elf/dl-load.c

   1 /* _dl_map_object -- Map in a shared object's segments from the file.
   2 Copyright (C) 1995, 1996 Free Software Foundation, Inc.
   3 This file is part of the GNU C Library.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 License, or (at your option) any later version.
   9
  10 The GNU C Library is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <link.h>
  21 #include <sys/types.h>
  22 #include <sys/mman.h>
  23 #include <string.h>
  24 #include <fcntl.h>
  25 #include <unistd.h>
  26 #include <stdlib.h>
  27 #include <errno.h>
  28 #include "dynamic-link.h"
  29
  30
  31 /* On some systems, no flag bits are given to specify file mapping.  */
  32 #ifndef MAP_FILE
  33 #define MAP_FILE        0
  34 #endif
  35
  36 /* The right way to map in the shared library files is MAP_COPY, which
  37    makes a virtual copy of the data at the time of the mmap call; this
  38    guarantees the mapped pages will be consistent even if the file is
  39    overwritten.  Some losing VM systems like Linux's lack MAP_COPY.  All we
  40    get is MAP_PRIVATE, which copies each page when it is modified; this
  41    means if the file is overwritten, we may at some point get some pages
  42    from the new version after starting with pages from the old version.  */
  43 #ifndef MAP_COPY
  44 #define MAP_COPY        MAP_PRIVATE
  45 #endif
  46
  47
  48 #include <endian.h>
  49 #if BYTE_ORDER == BIG_ENDIAN
  50 #define byteorder ELFDATA2MSB
  51 #define byteorder_name "big-endian"
  52 #elif BYTE_ORDER == LITTLE_ENDIAN
  53 #define byteorder ELFDATA2LSB
  54 #define byteorder_name "little-endian"
  55 #else
  56 #error "Unknown BYTE_ORDER " BYTE_ORDER
  57 #define byteorder ELFDATANONE
  58 #endif
  59
  60 #define STRING(x) #x
  61
  62 #ifdef MAP_ANON
  63 /* The fd is not examined when using MAP_ANON.  */
  64 #define ANONFD -1
  65 #else
  66 int _dl_zerofd = -1;
  67 #define ANONFD _dl_zerofd
  68 #endif
  69
  70 size_t _dl_pagesize;
  71
  72
  73 /* Map in the shared object NAME, actually located in REALNAME, and already
  74    opened on FD.  */
  75
  76 struct link_map *
  77 _dl_map_object_from_fd (const char *name, int fd, char *realname,
  78                         struct link_map *loader, int l_type)
  79 {
  80   struct link_map *l = NULL;
  81   void *file_mapping = NULL;
  82   size_t mapping_size = 0;
  83
  84 #define LOSE(s) lose (0, (s))
  85   void lose (int code, const char *msg)
  86     {
  87       (void) __close (fd);
  88       if (file_mapping)
  89         __munmap (file_mapping, mapping_size);
  90       if (l)
  91         {
  92           /* Remove the stillborn object from the list and free it.  */
  93           if (l->l_prev)
  94             l->l_prev->l_next = l->l_next;
  95           if (l->l_next)
  96             l->l_next->l_prev = l->l_prev;
  97           free (l);
  98         }
  99       free (realname);
 100       _dl_signal_error (code, name, msg);
 101     }
 102
 103   inline caddr_t map_segment (ElfW(Addr) mapstart, size_t len,
 104                               int prot, int fixed, off_t offset)
 105     {
 106       caddr_t mapat = __mmap ((caddr_t) mapstart, len, prot,
 107                               fixed|MAP_COPY|MAP_FILE,
 108                               fd, offset);
 109       if (mapat == (caddr_t) -1)
 110         lose (errno, "failed to map segment from shared object");
 111       return mapat;
 112     }
 113
 114   /* Make sure LOCATION is mapped in.  */
 115   void *map (off_t location, size_t size)
 116     {
 117       if ((off_t) mapping_size <= location + (off_t) size)
 118         {
 119           void *result;
 120           if (file_mapping)
 121             __munmap (file_mapping, mapping_size);
 122           mapping_size = (location + size + 1 + _dl_pagesize - 1);
 123           mapping_size &= ~(_dl_pagesize - 1);
 124           result = __mmap (file_mapping, mapping_size, PROT_READ,
 125                            MAP_COPY|MAP_FILE, fd, 0);
 126           if (result == (void *) -1)
 127             lose (errno, "cannot map file data");
 128           file_mapping = result;
 129         }
 130       return file_mapping + location;
 131     }
 132
 133   const ElfW(Ehdr) *header;
 134   const ElfW(Phdr) *phdr;
 135   const ElfW(Phdr) *ph;
 136   int type;
 137
 138   /* Look again to see if the real name matched another already loaded.  */
 139   for (l = _dl_loaded; l; l = l->l_next)
 140     if (! strcmp (realname, l->l_name))
 141       {
 142         /* The object is already loaded.
