Document requirements for calling mmcheck to install corruption checking

hooks and set up to enforce the requirements.  However, we still allow
unconditional installation until some complications are resolved.

1 files changed, 196 insertions, 0 deletions

diff --git a/mmalloc/mmcheck.c b/mmalloc/mmcheck.c
new file mode 100644
index 0000000..2a4b09e
--- /dev/null
+++ b/mmalloc/mmcheck.c
@@ -0,0 +1,196 @@
+/* Standard debugging hooks for `mmalloc'.
+   Copyright 1990, 1991, 1992 Free Software Foundation
+
+   Written May 1989 by Mike Haertel.
+   Heavily modified Mar 1992 by Fred Fish (fnf@cygnus.com)
+
+The GNU C Library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public License as
+published by the Free Software Foundation; either version 2 of the
+License, or (at your option) any later version.
+
+The GNU C Library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA.
+
+ The author may be reached (Email) at the address mike@ai.mit.edu,
+ or (US mail) as Mike Haertel c/o Free Software Foundation. */
+
+#include "mmalloc.h"
+
+/* Default function to call when something awful happens.  The application
+   can specify an alternate function to be called instead (and probably will
+   want to). */
+
+extern void abort PARAMS ((void));
+
+/* Arbitrary magical numbers.  */
+
+#define MAGICWORD	0xfedabeeb	/* Magic word for active chunk */
+#define MAGICWORDFREE	0xdeadbeef	/* Magic word for inactive chunk */
+#define MAGICBYTE	((char) 0xd7)
+
+/* Each memory allocation is bounded by a header structure and a trailer
+   byte.  I.E.
+
+	<size><magicword><user's allocation><magicbyte>
+
+   The pointer returned to the user points to the first byte in the
+   user's allocation area.  The magic word can be tested to detect
+   buffer underruns and the magic byte can be tested to detect overruns. */
+
+struct hdr
+  {
+    size_t size;		/* Exact size requested by user.  */
+    unsigned long int magic;	/* Magic number to check header integrity.  */
+  };
+
+/* Check the magicword and magicbyte, and if either is corrupted then
+   call the emergency abort function specified for the heap in use. */
+
+static void
+checkhdr (mdp, hdr)
+  struct mdesc *mdp;
+  CONST struct hdr *hdr;
+{
+  if (hdr -> magic != MAGICWORD ||
+      ((char *) &hdr[1])[hdr -> size] != MAGICBYTE)
+    {
+      (*mdp -> abortfunc)();
+    }
+}
+
+static void
+mfree_check (md, ptr)
+  PTR md;
+  PTR ptr;
+{
+  struct hdr *hdr = ((struct hdr *) ptr) - 1;
+  struct mdesc *mdp;
+
+  mdp = MD_TO_MDP (md);
+  checkhdr (mdp, hdr);
+  hdr -> magic = MAGICWORDFREE;
+  mdp -> mfree_hook = NULL;
+  mfree (md, hdr);
+  mdp -> mfree_hook = mfree_check;
+}
+
+static PTR
+mmalloc_check (md, size)
+  PTR md;
+  size_t size;
+{
+  struct hdr *hdr;
+  struct mdesc *mdp;
+  size_t nbytes;
+
+  mdp = MD_TO_MDP (md);
+  mdp -> mmalloc_hook = NULL;
+  nbytes = sizeof (struct hdr) + size + 1;
+  hdr = (struct hdr *) mmalloc (md, nbytes);
+  mdp -> mmalloc_hook = mmalloc_check;
+  if (hdr != NULL)
+    {
+      hdr -> size = size;
+      hdr -> magic = MAGICWORD;
+      hdr++;
+      *((char *) hdr + size) = MAGICBYTE;
+    }
+  return ((PTR) hdr);
+}
+
+static PTR
+mrealloc_check (md, ptr, size)
+  PTR md;
+  PTR ptr;
+  size_t size;
+{
+  struct hdr *hdr = ((struct hdr *) ptr) - 1;
+  struct mdesc *mdp;
+  size_t nbytes;
+
+  mdp = MD_TO_MDP (md);
+  checkhdr (mdp, hdr);
+  mdp -> mfree_hook = NULL;
+  mdp -> mmalloc_hook = NULL;
+  mdp -> mrealloc_hook = NULL;
+  nbytes = sizeof (struct hdr) + size + 1;
+  hdr = (struct hdr *) mrealloc (md, (PTR) hdr, nbytes);
+  mdp -> mfree_hook = mfree_check;
+  mdp -> mmalloc_hook = mmalloc_check;
+  mdp -> mrealloc_hook = mrealloc_check;
+  if (hdr != NULL)
+    {
+      hdr -> size = size;
+      hdr++;
+      *((char *) hdr + size) = MAGICBYTE;
+    }
+  return ((PTR) hdr);
+}
+
+/* Turn on default checking for mmalloc/mrealloc/mfree, for the heap specified
+   by MD.  If FUNC is non-NULL, it is a pointer to the function to call
+   to abort whenever memory corruption is detected.  By default, this is the
+   standard library function abort().
+
+   Note that we disallow installation of initial checking hooks if mmalloc
+   has been called at any time for this particular heap, since if any region
+   that is allocated prior to installation of the hooks is subsequently
+   reallocated or freed after installation of the hooks, it is guaranteed
+   to trigger a memory corruption error.  We do this by checking the state
+   of the MMALLOC_INITIALIZED flag.
+
+   However, we can call this function at any time after the initial call,
+   to update the function pointers to the checking routines and to the
+   user defined corruption handler routine, as long as these function pointers
+   have been previously extablished by the initial call.  Note that we
+   do this automatically when remapping an previously used heap, to ensure
+   that the hooks get updated to the correct values, although the corruption
+   handler pointer gets set back to the default.  The application can then
+   call mmcheck to use a different corruption handler if desired.
+
+   Returns non-zero if checking is successfully enabled, zero otherwise. */
+
+int
+mmcheck (md, func)
+  PTR md;
+  void (*func) PARAMS ((void));
+{
+  struct mdesc *mdp;
+  int rtnval;
+
+  mdp = MD_TO_MDP (md);
+
+  /* We can safely set or update the abort function at any time, regardless
+     of whether or not we successfully do anything else. */
+
+  mdp -> abortfunc = (func != NULL ? func : abort);
+
+  /* If we haven't yet called mmalloc the first time for this heap, or if we
+     have hooks that were previously installed, then allow the hooks to be
+     initialized or updated. */
+
+  if (1 /* FIXME: Always allow installation for now. */ ||
+      !(mdp -> flags & MMALLOC_INITIALIZED) ||
+      (mdp -> mfree_hook != NULL))
+    {
+      mdp -> mfree_hook = mfree_check;
+      mdp -> mmalloc_hook = mmalloc_check;
+      mdp -> mrealloc_hook = mrealloc_check;
+      mdp -> flags |= MMALLOC_MMCHECK_USED;
+      rtnval = 1;
+    }
+  else
+    {
+      rtnval = 0;
+    }
+
+  return (rtnval);
+}