src/unexsunos4.c

   1 /* Unexec for Sunos 4 using shared libraries.
   2    Copyright (C) 1990, 1994 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Emacs.
   5
   6 GNU Emacs 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, or (at your option)
   9 any later version.
  10
  11 GNU Emacs 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 GNU Emacs; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20 /* Contributed by Viktor Dukhovni.  */
  21 /*
  22  * Unexec for Berkeley a.out format + SUNOS shared libraries
  23  * The unexeced executable contains the __DYNAMIC area from the
  24  * original text file,  and then the rest of data + bss + malloced area of
  25  * the current process.  (The __DYNAMIC area is at the top of the process
  26  * data segment,  we use "data_start" defined externally to mark the start
  27  * of the "real" data segment.)
  28  *
  29  * For programs that want to remap some of the data segment read only
  30  * a run_time_remap is provided.  This attempts to remap largest area starting
  31  * and ending on page boundaries between "data_start" and "bndry"
  32  * For this it to figure out where the text file is located.  A path search
  33  * is attempted after trying argv[0] and if all fails we simply do not remap
  34  *
  35  * One feature of run_time_remap () is mandatory:  reseting the break.
  36  *
  37  *  Note that we can no longer map data into the text segment,  as this causes
  38  *  the __DYNAMIC struct to become read only,  breaking the runtime loader.
  39  *  Thus we no longer need to mess with a private crt0.c,  the standard one
  40  *  will do just fine,  since environ can live in the writable area between
  41  *  __DYNAMIC and data_start,  just make sure that pre-crt0.o (the name
  42  *  is somewhat abused here) is loaded first!
  43  *
  44  */
  45 #include <sys/param.h>
  46 #include <sys/mman.h>
  47 #include <sys/file.h>
  48 #include <sys/stat.h>
  49 #include <string.h>
  50 #include <stdio.h>
  51 #include <a.out.h>
  52
  53 /* Do this after the above #include's in case a configuration file wants
  54    to define things for this file based on what <a.out.h> defines.  */
  55 #ifdef emacs
  56 #include <config.h>
  57 #endif
  58
  59 #if defined (SUNOS4) || defined (__FreeBSD__)
  60 #define UNDO_RELOCATION
  61 #endif
  62
  63 #ifdef UNDO_RELOCATION
  64 #include <link.h>
  65 #endif
  66
  67 #ifdef HAVE_UNISTD_H
  68 #include <unistd.h>
  69 #endif
  70
  71 /* NetBSD needs this bit, but SunOS does not have it.  */
  72 #ifndef MAP_FILE
  73 #define MAP_FILE 0
  74 #endif
  75
  76
  77 /*
  78  * for programs other than emacs
  79  * define data_start + initialized here,  and make sure
  80  * this object is loaded first!
  81  * emacs will define these elsewhere,  and load the object containing
  82  * data_start (pre-crt0.o or firstfile.o?) first!
  83  * The custom crt0.o *must not* be loaded!
  84  */
  85 #ifndef emacs
  86   static int data_start = 0;
  87   static int initialized = 0;
  88 #else
  89   extern int initialized;
  90   extern unsigned data_start;
  91   extern int pureptr;
  92 #endif
  93
  94 extern char *getenv ();
  95 static unsigned Brk;
  96 static struct exec nhdr;
  97 static int rd_only_len;
  98 static long cookie;
  99
 100
 101 unexec (new_name, a_name, bndry, bss_start, entry)
 102      char *new_name, *a_name;
 103      unsigned bndry, bss_start, entry;
 104 {
 105   int fd, new;
 106   char *old;
 107   struct exec ohdr;             /* Allocate on the stack,  not needed in the next life */
 108   struct stat stat;
 109
 110   if ((fd = open (a_name, O_RDONLY)) < 0)
 111     {
 112       fprintf (stderr, "%s: open: ", a_name);
 113       perror (a_name);
 114       exit (1);
 115     }
 116   if ((new = open (new_name, O_WRONLY | O_CREAT, 0666)) == -1)
 117     {
 118       fprintf (stderr, "%s: open: ", a_name);
 119       perror (new_name);
 120       exit (1);
 121     }
 122
 123   if ((fstat (fd, &stat) == -1))
 124     {
 125       fprintf (stderr, "%s: ", a_name);
 126       perror ("fstat");
 127       exit (1);
 128     }
 129
 130   old = (char *)mmap (0, stat.st_size, PROT_READ, MAP_FILE|MAP_SHARED, fd, 0);
 131   if (old == (char *)-1)
 132     {
 133       fprintf (stderr, "%s: ", a_name);
 134       perror ("mmap");
 135       exit (1);
 136     }
 137   close (fd);
 138
 139   nhdr = ohdr = (*(struct exec *)old);
 140
 141
 142   /*
 143    * Remember a magic cookie so we know we've got the right binary
 144    * when remapping.
