mmalloc/attach.c

   1 /* Initialization for access to a mmap'd malloc managed region.
   2    Copyright 1992 Free Software Foundation, Inc.
   3
   4    Contributed by Fred Fish at Cygnus Support.   fnf@cygnus.com
   5
   6 This file is part of the GNU C Library.
   7
   8 The GNU C Library is free software; you can redistribute it and/or
   9 modify it under the terms of the GNU Library General Public License as
  10 published by the Free Software Foundation; either version 2 of the
  11 License, or (at your option) any later version.
  12
  13 The GNU C Library is distributed in the hope that it will be useful,
  14 but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16 Library General Public License for more details.
  17
  18 You should have received a copy of the GNU Library General Public
  19 License along with the GNU C Library; see the file COPYING.LIB.  If
  20 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  21 Boston, MA 02111-1307, USA.  */
  22
  23 #include <sys/types.h>
  24 #include <fcntl.h> /* After sys/types.h, at least for dpx/2.  */
  25 #include <sys/stat.h>
  26 #include <string.h>
  27 #include "mmprivate.h"
  28
  29 #ifndef SEEK_SET
  30 #define SEEK_SET 0
  31 #endif
  32
  33
  34 #if defined(HAVE_MMAP)
  35
  36 /* Forward declarations/prototypes for local functions */
  37
  38 static struct mdesc *reuse PARAMS ((int));
  39
  40 /* Initialize access to a mmalloc managed region.
  41
  42    If FD is a valid file descriptor for an open file then data for the
  43    mmalloc managed region is mapped to that file, otherwise "/dev/zero"
  44    is used and the data will not exist in any filesystem object.
  45
  46    If the open file corresponding to FD is from a previous use of
  47    mmalloc and passes some basic sanity checks to ensure that it is
  48    compatible with the current mmalloc package, then it's data is
  49    mapped in and is immediately accessible at the same addresses in
  50    the current process as the process that created the file.
  51
  52    If BASEADDR is not NULL, the mapping is established starting at the
  53    specified address in the process address space.  If BASEADDR is NULL,
  54    the mmalloc package chooses a suitable address at which to start the
  55    mapped region, which will be the value of the previous mapping if
  56    opening an existing file which was previously built by mmalloc, or
  57    for new files will be a value chosen by mmap.
  58
  59    Specifying BASEADDR provides more control over where the regions
  60    start and how big they can be before bumping into existing mapped
  61    regions or future mapped regions.
  62
  63    On success, returns a "malloc descriptor" which is used in subsequent
  64    calls to other mmalloc package functions.  It is explicitly "void *"
  65    ("char *" for systems that don't fully support void) so that users
  66    of the package don't have to worry about the actual implementation
  67    details.
  68
  69    On failure returns NULL. */
  70
  71 PTR
  72 mmalloc_attach (fd, baseaddr)
  73   int fd;
  74   PTR baseaddr;
  75 {
  76   struct mdesc mtemp;
  77   struct mdesc *mdp;
  78   PTR mbase;
  79   struct stat sbuf;
  80
  81   /* First check to see if FD is a valid file descriptor, and if so, see
  82      if the file has any current contents (size > 0).  If it does, then
  83      attempt to reuse the file.  If we can't reuse the file, either
  84      because it isn't a valid mmalloc produced file, was produced by an
  85      obsolete version, or any other reason, then we fail to attach to
  86      this file. */
  87
  88   if (fd >= 0)
  89     {
  90       if (fstat (fd, &sbuf) < 0)
  91         {
  92           return (NULL);
  93         }
  94       else if (sbuf.st_size > 0)
  95         {
  96           return ((PTR) reuse (fd));
  97         }
  98     }
  99
 100   /* We start off with the malloc descriptor allocated on the stack, until
 101      we build it up enough to call _mmalloc_mmap_morecore() to allocate the
 102      first page of the region and copy it there.  Ensure that it is zero'd and
