not in the standard C library, but it is an
+   increasingly popular extension.  See
+   http://www.courtesan.com/todd/papers/strlcpy.html for
+   information on strlcpy(). */
+size_t
+strlcat (char *dst, const char *src, size_t size) 
+{
+  size_t src_len, dst_len;
+
+  ASSERT (dst != NULL);
+  ASSERT (src != NULL);
+
+  src_len = strlen (src);
+  dst_len = strlen (dst);
+  if (size > 0 && dst_len < size) 
+    {
+      size_t copy_cnt = size - dst_len - 1;
+      if (src_len < copy_cnt)
+        copy_cnt = src_len;
+      memcpy (dst + dst_len, src, copy_cnt);
+      dst[dst_len + copy_cnt] = '\0';
+    }
+  return src_len + dst_len;
+}
+
diff --git a/src/lib/string.h b/src/lib/string.h
new file mode 100644
index 0000000..1fff82a
--- /dev/null
+++ b/src/lib/string.h
@@ -0,0 +1,35 @@
+#ifndef __LIB_STRING_H
+#define __LIB_STRING_H
+
+#include <stddef.h>
+
+/* Standard. */
+void *memcpy (void *, const void *, size_t);
+void *memmove (void *, const void *, size_t);
+char *strncat (char *, const char *, size_t);
+int memcmp (const void *, const void *, size_t);
+int strcmp (const char *, const char *);
+void *memchr (const void *, int, size_t);
+char *strchr (const char *, int);
+size_t strcspn (const char *, const char *);
+char *strpbrk (const char *, const char *);
+char *strrchr (const char *, int);
+size_t strspn (const char *, const char *);
+char *strstr (const char *, const char *);
+void *memset (void *, int, size_t);
+size_t strlen (const char *);
+
+/* Extensions. */
+size_t strlcpy (char *, const char *, size_t);
+size_t strlcat (char *, const char *, size_t);
+char *strtok_r (char *, const char *, char **);
+size_t strnlen (const char *, size_t);
+
+/* Try to be helpful. */
+#define strcpy dont_use_strcpy_use_strlcpy
+#define strncpy dont_use_strncpy_use_strlcpy
+#define strcat dont_use_strcat_use_strlcat
+#define strncat dont_use_strncat_use_strlcat
+#define strtok dont_use_strtok_use_strtok_r
+
+#endif /* lib/string.h */
diff --git a/src/lib/syscall-nr.h b/src/lib/syscall-nr.h
new file mode 100644
index 0000000..21a7af9
--- /dev/null
+++ b/src/lib/syscall-nr.h
@@ -0,0 +1,34 @@
+#ifndef __LIB_SYSCALL_NR_H
+#define __LIB_SYSCALL_NR_H
+
+/* System call numbers. */
+enum 
+  {
+    /* Projects 2 and later. */
+    SYS_HALT,                   /* Halt the operating system. */
+    SYS_EXIT,                   /* Terminate this process. */
+    SYS_EXEC,                   /* Start another process. */
+    SYS_WAIT,                   /* Wait for a child process to die. */
+    SYS_CREATE,                 /* Create a file. */
+    SYS_REMOVE,                 /* Delete a file. */
+    SYS_OPEN,                   /* Open a file. */
+    SYS_FILESIZE,               /* Obtain a file's size. */
+    SYS_READ,                   /* Read from a file. */
+    SYS_WRITE,                  /* Write to a file. */
+    SYS_SEEK,                   /* Change position in a file. */
+    SYS_TELL,                   /* Report current position in a file. */
+    SYS_CLOSE,                  /* Close a file. */
+
+    /* Project 3 and optionally project 4. */
+    SYS_MMAP,                   /* Map a file into memory. */
+    SYS_MUNMAP,                 /* Remove a memory mapping. */
+
+    /* Project 4 only. */
+    SYS_CHDIR,                  /* Change the current directory. */
+    SYS_MKDIR,                  /* Create a directory. */
+    SYS_READDIR,                /* Reads a directory entry. */
+    SYS_ISDIR,                  /* Tests if a fd represents a directory. */
+    SYS_INUMBER                 /* Returns the inode number for a fd. */
+  };
+
+#endif /* lib/syscall-nr.h */
diff --git a/src/lib/user/console.c b/src/lib/user/console.c
new file mode 100644
index 0000000..22bdc8c
--- /dev/null
+++ b/src/lib/user/console.c
@@ -0,0 +1,94 @@
+#include <stdio.h>
+#include <string.h>
+#include <syscall.h>
+#include <syscall-nr.h>
+
+/* The standard vprintf() function,
+   which is like printf() but uses a va_list. */
+int
+vprintf (const char *format, va_list args) 
+{
+  return vhprintf (STDOUT_FILENO, format, args);
+}
+
+/* Like printf(), but writes output to the given HANDLE. */
+int
+hprintf (int handle, const char *format, ...) 
