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[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.5.1/] [gcc/] [config/] [host-linux.c] - Blame information for rev 282

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1 282 jeremybenn
/* Linux host-specific hook definitions.
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   Copyright (C) 2004, 2005, 2007, 2008 Free Software Foundation, Inc.
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   This file is part of GCC.
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   GCC is free software; you can redistribute it and/or modify it
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   under the terms of the GNU General Public License as published
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   by the Free Software Foundation; either version 3, or (at your
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   option) any later version.
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   GCC is distributed in the hope that it will be useful, but WITHOUT
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   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
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   License for more details.
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   You should have received a copy of the GNU General Public License
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   along with GCC; see the file COPYING3.  If not see
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   <http://www.gnu.org/licenses/>.  */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include <sys/mman.h>
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#include <limits.h>
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#include "hosthooks.h"
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#include "hosthooks-def.h"
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/* Linux has a feature called exec-shield-randomize that perturbs the
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   address of non-fixed mapped segments by a (relatively) small amount.
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   The feature is intended to make it harder to attack the system with
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   buffer overflow attacks, since every invocation of a program will
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   have its libraries and data segments at slightly different addresses.
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   This feature causes us problems with PCH because it makes it that
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   much harder to acquire a stable location at which to map our PCH
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   data file.
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   [ The feature causes other points of non-determinism within the
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     compiler as well, so we'd *really* like to be able to have the
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     driver disable exec-shield-randomize for the process group, but
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     that isn't possible at present.  ]
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   We're going to try several things:
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      * Select an architecture specific address as "likely" and see
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        if that's free.  For our 64-bit hosts, we can easily choose
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        an address in Never Never Land.
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      * If exec-shield-randomize is disabled, then just use the
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        address chosen by mmap in step one.
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      * If exec-shield-randomize is enabled, then temporarily allocate
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        32M of memory as a buffer, then allocate PCH memory, then
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        free the buffer.  The theory here is that the perturbation is
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        no more than 16M, and so by allocating our buffer larger than
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        that we make it considerably more likely that the address will
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        be free when we want to load the data back.
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*/
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#undef HOST_HOOKS_GT_PCH_GET_ADDRESS
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#define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
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#undef HOST_HOOKS_GT_PCH_USE_ADDRESS
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#define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
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/* For various ports, try to guess a fixed spot in the vm space
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   that's probably free.  */
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#if defined(__alpha)
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# define TRY_EMPTY_VM_SPACE     0x10000000000
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#elif defined(__ia64)
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# define TRY_EMPTY_VM_SPACE     0x2000000100000000
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#elif defined(__x86_64)
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# define TRY_EMPTY_VM_SPACE     0x1000000000
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#elif defined(__i386)
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# define TRY_EMPTY_VM_SPACE     0x60000000
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#elif defined(__powerpc__)
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# define TRY_EMPTY_VM_SPACE     0x60000000
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#elif defined(__s390x__)
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# define TRY_EMPTY_VM_SPACE     0x8000000000
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#elif defined(__s390__)
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# define TRY_EMPTY_VM_SPACE     0x60000000
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#elif defined(__sparc__) && defined(__LP64__)
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# define TRY_EMPTY_VM_SPACE     0x8000000000
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#elif defined(__sparc__)
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# define TRY_EMPTY_VM_SPACE     0x60000000
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#elif defined(__mc68000__)
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# define TRY_EMPTY_VM_SPACE     0x40000000
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#else
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# define TRY_EMPTY_VM_SPACE     0
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#endif
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/* Determine a location where we might be able to reliably allocate SIZE
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   bytes.  FD is the PCH file, though we should return with the file
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   unmapped.  */
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static void *
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linux_gt_pch_get_address (size_t size, int fd)
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{
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  size_t buffer_size = 32 * 1024 * 1024;
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  void *addr, *buffer;
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  FILE *f;
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  bool randomize_on;
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  addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
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               MAP_PRIVATE, fd, 0);
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  /* If we failed the map, that means there's *no* free space.  */
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  if (addr == (void *) MAP_FAILED)
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    return NULL;
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  /* Unmap the area before returning.  */
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  munmap (addr, size);
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  /* If we got the exact area we requested, then that's great.  */
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  if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
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    return addr;
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  /* If we didn't, then we need to look to see if virtual address
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     randomization is on.  That is recorded in
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     kernel.randomize_va_space.  An older implementation used
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     kernel.exec-shield-randomize.  */
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  f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
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  if (f == NULL)
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    f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
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  randomize_on = false;
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  if (f != NULL)
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    {
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      char buf[100];
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      size_t c;
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      c = fread (buf, 1, sizeof buf - 1, f);
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      if (c > 0)
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        {
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          buf[c] = '\0';
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          randomize_on = (atoi (buf) > 0);
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        }
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      fclose (f);
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    }
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  /* If it isn't, then accept the address that mmap selected as fine.  */
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  if (!randomize_on)
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    return addr;
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  /* Otherwise, we need to try again with buffer space.  */
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  buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
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  addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
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  if (buffer != (void *) MAP_FAILED)
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    munmap (buffer, buffer_size);
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  if (addr == (void *) MAP_FAILED)
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    return NULL;
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  munmap (addr, size);
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  return addr;
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}
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/* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
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   mapping the data at BASE, -1 if we couldn't.
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   It's not possibly to reliably mmap a file using MAP_PRIVATE to
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   a specific START address on either hpux or linux.  First we see
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   if mmap with MAP_PRIVATE works.  If it does, we are off to the
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   races.  If it doesn't, we try an anonymous private mmap since the
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   kernel is more likely to honor the BASE address in anonymous maps.
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   We then copy the data to the anonymous private map.  This assumes
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   of course that we don't need to change the data in the PCH file
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   after it is created.
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   This approach obviously causes a performance penalty but there is
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   little else we can do given the current PCH implementation.  */
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static int
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linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
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{
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  void *addr;
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  /* We're called with size == 0 if we're not planning to load a PCH
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     file at all.  This allows the hook to free any static space that
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     we might have allocated at link time.  */
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  if (size == 0)
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    return -1;
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  /* Try to map the file with MAP_PRIVATE.  */
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  addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
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  if (addr == base)
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    return 1;
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  if (addr != (void *) MAP_FAILED)
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    munmap (addr, size);
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  /* Try to make an anonymous private mmap at the desired location.  */
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  addr = mmap (base, size, PROT_READ | PROT_WRITE,
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               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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  if (addr != base)
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    {
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      if (addr != (void *) MAP_FAILED)
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        munmap (addr, size);
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      return -1;
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    }
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  if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
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    return -1;
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  while (size)
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    {
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      ssize_t nbytes;
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      nbytes = read (fd, base, MIN (size, SSIZE_MAX));
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      if (nbytes <= 0)
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        return -1;
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      base = (char *) base + nbytes;
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      size -= nbytes;
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    }
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  return 1;
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}
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const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;

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