libmudflap/mf-heuristics.c

   1 /* Mudflap: narrow-pointer bounds-checking by tree rewriting.
   2    Copyright (C) 2002-2013 Free Software Foundation, Inc.
   3    Contributed by Frank Ch. Eigler <fche@redhat.com>
   4    and Graydon Hoare <graydon@redhat.com>
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 Under Section 7 of GPL version 3, you are granted additional
  19 permissions described in the GCC Runtime Library Exception, version
  20 3.1, as published by the Free Software Foundation.
  21
  22 You should have received a copy of the GNU General Public License and
  23 a copy of the GCC Runtime Library Exception along with this program;
  24 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  25 <http://www.gnu.org/licenses/>.  */
  26
  27 #include "config.h"
  28
  29 #include <stdio.h>
  30
  31 #include "mf-runtime.h"
  32 #include "mf-impl.h"
  33
  34 #ifdef _MUDFLAP
  35 #error "Do not compile this file with -fmudflap!"
  36 #endif
  37
  38
  39 extern char _end[];
  40 extern char ENTRY_POINT[];
  41
  42
  43 /* Run some quick validation of the given region.
  44    Return -1 / 0 / 1 if the access known-invalid, possibly-valid, or known-valid.
  45 */
  46 int
  47 __mf_heuristic_check (uintptr_t ptr, uintptr_t ptr_high)
  48 {
  49   VERBOSE_TRACE ("mf: heuristic check\n");
  50
  51   /* XXX: Disable the stack bounding check for libmudflapth.  We do
  52      actually have enough information to track stack bounds (see
  53      __mf_pthread_info in mf-hooks.c), so with a bit of future work,
  54      this heuristic can be turned on.  */
  55 #ifndef LIBMUDFLAPTH
  56
  57   /* The first heuristic is to check stack bounds.  This is a
  58      transient condition and quick to check. */
  59   if (__mf_opts.heur_stack_bound)
  60     {
  61       uintptr_t stack_top_guess = (uintptr_t)__builtin_frame_address(0);
  62 #if defined(__i386__) && defined (__linux__)
  63       uintptr_t stack_segment_base = 0xC0000000; /* XXX: Bad assumption. */
  64 #else
  65       /* Cause tests to fail. */
  66       uintptr_t stack_segment_base = 0;
  67 #endif
  68
  69       VERBOSE_TRACE ("mf: stack estimated as %p-%p\n",
  70                      (void *) stack_top_guess, (void *) stack_segment_base);
  71
  72       if (ptr_high <= stack_segment_base &&
  73           ptr >= stack_top_guess &&
  74           ptr_high >= ptr)
  75         {
  76           return 1;
  77         }
  78     }
  79 #endif
  80
  81
  82   /* The second heuristic is to scan the range of memory regions
  83      listed in /proc/self/maps, a special file provided by the Linux
  84      kernel.  Its results may be cached, and in fact, a GUESS object
  85      may as well be recorded for interesting matching sections.  */
  86   if (__mf_opts.heur_proc_map)
  87     {
  88       /* Keep a record of seen records from /proc/self/map.  */
  89       enum { max_entries = 500 };
  90       struct proc_self_map_entry
  91       {
  92         uintptr_t low;
  93         uintptr_t high;
  94       };
  95       static struct proc_self_map_entry entry [max_entries];
  96       static unsigned entry_used [max_entries];
  97
  98       /* Look for a known proc_self_map entry that may cover this
  99          region.  If one exists, then this heuristic has already run,
 100          and should not be run again.  The check should be allowed to
 101          fail.  */
 102       unsigned i;
 103       unsigned deja_vu = 0;
 104       for (i=0; i<max_entries; i++)
 105         {
 106           if (entry_used[i] &&
 107               (entry[i].low <= ptr) &&
 108               (entry[i].high >= ptr_high))
 109             deja_vu = 1;
 110         }
 111
 112       if (! deja_vu)
 113         {
 114           /* Time to run the heuristic.  Rescan /proc/self/maps; update the
 115              entry[] array; XXX: remove expired entries, add new ones.
 116              XXX: Consider entries that have grown (e.g., stack).  */
 117           char buf[512];
 118           char flags[4];
 119           void *low, *high;
 120           FILE *fp;
 121
 122           fp = fopen ("/proc/self/maps", "r");
 123           if (fp)
 124             {
 125               while (fgets (buf, sizeof(buf), fp))
 126                 {
 127                   if (sscanf (buf, "%p-%p %4c", &low, &high, flags) == 3)
 128                     {
 129                       if ((uintptr_t) low <= ptr &&
 130                           (uintptr_t) high >= ptr_high)
 131                         {
 132                           for (i=0; i<max_entries; i++)
 133                             {
 134                               if (! entry_used[i])
 135                                 {
 136                                   entry[i].low = (uintptr_t) low;
 137                                   entry[i].high = (uintptr_t) high;
 138                                   entry_used[i] = 1;
 139                                   break;
 140                                 }
 141                             }
 142
 143                           VERBOSE_TRACE ("mf: registering region #%d "
 144                                          "%p-%p given %s",
 145                                          i, (void *) low, (void *) high, buf);
 146
 147                           __mfu_register ((void *) low, (size_t) (high-low),
 148                                           __MF_TYPE_GUESS,
 149                                           "/proc/self/maps segment");
 150
 151                           return 0; /* undecided (tending to cachable) */
 152                         }
 153                     }
 154                 }
 155               fclose (fp);
 156             }
 157         }
 158     }
 159
 160
 161   /* The third heuristic is to approve all accesses between _start (or its
 162      equivalent for the given target) and _end, which should include all
 163      text and initialized data.  */
 164   if (__mf_opts.heur_start_end)
 165     if (ptr >= (uintptr_t) & ENTRY_POINT && ptr_high <= (uintptr_t) & _end)
 166       return 1; /* uncacheable */
 167
 168   return 0; /* unknown */
 169 }