+{
+  va_list args;
+  int retval;
+
+  va_start (args, format);
+  retval = vhprintf (handle, format, args);
+  va_end (args);
+
+  return retval;
+}
+
+/* Writes string S to the console, followed by a new-line
+   character. */
+int
+puts (const char *s) 
+{
+  write (STDOUT_FILENO, s, strlen (s));
+  putchar ('\n');
+
+  return 0;
+}
+
+/* Writes C to the console. */
+int
+putchar (int c) 
+{
+  char c2 = c;
+  write (STDOUT_FILENO, &c2, 1);
+  return c;
+}
+
+/* Auxiliary data for vhprintf_helper(). */
+struct vhprintf_aux 
+  {
+    char buf[64];       /* Character buffer. */
+    char *p;            /* Current position in buffer. */
+    int char_cnt;       /* Total characters written so far. */
+    int handle;         /* Output file handle. */
+  };
+
+static void add_char (char, void *);
+static void flush (struct vhprintf_aux *);
+
+/* Formats the printf() format specification FORMAT with
+   arguments given in ARGS and writes the output to the given
+   HANDLE. */
+int
+vhprintf (int handle, const char *format, va_list args) 
+{
+  struct vhprintf_aux aux;
+  aux.p = aux.buf;
+  aux.char_cnt = 0;
+  aux.handle = handle;
+  __vprintf (format, args, add_char, &aux);
+  flush (&aux);
+  return aux.char_cnt;
+}
+
+/* Adds C to the buffer in AUX, flushing it if the buffer fills
+   up. */
+static void
+add_char (char c, void *aux_) 
+{
+  struct vhprintf_aux *aux = aux_;
+  *aux->p++ = c;
+  if (aux->p >= aux->buf + sizeof aux->buf)
+    flush (aux);
+  aux->char_cnt++;
+}
+
+/* Flushes the buffer in AUX. */
+static void
+flush (struct vhprintf_aux *aux)
+{
+  if (aux->p > aux->buf)
+    write (aux->handle, aux->buf, aux->p - aux->buf);
+  aux->p = aux->buf;
+}
diff --git a/src/lib/user/debug.c b/src/lib/user/debug.c
new file mode 100644
index 0000000..f49b874
--- /dev/null
+++ b/src/lib/user/debug.c
@@ -0,0 +1,25 @@
+#include <debug.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <syscall.h>
+
+/* Aborts the user program, printing the source file name, line
+   number, and function name, plus a user-specific message. */
+void
+debug_panic (const char *file, int line, const char *function,
+             const char *message, ...)
+{
+  va_list args;
+
+  printf ("User process ABORT at %s:%d in %s(): ", file, line, function);
+
+  va_start (args, message);
+  vprintf (message, args);
+  printf ("\n");
+  va_end (args);
+
+  debug_backtrace ();
+  
+  exit (1);
+}
diff --git a/src/lib/user/entry.c b/src/lib/user/entry.c
new file mode 100644
index 0000000..a707c70
--- /dev/null
+++ b/src/lib/user/entry.c
@@ -0,0 +1,10 @@
+#include <syscall.h>
+
+int main (int, char *[]);
+void _start (int argc, char *argv[]);
+
+void
+_start (int argc, char *argv[]) 
+{
+  exit (main (argc, argv));
+}
diff --git a/src/lib/user/stdio.h b/src/lib/user/stdio.h
new file mode 100644
index 0000000..b9f3cc6
--- /dev/null
+++ b/src/lib/user/stdio.h
@@ -0,0 +1,7 @@
+#ifndef __LIB_USER_STDIO_H
+#define __LIB_USER_STDIO_H
+
+int hprintf (int, const char *, ...) PRINTF_FORMAT (2, 3);
+int vhprintf (int, const char *, va_list) PRINTF_FORMAT (2, 0);
+
+#endif /* lib/user/stdio.h */
diff --git a/src/lib/user/syscall.c b/src/lib/user/syscall.c
new file mode 100644
index 0000000..a9c5bc8
--- /dev/null
+++ b/src/lib/user/syscall.c
@@ -0,0 +1,184 @@
+#include <syscall.h>
+#include "../syscall-nr.h"
+
+/* Invokes syscall NUMBER, passing no arguments, and returns the
+   return value as an `int'. */
+#define syscall0(NUMBER)                                        \
+        ({                                                      \
+          int retval;                                           \
+          asm volatile                                          \
+            ("pushl %[number]; int $0x30; addl $4, %%esp"       \
+               : "=a" (retval)                                  \
+               : [number] "i" (NUMBER)                          \
+               : "memory");                                     \
+          retval;                                               \
+        })
+
