mmalloc/mmcheck.c

   1 /* Standard debugging hooks for `mmalloc'.
   2    Copyright 1990, 1991, 1992 Free Software Foundation
   3
   4    Written May 1989 by Mike Haertel.
   5    Heavily modified Mar 1992 by Fred Fish (fnf@cygnus.com)
   6
   7 The GNU C Library is free software; you can redistribute it and/or
   8 modify it under the terms of the GNU Library General Public License as
   9 published by the Free Software Foundation; either version 2 of the
  10 License, or (at your option) any later version.
  11
  12 The GNU C Library is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 Library General Public License for more details.
  16
  17 You should have received a copy of the GNU Library General Public
  18 License along with the GNU C Library; see the file COPYING.LIB.  If
  19 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20 Boston, MA 02111-1307, USA.
  21
  22  The author may be reached (Email) at the address mike@ai.mit.edu,
  23  or (US mail) as Mike Haertel c/o Free Software Foundation. */
  24
  25 #include "mmprivate.h"
  26
  27 /* Default function to call when something awful happens.  The application
  28    can specify an alternate function to be called instead (and probably will
  29    want to). */
  30
  31 extern void abort PARAMS ((void));
  32
  33 /* Arbitrary magical numbers.  */
  34
  35 #define MAGICWORD       (unsigned int) 0xfedabeeb       /* Active chunk */
  36 #define MAGICWORDFREE   (unsigned int) 0xdeadbeef       /* Inactive chunk */
  37 #define MAGICBYTE       ((char) 0xd7)
  38
  39 /* Each memory allocation is bounded by a header structure and a trailer
  40    byte.  I.E.
  41
  42         <size><magicword><user's allocation><magicbyte>
  43
  44    The pointer returned to the user points to the first byte in the
  45    user's allocation area.  The magic word can be tested to detect
  46    buffer underruns and the magic byte can be tested to detect overruns. */
  47
  48 struct hdr
  49   {
  50     size_t size;                /* Exact size requested by user.  */
  51     unsigned long int magic;    /* Magic number to check header integrity.  */
  52   };
  53
  54 static void checkhdr PARAMS ((struct mdesc *, CONST struct hdr *));
  55 static void mfree_check PARAMS ((PTR, PTR));
  56 static PTR mmalloc_check PARAMS ((PTR, size_t));
  57 static PTR mrealloc_check PARAMS ((PTR, PTR, size_t));
  58
  59 /* Check the magicword and magicbyte, and if either is corrupted then
  60    call the emergency abort function specified for the heap in use. */
  61
  62 static void
  63 checkhdr (mdp, hdr)
  64   struct mdesc *mdp;
  65   CONST struct hdr *hdr;
  66 {
  67   if (hdr -> magic != MAGICWORD ||
  68       ((char *) &hdr[1])[hdr -> size] != MAGICBYTE)
  69     {
  70       (*mdp -> abortfunc)();
  71     }
  72 }
  73
  74 static void
  75 mfree_check (md, ptr)
  76   PTR md;
  77   PTR ptr;
  78 {
  79   struct hdr *hdr = ((struct hdr *) ptr) - 1;
  80   struct mdesc *mdp;
  81
  82   mdp = MD_TO_MDP (md);
  83   checkhdr (mdp, hdr);
  84   hdr -> magic = MAGICWORDFREE;
  85   mdp -> mfree_hook = NULL;
  86   mfree (md, (PTR)hdr);
  87   mdp -> mfree_hook = mfree_check;
  88 }
  89
  90 static PTR
  91 mmalloc_check (md, size)
  92   PTR md;
  93   size_t size;
  94 {
  95   struct hdr *hdr;
  96   struct mdesc *mdp;
  97   size_t nbytes;
  98
  99   mdp = MD_TO_MDP (md);
 100   mdp -> mmalloc_hook = NULL;
 101   nbytes = sizeof (struct hdr) + size + 1;
 102   hdr = (struct hdr *) mmalloc (md, nbytes);
 103   mdp -> mmalloc_hook = mmalloc_check;
 104   if (hdr != NULL)
 105     {
 106       hdr -> size = size;
 107       hdr -> magic = MAGICWORD;
 108       hdr++;
 109       *((char *) hdr + size) = MAGICBYTE;
 110     }
 111   return ((PTR) hdr);
 112 }
 113
 114 static PTR
 115 mrealloc_check (md, ptr, size)
 116   PTR md;
 117   PTR ptr;
 118   size_t size;
 119 {
 120   struct hdr *hdr = ((struct hdr *) ptr) - 1;
 121   struct mdesc *mdp;
 122   size_t nbytes;