 143            Just bump its reference count and return it.  */
 144         __close (fd);
 145         free (realname);
 146         ++l->l_opencount;
 147         return l;
 148       }
 149
 150   if (_dl_pagesize == 0)
 151     _dl_pagesize = __getpagesize ();
 152
 153   /* Map in the first page to read the header.  */
 154   header = map (0, sizeof *header);
 155
 156   /* Check the header for basic validity.  */
 157   if (*(Elf32_Word *) &header->e_ident !=
 158 #if BYTE_ORDER == LITTLE_ENDIAN
 159       ((ELFMAG0 << (EI_MAG0 * 8)) |
 160        (ELFMAG1 << (EI_MAG1 * 8)) |
 161        (ELFMAG2 << (EI_MAG2 * 8)) |
 162        (ELFMAG3 << (EI_MAG3 * 8)))
 163 #else
 164       ((ELFMAG0 << (EI_MAG3 * 8)) |
 165        (ELFMAG1 << (EI_MAG2 * 8)) |
 166        (ELFMAG2 << (EI_MAG1 * 8)) |
 167        (ELFMAG3 << (EI_MAG0 * 8)))
 168 #endif
 169       )
 170     LOSE ("invalid ELF header");
 171 #define ELF32_CLASS ELFCLASS32
 172 #define ELF64_CLASS ELFCLASS64
 173   if (header->e_ident[EI_CLASS] != ELFW(CLASS))
 174     LOSE ("ELF file class not " STRING(__ELF_WORDSIZE) "-bit");
 175   if (header->e_ident[EI_DATA] != byteorder)
 176     LOSE ("ELF file data encoding not " byteorder_name);
 177   if (header->e_ident[EI_VERSION] != EV_CURRENT)
 178     LOSE ("ELF file version ident not " STRING(EV_CURRENT));
 179   if (header->e_version != EV_CURRENT)
 180     LOSE ("ELF file version not " STRING(EV_CURRENT));
 181   if (! elf_machine_matches_host (header->e_machine))
 182     LOSE ("ELF file machine architecture not " ELF_MACHINE_NAME);
 183   if (header->e_phentsize != sizeof (ElfW(Phdr)))
 184     LOSE ("ELF file's phentsize not the expected size");
 185
 186 #ifndef MAP_ANON
 187 #define MAP_ANON 0
 188   if (_dl_zerofd == -1)
 189     {
 190       _dl_zerofd = _dl_sysdep_open_zero_fill ();
 191       if (_dl_zerofd == -1)
 192         {
 193           __close (fd);
 194           _dl_signal_error (errno, NULL, "cannot open zero fill device");
 195         }
 196     }
 197 #endif
 198
 199   /* Enter the new object in the list of loaded objects.  */
 200   l = _dl_new_object (realname, name, l_type);
 201   if (! l)
 202     lose (ENOMEM, "cannot create shared object descriptor");
 203   l->l_opencount = 1;
 204   l->l_loader = loader;
 205
 206   /* Extract the remaining details we need from the ELF header
 207      and then map in the program header table.  */
 208   l->l_entry = header->e_entry;
 209   type = header->e_type;
 210   l->l_phnum = header->e_phnum;
 211   phdr = map (header->e_phoff, l->l_phnum * sizeof (ElfW(Phdr)));
 212
 213   {
 214     /* Scan the program header table, collecting its load commands.  */
 215     struct loadcmd
 216       {
 217         ElfW(Addr) mapstart, mapend, dataend, allocend;
 218         off_t mapoff;
 219         int prot;
 220       } loadcmds[l->l_phnum], *c;
 221     size_t nloadcmds = 0;
 222
 223     l->l_ld = 0;
 224     l->l_phdr = 0;
 225     l->l_addr = 0;
 226     for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
 227       switch (ph->p_type)
 228         {
 229           /* These entries tell us where to find things once the file's
 230              segments are mapped in.  We record the addresses it says
 231              verbatim, and later correct for the run-time load address.  */
 232         case PT_DYNAMIC:
 233           l->l_ld = (void *) ph->p_vaddr;
 234           break;
 235         case PT_PHDR:
 236           l->l_phdr = (void *) ph->p_vaddr;
 237           break;
 238
 239         case PT_LOAD:
 240           /* A load command tells us to map in part of the file.
