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, Inc., 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 /* Contributed by Viktor Dukhovni.  */
  22 /*
  23  * Unexec for Berkeley a.out format + SUNOS shared libraries
  24  * The unexeced executable contains the __DYNAMIC area from the
  25  * original text file,  and then the rest of data + bss + malloced area of
  26  * the current process.  (The __DYNAMIC area is at the top of the process
  27  * data segment,  we use "data_start" defined externally to mark the start
  28  * of the "real" data segment.)
  29  *
  30  * For programs that want to remap some of the data segment read only
  31  * a run_time_remap is provided.  This attempts to remap largest area starting
  32  * and ending on page boundaries between "data_start" and "bndry"
  33  * For this it to figure out where the text file is located.  A path search
  34  * is attempted after trying argv[0] and if all fails we simply do not remap
  35  *
  36  * One feature of run_time_remap () is mandatory:  reseting the break.
  37  *
  38  *  Note that we can no longer map data into the text segment,  as this causes
  39  *  the __DYNAMIC struct to become read only,  breaking the runtime loader.
  40  *  Thus we no longer need to mess with a private crt0.c,  the standard one
  41  *  will do just fine,  since environ can live in the writable area between
  42  *  __DYNAMIC and data_start,  just make sure that pre-crt0.o (the name
  43  *  is somewhat abused here) is loaded first!
  44  *
  45  */
  46 #include <sys/param.h>
  47 #include <sys/mman.h>
  48 #include <sys/file.h>
  49 #include <sys/stat.h>
  50 #include <string.h>
  51 #include <stdio.h>
  52 #include <a.out.h>
  53
  54 /* Do this after the above #include's in case a configuration file wants
  55    to define things for this file based on what <a.out.h> defines.  */
  56 #ifdef emacs
  57 #include <config.h>
  58 #endif
  59
  60 #if defined (SUNOS4) || defined (__FreeBSD__) || defined (__NetBSD__)
  61 #define UNDO_RELOCATION
  62 #endif
  63
  64 #ifdef UNDO_RELOCATION
  65 #include <link.h>
  66 #endif
  67
  68 #ifdef HAVE_UNISTD_H
  69 #include <unistd.h>
  70 #endif
  71
  72 /* NetBSD needs this bit, but SunOS does not have it.  */
  73 #ifndef MAP_FILE
  74 #define MAP_FILE 0
  75 #endif
  76
  77
  78 /*
  79  * for programs other than emacs
  80  * define data_start + initialized here,  and make sure
  81  * this object is loaded first!
  82  * emacs will define these elsewhere,  and load the object containing
  83  * data_start (pre-crt0.o or firstfile.o?) first!
  84  * The custom crt0.o *must not* be loaded!
  85  */
  86 #ifndef emacs
  87   static int data_start = 0;
  88   static int initialized = 0;
  89 #else
  90   extern int initialized;
  91   extern unsigned data_start;
  92   extern int pureptr;
  93 #endif
  94
  95 extern char *getenv ();
  96 static unsigned brk_value;
  97 static struct exec nhdr;
  98 static int rd_only_len;
  99 static long cookie;
 100
 101
 102 unexec (new_name, a_name, bndry, bss_start, entry)
 103      char *new_name, *a_name;
 104      unsigned bndry, bss_start, entry;
 105 {
 106   int fd, new;
 107   char *old;
 108   struct exec ohdr;             /* Allocate on the stack,  not needed in the next life */
 109   struct stat stat;
 110
 111   if ((fd = open (a_name, O_RDONLY)) < 0)
 112     {
 113       fprintf (stderr, "%s: open: ", a_name);
 114       perror (a_name);
 115       exit (1);
 116     }
 117   if ((new = open (new_name, O_WRONLY | O_CREAT, 0666)) == -1)
 118     {
 119       fprintf (stderr, "%s: open: ", a_name);
 120       perror (new_name);
 121       exit (1);
 122     }
 123
 124   if ((fstat (fd, &stat) == -1))
 125     {
 126       fprintf (stderr, "%s: ", a_name);
 127       perror ("fstat");
 128       exit (1);
 129     }
 130
 131   old = (char *)mmap (0, stat.st_size, PROT_READ, MAP_FILE|MAP_SHARED, fd, 0);
 132   if (old == (char *)-1)
 133     {
 134       fprintf (stderr, "%s: ", a_name);
 135       perror ("mmap");
 136       exit (1);
 137     }
 138   close (fd);
 139
 140   nhdr = ohdr = (*(struct exec *)old);
 141
 142
 143   /*
 144    * Remember a magic cookie so we know we've got the right binary
 145    * when remapping.