 103      then initialize the fields that we know values for. */
 104
 105   mdp = &mtemp;
 106   memset ((char *) mdp, 0, sizeof (mtemp));
 107   strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
 108   mdp -> headersize = sizeof (mtemp);
 109   mdp -> version = MMALLOC_VERSION;
 110   mdp -> morecore = __mmalloc_mmap_morecore;
 111   mdp -> fd = fd;
 112   mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
 113
 114   /* If we have not been passed a valid open file descriptor for the file
 115      to map to, then open /dev/zero and use that to map to. */
 116
 117   if (mdp -> fd < 0)
 118     {
 119       if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
 120         {
 121           return (NULL);
 122         }
 123       else
 124         {
 125           mdp -> flags |= MMALLOC_DEVZERO;
 126         }
 127     }
 128
 129   /*  Now try to map in the first page, copy the malloc descriptor structure
 130       there, and arrange to return a pointer to this new copy.  If the mapping
 131       fails, then close the file descriptor if it was opened by us, and arrange
 132       to return a NULL. */
 133
 134   if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
 135     {
 136       memcpy (mbase, mdp, sizeof (mtemp));
 137       mdp = (struct mdesc *) mbase;
 138     }
 139   else
 140     {
 141       if (mdp -> flags & MMALLOC_DEVZERO)
 142         {
 143           close (mdp -> fd);
 144         }
 145       mdp = NULL;
 146     }
 147
 148   return ((PTR) mdp);
 149 }
 150
 151 /* Given an valid file descriptor on an open file, test to see if that file
 152    is a valid mmalloc produced file, and if so, attempt to remap it into the
 153    current process at the same address to which it was previously mapped.
 154
 155    Note that we have to update the file descriptor number in the malloc-
 156    descriptor read from the file to match the current valid one, before
 157    trying to map the file in, and again after a successful mapping and
 158    after we've switched over to using the mapped in malloc descriptor
 159    rather than the temporary one on the stack.
 160
 161    Once we've switched over to using the mapped in malloc descriptor, we
 162    have to update the pointer to the morecore function, since it almost
 163    certainly will be at a different address if the process reusing the
 164    mapped region is from a different executable.
 165
 166    Also note that if the heap being remapped previously used the mmcheckf()
 167    routines, we need to update the hooks since their target functions
 168    will have certainly moved if the executable has changed in any way.
 169    We do this by calling mmcheckf() internally.
 170
 171    Returns a pointer to the malloc descriptor if successful, or NULL if
 172    unsuccessful for some reason. */
 173
 174 static struct mdesc *
 175 reuse (fd)
 176   int fd;
 177 {
 178   struct mdesc mtemp;
 179   struct mdesc *mdp = NULL;
 180
 181   if ((lseek (fd, 0L, SEEK_SET) == 0) &&
 182       (read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
 183       (mtemp.headersize == sizeof (mtemp)) &&
 184       (strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
 185       (mtemp.version <= MMALLOC_VERSION))
 186     {
 187       mtemp.fd = fd;
 188       if (__mmalloc_remap_core (&mtemp) == mtemp.base)
 189         {
 190           mdp = (struct mdesc *) mtemp.base;
 191           mdp -> fd = fd;
 192           mdp -> morecore = __mmalloc_mmap_morecore;
 193           if (mdp -> mfree_hook != NULL)
 194             {
 195               mmcheckf ((PTR) mdp, (void (*) PARAMS ((void))) NULL, 1);
 196             }
 197         }
 198     }
 199   return (mdp);
 200 }
 201
 202 #else   /* !defined (HAVE_MMAP) */
 203
 204 /* For systems without mmap, the library still supplies an entry point
 205    to link to, but trying to initialize access to an mmap'd managed region
 206    always fails. */
 207
 208 /* ARGSUSED */
 209 PTR
 210 mmalloc_attach (fd, baseaddr)
 211   int fd;
 212   PTR baseaddr;
 213 {
 214    return (NULL);
 215 }
 216
 217 #endif  /* defined (HAVE_MMAP) */
 218