csu/libc-tls.c

   1 /* Initialization code for TLS in statically linked application.
   2    Copyright (C) 2002-2021 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 #include <array_length.h>
  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 dtv_slotinfo_list static_slotinfo =
  36   {
  37    /* Allocate an array of 2 + TLS_SLOTINFO_SURPLUS elements.  */
  38    .slotinfo =  { [array_length (_dl_static_dtv) - 1] = { 0 } },
  39   };
  40
  41 /* Highest dtv index currently needed.  */
  42 size_t _dl_tls_max_dtv_idx;
  43 /* Flag signalling whether there are gaps in the module ID allocation.  */
  44 bool _dl_tls_dtv_gaps;
  45 /* Information about the dtv slots.  */
  46 struct dtv_slotinfo_list *_dl_tls_dtv_slotinfo_list;
  47 /* Number of modules in the static TLS block.  */
  48 size_t _dl_tls_static_nelem;
  49 /* Size of the static TLS block.  */
  50 size_t _dl_tls_static_size;
  51 /* Size actually allocated in the static TLS block.  */
  52 size_t _dl_tls_static_used;
  53 /* Alignment requirement of the static TLS block.  */
  54 size_t _dl_tls_static_align;
  55 /* Size of surplus space in the static TLS area for dynamically
  56    loaded modules with IE-model TLS or for TLSDESC optimization.
  57    See comments in elf/dl-tls.c where it is initialized.  */
  58 size_t _dl_tls_static_surplus;
  59 /* Remaining amount of static TLS that may be used for optimizing
  60    dynamic TLS access (e.g. with TLSDESC).  */
  61 size_t _dl_tls_static_optional;
  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.  Note that the type of static_slotinfo
  76      has effectively a zero-length array, so we cannot use the size of
  77      static_slotinfo to determine the array length.  */
  78   static_slotinfo.len = array_length (_dl_static_dtv);
  79   /* static_slotinfo.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;
  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.  */
  91   GL(dl_tls_static_size) = roundup (memsz + GLRO(dl_tls_static_surplus),
  92                                     TLS_TCB_ALIGN);
  93 #if TLS_TCB_AT_TP
  94   GL(dl_tls_static_size) += TLS_TCB_SIZE;
  95 #endif
  96   GL(dl_tls_static_used) = memsz;
  97   /* The alignment requirement for the static TLS block.  */
  98   GL(dl_tls_static_align) = align;
  99   /* Number of elements in the static TLS block.  */
 100   GL(dl_tls_static_nelem) = GL(dl_tls_max_dtv_idx);
 101 }
 102
 103 void
 104 __libc_setup_tls (void)
 105 {
 106   void *tlsblock;
 107   size_t memsz = 0;
 108   size_t filesz = 0;
 109   void *initimage = NULL;
 110   size_t align = 0;
 111   size_t max_align = TCB_ALIGNMENT;
 112   size_t tcb_offset;
 113   const ElfW(Phdr) *phdr;
 114
 115   struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
 116
 117   __tls_pre_init_tp ();
 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   /* Calculate the size of the static TLS surplus, with 0 auditors.  */
 135   _dl_tls_static_surplus_init (0);
 136
 137   /* We have to set up the TCB block which also (possibly) contains
 138      'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
 139      Instead we use 'sbrk' which would only uses 'errno' if it fails.
 140      In this case we are right away out of memory and the user gets
 141      what she/he deserves.  */
 142 #if TLS_TCB_AT_TP
 143   /* Align the TCB offset to the maximum alignment, as
 144      _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
 145      and dl_tls_static_align.  */
 146   tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
 147   tlsblock = __sbrk (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
 148 #elif TLS_DTV_AT_TP
 149   tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
 150   tlsblock = __sbrk (tcb_offset + memsz + max_align
 151                      + TLS_PRE_TCB_SIZE + GLRO(dl_tls_static_surplus));
 152   tlsblock += TLS_PRE_TCB_SIZE;
 153 #else
 154   /* In case a model with a different layout for the TCB and DTV
 155      is defined add another #elif here and in the following #ifs.  */
 156 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 157 #endif
 158
 159   /* Align the TLS block.  */
 160   tlsblock = (void *) (((uintptr_t) tlsblock + max_align - 1)
 161                        & ~(max_align - 1));
 162
 163   /* Initialize the dtv.  [0] is the length, [1] the generation counter.  */
 164   _dl_static_dtv[0].counter = (sizeof (_dl_static_dtv) / sizeof (_dl_static_dtv[0])) - 2;
 165   // _dl_static_dtv[1].counter = 0;             would be needed if not already done
 166
 167   /* Initialize the TLS block.  */
 168 #if TLS_TCB_AT_TP
 169   _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
 170                                - roundup (memsz, align ?: 1));
 171   main_map->l_tls_offset = roundup (memsz, align ?: 1);
 172 #elif TLS_DTV_AT_TP
 173   _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
 174   main_map->l_tls_offset = tcb_offset;
 175 #else
 176 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 177 #endif
 178   _dl_static_dtv[2].pointer.to_free = NULL;
 179   /* sbrk gives us zero'd memory, so we don't need to clear the remainder.  */
 180   memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz);
 181
 182   /* Install the pointer to the dtv.  */
 183
 184   /* Initialize the thread pointer.  */
 185 #if TLS_TCB_AT_TP
 186   INSTALL_DTV ((char *) tlsblock + tcb_offset, _dl_static_dtv);
 187
 188   const char *lossage = TLS_INIT_TP ((char *) tlsblock + tcb_offset);
 189 #elif TLS_DTV_AT_TP
 190   INSTALL_DTV (tlsblock, _dl_static_dtv);
 191   const char *lossage = TLS_INIT_TP (tlsblock);
 192 #else
 193 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 194 #endif
 195   if (__builtin_expect (lossage != NULL, 0))
 196     _startup_fatal (lossage);
 197   __tls_init_tp ();
 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.slotinfo[1].gen = 0; -- Already zero.  */
 209   static_slotinfo.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 }