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 int _dl_zerofd = -1;
  63
  64
  65 /* Try to open NAME in one of the directories in DIRPATH.
  66    Return the fd, or -1.  If successful, fill in *REALNAME
  67    with the malloc'd full directory name.  */
  68
  69 static int
  70 open_path (const char *name, size_t namelen,
  71            const char *dirpath,
  72            char **realname)
  73 {
  74   char *buf;
  75   const char *p;
  76   int fd;
  77
  78   p = dirpath;
  79   if (p == NULL || *p == '\0')
  80     {
  81       errno = ENOENT;
  82       return -1;
  83     }
  84
  85   buf = alloca (strlen (dirpath) + 1 + namelen);
  86   do
  87     {
  88       dirpath = p;
  89       p = strpbrk (dirpath, ":;");
  90       if (p == NULL)
  91         p = strchr (dirpath, '\0');
  92
  93       if (p == dirpath)
  94         /* Two adjacent colons, or a colon at the beginning or the end of
  95            the path means to search the current directory.  */
  96         (void) memcpy (buf, name, namelen);
  97       else
  98         {
  99           /* Construct the pathname to try.  */
 100           (void) memcpy (buf, dirpath, p - dirpath);
 101           buf[p - dirpath] = '/';
 102           (void) memcpy (&buf[(p - dirpath) + 1], name, namelen);
 103         }
 104
 105       fd = open (buf, O_RDONLY);
 106       if (fd != -1)
 107         {
 108           *realname = strdup (buf);
 109           return fd;
 110         }
 111       if (errno != ENOENT && errno != EACCES)
 112         /* The file exists and is readable, but something went wrong.  */
 113         return -1;
 114     }
 115   while (*p++ != '\0');
 116
 117   return -1;
 118 }
 119
 120
 121 /* Map in the shared object file NAME.  */
 122
 123 struct link_map *
 124 _dl_map_object (struct link_map *loader, const char *name)
 125 {
 126   int fd;
 127   char *realname;
 128   struct link_map *l;
 129
 130   /* Look for this name among those already loaded.  */
 131   for (l = _dl_loaded; l; l = l->l_next)
 132     if (! strcmp (name, l->l_libname))
 133       {
 134         /* The object is already loaded.
 135            Just bump its reference count and return it.  */
 136         ++l->l_opencount;
 137         return l;
 138       }
 139
 140   if (strchr (name, '/') == NULL)
 141     {
 142       /* Search for NAME in several places.  */
 143
 144       size_t namelen = strlen (name) + 1;
 145
 146       inline void trypath (const char *dirpath)
 147         {
 148           fd = open_path (name, namelen, dirpath, &realname);
 149         }
 150
 151       fd = -1;
 152       if (loader && loader->l_info[DT_RPATH])
 153         trypath ((const char *) (loader->l_addr +
 154                                  loader->l_info[DT_STRTAB]->d_un.d_ptr +
 155                                  loader->l_info[DT_RPATH]->d_un.d_val));
 156       if (fd == -1 && ! _dl_secure)
 157         trypath (getenv ("LD_LIBRARY_PATH"));
 158       if (fd == -1)
 159         {
 160           extern const char *_dl_rpath; /* Set in rtld.c. */
 161           trypath (_dl_rpath);
 162         }
 163     }
 164   else
 165     {
 166       fd = open (name, O_RDONLY);
 167       if (fd != -1)
 168         realname = strdup (name);
 169     }
 170
 171   if (fd == -1)
 172     _dl_signal_error (errno, name, "cannot open shared object file");
 173
 174   return _dl_map_object_from_fd (name, fd, realname);
 175 }
 176
 177
 178 /* Map in the shared object NAME, actually located in REALNAME, and already
 179    opened on FD.  */
 180
 181 struct link_map *
 182 _dl_map_object_from_fd (const char *name, int fd, char *realname)
 183 {
 184   struct link_map *l = NULL;
 185   const size_t pagesize = getpagesize ();
 186   void *file_mapping = NULL;
 187   size_t mapping_size = 0;
 188
 189 #define LOSE(s) lose (0, (s))
 190   void lose (int code, const char *msg)
 191     {
 192       (void) close (fd);
 193       if (file_mapping)
 194         munmap (file_mapping, mapping_size);
 195       _dl_signal_error (code, l ? l->l_name : name, msg);
 196     }
 197
 198   inline caddr_t map_segment (Elf32_Addr mapstart, size_t len,
 199                               int prot, int fixed, off_t offset)
 200     {
 201       caddr_t mapat = mmap ((caddr_t) mapstart, len, prot,
 202                             fixed|MAP_COPY|MAP_FILE,
 203                             fd, offset);
 204       if (mapat == (caddr_t) -1)
 205         lose (errno, "failed to map segment from shared object");
 206       return mapat;
 207     }
 208
 209   /* Make sure LOCATION is mapped in.  */
 210   void *map (off_t location, size_t size)
 211     {
 212       if ((off_t) mapping_size <= location + (off_t) size)
 213         {
 214           void *result;
 215           if (file_mapping)
 216             munmap (file_mapping, mapping_size);
 217           mapping_size = (location + size + 1 + pagesize - 1);
 218           mapping_size &= ~(pagesize - 1);
 219           result = mmap (file_mapping, mapping_size, PROT_READ,
 220                          MAP_COPY|MAP_FILE, fd, 0);
 221           if (result == (void *) -1)
 222             lose (errno, "cannot map file data");
 223           file_mapping = result;
 224         }
 225       return file_mapping + location;
 226     }
 227
 228   const Elf32_Ehdr *header;
 229   const Elf32_Phdr *phdr;
 230   const Elf32_Phdr *ph;
 231   int type;
 232
 233   /* Look again to see if the real name matched another already loaded.  */
 234   for (l = _dl_loaded; l; l = l->l_next)
 235     if (! strcmp (realname, l->l_name))
 236       {
 237         /* The object is already loaded.
