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 program is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or
   9 (at your option) any later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program; if not, write to the Free Software
  18 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20
  21 #include <fcntl.h>
  22 #include <sys/types.h>
  23 #include <sys/stat.h>
  24 #include "mmalloc.h"
  25
  26 #ifndef SEEK_SET
  27 #define SEEK_SET 0
  28 #endif
  29
  30 /* Forward declarations/prototypes for local functions */
  31
  32 static struct mdesc *reuse PARAMS ((int));
  33
  34 /* Initialize access to a mmalloc managed region.
  35
  36    If FD is a valid file descriptor for an open file then data for the
  37    mmalloc managed region is mapped to that file, otherwise "/dev/zero"
  38    is used and the data will not exist in any filesystem object.
  39
  40    If the open file corresponding to FD is from a previous use of
  41    mmalloc and passes some basic sanity checks to ensure that it is
  42    compatible with the current mmalloc package, then it's data is
  43    mapped in and is immediately accessible at the same addresses in
  44    the current process as the process that created the file.
  45
  46    If BASEADDR is not NULL, the mapping is established starting at the
  47    specified address in the process address space.  If BASEADDR is NULL,
  48    the mmalloc package chooses a suitable address at which to start the
  49    mapped region, which will be the value of the previous mapping if
  50    opening an existing file which was previously built by mmalloc, or
  51    for new files will be a value chosen by mmap.
  52
  53    Specifying BASEADDR provides more control over where the regions
  54    start and how big they can be before bumping into existing mapped
  55    regions or future mapped regions.
  56
  57    On success, returns a "malloc descriptor" which is used in subsequent
  58    calls to other mmalloc package functions.  It is explicitly "void *"
  59    ("char *" for systems that don't fully support void) so that users
  60    of the package don't have to worry about the actual implementation
  61    details.
  62
  63    On failure returns NULL. */
  64
  65
  66 #if defined(HAVE_MMAP)
  67
  68 PTR
  69 mmalloc_attach (fd, baseaddr)
  70   int fd;
  71   PTR baseaddr;
  72 {
  73   struct mdesc mtemp;
  74   struct mdesc *mdp;
  75   PTR mbase;
  76   struct stat sbuf;
  77
  78   /* First check to see if FD is a valid file descriptor, and if so, see
  79      if the file has any current contents (size > 0).  If it does, then
  80      attempt to reuse the file.  If we can't reuse the file, either
  81      because it isn't a valid mmalloc produced file, was produced by an
  82      obsolete version, or any other reason, then we fail to attach to
  83      this file. */
  84
  85   if (fd >= 0)
  86     {
  87       if (fstat (fd, &sbuf) < 0)
  88         {
  89           return (NULL);
  90         }
  91       else if (sbuf.st_size > 0)
  92         {
  93           return ((PTR) reuse (fd));
  94         }
  95     }
  96
  97   /* We start off with the malloc descriptor allocated on the stack, until
  98      we build it up enough to call _mmalloc_mmap_morecore() to allocate the
  99      first page of the region and copy it there.  Ensure that it is zero'd and
 100      then initialize the fields that we know values for. */
 101
 102   mdp = &mtemp;
 103   memset ((char *) mdp, 0, sizeof (mtemp));
 104   strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
 105   mdp -> headersize = sizeof (mtemp);
 106   mdp -> version = MMALLOC_VERSION;
 107   mdp -> morecore = __mmalloc_mmap_morecore;
 108   mdp -> fd = fd;
 109   mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
 110
 111   /* If we have not been passed a valid open file descriptor for the file
 112      to map to, then open /dev/zero and use that to map to. */
 113
 114   if (mdp -> fd < 0)
 115     {
 116       if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
 117         {
 118           return (NULL);
 119         }
 120       else
 121         {
 122           mdp -> flags |= MMALLOC_DEVZERO;
 123         }
 124     }
 125
 126   /*  Now try to map in the first page, copy the malloc descriptor structure
 127       there, and arrange to return a pointer to this new copy.  If the mapping
 128       fails, then close the file descriptor if it was opened by us, and arrange
 129       to return a NULL. */
 130
 131   if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
 132     {
 133       memcpy (mbase, mdp, sizeof (mtemp));
 134       mdp = (struct mdesc *) mbase;
 135     }
 136   else
 137     {
 138       if (mdp -> flags & MMALLOC_DEVZERO)
 139         {
 140           close (mdp -> fd);
 141         }
 142       mdp = NULL;
 143     }
 144
 145   return ((PTR) mdp);
 146 }
 147
 148 /* Given an valid file descriptor on an open file, test to see if that file
 149    is a valid mmalloc produced file, and if so, attempt to remap it into the
 150    current process at the same address to which it was previously mapped.
 151
 152    Note that we have to update the file descriptor number in the malloc-
 153    descriptor read from the file to match the current valid one, before
 154    trying to map the file in, and again after a successful mapping and
 155    after we've switched over to using the mapped in malloc descriptor
 156    rather than the temporary one on the stack.
 157
 158    Also note that if the heap being remapped previously used the mmcheck()
 159    routines, we need to update the hooks since their target functions
 160    will have certainly moved if the executable has changed in any way.
 161    We do this by calling mmcheck() internally.
 162
 163    Returns a pointer to the malloc descriptor if successful, or NULL if
 164    unsuccessful for some reason. */
 165
 166 static struct mdesc *
 167 reuse (fd)
 168   int fd;
 169 {
 170   struct mdesc mtemp;
 171   struct mdesc *mdp = NULL;
 172
 173   if ((lseek (fd, 0L, SEEK_SET) == 0) &&
 174       (read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
 175       (mtemp.headersize == sizeof (mtemp)) &&
 176       (strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
 177       (mtemp.version <= MMALLOC_VERSION))
 178     {
 179       mtemp.fd = fd;
 180       if (__mmalloc_remap_core (&mtemp) == mtemp.base)
 181         {
 182           mdp = (struct mdesc *) mtemp.base;
 183           mdp -> fd = fd;
 184           if (mdp -> mfree_hook != NULL)
 185             {
 186               (void) mmcheck ((PTR) mdp, (void (*) PARAMS ((void))) NULL);
 187             }
 188         }
 189     }
 190   return (mdp);
 191 }
 192
 193 #else   /* !defined (HAVE_MMAP) */
 194
 195 /* For systems without mmap, the library still supplies an entry point
 196    to link to, but trying to initialize access to an mmap'd managed region
 197    always fails. */
 198
 199 PTR
 200 mmalloc_attach (fd, baseaddr)
 201   int fd;
 202   PTR baseaddr;
 203 {
 204    return (NULL);
 205 }
 206
 207 #endif  /* defined (HAVE_MMAP) */
 208