 241              We record the load commands and process them all later.  */
 242           if (ph->p_align % _dl_pagesize != 0)
 243             LOSE ("ELF load command alignment not page-aligned");
 244           if ((ph->p_vaddr - ph->p_offset) % ph->p_align)
 245             LOSE ("ELF load command address/offset not properly aligned");
 246           {
 247             struct loadcmd *c = &loadcmds[nloadcmds++];
 248             c->mapstart = ph->p_vaddr & ~(ph->p_align - 1);
 249             c->mapend = ((ph->p_vaddr + ph->p_filesz + _dl_pagesize - 1)
 250                          & ~(_dl_pagesize - 1));
 251             c->dataend = ph->p_vaddr + ph->p_filesz;
 252             c->allocend = ph->p_vaddr + ph->p_memsz;
 253             c->mapoff = ph->p_offset & ~(ph->p_align - 1);
 254             c->prot = 0;
 255             if (ph->p_flags & PF_R)
 256               c->prot |= PROT_READ;
 257             if (ph->p_flags & PF_W)
 258               c->prot |= PROT_WRITE;
 259             if (ph->p_flags & PF_X)
 260               c->prot |= PROT_EXEC;
 261             break;
 262           }
 263         }
 264
 265     /* We are done reading the file's headers now.  Unmap them.  */
 266     __munmap (file_mapping, mapping_size);
 267
 268     /* Now process the load commands and map segments into memory.  */
 269     c = loadcmds;
 270
 271     if (type == ET_DYN || type == ET_REL)
 272       {
 273         /* This is a position-independent shared object.  We can let the
 274            kernel map it anywhere it likes, but we must have space for all
 275            the segments in their specified positions relative to the first.
 276            So we map the first segment without MAP_FIXED, but with its
 277            extent increased to cover all the segments.  Then we remove
 278            access from excess portion, and there is known sufficient space
 279            there to remap from the later segments.  */
 280         caddr_t mapat;
 281         mapat = map_segment (c->mapstart,
 282                              loadcmds[nloadcmds - 1].allocend - c->mapstart,
 283                              c->prot, 0, c->mapoff);
 284         l->l_addr = (ElfW(Addr)) mapat - c->mapstart;
 285
 286         /* Change protection on the excess portion to disallow all access;
 287            the portions we do not remap later will be inaccessible as if
 288            unallocated.  Then jump into the normal segment-mapping loop to
 289            handle the portion of the segment past the end of the file
 290            mapping.  */
 291         __mprotect ((caddr_t) (l->l_addr + c->mapend),
 292                     loadcmds[nloadcmds - 1].allocend - c->mapend,
 293                     0);
 294         goto postmap;
 295       }
 296
 297     while (c < &loadcmds[nloadcmds])
 298       {
 299         if (c->mapend > c->mapstart)
 300           /* Map the segment contents from the file.  */
 301           map_segment (l->l_addr + c->mapstart, c->mapend - c->mapstart,
 302                        c->prot, MAP_FIXED, c->mapoff);
 303
 304       postmap:
 305         if (c->allocend > c->dataend)
 306           {
 307             /* Extra zero pages should appear at the end of this segment,
 308                after the data mapped from the file.   */
 309             ElfW(Addr) zero, zeroend, zeropage;
 310
 311             zero = l->l_addr + c->dataend;
 312             zeroend = l->l_addr + c->allocend;
 313             zeropage = (zero + _dl_pagesize - 1) & ~(_dl_pagesize - 1);
 314
 315             if (zeroend < zeropage)
 316               /* All the extra data is in the last page of the segment.
