dlalloc.c

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/*
    To help compensate for the large number of bins, a one-level index
    structure is used for bin-by-bin searching.  `binblocks' is a
    one-word bitvector recording whether groups of BINBLOCKWIDTH bins
    have any (possibly) non-empty bins, so they can be skipped over
    all at once during during traversals. The bits are NOT always
    cleared as soon as all bins in a block are empty, but instead only
    when all are noticed to be empty during traversal in malloc.
*/

#define BINBLOCKWIDTH     4   /* bins per block */

#define binblocks      (bin_at(0)->size) /* bitvector of nonempty blocks */

/* bin<->block macros */

#define idx2binblock(ix)    ((unsigned)1 << (ix / BINBLOCKWIDTH))
#define mark_binblock(ii)   (binblocks |= idx2binblock(ii))
#define clear_binblock(ii)  (binblocks &= ~(idx2binblock(ii)))





/*  Other static bookkeeping data */

/* variables holding tunable values */

static INTERNAL_SIZE_T trim_threshold   = DEFAULT_TRIM_THRESHOLD;
static INTERNAL_SIZE_T top_pad          = DEFAULT_TOP_PAD;
static unsigned int  n_mmaps_max      = DEFAULT_MMAP_MAX;
static INTERNAL_SIZE_T mmap_threshold   = DEFAULT_MMAP_THRESHOLD;

/* The first value returned from sbrk */
static char* sbrk_base = (char*)(-1);

/* The maximum memory obtained from system via sbrk */
static INTERNAL_SIZE_T max_sbrked_mem = 0; 

/* The maximum via either sbrk or mmap */
static INTERNAL_SIZE_T max_total_mem = 0; 

/* internal working copy of mallinfo */
static struct mallinfo current_mallinfo = {  0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

/* The total memory obtained from system via sbrk */
#define sbrked_mem  (current_mallinfo.arena)

/* Tracking mmaps */

static unsigned int n_mmaps = 0;
static unsigned int max_n_mmaps = 0;
static INTERNAL_SIZE_T mmapped_mem = 0;
static INTERNAL_SIZE_T max_mmapped_mem = 0;



/* 
  Debugging support 
*/

#if DEBUG


/*
  These routines make a number of assertions about the states
  of data structures that should be true at all times. If any
  are not true, it's very likely that a user program has somehow
  trashed memory. (It's also possible that there is a coding error
  in malloc. In which case, please report it!)
*/

#if __STD_C
static void do_check_chunk(mchunkptr p) 
#else
static void do_check_chunk(p) mchunkptr p;
#endif
{ 
  INTERNAL_SIZE_T sz = p->size & ~PREV_INUSE;

  /* No checkable chunk is mmapped */
  assert(!chunk_is_mmapped(p));

  /* Check for legal address ... */
  assert((char*)p >= sbrk_base);
  /* SUN: Add braces for case that assert is multiple statements */
  if (p != top) {    
    assert((char*)p + sz <= (char*)top);
  } else {
    assert((char*)p + sz <= sbrk_base + sbrked_mem);
  }
}


#if __STD_C
static void do_check_free_chunk(mchunkptr p) 
#else
static void do_check_free_chunk(p) mchunkptr p;
#endif
{ 
  INTERNAL_SIZE_T sz = p->size & ~PREV_INUSE;
  mchunkptr next = chunk_at_offset(p, sz);

  do_check_chunk(p);

  /* Check whether it claims to be free ... */
  assert(!inuse(p));

  /* Unless a special marker, must have OK fields */
  if ((INTERNAL_SSIZE_T)sz >= (INTERNAL_SSIZE_T)MINSIZE)
  {
    assert((sz & MALLOC_ALIGN_MASK) == 0);
    assert(aligned_OK(chunk2mem(p)));
    /* ... matching footer field */
    assert(next->prev_size == sz);
    /* ... and is fully consolidated */
    assert(prev_inuse(p));
    assert (next == top || inuse(next));
    
    /* ... and has minimally sane links */
    assert(p->fd->bk == p);
    assert(p->bk->fd == p);
  }
  else /* markers are always of size SIZE_SZ */
    assert(sz == SIZE_SZ); 
}

#if __STD_C
static void do_check_inuse_chunk(mchunkptr p) 
#else
static void do_check_inuse_chunk(p) mchunkptr p;
#endif
{ 
  mchunkptr next = next_chunk(p);
  do_check_chunk(p);

  /* Check whether it claims to be in use ... */
  assert(inuse(p));