 145    */
 146   cookie = time (0);
 147
 148   Brk = sbrk (0);               /* Save the break, it is reset to &_end (by ld.so?) */
 149
 150   /*
 151    * Round up data start to a page boundary (Lose if not a 2 power!)
 152    */
 153   data_start = ((((int)&data_start) - 1) & ~(N_PAGSIZ (nhdr) - 1)) + N_PAGSIZ (nhdr);
 154
 155   /*
 156    * Round down read only pages to a multiple of the page size
 157    */
 158   if (bndry)
 159     rd_only_len = ((int)bndry & ~(N_PAGSIZ (nhdr) - 1)) - data_start;
 160
 161 #ifndef emacs
 162   /* Have to do this some time before dumping the data */
 163   initialized = 1;
 164 #endif
 165
 166   /*
 167    * Handle new data and bss sizes and optional new entry point.
 168    * No one actually uses bss_start and entry,  but tradition compels
 169    * one to support them.
 170    * Could complain if bss_start > Brk,  but the caller is *supposed* to know
 171    * what she is doing.
 172    */
 173   nhdr.a_data = (bss_start ? bss_start : Brk) - N_DATADDR (nhdr);
 174   nhdr.a_bss  = bss_start ? Brk - bss_start : 0;
 175   if (entry)
 176     nhdr.a_entry = entry;
 177
 178   /*
 179    * Write out the text segment with new header
 180    * Dynamic executables are ZMAGIC with N_TXTOFF==0 and the header
 181    * part of the text segment, but no need to rely on this.
 182    * So write the TEXT first,  then go back replace the header.
 183    * Doing it in the other order is less general!
 184    */
 185   lseek (new, N_TXTOFF (nhdr), L_SET);
 186   write (new, old + N_TXTOFF (ohdr), N_TXTOFF (ohdr) + ohdr.a_text);
 187   lseek (new, 0L, L_SET);
 188   write (new, &nhdr, sizeof (nhdr));
 189
 190   /*
 191    * Write out the head of the old data segment from the file not
 192    * from core, this has the unresolved __DYNAMIC relocation data
 193    * we need to reload
 194    */
 195   lseek (new, N_DATOFF (nhdr), L_SET);
 196   write (new, old + N_DATOFF (ohdr), (int)&data_start - N_DATADDR (ohdr));
 197
 198   /*
 199    * Copy the rest of the data from core
 200    */
 201   write (new, &data_start, N_BSSADDR (nhdr) - (int)&data_start);
 202
 203   /*
 204    * Copy the symbol table and line numbers
 205    */
 206   lseek (new, N_TRELOFF (nhdr), L_SET);
 207   write (new, old + N_TRELOFF (ohdr), stat.st_size - N_TRELOFF (ohdr));
 208
 209   /* Some other BSD systems use this file.
 210      We don't know whether this change is right for them.  */
 211 #ifdef UNDO_RELOCATION
 212   /* Undo the relocations done at startup by ld.so.