 317                  We can just zero it.  */
 318               zeropage = zeroend;
 319
 320             if (zeropage > zero)
 321               {
 322                 /* Zero the final part of the last page of the segment.  */
 323                 if ((c->prot & PROT_WRITE) == 0)
 324                   {
 325                     /* Dag nab it.  */
 326                     if (__mprotect ((caddr_t) (zero & ~(_dl_pagesize - 1)),
 327                                     _dl_pagesize, c->prot|PROT_WRITE) < 0)
 328                       lose (errno, "cannot change memory protections");
 329                   }
 330                 memset ((void *) zero, 0, zeropage - zero);
 331                 if ((c->prot & PROT_WRITE) == 0)
 332                   __mprotect ((caddr_t) (zero & ~(_dl_pagesize - 1)),
 333                               _dl_pagesize, c->prot);
 334               }
 335
 336             if (zeroend > zeropage)
 337               {
 338                 /* Map the remaining zero pages in from the zero fill FD.  */
 339                 caddr_t mapat;
 340                 mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage,
 341                                 c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
 342                                 ANONFD, 0);
 343                 if (mapat == (caddr_t) -1)
 344                   lose (errno, "cannot map zero-fill pages");
 345               }
 346           }
 347
 348         ++c;
 349       }
 350
 351     if (l->l_phdr == 0)
 352       {
 353         /* There was no PT_PHDR specified.  We need to find the phdr in the
 354            load image ourselves.  We assume it is in fact in the load image
 355            somewhere, and that the first load command starts at the
 356            beginning of the file and thus contains the ELF file header.  */
 357         ElfW(Addr) bof = l->l_addr + loadcmds[0].mapstart;
 358         assert (loadcmds[0].mapoff == 0);
 359         l->l_phdr = (void *) (bof + ((const ElfW(Ehdr) *) bof)->e_phoff);
 360       }
 361     else
 362       /* Adjust the PT_PHDR value by the runtime load address.  */
 363       (ElfW(Addr)) l->l_phdr += l->l_addr;
 364   }
 365
 366   /* We are done mapping in the file.  We no longer need the descriptor.  */
 367   __close (fd);
 368
 369   if (l->l_type == lt_library && type == ET_EXEC)
 370     l->l_type = lt_executable;
 371
 372   if (l->l_ld == 0)
 373     {
 374       if (type == ET_DYN)
 375         LOSE ("object file has no dynamic section");
 376     }
 377   else
 378     (ElfW(Addr)) l->l_ld += l->l_addr;
 379
 380   l->l_entry += l->l_addr;
 381
 382   elf_get_dynamic_info (l->l_ld, l->l_info);
 383   if (l->l_info[DT_HASH])
 384     _dl_setup_hash (l);
 385
 386   return l;
 387 }
 388 \f
 389 /* Try to open NAME in one of the directories in DIRPATH.