  /* ... and is surrounded by OK chunks.
    Since more things can be checked with free chunks than inuse ones,
    if an inuse chunk borders them and debug is on, it's worth doing them.
  */
  if (!prev_inuse(p)) 
  {
    mchunkptr prv = prev_chunk(p);
    assert(next_chunk(prv) == p);
    do_check_free_chunk(prv);
  }
  if (next == top)
  {
    assert(prev_inuse(next));
    assert(chunksize(next) >= MINSIZE);
  }
  else if (!inuse(next))
    do_check_free_chunk(next);

}

#if __STD_C
static void do_check_malloced_chunk(mchunkptr p, INTERNAL_SIZE_T s) 
#else
static void do_check_malloced_chunk(p, s) mchunkptr p; INTERNAL_SIZE_T s;
#endif
{
  INTERNAL_SIZE_T sz = p->size & ~PREV_INUSE;
  INTERNAL_SSIZE_T room = sz - s;

  do_check_inuse_chunk(p);

  /* Legal size ... */
  assert((INTERNAL_SSIZE_T)sz >= (INTERNAL_SSIZE_T)MINSIZE);
  assert((sz & MALLOC_ALIGN_MASK) == 0);
  assert(room >= 0);
  assert(room < (INTERNAL_SSIZE_T)MINSIZE);

  /* ... and alignment */
  assert(aligned_OK(chunk2mem(p)));


  /* ... and was allocated at front of an available chunk */
  assert(prev_inuse(p));

}


#define check_free_chunk(P)  do_check_free_chunk(P)
#define check_inuse_chunk(P) do_check_inuse_chunk(P)
#define check_chunk(P) do_check_chunk(P)
#define check_malloced_chunk(P,N) do_check_malloced_chunk(P,N)
#else
#define check_free_chunk(P) 
#define check_inuse_chunk(P)
#define check_chunk(P)
#define check_malloced_chunk(P,N)
#endif



/* 
  Macro-based internal utilities
*/


/*  
  Linking chunks in bin lists.
  Call these only with variables, not arbitrary expressions, as arguments.
*/

/* 
  Place chunk p of size s in its bin, in size order,
  putting it ahead of others of same size.
*/


#define frontlink(P, S, IDX, BK, FD)                                          \
{                                                                             \
  if (S < MAX_SMALLBIN_SIZE)                                                  \
  {                                                                           \
    IDX = smallbin_index(S);                                                  \
    mark_binblock(IDX);                                                       \
    BK = bin_at(IDX);                                                         \
    FD = BK->fd;                                                              \
    P->bk = BK;                                                               \
    P->fd = FD;                                                               \
    FD->bk = BK->fd = P;                                                      \
  }                                                                           \
  else                                                                        \
  {                                                                           \
    IDX = bin_index(S);                                                       \
    BK = bin_at(IDX);                                                         \
    FD = BK->fd;                                                              \
    if (FD == BK) mark_binblock(IDX);                                         \
    else                                                                      \
    {                                                                         \
      while (FD != BK && S < chunksize(FD)) FD = FD->fd;                      \
      BK = FD->bk;                                                            \
    }                                                                         \
    P->bk = BK;                                                               \
    P->fd = FD;                                                               \
    FD->bk = BK->fd = P;                                                      \
  }                                                                           \
}


/* take a chunk off a list */

#define unlink(P, BK, FD)                                                     \
{                                                                             \
  BK = P->bk;                                                                 \
  FD = P->fd;                                                                 \
  FD->bk = BK;                                                                \
  BK->fd = FD;                                                                \
}                                                                             \

/* Place p as the last remainder */

#define link_last_remainder(P)                                                \
{                                                                             \
  last_remainder->fd = last_remainder->bk =  P;                               \
  P->fd = P->bk = last_remainder;                                             \
}

/* Clear the last_remainder bin */

#define clear_last_remainder \
  (last_remainder->fd = last_remainder->bk = last_remainder)






/* Routines dealing with mmap(). */

#if HAVE_MMAP

#if __STD_C
static mchunkptr mmap_chunk(size_t size)
#else
static mchunkptr mmap_chunk(size) size_t size;
#endif
{
  size_t page_mask = malloc_getpagesize - 1;
  mchunkptr p;

#ifndef MAP_ANONYMOUS
  static int fd = -1;
#endif

  if(n_mmaps >= n_mmaps_max) return 0; /* too many regions */

  /* For mmapped chunks, the overhead is one SIZE_SZ unit larger, because
   * there is no following chunk whose prev_size field could be used.
   */
  size = (size + SIZE_SZ + page_mask) & ~page_mask;