 238            Just bump its reference count and return it.  */
 239         close (fd);
 240         free (realname);
 241         ++l->l_opencount;
 242         return l;
 243       }
 244
 245   /* Map in the first page to read the header.  */
 246   header = map (0, sizeof *header);
 247
 248   /* Check the header for basic validity.  */
 249   if (*(Elf32_Word *) &header->e_ident !=
 250 #if BYTE_ORDER == LITTLE_ENDIAN
 251       ((ELFMAG0 << (EI_MAG0 * 8)) |
 252        (ELFMAG1 << (EI_MAG1 * 8)) |
 253        (ELFMAG2 << (EI_MAG2 * 8)) |
 254        (ELFMAG3 << (EI_MAG3 * 8)))
 255 #else
 256       ((ELFMAG0 << (EI_MAG3 * 8)) |
 257        (ELFMAG1 << (EI_MAG2 * 8)) |
 258        (ELFMAG2 << (EI_MAG1 * 8)) |
 259        (ELFMAG3 << (EI_MAG0 * 8)))
 260 #endif
 261       )
 262     LOSE ("invalid ELF header");
 263   if (header->e_ident[EI_CLASS] != ELFCLASS32)
 264     LOSE ("ELF file class not 32-bit");
 265   if (header->e_ident[EI_DATA] != byteorder)
 266     LOSE ("ELF file data encoding not " byteorder_name);
 267   if (header->e_ident[EI_VERSION] != EV_CURRENT)
 268     LOSE ("ELF file version ident not " STRING(EV_CURRENT));
 269   if (header->e_version != EV_CURRENT)
 270     LOSE ("ELF file version not " STRING(EV_CURRENT));
 271   if (! elf_machine_matches_host (header->e_machine))
 272     LOSE ("ELF file machine architecture not " ELF_MACHINE_NAME);
 273   if (header->e_phentsize != sizeof (Elf32_Phdr))
 274     LOSE ("ELF file's phentsize not the expected size");
 275
 276   /* Enter the new object in the list of loaded objects.  */
 277   l = _dl_new_object (realname, name, lt_loaded);
 278   l->l_opencount = 1;
 279
 280   if (_dl_zerofd == -1)
 281     {
 282       _dl_zerofd = _dl_sysdep_open_zero_fill ();
 283       if (_dl_zerofd == -1)
 284         _dl_signal_error (errno, NULL, "cannot open zero fill device");
 285     }
 286
 287   /* Extract the remaining details we need from the ELF header
 288      and then map in the program header table.  */
 289   l->l_entry = header->e_entry;
 290   type = header->e_type;
 291   l->l_phnum = header->e_phnum;
 292   phdr = map (header->e_phoff, l->l_phnum * sizeof (Elf32_Phdr));
 293
 294   {
 295     /* Scan the program header table, collecting its load commands.  */
 296     struct loadcmd
 297       {
 298         Elf32_Addr mapstart, mapend, dataend, allocend;
 299         off_t mapoff;
 300         int prot;
 301       } loadcmds[l->l_phnum], *c;
 302     size_t nloadcmds = 0;
 303
 304     l->l_ld = 0;
 305     l->l_phdr = 0;
 306     l->l_addr = 0;
 307     for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
 308       switch (ph->p_type)
 309         {
 310           /* These entries tell us where to find things once the file's
 311              segments are mapped in.  We record the addresses it says
 312              verbatim, and later correct for the run-time load address.  */
 313         case PT_DYNAMIC:
 314           l->l_ld = (void *) ph->p_vaddr;
 315           break;
 316         case PT_PHDR:
 317           l->l_phdr = (void *) ph->p_vaddr;
 318           break;
 319
 320         case PT_LOAD:
 321           /* A load command tells us to map in part of the file.
