elf/setup-vdso.h

   1 /* Set up the data structures for the system-supplied DSO.
   2    Copyright (C) 2012-2020 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    <https://www.gnu.org/licenses/>.  */
  18
  19 static inline void __attribute__ ((always_inline))
  20 setup_vdso (struct link_map *main_map __attribute__ ((unused)),
  21             struct link_map ***first_preload __attribute__ ((unused)))
  22 {
  23 #ifdef NEED_DL_SYSINFO_DSO
  24   if (GLRO(dl_sysinfo_dso) == NULL)
  25     return;
  26
  27   /* Do an abridged version of the work _dl_map_object_from_fd would do
  28      to map in the object.  It's already mapped and prelinked (and
  29      better be, since it's read-only and so we couldn't relocate it).
  30      We just want our data structures to describe it as if we had just
  31      mapped and relocated it normally.  */
  32   struct link_map *l = _dl_new_object ((char *) "", "", lt_library, NULL,
  33                                        0, LM_ID_BASE);
  34   if (__glibc_likely (l != NULL))
  35     {
  36       static ElfW(Dyn) dyn_temp[DL_RO_DYN_TEMP_CNT] attribute_relro;
  37
  38       l->l_phdr = ((const void *) GLRO(dl_sysinfo_dso)
  39                    + GLRO(dl_sysinfo_dso)->e_phoff);
  40       l->l_phnum = GLRO(dl_sysinfo_dso)->e_phnum;
  41       for (uint_fast16_t i = 0; i < l->l_phnum; ++i)
  42         {
  43           const ElfW(Phdr) *const ph = &l->l_phdr[i];
  44           if (ph->p_type == PT_DYNAMIC)
  45             {
  46               l->l_ld = (void *) ph->p_vaddr;
  47               l->l_ldnum = ph->p_memsz / sizeof (ElfW(Dyn));
  48             }
  49           else if (ph->p_type == PT_LOAD)
  50             {
  51               if (! l->l_addr)
  52                 l->l_addr = ph->p_vaddr;
  53               if (ph->p_vaddr + ph->p_memsz >= l->l_map_end)
  54                 l->l_map_end = ph->p_vaddr + ph->p_memsz;
  55               if ((ph->p_flags & PF_X)
  56                   && ph->p_vaddr + ph->p_memsz >= l->l_text_end)
  57                 l->l_text_end = ph->p_vaddr + ph->p_memsz;
  58             }
  59           else
  60             /* There must be no TLS segment.  */
  61             assert (ph->p_type != PT_TLS);
  62         }
  63       l->l_map_start = (ElfW(Addr)) GLRO(dl_sysinfo_dso);
  64       l->l_addr = l->l_map_start - l->l_addr;
  65       l->l_map_end += l->l_addr;
  66       l->l_text_end += l->l_addr;
  67       l->l_ld = (void *) ((ElfW(Addr)) l->l_ld + l->l_addr);
  68       elf_get_dynamic_info (l, dyn_temp);
  69       _dl_setup_hash (l);
  70       l->l_relocated = 1;
  71
  72       /* The vDSO is always used.  */
  73       l->l_used = 1;
  74
  75       /* Initialize l_local_scope to contain just this map.  This allows
  76          the use of dl_lookup_symbol_x to resolve symbols within the vdso.
  77          So we create a single entry list pointing to l_real as its only
  78          element */
  79       l->l_local_scope[0]->r_nlist = 1;
  80       l->l_local_scope[0]->r_list = &l->l_real;
  81
  82       /* Now that we have the info handy, use the DSO image's soname
  83          so this object can be looked up by name.  Note that we do not
  84          set l_name here.  That field gives the file name of the DSO,
  85          and this DSO is not associated with any file.  */
  86       if (l->l_info[DT_SONAME] != NULL)
  87         {
  88           /* Work around a kernel problem.  The kernel cannot handle
  89              addresses in the vsyscall DSO pages in writev() calls.  */
  90           const char *dsoname = ((char *) D_PTR (l, l_info[DT_STRTAB])
  91                                  + l->l_info[DT_SONAME]->d_un.d_val);
  92           size_t len = strlen (dsoname) + 1;
  93           char *copy = malloc (len);
  94           if (copy == NULL)
  95             _dl_fatal_printf ("out of memory\n");
  96           l->l_libname->name = l->l_name = memcpy (copy, dsoname, len);
  97         }
  98
  99       /* Add the vDSO to the object list.  */
 100       _dl_add_to_namespace_list (l, LM_ID_BASE);
 101
 102 # if IS_IN (rtld)
 103       /* Rearrange the list so this DSO appears after rtld_map.  */
 104       assert (l->l_next == NULL);
 105       assert (l->l_prev == main_map);
 106       GL(dl_rtld_map).l_next = l;
 107       l->l_prev = &GL(dl_rtld_map);
 108       *first_preload = &l->l_next;
 109 # else
 110       GL(dl_nns) = 1;
 111 # endif
 112
 113       /* We have a prelinked DSO preloaded by the system.  */
 114       GLRO(dl_sysinfo_map) = l;
 115 # ifdef NEED_DL_SYSINFO
 116       if (GLRO(dl_sysinfo) == DL_SYSINFO_DEFAULT)
 117         GLRO(dl_sysinfo) = GLRO(dl_sysinfo_dso)->e_entry + l->l_addr;
 118 # endif
 119     }
 120 #endif
 121 }