#ifdef MAP_ANONYMOUS
  p = (mchunkptr)mmap(0, size, PROT_READ|PROT_WRITE,
                      MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
#else /* !MAP_ANONYMOUS */
  if (fd < 0) 
  {
    fd = open("/dev/zero", O_RDWR);
    if(fd < 0) return 0;
  }
  p = (mchunkptr)mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
#endif

  if(p == (mchunkptr)-1) return 0;

  n_mmaps++;
  if (n_mmaps > max_n_mmaps) max_n_mmaps = n_mmaps;
  
  /* We demand that eight bytes into a page must be 8-byte aligned. */
  assert(aligned_OK(chunk2mem(p)));

  /* The offset to the start of the mmapped region is stored
   * in the prev_size field of the chunk; normally it is zero,
   * but that can be changed in memalign().
   */
  p->prev_size = 0;
  set_head(p, size|IS_MMAPPED);
  
  mmapped_mem += size;
  if ((INTERNAL_SIZE_T)mmapped_mem > (INTERNAL_SIZE_T)max_mmapped_mem) 
    max_mmapped_mem = mmapped_mem;
  if ((INTERNAL_SIZE_T)(mmapped_mem + sbrked_mem) > (INTERNAL_SIZE_T)max_total_mem) 
    max_total_mem = mmapped_mem + sbrked_mem;
  return p;
}

#if __STD_C
static void munmap_chunk(mchunkptr p)
#else
static void munmap_chunk(p) mchunkptr p;
#endif
{
  INTERNAL_SIZE_T size = chunksize(p);
  int ret;

  assert (chunk_is_mmapped(p));
  assert(! ((char*)p >= sbrk_base && (char*)p < sbrk_base + sbrked_mem));
  assert((n_mmaps > 0));
  assert(((p->prev_size + size) & (malloc_getpagesize-1)) == 0);

  n_mmaps--;
  mmapped_mem -= (size + p->prev_size);

  ret = munmap((char *)p - p->prev_size, size + p->prev_size);

  /* munmap returns non-zero on failure */
  assert(ret == 0);
}

#if HAVE_MREMAP

#if __STD_C
static mchunkptr mremap_chunk(mchunkptr p, size_t new_size)
#else
static mchunkptr mremap_chunk(p, new_size) mchunkptr p; size_t new_size;
#endif
{
  size_t page_mask = malloc_getpagesize - 1;
  INTERNAL_SIZE_T offset = p->prev_size;
  INTERNAL_SIZE_T size = chunksize(p);
  char *cp;

  assert (chunk_is_mmapped(p));
  assert(! ((char*)p >= sbrk_base && (char*)p < sbrk_base + sbrked_mem));
  assert((n_mmaps > 0));
  assert(((size + offset) & (malloc_getpagesize-1)) == 0);

  /* Note the extra SIZE_SZ overhead as in mmap_chunk(). */
  new_size = (new_size + offset + SIZE_SZ + page_mask) & ~page_mask;

  cp = (char *)mremap((char *)p - offset, size + offset, new_size, 1);

  if (cp == (char *)-1) return 0;

  p = (mchunkptr)(cp + offset);

  assert(aligned_OK(chunk2mem(p)));

  assert((p->prev_size == offset));
  set_head(p, (new_size - offset)|IS_MMAPPED);

  mmapped_mem -= size + offset;
  mmapped_mem += new_size;
  if ((INTERNAL_SIZE_T)mmapped_mem > (INTERNAL_SIZE_T)max_mmapped_mem) 
    max_mmapped_mem = mmapped_mem;
  if ((INTERNAL_SIZE_T)(mmapped_mem + sbrked_mem) > (INTERNAL_SIZE_T)max_total_mem)
    max_total_mem = mmapped_mem + sbrked_mem;
  return p;
}

#endif /* HAVE_MREMAP */

#endif /* HAVE_MMAP */




/* 
  Extend the top-most chunk by obtaining memory from system.
  Main interface to sbrk (but see also malloc_trim).
*/

#if __STD_C
static void malloc_extend_top(INTERNAL_SIZE_T nb)
#else
static void malloc_extend_top(nb) INTERNAL_SIZE_T nb;
#endif
{
  char*     brk;                  /* return value from sbrk */
  INTERNAL_SIZE_T front_misalign; /* unusable bytes at front of sbrked space */
  INTERNAL_SIZE_T correction;     /* bytes for 2nd sbrk call */
  char*     new_brk;              /* return of 2nd sbrk call */
  INTERNAL_SIZE_T top_size;       /* new size of top chunk */

  mchunkptr old_top     = top;  /* Record state of old top */
  INTERNAL_SIZE_T old_top_size = chunksize(old_top);
  char*     old_end      = (char*)(chunk_at_offset(old_top, old_top_size));