 213      It will do these relocations again when we start the dumped Emacs.
 214      Doing them twice gives incorrect results.  */
 215   {
 216     unsigned long daddr = N_DATADDR (ohdr);
 217     unsigned long rel, erel;
 218 #ifdef SUNOS4
 219     extern struct link_dynamic _DYNAMIC;
 220
 221     /*  SunOS4.x's ld_rel is relative to N_TXTADDR. */
 222     if (_DYNAMIC.ld_version < 2)
 223       {
 224         rel = _DYNAMIC.ld_un.ld_1->ld_rel + N_TXTADDR (ohdr);
 225         erel = _DYNAMIC.ld_un.ld_1->ld_hash + N_TXTADDR (ohdr);
 226       }
 227     else
 228       {
 229         rel = _DYNAMIC.ld_un.ld_2->ld_rel + N_TXTADDR (ohdr);
 230         erel = _DYNAMIC.ld_un.ld_2->ld_hash + N_TXTADDR (ohdr);
 231       }
 232 #ifdef sparc
 233 #define REL_INFO_TYPE           struct reloc_info_sparc
 234 #else
 235 #define REL_INFO_TYPE           struct reloc_info_m68k
 236 #endif /* sparc */
 237 #define REL_TARGET_ADDRESS(r)   (((REL_INFO_TYPE *)(r))->r_address)
 238 #endif /* SUNOS4 */
 239 #ifdef __FreeBSD__
 240     extern struct _dynamic _DYNAMIC;
 241
 242     /*  FreeBSD's LD_REL is a virtual address itself. */
 243     rel = LD_REL (&_DYNAMIC);
 244     erel = rel + LD_RELSZ (&_DYNAMIC);
 245 #define REL_INFO_TYPE           struct relocation_info
 246 #define REL_TARGET_ADDRESS(r)   (((REL_INFO_TYPE *)(r))->r_address)
 247 #endif
 248
 249     for (; rel < erel; rel += sizeof (REL_INFO_TYPE))
 250       {
 251         /*  This is the virtual address where ld.so will do relocation.  */
 252         unsigned long target = REL_TARGET_ADDRESS (rel);
 253         /*  This is the offset in the data segment.  */
 254         unsigned long segoffset = target - daddr;
 255
 256         /*  If it is located below data_start, we have to do nothing here,
 257             because the old data has been already written to the location. */
 258         if (target < (unsigned long)&data_start)
 259             continue;
 260
 261         lseek (new, N_DATOFF (nhdr) + segoffset, L_SET);
 262         write (new, old + N_DATOFF (ohdr) + segoffset, sizeof (unsigned long));
 263       }
 264   }
 265 #endif /* UNDO_RELOCATION */
 266
 267   fchmod (new, 0755);
 268 }
 269
 270 void
 271 run_time_remap (progname)
 272      char *progname;
 273 {
 274   char aout[MAXPATHLEN];
 275   register char *path, *p;
 276
 277   /* Just in case */
 278   if (!initialized)
 279     return;
 280
 281   /* Restore the break */
 282   brk (Brk);
 283
 284   /*  If nothing to remap:  we are done! */
 285   if (rd_only_len == 0)
 286     return;
 287
 288   /*
 289    * Attempt to find the executable
 290    * First try argv[0],  will almost always succeed as shells tend to give
 291    * the full path from the hash list rather than using execvp ()
 292    */
 293   if (is_it (progname))
 294     return;
 295
 296   /*
 297    * If argv[0] is a full path and does not exist,  not much sense in
 298    * searching further
 299    */
 300   if (strchr (progname, '/'))
 301     return;
 302
 303   /*
 304    * Try to search for  argv[0] on the PATH
 305    */
 306   path = getenv ("PATH");
 307   if (path == NULL)
 308     return;
 309
 310   while (*path)
 311     {
 312       /* copy through ':' or end */
 313       for (p = aout; *p = *path; ++p, ++path)
 314         if (*p == ':')
 315           {
 316             ++path;             /* move past ':' */
 317             break;
 318           }
 319       *p++ = '/';
 320       strcpy (p, progname);
 321       /*
 322        * aout is a candidate full path name
 323        */
 324       if (is_it (aout))
 325         return;
 326     }
 327 }
 328
 329 is_it (filename)
 330   char *filename;
 331 {
 332   int fd;
 333   long filenames_cookie;
 334   struct exec hdr;
 335
 336   /*
 337    * Open an executable  and check for a valid header!
 338    * Can't bcmp the header with what we had,  it may have been stripped!
 339    * so we may save looking at non executables with the same name, mostly
 340    * directories.
 341    */
 342   fd = open (filename, O_RDONLY);
 343   if (fd != -1)
 344     {
 345       if (read (fd, &hdr, sizeof (hdr)) == sizeof (hdr)
 346           && !N_BADMAG (hdr) && N_DATOFF (hdr) == N_DATOFF (nhdr)
 347           && N_TRELOFF (hdr) == N_TRELOFF (nhdr))
 348         {
 349           /* compare cookies */
 350           lseek (fd, N_DATOFF (hdr) + (int)&cookie - N_DATADDR (hdr), L_SET);
 351           read (fd, &filenames_cookie, sizeof (filenames_cookie));
 352           if (filenames_cookie == cookie)
 353             {                   /* Eureka */
 354
 355               /*
 356                * Do the mapping
 357                * The PROT_EXEC may not be needed,  but it is safer this way.
 358                * should the shared library decide to indirect through
 359                * addresses in the data segment not part of __DYNAMIC
 360                */
 361               mmap (data_start, rd_only_len, PROT_READ | PROT_EXEC,
 362                     MAP_FILE | MAP_SHARED | MAP_FIXED, fd,
 363                     N_DATOFF (hdr) + data_start - N_DATADDR (hdr));
 364               close (fd);
 365               return 1;
 366             }
 367         }
 368       close (fd);
 369     }
 370   return 0;
 371 }