csu/libc-tls.c

   1 /* Initialization code for TLS in statically linked application.
   2    Copyright (C) 2002-2019 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 #include <startup.h>
  20 #include <errno.h>
  21 #include <ldsodefs.h>
  22 #include <tls.h>
  23 #include <unistd.h>
  24 #include <stdio.h>
  25 #include <sys/param.h>
  26
  27
  28 #ifdef SHARED
  29  #error makefile bug, this file is for static only
  30 #endif
  31
  32 dtv_t _dl_static_dtv[2 + TLS_SLOTINFO_SURPLUS];
  33
  34
  35 static struct
  36 {
  37   struct dtv_slotinfo_list si;
  38   /* The dtv_slotinfo_list data structure does not include the actual
  39      information since it is defined as an array of size zero.  We define
  40      here the necessary entries.  Note that it is not important whether
  41      there is padding or not since we will always access the information
  42      through the 'si' element.  */
  43   struct dtv_slotinfo info[2 + TLS_SLOTINFO_SURPLUS];
  44 } static_slotinfo;
  45
  46
  47 /* Highest dtv index currently needed.  */
  48 size_t _dl_tls_max_dtv_idx;
  49 /* Flag signalling whether there are gaps in the module ID allocation.  */
  50 bool _dl_tls_dtv_gaps;
  51 /* Information about the dtv slots.  */
  52 struct dtv_slotinfo_list *_dl_tls_dtv_slotinfo_list;
  53 /* Number of modules in the static TLS block.  */
  54 size_t _dl_tls_static_nelem;
  55 /* Size of the static TLS block.  Giving this initialized value
  56    preallocates some surplus bytes in the static TLS area.  */
  57 size_t _dl_tls_static_size = 2048;
  58 /* Size actually allocated in the static TLS block.  */
  59 size_t _dl_tls_static_used;
  60 /* Alignment requirement of the static TLS block.  */
  61 size_t _dl_tls_static_align;
  62
  63 /* Generation counter for the dtv.  */
  64 size_t _dl_tls_generation;
  65
  66
  67 /* Additional definitions needed by TLS initialization.  */
  68 #ifdef TLS_INIT_HELPER
  69 TLS_INIT_HELPER
  70 #endif
  71
  72 static void
  73 init_slotinfo (void)
  74 {
  75   /* Create the slotinfo list.  */
  76   static_slotinfo.si.len = (((char *) (&static_slotinfo + 1)
  77                              - (char *) &static_slotinfo.si.slotinfo[0])
  78                             / sizeof static_slotinfo.si.slotinfo[0]);
  79   // static_slotinfo.si.next = NULL;    already zero
  80
  81   /* The slotinfo list.  Will be extended by the code doing dynamic
  82      linking.  */
  83   GL(dl_tls_max_dtv_idx) = 1;
  84   GL(dl_tls_dtv_slotinfo_list) = &static_slotinfo.si;
  85 }
  86
  87 static void
  88 init_static_tls (size_t memsz, size_t align)
  89 {
  90   /* That is the size of the TLS memory for this object.  The initialized
  91      value of _dl_tls_static_size is provided by dl-open.c to request some
  92      surplus that permits dynamic loading of modules with IE-model TLS.  */
  93   GL(dl_tls_static_size) = roundup (memsz + GL(dl_tls_static_size),
  94                                     TLS_TCB_ALIGN);
  95 #if TLS_TCB_AT_TP
  96   GL(dl_tls_static_size) += TLS_TCB_SIZE;
  97 #endif
  98   GL(dl_tls_static_used) = memsz;
  99   /* The alignment requirement for the static TLS block.  */
 100   GL(dl_tls_static_align) = align;
 101   /* Number of elements in the static TLS block.  */
 102   GL(dl_tls_static_nelem) = GL(dl_tls_max_dtv_idx);
 103 }
 104
 105 void
 106 __libc_setup_tls (void)
 107 {
 108   void *tlsblock;
 109   size_t memsz = 0;
 110   size_t filesz = 0;
 111   void *initimage = NULL;
 112   size_t align = 0;
 113   size_t max_align = TCB_ALIGNMENT;
 114   size_t tcb_offset;
 115   const ElfW(Phdr) *phdr;
 116
 117   struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
 118
 119   /* Look through the TLS segment if there is any.  */
 120   if (_dl_phdr != NULL)
 121     for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
 122       if (phdr->p_type == PT_TLS)
 123         {
 124           /* Remember the values we need.  */
 125           memsz = phdr->p_memsz;
 126           filesz = phdr->p_filesz;
 127           initimage = (void *) phdr->p_vaddr + main_map->l_addr;
 128           align = phdr->p_align;
 129           if (phdr->p_align > max_align)
 130             max_align = phdr->p_align;
 131           break;
