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diff --git a/libmudflap/mf-heuristics.c b/libmudflap/mf-heuristics.c
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+/* Mudflap: narrow-pointer bounds-checking by tree rewriting.
+   Copyright (C) 2002, 2003, 2009 Free Software Foundation, Inc.
+   Contributed by Frank Ch. Eigler <fche@redhat.com>
+   and Graydon Hoare <graydon@redhat.com>
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC 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 General Public License
+for more details.
+
+Under Section 7 of GPL version 3, you are granted additional
+permissions described in the GCC Runtime Library Exception, version
+3.1, as published by the Free Software Foundation.
+
+You should have received a copy of the GNU General Public License and
+a copy of the GCC Runtime Library Exception along with this program;
+see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+
+#include <stdio.h>
+
+#include "mf-runtime.h"
+#include "mf-impl.h"
+
+#ifdef _MUDFLAP
+#error "Do not compile this file with -fmudflap!"
+#endif
+
+
+extern char _end[];
+extern char ENTRY_POINT[];
+
+
+/* Run some quick validation of the given region.
+   Return -1 / 0 / 1 if the access known-invalid, possibly-valid, or known-valid.
+*/
+int
+__mf_heuristic_check (uintptr_t ptr, uintptr_t ptr_high)
+{
+  VERBOSE_TRACE ("mf: heuristic check\n");
+
+  /* XXX: Disable the stack bounding check for libmudflapth.  We do
+     actually have enough information to track stack bounds (see
+     __mf_pthread_info in mf-hooks.c), so with a bit of future work,
+     this heuristic can be turned on.  */
+#ifndef LIBMUDFLAPTH
+
+  /* The first heuristic is to check stack bounds.  This is a
+     transient condition and quick to check. */
+  if (__mf_opts.heur_stack_bound)
+    {
+      uintptr_t stack_top_guess = (uintptr_t)__builtin_frame_address(0);
+#if defined(__i386__) && defined (__linux__)
+      uintptr_t stack_segment_base = 0xC0000000; /* XXX: Bad assumption. */
+#else
+      /* Cause tests to fail. */
+      uintptr_t stack_segment_base = 0;
+#endif
+
+      VERBOSE_TRACE ("mf: stack estimated as %p-%p\n",
+		     (void *) stack_top_guess, (void *) stack_segment_base);
+
+      if (ptr_high <= stack_segment_base &&
+	  ptr >= stack_top_guess &&
+	  ptr_high >= ptr)
+	{
+	  return 1;
+	}
+    }
+#endif
+
+
+  /* The second heuristic is to scan the range of memory regions
+     listed in /proc/self/maps, a special file provided by the Linux
+     kernel.  Its results may be cached, and in fact, a GUESS object
+     may as well be recorded for interesting matching sections.  */
+  if (__mf_opts.heur_proc_map)
+    {
+      /* Keep a record of seen records from /proc/self/map.  */
+      enum { max_entries = 500 };
+      struct proc_self_map_entry
+      {
+	uintptr_t low;
+	uintptr_t high;
+      };
+      static struct proc_self_map_entry entry [max_entries];
+      static unsigned entry_used [max_entries];
+
+      /* Look for a known proc_self_map entry that may cover this
+	 region.  If one exists, then this heuristic has already run,
+	 and should not be run again.  The check should be allowed to
+	 fail.  */
+      unsigned i;
+      unsigned deja_vu = 0;
+      for (i=0; i<max_entries; i++)
+	{
+	  if (entry_used[i] &&
+	      (entry[i].low <= ptr) &&
+	      (entry[i].high >= ptr_high))
+	    deja_vu = 1;
+	}
+
+      if (! deja_vu)
+	{
+	  /* Time to run the heuristic.  Rescan /proc/self/maps; update the
+	     entry[] array; XXX: remove expired entries, add new ones.
+	     XXX: Consider entries that have grown (e.g., stack).  */
+	  char buf[512];
+	  char flags[4];
+	  void *low, *high;
+	  FILE *fp;
+
+	  fp = fopen ("/proc/self/maps", "r");
+	  if (fp)
+	    {
+	      while (fgets (buf, sizeof(buf), fp))
+		{
+		  if (sscanf (buf, "%p-%p %4c", &low, &high, flags) == 3)
+		    {
+		      if ((uintptr_t) low <= ptr &&
+			  (uintptr_t) high >= ptr_high)
+			{
+			  for (i=0; i<max_entries; i++)
+			    {
+			      if (! entry_used[i])
+				{
+				  entry[i].low = (uintptr_t) low;
+				  entry[i].high = (uintptr_t) high;
+				  entry_used[i] = 1;
+				  break;
+				}
+			    }
+
+			  VERBOSE_TRACE ("mf: registering region #%d "
+					 "%p-%p given %s",
+					 i, (void *) low, (void *) high, buf);
+
+			  __mfu_register ((void *) low, (size_t) (high-low),
+					  __MF_TYPE_GUESS,
+					  "/proc/self/maps segment");
+
+			  return 0; /* undecided (tending to cachable) */
+			}
+		    }
+		}
+	      fclose (fp);
+	    }
+	}
+    }
+
+
+  /* The third heuristic is to approve all accesses between _start (or its
+     equivalent for the given target) and _end, which should include all
+     text and initialized data.  */
+  if (__mf_opts.heur_start_end)
+    if (ptr >= (uintptr_t) & ENTRY_POINT && ptr_high <= (uintptr_t) & _end)
+      return 1; /* uncacheable */
+
+  return 0; /* unknown */
+}