mmalloc/attach.c

   1 /* Initialization for access to a mmap'd malloc managed region.
   2    Copyright 1992, 2000 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 #ifdef HAVE_UNISTD_H
  28 #include <unistd.h>     /* Prototypes for lseek */
  29 #endif
  30 #include "mmprivate.h"
  31
  32 #ifndef SEEK_SET
  33 #define SEEK_SET 0
  34 #endif
  35
  36
  37 #if defined(HAVE_MMAP)
  38
  39 /* Forward declarations/prototypes for local functions */
  40
  41 static struct mdesc *reuse PARAMS ((int));
  42
  43 /* Initialize access to a mmalloc managed region.
  44
  45    If FD is a valid file descriptor for an open file then data for the
  46    mmalloc managed region is mapped to that file, otherwise "/dev/zero"
  47    is used and the data will not exist in any filesystem object.
  48
  49    If the open file corresponding to FD is from a previous use of
  50    mmalloc and passes some basic sanity checks to ensure that it is
  51    compatible with the current mmalloc package, then it's data is
  52    mapped in and is immediately accessible at the same addresses in
  53    the current process as the process that created the file.
  54
  55    If BASEADDR is not NULL, the mapping is established starting at the
  56    specified address in the process address space.  If BASEADDR is NULL,
  57    the mmalloc package chooses a suitable address at which to start the
  58    mapped region, which will be the value of the previous mapping if
  59    opening an existing file which was previously built by mmalloc, or
  60    for new files will be a value chosen by mmap.
  61
  62    Specifying BASEADDR provides more control over where the regions
  63    start and how big they can be before bumping into existing mapped
  64    regions or future mapped regions.
  65
  66    On success, returns a "malloc descriptor" which is used in subsequent
  67    calls to other mmalloc package functions.  It is explicitly "void *"
  68    ("char *" for systems that don't fully support void) so that users
  69    of the package don't have to worry about the actual implementation
  70    details.
  71
  72    On failure returns NULL. */
  73
  74 PTR
  75 mmalloc_attach (fd, baseaddr)
  76   int fd;
  77   PTR baseaddr;
  78 {
  79   struct mdesc mtemp;
  80   struct mdesc *mdp;
  81   PTR mbase;
  82   struct stat sbuf;
  83
  84   /* First check to see if FD is a valid file descriptor, and if so, see
  85      if the file has any current contents (size > 0).  If it does, then
  86      attempt to reuse the file.  If we can't reuse the file, either
  87      because it isn't a valid mmalloc produced file, was produced by an
  88      obsolete version, or any other reason, then we fail to attach to
  89      this file. */
  90
  91   if (fd >= 0)
  92     {
  93       if (fstat (fd, &sbuf) < 0)
  94         {
  95           return (NULL);
  96         }
  97       else if (sbuf.st_size > 0)
  98         {
  99           return ((PTR) reuse (fd));
 100         }
 101     }
 102
 103   /* We start off with the malloc descriptor allocated on the stack, until
 104      we build it up enough to call _mmalloc_mmap_morecore() to allocate the
 105      first page of the region and copy it there.  Ensure that it is zero'd and
 106      then initialize the fields that we know values for. */
 107
 108   mdp = &mtemp;
 109   memset ((char *) mdp, 0, sizeof (mtemp));
 110   strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
 111   mdp -> headersize = sizeof (mtemp);
 112   mdp -> version = MMALLOC_VERSION;
 113   mdp -> morecore = __mmalloc_mmap_morecore;
 114   mdp -> fd = fd;
 115   mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
 116
 117   /* If we have not been passed a valid open file descriptor for the file
 118      to map to, then open /dev/zero and use that to map to. */
 119
 120   if (mdp -> fd < 0)
 121     {
 122       if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
 123         {
 124           return (NULL);
 125         }
 126       else
 127         {
 128           mdp -> flags |= MMALLOC_DEVZERO;
 129         }
 130     }
 131
 132   /*  Now try to map in the first page, copy the malloc descriptor structure
 133       there, and arrange to return a pointer to this new copy.  If the mapping
 134       fails, then close the file descriptor if it was opened by us, and arrange
 135       to return a NULL. */
 136
 137   if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
 138     {
 139       memcpy (mbase, mdp, sizeof (mtemp));
 140       mdp = (struct mdesc *) mbase;
 141     }
 142   else
 143     {
 144       if (mdp -> flags & MMALLOC_DEVZERO)
 145         {
 146           close (mdp -> fd);
 147         }
 148       mdp = NULL;
 149     }
 150
 151   return ((PTR) mdp);
 152 }
 153
 154 /* Given an valid file descriptor on an open file, test to see if that file
 155    is a valid mmalloc produced file, and if so, attempt to remap it into the
 156    current process at the same address to which it was previously mapped.
 157
 158    Note that we have to update the file descriptor number in the malloc-
 159    descriptor read from the file to match the current valid one, before
 160    trying to map the file in, and again after a successful mapping and
 161    after we've switched over to using the mapped in malloc descriptor
 162    rather than the temporary one on the stack.
 163
 164    Once we've switched over to using the mapped in malloc descriptor, we
 165    have to update the pointer to the morecore function, since it almost
 166    certainly will be at a different address if the process reusing the
 167    mapped region is from a different executable.
 168
 169    Also note that if the heap being remapped previously used the mmcheckf()
 170    routines, we need to update the hooks since their target functions
 171    will have certainly moved if the executable has changed in any way.
 172    We do this by calling mmcheckf() internally.
 173
 174    Returns a pointer to the malloc descriptor if successful, or NULL if
 175    unsuccessful for some reason. */
 176
 177 static struct mdesc *
 178 reuse (fd)
 179   int fd;
 180 {
 181   struct mdesc mtemp;
 182   struct mdesc *mdp = NULL;
 183
 184   if ((lseek (fd, 0L, SEEK_SET) == 0) &&
 185       (read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
 186       (mtemp.headersize == sizeof (mtemp)) &&
 187       (strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
 188       (mtemp.version <= MMALLOC_VERSION))
 189     {
 190       mtemp.fd = fd;
 191       if (__mmalloc_remap_core (&mtemp) == mtemp.base)
 192         {
 193           mdp = (struct mdesc *) mtemp.base;
 194           mdp -> fd = fd;
 195           mdp -> morecore = __mmalloc_mmap_morecore;
 196           if (mdp -> mfree_hook != NULL)
 197             {
 198               mmcheckf ((PTR) mdp, (void (*) PARAMS ((void))) NULL, 1);
 199             }
 200         }
 201     }
 202   return (mdp);
 203 }
 204
 205 #else   /* !defined (HAVE_MMAP) */
 206
 207 /* For systems without mmap, the library still supplies an entry point
 208    to link to, but trying to initialize access to an mmap'd managed region
 209    always fails. */
 210
 211 /* ARGSUSED */
 212 PTR
 213 mmalloc_attach (fd, baseaddr)
 214   int fd;
 215   PTR baseaddr;
 216 {
 217    return (NULL);
 218 }
 219
 220 #endif  /* defined (HAVE_MMAP) */
 221