elf/dl-load.h

   1 /* Map in a shared object's segments from the file.
   2    Copyright (C) 1995-2017 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _DL_LOAD_H
  20 #define _DL_LOAD_H      1
  21
  22 #include <link.h>
  23 #include <sys/mman.h>
  24
  25
  26 /* On some systems, no flag bits are given to specify file mapping.  */
  27 #ifndef MAP_FILE
  28 # define MAP_FILE       0
  29 #endif
  30
  31 /* The right way to map in the shared library files is MAP_COPY, which
  32    makes a virtual copy of the data at the time of the mmap call; this
  33    guarantees the mapped pages will be consistent even if the file is
  34    overwritten.  Some losing VM systems like Linux's lack MAP_COPY.  All we
  35    get is MAP_PRIVATE, which copies each page when it is modified; this
  36    means if the file is overwritten, we may at some point get some pages
  37    from the new version after starting with pages from the old version.
  38
  39    To make up for the lack and avoid the overwriting problem,
  40    what Linux does have is MAP_DENYWRITE.  This prevents anyone
  41    from modifying the file while we have it mapped.  */
  42 #ifndef MAP_COPY
  43 # ifdef MAP_DENYWRITE
  44 #  define MAP_COPY      (MAP_PRIVATE | MAP_DENYWRITE)
  45 # else
  46 #  define MAP_COPY      MAP_PRIVATE
  47 # endif
  48 #endif
  49
  50 /* Some systems link their relocatable objects for another base address
  51    than 0.  We want to know the base address for these such that we can
  52    subtract this address from the segment addresses during mapping.
  53    This results in a more efficient address space usage.  Defaults to
  54    zero for almost all systems.  */
  55 #ifndef MAP_BASE_ADDR
  56 # define MAP_BASE_ADDR(l)       0
  57 #endif
  58
  59
  60 /* Handle situations where we have a preferred location in memory for
  61    the shared objects.  */
  62 #ifdef ELF_PREFERRED_ADDRESS_DATA
  63 ELF_PREFERRED_ADDRESS_DATA;
  64 #endif
  65 #ifndef ELF_PREFERRED_ADDRESS
  66 # define ELF_PREFERRED_ADDRESS(loader, maplength, mapstartpref) (mapstartpref)
  67 #endif
  68 #ifndef ELF_FIXED_ADDRESS
  69 # define ELF_FIXED_ADDRESS(loader, mapstart) ((void) 0)
  70 #endif
  71
  72
  73 /* This structure describes one PT_LOAD command.
  74    Its details have been expanded out and converted.  */
  75 struct loadcmd
  76 {
  77   ElfW(Addr) mapstart, mapend, dataend, allocend;
  78   ElfW(Off) mapoff;
  79   int prot;                             /* PROT_* bits.  */
  80 };
  81
  82
  83 /* This is a subroutine of _dl_map_segments.  It should be called for each
  84    load command, some time after L->l_addr has been set correctly.  It is
  85    responsible for setting up the l_text_end and l_phdr fields.  */
  86 static void __always_inline
  87 _dl_postprocess_loadcmd (struct link_map *l, const ElfW(Ehdr) *header,
  88                          const struct loadcmd *c)
  89 {
  90   if (c->prot & PROT_EXEC)
  91     l->l_text_end = l->l_addr + c->mapend;
  92
  93   if (l->l_phdr == 0
  94       && c->mapoff <= header->e_phoff
  95       && ((size_t) (c->mapend - c->mapstart + c->mapoff)
  96           >= header->e_phoff + header->e_phnum * sizeof (ElfW(Phdr))))
  97     /* Found the program header in this segment.  */
  98     l->l_phdr = (void *) (uintptr_t) (c->mapstart + header->e_phoff
  99                                       - c->mapoff);
 100 }
 101
 102
 103 /* This is a subroutine of _dl_map_object_from_fd.  It is responsible
 104    for filling in several fields in *L: l_map_start, l_map_end, l_addr,
 105    l_contiguous, l_text_end, l_phdr.  On successful return, all the
 106    segments are mapped (or copied, or whatever) from the file into their
 107    final places in the address space, with the correct page permissions,
 108    and any bss-like regions already zeroed.  It returns a null pointer
 109    on success, or an error message string (to be translated) on error
 110    (having also set errno).
 111
 112    The file <dl-map-segments.h> defines this function.  The canonical
 113    implementation in elf/dl-map-segments.h might be replaced by a sysdeps
 114    version.  */
 115 static const char *_dl_map_segments (struct link_map *l, int fd,
 116                                      const ElfW(Ehdr) *header, int type,
 117                                      const struct loadcmd loadcmds[],
 118                                      size_t nloadcmds,
 119                                      const size_t maplength,
 120                                      bool has_holes,
 121                                      struct link_map *loader);
 122
 123 /* All the error message strings _dl_map_segments might return are
 124    listed here so that different implementations in different sysdeps
 125    dl-map-segments.h files all use consistent strings that are
 126    guaranteed to have translations.  */
 127 #define DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT \
 128   N_("failed to map segment from shared object")
 129 #define DL_MAP_SEGMENTS_ERROR_MPROTECT \
 130   N_("cannot change memory protections")
 131 #define DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL \
 132   N_("cannot map zero-fill pages")
 133
 134
 135 #endif  /* dl-load.h */