 146    */
 147   cookie = time (0);
 148
 149   /* Save the break, it is reset to &_end (by ld.so?).  */
 150   brk_value = (unsigned) sbrk (0);
 151
 152   /*
 153    * Round up data start to a page boundary (Lose if not a 2 power!)
 154    */
 155   data_start = ((((int)&data_start) - 1) & ~(N_PAGSIZ (nhdr) - 1)) + N_PAGSIZ (nhdr);
 156
 157   /*
 158    * Round down read only pages to a multiple of the page size
 159    */
 160   if (bndry)
 161     rd_only_len = ((int)bndry & ~(N_PAGSIZ (nhdr) - 1)) - data_start;
 162
 163 #ifndef emacs
 164   /* Have to do this some time before dumping the data */
 165   initialized = 1;
 166 #endif
 167
 168   /* Handle new data and bss sizes and optional new entry point.
 169      No one actually uses bss_start and entry,  but tradition compels
 170      one to support them.
 171      Could complain if bss_start > brk_value,
 172      but the caller is *supposed* to know what she is doing.  */
 173   nhdr.a_data = (bss_start ? bss_start : brk_value) - N_DATADDR (nhdr);
 174   nhdr.a_bss  = bss_start ? brk_value - 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 #ifdef SUNOS4_SHARED_LIBRARIES
 220     extern struct link_dynamic _DYNAMIC;
 221
 222     /*  SunOS4.x's ld_rel is relative to N_TXTADDR. */
 223     if (!ohdr.a_dynamic)
 224       /* This was statically linked.  */
 225       rel = erel = 0;
 226     else if (_DYNAMIC.ld_version < 2)
 227       {
 228         rel = _DYNAMIC.ld_un.ld_1->ld_rel + N_TXTADDR (ohdr);
 229         erel = _DYNAMIC.ld_un.ld_1->ld_hash + N_TXTADDR (ohdr);
 230       }
 231     else
 232       {
 233         rel = _DYNAMIC.ld_un.ld_2->ld_rel + N_TXTADDR (ohdr);
 234         erel = _DYNAMIC.ld_un.ld_2->ld_hash + N_TXTADDR (ohdr);
 235       }
 236 #else /* not SUNOS4_SHARED_LIBRARIES */
 237     rel = erel = 0;
 238 #endif /* not SUNOS4_SHARED_LIBRARIES */
 239 #ifdef sparc
 240 #define REL_INFO_TYPE           struct reloc_info_sparc
 241 #else
 242 #define REL_INFO_TYPE           struct relocation_info
 243 #endif /* sparc */
 244 #define REL_TARGET_ADDRESS(r)   (((REL_INFO_TYPE *)(r))->r_address)
 245 #endif /* SUNOS4 */
 246 #if defined (__FreeBSD__) || defined (__NetBSD__)
 247     extern struct _dynamic _DYNAMIC;
 248
 249     /*  FreeBSD's LD_REL is a virtual address itself. */
 250     rel = LD_REL (&_DYNAMIC);
 251     erel = rel + LD_RELSZ (&_DYNAMIC);
 252 #define REL_INFO_TYPE           struct relocation_info
 253 #define REL_TARGET_ADDRESS(r)   (((REL_INFO_TYPE *)(r))->r_address)
 254 #endif
 255
 256     for (; rel < erel; rel += sizeof (REL_INFO_TYPE))
 257       {
 258         /*  This is the virtual address where ld.so will do relocation.  */
 259         unsigned long target = REL_TARGET_ADDRESS (rel);
 260         /*  This is the offset in the data segment.  */
 261         unsigned long segoffset = target - daddr;
 262
 263         /*  If it is located below data_start, we have to do nothing here,
 264             because the old data has been already written to the location. */
 265         if (target < (unsigned long)&data_start)
 266             continue;
 267
 268         lseek (new, N_DATOFF (nhdr) + segoffset, L_SET);
 269         write (new, old + N_DATOFF (ohdr) + segoffset, sizeof (unsigned long));
