libmudflap/mf-heuristics.c

   1 /* Mudflap: narrow-pointer bounds-checking by tree rewriting.
   2    Copyright (C) 2002, 2003 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 2, or (at your option) any later
  11 version.
  12
  13 In addition to the permissions in the GNU General Public License, the
  14 Free Software Foundation gives you unlimited permission to link the
  15 compiled version of this file into combinations with other programs,
  16 and to distribute those combinations without any restriction coming
  17 from the use of this file.  (The General Public License restrictions
  18 do apply in other respects; for example, they cover modification of
  19 the file, and distribution when not linked into a combine
  20 executable.)
  21
  22 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  23 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  24 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  25 for more details.
  26
  27 You should have received a copy of the GNU General Public License
  28 along with GCC; see the file COPYING.  If not, write to the Free
  29 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  30 02110-1301, USA.  */
  31
  32
  33 #include "config.h"
  34
  35 #include <stdio.h>
  36
  37 #include "mf-runtime.h"
  38 #include "mf-impl.h"
  39
  40 #ifdef _MUDFLAP
  41 #error "Do not compile this file with -fmudflap!"
  42 #endif
  43
  44
  45 extern char _end[];
  46 extern char ENTRY_POINT[];
  47
  48
  49 /* Run some quick validation of the given region.
  50    Return -1 / 0 / 1 if the access known-invalid, possibly-valid, or known-valid.
  51 */
  52 int
  53 __mf_heuristic_check (uintptr_t ptr, uintptr_t ptr_high)
  54 {
  55   VERBOSE_TRACE ("mf: heuristic check\n");
  56
  57   /* XXX: Disable the stack bounding check for libmudflapth.  We do
  58      actually have enough information to track stack bounds (see
  59      __mf_pthread_info in mf-hooks.c), so with a bit of future work,
  60      this heuristic can be turned on.  */
  61 #ifndef LIBMUDFLAPTH
  62
  63   /* The first heuristic is to check stack bounds.  This is a
  64      transient condition and quick to check. */
  65   if (__mf_opts.heur_stack_bound)
  66     {
  67       uintptr_t stack_top_guess = (uintptr_t)__builtin_frame_address(0);
  68 #if defined(__i386__) && defined (__linux__)
  69       uintptr_t stack_segment_base = 0xC0000000; /* XXX: Bad assumption. */
  70 #else
  71       /* Cause tests to fail. */
  72       uintptr_t stack_segment_base = 0;
  73 #endif
  74
  75       VERBOSE_TRACE ("mf: stack estimated as %p-%p\n",
  76                      (void *) stack_top_guess, (void *) stack_segment_base);
  77
  78       if (ptr_high <= stack_segment_base &&
  79           ptr >= stack_top_guess &&
  80           ptr_high >= ptr)
  81         {
  82           return 1;
  83         }
  84     }
  85 #endif
  86
  87
  88   /* The second heuristic is to scan the range of memory regions
  89      listed in /proc/self/maps, a special file provided by the Linux
  90      kernel.  Its results may be cached, and in fact, a GUESS object
  91      may as well be recorded for interesting matching sections.  */
  92   if (__mf_opts.heur_proc_map)
  93     {
  94       /* Keep a record of seen records from /proc/self/map.  */
  95       enum { max_entries = 500 };
  96       struct proc_self_map_entry
  97       {
  98         uintptr_t low;
  99         uintptr_t high;
 100       };
 101       static struct proc_self_map_entry entry [max_entries];
 102       static unsigned entry_used [max_entries];
 103
 104       /* Look for a known proc_self_map entry that may cover this
 105          region.  If one exists, then this heuristic has already run,
 106          and should not be run again.  The check should be allowed to
 107          fail.  */
 108       unsigned i;
 109       unsigned deja_vu = 0;
 110       for (i=0; i<max_entries; i++)
 111         {
 112           if (entry_used[i] &&
 113               (entry[i].low <= ptr) &&
 114               (entry[i].high >= ptr_high))
 115             deja_vu = 1;
 116         }
 117
 118       if (! deja_vu)
 119         {
 120           /* Time to run the heuristic.  Rescan /proc/self/maps; update the
 121              entry[] array; XXX: remove expired entries, add new ones.
 122              XXX: Consider entries that have grown (e.g., stack).  */
 123           char buf[512];
 124           char flags[4];
 125           void *low, *high;
 126           FILE *fp;
 127
 128           fp = fopen ("/proc/self/maps", "r");
 129           if (fp)
 130             {
 131               while (fgets (buf, sizeof(buf), fp))
 132                 {
 133                   if (sscanf (buf, "%p-%p %4c", &low, &high, flags) == 3)
 134                     {
 135                       if ((uintptr_t) low <= ptr &&
 136                           (uintptr_t) high >= ptr_high)
 137                         {
 138                           for (i=0; i<max_entries; i++)
 139                             {
 140                               if (! entry_used[i])
 141                                 {
 142                                   entry[i].low = (uintptr_t) low;
 143                                   entry[i].high = (uintptr_t) high;
 144                                   entry_used[i] = 1;
 145                                   break;
 146                                 }
 147                             }
 148
 149                           VERBOSE_TRACE ("mf: registering region #%d "
 150                                          "%p-%p given %s",
 151                                          i, (void *) low, (void *) high, buf);
 152
 153                           __mfu_register ((void *) low, (size_t) (high-low),
 154                                           __MF_TYPE_GUESS,
 155                                           "/proc/self/maps segment");
 156
 157                           return 0; /* undecided (tending to cachable) */
 158                         }
 159                     }
 160                 }
 161               fclose (fp);
 162             }
 163         }
 164     }
 165
 166
 167   /* The third heuristic is to approve all accesses between _start (or its
 168      equivalent for the given target) and _end, which should include all
 169      text and initialized data.  */
 170   if (__mf_opts.heur_start_end)
 171     if (ptr >= (uintptr_t) & ENTRY_POINT && ptr_high <= (uintptr_t) & _end)
 172       return 1; /* uncacheable */
 173
 174   return 0; /* unknown */
 175 }