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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 */

}