 270       }
 271   }
 272 #endif /* UNDO_RELOCATION */
 273
 274   fchmod (new, 0755);
 275 }
 276
 277 void
 278 run_time_remap (progname)
 279      char *progname;
 280 {
 281   char aout[MAXPATHLEN];
 282   register char *path, *p;
 283
 284   /* Just in case */
 285   if (!initialized)
 286     return;
 287
 288   /* Restore the break */
 289   brk ((char *) brk_value);
 290
 291   /*  If nothing to remap:  we are done! */
 292   if (rd_only_len == 0)
 293     return;
 294
 295   /*
 296    * Attempt to find the executable
 297    * First try argv[0],  will almost always succeed as shells tend to give
 298    * the full path from the hash list rather than using execvp ()
 299    */
 300   if (is_it (progname))
 301     return;
 302
 303   /*
 304    * If argv[0] is a full path and does not exist,  not much sense in
 305    * searching further
 306    */
 307   if (strchr (progname, '/'))
 308     return;
 309
 310   /*
 311    * Try to search for  argv[0] on the PATH
 312    */
 313   path = getenv ("PATH");
 314   if (path == NULL)
 315     return;
 316
 317   while (*path)
 318     {
 319       /* copy through ':' or end */
 320       for (p = aout; *p = *path; ++p, ++path)
 321         if (*p == ':')
 322           {
 323             ++path;             /* move past ':' */
 324             break;
 325           }
 326       *p++ = '/';
 327       strcpy (p, progname);
 328       /*
 329        * aout is a candidate full path name
 330        */
 331       if (is_it (aout))
 332         return;
 333     }
 334 }
 335
 336 is_it (filename)
 337   char *filename;
 338 {
 339   int fd;
 340   long filenames_cookie;
 341   struct exec hdr;
 342
 343   /*
 344    * Open an executable  and check for a valid header!
 345    * Can't bcmp the header with what we had,  it may have been stripped!
 346    * so we may save looking at non executables with the same name, mostly
 347    * directories.
 348    */
 349   fd = open (filename, O_RDONLY);
 350   if (fd != -1)
 351     {
 352       if (read (fd, &hdr, sizeof (hdr)) == sizeof (hdr)
 353           && !N_BADMAG (hdr) && N_DATOFF (hdr) == N_DATOFF (nhdr)
 354           && N_TRELOFF (hdr) == N_TRELOFF (nhdr))
 355         {
 356           /* compare cookies */
 357           lseek (fd, N_DATOFF (hdr) + (int)&cookie - N_DATADDR (hdr), L_SET);
 358           read (fd, &filenames_cookie, sizeof (filenames_cookie));
 359           if (filenames_cookie == cookie)
 360             {                   /* Eureka */
 361
 362               /*
 363                * Do the mapping
 364                * The PROT_EXEC may not be needed,  but it is safer this way.
 365                * should the shared library decide to indirect through
 366                * addresses in the data segment not part of __DYNAMIC
 367                */
 368               mmap ((char *) data_start, rd_only_len, PROT_READ | PROT_EXEC,
 369                     MAP_FILE | MAP_SHARED | MAP_FIXED, fd,
 370                     N_DATOFF (hdr) + data_start - N_DATADDR (hdr));
 371               close (fd);
 372               return 1;
 373             }
 374         }
 375       close (fd);
 376     }
 377   return 0;
 378 }