+/* Invokes syscall NUMBER, passing argument ARG0, and returns the
+   return value as an `int'. */
+#define syscall1(NUMBER, ARG0)                                           \
+        ({                                                               \
+          int retval;                                                    \
+          asm volatile                                                   \
+            ("pushl %[arg0]; pushl %[number]; int $0x30; addl $8, %%esp" \
+               : "=a" (retval)                                           \
+               : [number] "i" (NUMBER),                                  \
+                 [arg0] "g" (ARG0)                                       \
+               : "memory");                                              \
+          retval;                                                        \
+        })
+
+/* Invokes syscall NUMBER, passing arguments ARG0 and ARG1, and
+   returns the return value as an `int'. */
+#define syscall2(NUMBER, ARG0, ARG1)                            \
+        ({                                                      \
+          int retval;                                           \
+          asm volatile                                          \
+            ("pushl %[arg1]; pushl %[arg0]; "                   \
+             "pushl %[number]; int $0x30; addl $12, %%esp"      \
+               : "=a" (retval)                                  \
+               : [number] "i" (NUMBER),                         \
+                 [arg0] "g" (ARG0),                             \
+                 [arg1] "g" (ARG1)                              \
+               : "memory");                                     \
+          retval;                                               \
+        })
+
+/* Invokes syscall NUMBER, passing arguments ARG0, ARG1, and
+   ARG2, and returns the return value as an `int'. */
+#define syscall3(NUMBER, ARG0, ARG1, ARG2)                      \
+        ({                                                      \
+          int retval;                                           \
+          asm volatile                                          \
+            ("pushl %[arg2]; pushl %[arg1]; pushl %[arg0]; "    \
+             "pushl %[number]; int $0x30; addl $16, %%esp"      \
+               : "=a" (retval)                                  \
+               : [number] "i" (NUMBER),                         \
+                 [arg0] "g" (ARG0),                             \
+                 [arg1] "g" (ARG1),                             \
+                 [arg2] "g" (ARG2)                              \
+               : "memory");                                     \
+          retval;                                               \
+        })
+
+void
+halt (void) 
+{
+  syscall0 (SYS_HALT);
+  NOT_REACHED ();
+}
+
+void
+exit (int status)
+{
+  syscall1 (SYS_EXIT, status);
+  NOT_REACHED ();
+}
+
+pid_t
+exec (const char *file)
+{
+  return (pid_t) syscall1 (SYS_EXEC, file);
+}
+
+int
+wait (pid_t pid)
+{
+  return syscall1 (SYS_WAIT, pid);
+}
+
+bool
+create (const char *file, unsigned initial_size)
+{
+  return syscall2 (SYS_CREATE, file, initial_size);
+}
+
+bool
+remove (const char *file)
+{
+  return syscall1 (SYS_REMOVE, file);
+}
+
+int
+open (const char *file)
+{
+  return syscall1 (SYS_OPEN, file);
+}
+
+int
+filesize (int fd) 
+{
+  return syscall1 (SYS_FILESIZE, fd);
+}
+
+int
+read (int fd, void *buffer, unsigned size)
+{
+  return syscall3 (SYS_READ, fd, buffer, size);
+}
+
+int
+write (int fd, const void *buffer, unsigned size)
+{
+  return syscall3 (SYS_WRITE, fd, buffer, size);
+}
+
+void
+seek (int fd, unsigned position) 
+{
+  syscall2 (SYS_SEEK, fd, position);
+}
+
+unsigned
+tell (int fd) 
+{
+  return syscall1 (SYS_TELL, fd);
+}
+
+void
+close (int fd)
+{
+  syscall1 (SYS_CLOSE, fd);
+}
+
+mapid_t
+mmap (int fd, void *addr)
+{
+  return syscall2 (SYS_MMAP, fd, addr);
+}
+
+void
+munmap (mapid_t mapid)
+{
+  syscall1 (SYS_MUNMAP, mapid);
+}
+
+bool
+chdir (const char *dir)