 322              We record the load commands and process them all later.  */
 323           if (ph->p_align % pagesize != 0)
 324             LOSE ("ELF load command alignment not page-aligned");
 325           if ((ph->p_vaddr - ph->p_offset) % ph->p_align)
 326             LOSE ("ELF load command address/offset not properly aligned");
 327           {
 328             struct loadcmd *c = &loadcmds[nloadcmds++];
 329             c->mapstart = ph->p_vaddr & ~(ph->p_align - 1);
 330             c->mapend = ((ph->p_vaddr + ph->p_filesz + pagesize - 1)
 331                          & ~(pagesize - 1));
 332             c->dataend = ph->p_vaddr + ph->p_filesz;
 333             c->allocend = ph->p_vaddr + ph->p_memsz;
 334             c->mapoff = ph->p_offset & ~(ph->p_align - 1);
 335             c->prot = 0;
 336             if (ph->p_flags & PF_R)
 337               c->prot |= PROT_READ;
 338             if (ph->p_flags & PF_W)
 339               c->prot |= PROT_WRITE;
 340             if (ph->p_flags & PF_X)
 341               c->prot |= PROT_EXEC;
 342             break;
 343           }
 344         }
 345
 346     /* We are done reading the file's headers now.  Unmap them.  */
 347     munmap (file_mapping, mapping_size);
 348
 349     /* Now process the load commands and map segments into memory.  */
 350     c = loadcmds;
 351
 352     if (type == ET_DYN || type == ET_REL)
 353       {
 354         /* This is a position-independent shared object.  We can let the
 355            kernel map it anywhere it likes, but we must have space for all
 356            the segments in their specified positions relative to the first.
 357            So we map the first segment without MAP_FIXED, but with its
 358            extent increased to cover all the segments.  Then we remove
 359            access from excess portion, and there is known sufficient space
 360            there to remap from the later segments.  */
 361         caddr_t mapat;
 362         mapat = map_segment (c->mapstart,
 363                              loadcmds[nloadcmds - 1].allocend - c->mapstart,
 364                              c->prot, 0, c->mapoff);
 365         l->l_addr = (Elf32_Addr) mapat - c->mapstart;
 366
 367         /* Change protection on the excess portion to disallow all access;
 368            the portions we do not remap later will be inaccessible as if
 369            unallocated.  Then jump into the normal segment-mapping loop to
 370            handle the portion of the segment past the end of the file
 371            mapping.  */
 372         mprotect (mapat + c->mapend,
 373                   loadcmds[nloadcmds - 1].allocend - c->mapend,
 374                   0);
 375         goto postmap;
 376       }
 377
 378     while (c < &loadcmds[nloadcmds])
 379       {
 380         if (c->mapend > c->mapstart)
 381           /* Map the segment contents from the file.  */
 382           map_segment (l->l_addr + c->mapstart, c->mapend - c->mapstart,
 383                        c->prot, MAP_FIXED, c->mapoff);
 384
 385       postmap:
 386         if (c->allocend > c->dataend)
 387           {
 388             /* Extra zero pages should appear at the end of this segment,
 389                after the data mapped from the file.   */
 390             Elf32_Addr zero, zeroend, zeropage;
 391
 392             zero = l->l_addr + c->dataend;
 393             zeroend = l->l_addr + c->allocend;
 394             zeropage = (zero + pagesize - 1) & ~(pagesize - 1);
 395
 396             if (zeroend < zeropage)
 397               /* All the extra data is in the last page of the segment.
 398                  We can just zero it.  */
 399               zeropage = zeroend;
 400
 401             if (zeropage > zero)
 402               {
 403                 /* Zero the final part of the last page of the segment.  */
 404                 if ((c->prot & PROT_WRITE) == 0)
 405                   {
 406                     /* Dag nab it.  */
 407                     if (mprotect ((caddr_t) (zero & ~(pagesize - 1)),
 408                                   pagesize, c->prot|PROT_WRITE) < 0)
 409                       lose (errno, "cannot change memory protections");
 410                   }
 411                 memset ((void *) zero, 0, zeropage - zero);
 412                 if ((c->prot & PROT_WRITE) == 0)
 413                   mprotect ((caddr_t) (zero & ~(pagesize - 1)),
 414                             pagesize, c->prot);
 415               }
 416
 417             if (zeroend > zeropage)
 418               {
 419                 /* Map the remaining zero pages in from the zero fill FD.  */
 420                 caddr_t mapat;
 421                 mapat = mmap ((caddr_t) zeropage, zeroend - zeropage, c->prot,
 422                               MAP_ANON|MAP_PRIVATE|MAP_FIXED,
 423                               _dl_zerofd, 0);
 424                 if (mapat == (caddr_t) -1)
 425                   lose (errno, "cannot map zero-fill pages");
 426               }
 427           }
 428
 429         ++c;
 430       }
 431   }
 432
 433   l->l_type = type == ET_EXEC ? lt_executable : lt_library;
 434
 435   if (l->l_ld == 0)
 436     {
 437       if (type == ET_DYN)
 438         LOSE ("object file has no dynamic section");
 439     }
 440   else
 441     (Elf32_Addr) l->l_ld += l->l_addr;
 442
 443   if (l->l_phdr == 0)
 444     l->l_phdr = (void *) ((const Elf32_Ehdr *) l->l_addr)->e_phoff;
 445   (Elf32_Addr) l->l_phdr += l->l_addr;
 446
 447   elf_get_dynamic_info (l->l_ld, l->l_info);
 448   if (l->l_info[DT_HASH])
 449     _dl_setup_hash (l);
 450
 451   return l;
 452 }