 123
 124   mdp = MD_TO_MDP (md);
 125   checkhdr (mdp, hdr);
 126   mdp -> mfree_hook = NULL;
 127   mdp -> mmalloc_hook = NULL;
 128   mdp -> mrealloc_hook = NULL;
 129   nbytes = sizeof (struct hdr) + size + 1;
 130   hdr = (struct hdr *) mrealloc (md, (PTR) hdr, nbytes);
 131   mdp -> mfree_hook = mfree_check;
 132   mdp -> mmalloc_hook = mmalloc_check;
 133   mdp -> mrealloc_hook = mrealloc_check;
 134   if (hdr != NULL)
 135     {
 136       hdr -> size = size;
 137       hdr++;
 138       *((char *) hdr + size) = MAGICBYTE;
 139     }
 140   return ((PTR) hdr);
 141 }
 142
 143 /* Turn on default checking for mmalloc/mrealloc/mfree, for the heap specified
 144    by MD.  If FUNC is non-NULL, it is a pointer to the function to call
 145    to abort whenever memory corruption is detected.  By default, this is the
 146    standard library function abort().
 147
 148    Note that we disallow installation of initial checking hooks if mmalloc
 149    has been called at any time for this particular heap, since if any region
 150    that is allocated prior to installation of the hooks is subsequently
 151    reallocated or freed after installation of the hooks, it is guaranteed
 152    to trigger a memory corruption error.  We do this by checking the state
 153    of the MMALLOC_INITIALIZED flag.  If the FORCE argument is non-zero, this
 154    checking is disabled and it is allowed to install the checking hooks at any
 155    time.  This is useful on systems where the C runtime makes one or more
 156    malloc calls before the user code had a chance to call mmcheck or mmcheckf,
 157    but never calls free with these values.  Thus if we are certain that only
 158    values obtained from mallocs after an mmcheck/mmcheckf will ever be passed
 159    to free(), we can go ahead and force installation of the useful checking
 160    hooks.
 161
 162    However, we can call this function at any time after the initial call,
 163    to update the function pointers to the checking routines and to the
 164    user defined corruption handler routine, as long as these function pointers
 165    have been previously extablished by the initial call.  Note that we
 166    do this automatically when remapping a previously used heap, to ensure
 167    that the hooks get updated to the correct values, although the corruption
 168    handler pointer gets set back to the default.  The application can then
 169    call mmcheck to use a different corruption handler if desired.
 170
 171    Returns non-zero if checking is successfully enabled, zero otherwise. */
 172
 173 int
 174 mmcheckf (md, func, force)
 175   PTR md;
 176   void (*func) PARAMS ((void));
 177   int force;
 178 {
 179   struct mdesc *mdp;
 180   int rtnval;
 181
 182   mdp = MD_TO_MDP (md);
 183
 184   /* We can safely set or update the abort function at any time, regardless
 185      of whether or not we successfully do anything else. */
 186
 187   mdp -> abortfunc = (func != NULL ? func : abort);
 188
 189   /* If we haven't yet called mmalloc the first time for this heap, or if we
 190      have hooks that were previously installed, then allow the hooks to be
 191      initialized or updated. */
 192
 193   if (force ||
 194       !(mdp -> flags & MMALLOC_INITIALIZED) ||
 195       (mdp -> mfree_hook != NULL))
 196     {
 197       mdp -> mfree_hook = mfree_check;
 198       mdp -> mmalloc_hook = mmalloc_check;
 199       mdp -> mrealloc_hook = mrealloc_check;
 200       mdp -> flags |= MMALLOC_MMCHECK_USED;
 201       rtnval = 1;
 202     }
 203   else
 204     {
 205       rtnval = 0;
 206     }
 207
 208   return (rtnval);
 209 }
 210
 211 /* This routine is for backwards compatibility only, in case there are
 212    still callers to the original mmcheck function. */
 213
 214 int
 215 mmcheck (md, func)
 216   PTR md;
 217   void (*func) PARAMS ((void));
 218 {
 219   int rtnval;
 220
 221   rtnval = mmcheckf (md, func, 0);
 222   return (rtnval);
 223 }