+{
+  return syscall1 (SYS_CHDIR, dir);
+}
+
+bool
+mkdir (const char *dir)
+{
+  return syscall1 (SYS_MKDIR, dir);
+}
+
+bool
+readdir (int fd, char name[READDIR_MAX_LEN + 1]) 
+{
+  return syscall2 (SYS_READDIR, fd, name);
+}
+
+bool
+isdir (int fd) 
+{
+  return syscall1 (SYS_ISDIR, fd);
+}
+
+int
+inumber (int fd) 
+{
+  return syscall1 (SYS_INUMBER, fd);
+}
diff --git a/src/lib/user/syscall.h b/src/lib/user/syscall.h
new file mode 100644
index 0000000..8a9e0c0
--- /dev/null
+++ b/src/lib/user/syscall.h
@@ -0,0 +1,48 @@
+#ifndef __LIB_USER_SYSCALL_H
+#define __LIB_USER_SYSCALL_H
+
+#include <stdbool.h>
+#include <debug.h>
+
+/* Process identifier. */
+typedef int pid_t;
+#define PID_ERROR ((pid_t) -1)
+
+/* Map region identifier. */
+typedef int mapid_t;
+#define MAP_FAILED ((mapid_t) -1)
+
+/* Maximum characters in a filename written by readdir(). */
+#define READDIR_MAX_LEN 14
+
+/* Typical return values from main() and arguments to exit(). */
+#define EXIT_SUCCESS 0          /* Successful execution. */
+#define EXIT_FAILURE 1          /* Unsuccessful execution. */
+
+/* Projects 2 and later. */
+void halt (void) NO_RETURN;
+void exit (int status) NO_RETURN;
+pid_t exec (const char *file);
+int wait (pid_t);
+bool create (const char *file, unsigned initial_size);
+bool remove (const char *file);
+int open (const char *file);
+int filesize (int fd);
+int read (int fd, void *buffer, unsigned length);
+int write (int fd, const void *buffer, unsigned length);
+void seek (int fd, unsigned position);
+unsigned tell (int fd);
+void close (int fd);
+
+/* Project 3 and optionally project 4. */
+mapid_t mmap (int fd, void *addr);
+void munmap (mapid_t);
+
+/* Project 4 only. */
+bool chdir (const char *dir);
+bool mkdir (const char *dir);
+bool readdir (int fd, char name[READDIR_MAX_LEN + 1]);
+bool isdir (int fd);
+int inumber (int fd);
+
+#endif /* lib/user/syscall.h */
diff --git a/src/lib/user/user.lds b/src/lib/user/user.lds
new file mode 100644
index 0000000..cc6d6c0
--- /dev/null
+++ b/src/lib/user/user.lds
@@ -0,0 +1,57 @@
+OUTPUT_FORMAT("elf32-i386")
+OUTPUT_ARCH(i386)
+ENTRY(_start)
+
+SECTIONS
+{
+  /* Read-only sections, merged into text segment: */
+  __executable_start = 0x08048000 + SIZEOF_HEADERS;
+  . = 0x08048000 + SIZEOF_HEADERS;
+  .text : { *(.text) } = 0x90
+  .rodata : { *(.rodata) }
+
+  /* Adjust the address for the data segment.  We want to adjust up to
+     the same address within the page on the next page up.  */
+  . = ALIGN (0x1000) - ((0x1000 - .) & (0x1000 - 1)); 
+  . = DATA_SEGMENT_ALIGN (0x1000, 0x1000);
+
+  .data : { *(.data) }
+  .bss : { *(.bss) }
+
+  /* Stabs debugging sections.  */
+  .stab          0 : { *(.stab) }
+  .stabstr       0 : { *(.stabstr) }
+  .stab.excl     0 : { *(.stab.excl) }
+  .stab.exclstr  0 : { *(.stab.exclstr) }
+  .stab.index    0 : { *(.stab.index) }
+  .stab.indexstr 0 : { *(.stab.indexstr) }
+  .comment       0 : { *(.comment) }
+
+  /* DWARF debug sections.
+  Symbols in the DWARF debugging sections are relative to the beginning
+  of the section so we begin them at 0.  */
+  /* DWARF 1 */
+  .debug          0 : { *(.debug) }
+  .line           0 : { *(.line) }
+  /* GNU DWARF 1 extensions */
+  .debug_srcinfo  0 : { *(.debug_srcinfo) }
+  .debug_sfnames  0 : { *(.debug_sfnames) }
+  /* DWARF 1.1 and DWARF 2 */
+  .debug_aranges  0 : { *(.debug_aranges) }
+  .debug_pubnames 0 : { *(.debug_pubnames) }
+  /* DWARF 2 */
+  .debug_info     0 : { *(.debug_info .gnu.linkonce.wi.*) }
+  .debug_abbrev   0 : { *(.debug_abbrev) }
+  .debug_line     0 : { *(.debug_line) }
+  .debug_frame    0 : { *(.debug_frame) }
+  .debug_str      0 : { *(.debug_str) }
+  .debug_loc      0 : { *(.debug_loc) }
+  .debug_macinfo  0 : { *(.debug_macinfo) }
+  /* SGI/MIPS DWARF 2 extensions */
+  .debug_weaknames 0 : { *(.debug_weaknames) }
+  .debug_funcnames 0 : { *(.debug_funcnames) }
+  .debug_typenames 0 : { *(.debug_typenames) }
+  .debug_varnames  0 : { *(.debug_varnames) }
+  /DISCARD/ : { *(.note.GNU-stack) }
+  /DISCARD/ : { *(.eh_frame) }
+}