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libiconv v1.14

    1: /* Safe automatic memory allocation.
    2:    Copyright (C) 2003, 2006-2007, 2009-2011 Free Software Foundation, Inc.
    3:    Written by Bruno Haible <bruno@clisp.org>, 2003.
    4: 
    5:    This program is free software; you can redistribute it and/or modify
    6:    it under the terms of the GNU General Public License as published by
    7:    the Free Software Foundation; either version 3, or (at your option)
    8:    any later version.
    9: 
   10:    This program is distributed in the hope that it will be useful,
   11:    but WITHOUT ANY WARRANTY; without even the implied warranty of
   12:    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   13:    GNU General Public License for more details.
   14: 
   15:    You should have received a copy of the GNU General Public License
   16:    along with this program; if not, write to the Free Software Foundation,
   17:    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
   18: 
   19: #define _GL_USE_STDLIB_ALLOC 1
   20: #include <config.h>
   21: 
   22: /* Specification.  */
   23: #include "malloca.h"
   24: 
   25: #include "verify.h"
   26: 
   27: /* The speed critical point in this file is freea() applied to an alloca()
   28:    result: it must be fast, to match the speed of alloca().  The speed of
   29:    mmalloca() and freea() in the other case are not critical, because they
   30:    are only invoked for big memory sizes.  */
   31: 
   32: #if HAVE_ALLOCA
   33: 
   34: /* Store the mmalloca() results in a hash table.  This is needed to reliably
   35:    distinguish a mmalloca() result and an alloca() result.
   36: 
   37:    Although it is possible that the same pointer is returned by alloca() and
   38:    by mmalloca() at different times in the same application, it does not lead
   39:    to a bug in freea(), because:
   40:      - Before a pointer returned by alloca() can point into malloc()ed memory,
   41:        the function must return, and once this has happened the programmer must
   42:        not call freea() on it anyway.
   43:      - Before a pointer returned by mmalloca() can point into the stack, it
   44:        must be freed.  The only function that can free it is freea(), and
   45:        when freea() frees it, it also removes it from the hash table.  */
   46: 
   47: #define MAGIC_NUMBER 0x1415fb4a
   48: #define MAGIC_SIZE sizeof (int)
   49: /* This is how the header info would look like without any alignment
   50:    considerations.  */
   51: struct preliminary_header { void *next; char room[MAGIC_SIZE]; };
   52: /* But the header's size must be a multiple of sa_alignment_max.  */
   53: #define HEADER_SIZE \
   54:   (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)
   55: struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; };
   56: verify (HEADER_SIZE == sizeof (struct header));
   57: /* We make the hash table quite big, so that during lookups the probability
   58:    of empty hash buckets is quite high.  There is no need to make the hash
   59:    table resizable, because when the hash table gets filled so much that the
   60:    lookup becomes slow, it means that the application has memory leaks.  */
   61: #define HASH_TABLE_SIZE 257
   62: static void * mmalloca_results[HASH_TABLE_SIZE];
   63: 
   64: #endif
   65: 
   66: void *
   67: mmalloca (size_t n)
   68: {
   69: #if HAVE_ALLOCA
   70:   /* Allocate one more word, that serves as an indicator for malloc()ed
   71:      memory, so that freea() of an alloca() result is fast.  */
   72:   size_t nplus = n + HEADER_SIZE;
   73: 
   74:   if (nplus >= n)
   75:     {
   76:       char *p = (char *) malloc (nplus);
   77: 
   78:       if (p != NULL)
   79:         {
   80:           size_t slot;
   81: 
   82:           p += HEADER_SIZE;
   83: 
   84:           /* Put a magic number into the indicator word.  */
   85:           ((int *) p)[-1] = MAGIC_NUMBER;
   86: 
   87:           /* Enter p into the hash table.  */
   88:           slot = (unsigned long) p % HASH_TABLE_SIZE;
   89:           ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot];
   90:           mmalloca_results[slot] = p;
   91: 
   92:           return p;
   93:         }
   94:     }
   95:   /* Out of memory.  */
   96:   return NULL;
   97: #else
   98: # if !MALLOC_0_IS_NONNULL
   99:   if (n == 0)
  100:     n = 1;
  101: # endif
  102:   return malloc (n);
  103: #endif
  104: }
  105: 
  106: #if HAVE_ALLOCA
  107: void
  108: freea (void *p)
  109: {
  110:   /* mmalloca() may have returned NULL.  */
  111:   if (p != NULL)
  112:     {
  113:       /* Attempt to quickly distinguish the mmalloca() result - which has
  114:          a magic indicator word - and the alloca() result - which has an
  115:          uninitialized indicator word.  It is for this test that sa_increment
  116:          additional bytes are allocated in the alloca() case.  */
  117:       if (((int *) p)[-1] == MAGIC_NUMBER)
  118:         {
  119:           /* Looks like a mmalloca() result.  To see whether it really is one,
  120:              perform a lookup in the hash table.  */
  121:           size_t slot = (unsigned long) p % HASH_TABLE_SIZE;
  122:           void **chain = &mmalloca_results[slot];
  123:           for (; *chain != NULL;)
  124:             {
  125:               if (*chain == p)
  126:                 {
  127:                   /* Found it.  Remove it from the hash table and free it.  */
  128:                   char *p_begin = (char *) p - HEADER_SIZE;
  129:                   *chain = ((struct header *) p_begin)->next;
  130:                   free (p_begin);
  131:                   return;
  132:                 }
  133:               chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next;
  134:             }
  135:         }
  136:       /* At this point, we know it was not a mmalloca() result.  */
  137:     }
  138: }
  139: #endif