/* Mudflap: narrow-pointer bounds-checking by tree rewriting.

Copyright (C) 2002-2013 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

};

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 */

}