 132         }
 133
 134   /* We have to set up the TCB block which also (possibly) contains
 135      'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
 136      Instead we use 'sbrk' which would only uses 'errno' if it fails.
 137      In this case we are right away out of memory and the user gets
 138      what she/he deserves.
 139
 140      The initialized value of _dl_tls_static_size is provided by dl-open.c
 141      to request some surplus that permits dynamic loading of modules with
 142      IE-model TLS.  */
 143 #if TLS_TCB_AT_TP
 144   /* Align the TCB offset to the maximum alignment, as
 145      _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
 146      and dl_tls_static_align.  */
 147   tcb_offset = roundup (memsz + GL(dl_tls_static_size), max_align);
 148   tlsblock = __sbrk (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
 149 #elif TLS_DTV_AT_TP
 150   tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
 151   tlsblock = __sbrk (tcb_offset + memsz + max_align
 152                      + TLS_PRE_TCB_SIZE + GL(dl_tls_static_size));
 153   tlsblock += TLS_PRE_TCB_SIZE;
 154 #else
 155   /* In case a model with a different layout for the TCB and DTV
 156      is defined add another #elif here and in the following #ifs.  */
 157 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 158 #endif
 159
 160   /* Align the TLS block.  */
 161   tlsblock = (void *) (((uintptr_t) tlsblock + max_align - 1)
 162                        & ~(max_align - 1));
 163
 164   /* Initialize the dtv.  [0] is the length, [1] the generation counter.  */
 165   _dl_static_dtv[0].counter = (sizeof (_dl_static_dtv) / sizeof (_dl_static_dtv[0])) - 2;
 166   // _dl_static_dtv[1].counter = 0;             would be needed if not already done
 167
 168   /* Initialize the TLS block.  */
 169 #if TLS_TCB_AT_TP
 170   _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
 171                                - roundup (memsz, align ?: 1));
 172   main_map->l_tls_offset = roundup (memsz, align ?: 1);
 173 #elif TLS_DTV_AT_TP
 174   _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
 175   main_map->l_tls_offset = tcb_offset;
 176 #else
 177 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 178 #endif
 179   _dl_static_dtv[2].pointer.to_free = NULL;
 180   /* sbrk gives us zero'd memory, so we don't need to clear the remainder.  */
 181   memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz);
 182
 183   /* Install the pointer to the dtv.  */
 184
 185   /* Initialize the thread pointer.  */
 186 #if TLS_TCB_AT_TP
 187   INSTALL_DTV ((char *) tlsblock + tcb_offset, _dl_static_dtv);
 188
 189   const char *lossage = TLS_INIT_TP ((char *) tlsblock + tcb_offset);
 190 #elif TLS_DTV_AT_TP
 191   INSTALL_DTV (tlsblock, _dl_static_dtv);
 192   const char *lossage = TLS_INIT_TP (tlsblock);
 193 #else
 194 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 195 #endif
 196   if (__builtin_expect (lossage != NULL, 0))
 197     _startup_fatal (lossage);
 198
 199   /* Update the executable's link map with enough information to make
 200      the TLS routines happy.  */
 201   main_map->l_tls_align = align;
 202   main_map->l_tls_blocksize = memsz;
 203   main_map->l_tls_initimage = initimage;
 204   main_map->l_tls_initimage_size = filesz;
 205   main_map->l_tls_modid = 1;
 206
 207   init_slotinfo ();
 208   // static_slotinfo.si.slotinfo[1].gen = 0; already zero
 209   static_slotinfo.si.slotinfo[1].map = main_map;
 210
 211   memsz = roundup (memsz, align ?: 1);
 212
 213 #if TLS_DTV_AT_TP
 214   memsz += tcb_offset;
 215 #endif
 216
 217   init_static_tls (memsz, MAX (TLS_TCB_ALIGN, max_align));
 218 }