 390    Return the fd, or -1.  If successful, fill in *REALNAME
 391    with the malloc'd full directory name.  */
 392
 393 static int
 394 open_path (const char *name, size_t namelen,
 395            const char *dirpath,
 396            char **realname)
 397 {
 398   char *buf;
 399   const char *p;
 400   int fd;
 401
 402   p = dirpath;
 403   if (p == NULL || *p == '\0')
 404     {
 405       errno = ENOENT;
 406       return -1;
 407     }
 408
 409   buf = __alloca (strlen (dirpath) + 1 + namelen);
 410   do
 411     {
 412       size_t buflen;
 413
 414       dirpath = p;
 415       p = strpbrk (dirpath, ":;");
 416       if (p == NULL)
 417         p = strchr (dirpath, '\0');
 418
 419       if (p == dirpath)
 420         {
 421           /* Two adjacent colons, or a colon at the beginning or the end of
 422              the path means to search the current directory.  */
 423           (void) memcpy (buf, name, namelen);
 424           buflen = namelen;
 425         }
 426       else
 427         {
 428           /* Construct the pathname to try.  */
 429           (void) memcpy (buf, dirpath, p - dirpath);
 430           buf[p - dirpath] = '/';
 431           (void) memcpy (&buf[(p - dirpath) + 1], name, namelen);
 432           buflen = p - dirpath + 1 + namelen;
 433         }
 434
 435       fd = __open (buf, O_RDONLY);
 436       if (fd != -1)
 437         {
 438           *realname = malloc (buflen);
 439           if (*realname)
 440             {
 441               memcpy (*realname, buf, buflen);
 442               return fd;
 443             }
 444           else
 445             {
 446               /* No memory for the name, we certainly won't be able
 447                  to load and link it.  */
 448               __close (fd);
 449               return -1;
 450             }
 451         }
 452       if (errno != ENOENT && errno != EACCES)
 453         /* The file exists and is readable, but something went wrong.  */
 454         return -1;
 455     }
 456   while (*p++ != '\0');
 457
 458   return -1;
 459 }
 460
 461 /* Map in the shared object file NAME.  */
 462
 463 struct link_map *
 464 _dl_map_object (struct link_map *loader, const char *name, int type)
 465 {
 466   int fd;
 467   char *realname;
 468   struct link_map *l;
 469
 470   /* Look for this name among those already loaded.  */
 471   for (l = _dl_loaded; l; l = l->l_next)
 472     if (! strcmp (name, l->l_libname) || /* NAME was requested before.  */
 473         ! strcmp (name, l->l_name) || /* NAME was found before.  */
 474         /* If the requested name matches the soname of a loaded object,
 475            use that object.  */
 476         (l->l_info[DT_SONAME] &&
 477          ! strcmp (name, (const char *) (l->l_addr +
 478                                          l->l_info[DT_STRTAB]->d_un.d_ptr +
 479                                          l->l_info[DT_SONAME]->d_un.d_val))))
 480       {
 481         /* The object is already loaded.
 482            Just bump its reference count and return it.  */
 483         ++l->l_opencount;
 484         return l;
 485       }
 486
 487   if (strchr (name, '/') == NULL)
 488     {
 489       /* Search for NAME in several places.  */
 490
 491       size_t namelen = strlen (name) + 1;
 492
 493       inline void trypath (const char *dirpath)
 494         {
 495           fd = open_path (name, namelen, dirpath, &realname);
 496         }
 497
 498       fd = -1;
 499
 500       /* First try the DT_RPATH of the dependent object that caused NAME
 501          to be loaded.  Then that object's dependent, and on up.  */
 502       for (l = loader; fd == -1 && l; l = l->l_loader)
 503         if (l && l->l_info[DT_RPATH])
 504           trypath ((const char *) (l->l_addr +
 505                                    l->l_info[DT_STRTAB]->d_un.d_ptr +
 506                                    l->l_info[DT_RPATH]->d_un.d_val));
 507       /* If dynamically linked, try the DT_RPATH of the executable itself.  */
 508       l = _dl_loaded;
 509       if (fd == -1 && l && l->l_type != lt_loaded && l->l_info[DT_RPATH])
 510         trypath ((const char *) (l->l_addr +
 511                                  l->l_info[DT_STRTAB]->d_un.d_ptr +
 512                                  l->l_info[DT_RPATH]->d_un.d_val));
 513       /* Try an environment variable (unless setuid).  */
 514       if (fd == -1 && ! _dl_secure)
 515         trypath (getenv ("LD_LIBRARY_PATH"));
 516       /* Finally, try the default path.  */
 517       if (fd == -1)
 518         {
 519           extern const char *_dl_rpath; /* Set in rtld.c. */
 520           trypath (_dl_rpath);
 521         }
 522     }
 523   else
 524     {
 525       fd = __open (name, O_RDONLY);
 526       if (fd != -1)
 527         {
 528           size_t len = strlen (name) + 1;
 529           realname = malloc (len);
 530           if (realname)
 531             memcpy (realname, name, len);
 532           else
 533             {
 534               __close (fd);
 535               fd = -1;
 536             }
 537         }
 538     }
 539
 540   if (fd == -1)
 541     _dl_signal_error (errno, name, "cannot open shared object file");
 542
 543   return _dl_map_object_from_fd (name, fd, realname, loader, type);
 544 }