csu/libc-tls.c

   1 /* Initialization code for TLS in statically linked application.
   2    Copyright (C) 2002-2020 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 #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.  Giving this initialized value
  50    preallocates some surplus bytes in the static TLS area.  */
  51 size_t _dl_tls_static_size = 2048;
  52 /* Size actually allocated in the static TLS block.  */
  53 size_t _dl_tls_static_used;
  54 /* Alignment requirement of the static TLS block.  */
  55 size_t _dl_tls_static_align;
  56
  57 /* Generation counter for the dtv.  */
  58 size_t _dl_tls_generation;
  59
  60
  61 /* Additional definitions needed by TLS initialization.  */
  62 #ifdef TLS_INIT_HELPER
  63 TLS_INIT_HELPER
  64 #endif
  65
  66 static void
  67 init_slotinfo (void)
  68 {
  69   /* Create the slotinfo list.  Note that the type of static_slotinfo
  70      has effectively a zero-length array, so we cannot use the size of
  71      static_slotinfo to determine the array length.  */
  72   static_slotinfo.len = array_length (_dl_static_dtv);
  73   /* static_slotinfo.next = NULL; -- Already zero.  */
  74
  75   /* The slotinfo list.  Will be extended by the code doing dynamic
  76      linking.  */
  77   GL(dl_tls_max_dtv_idx) = 1;
  78   GL(dl_tls_dtv_slotinfo_list) = &static_slotinfo;
  79 }
  80
  81 static void
  82 init_static_tls (size_t memsz, size_t align)
  83 {
  84   /* That is the size of the TLS memory for this object.  The initialized
  85      value of _dl_tls_static_size is provided by dl-open.c to request some
  86      surplus that permits dynamic loading of modules with IE-model TLS.  */
  87   GL(dl_tls_static_size) = roundup (memsz + GL(dl_tls_static_size),
  88                                     TLS_TCB_ALIGN);
  89 #if TLS_TCB_AT_TP
  90   GL(dl_tls_static_size) += TLS_TCB_SIZE;
  91 #endif
  92   GL(dl_tls_static_used) = memsz;
  93   /* The alignment requirement for the static TLS block.  */
  94   GL(dl_tls_static_align) = align;
  95   /* Number of elements in the static TLS block.  */
  96   GL(dl_tls_static_nelem) = GL(dl_tls_max_dtv_idx);
  97 }
  98
  99 void
 100 __libc_setup_tls (void)
 101 {
 102   void *tlsblock;
 103   size_t memsz = 0;
 104   size_t filesz = 0;
 105   void *initimage = NULL;
 106   size_t align = 0;
 107   size_t max_align = TCB_ALIGNMENT;
 108   size_t tcb_offset;
 109   const ElfW(Phdr) *phdr;
 110
 111   struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
 112
 113   /* Look through the TLS segment if there is any.  */
 114   if (_dl_phdr != NULL)
 115     for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
 116       if (phdr->p_type == PT_TLS)
 117         {
 118           /* Remember the values we need.  */
 119           memsz = phdr->p_memsz;
 120           filesz = phdr->p_filesz;
 121           initimage = (void *) phdr->p_vaddr + main_map->l_addr;
 122           align = phdr->p_align;
 123           if (phdr->p_align > max_align)
 124             max_align = phdr->p_align;
 125           break;
 126         }
 127
 128   /* We have to set up the TCB block which also (possibly) contains
 129      'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
 130      Instead we use 'sbrk' which would only uses 'errno' if it fails.
 131      In this case we are right away out of memory and the user gets
 132      what she/he deserves.
 133
 134      The initialized value of _dl_tls_static_size is provided by dl-open.c
 135      to request some surplus that permits dynamic loading of modules with
 136      IE-model TLS.  */
 137 #if TLS_TCB_AT_TP
 138   /* Align the TCB offset to the maximum alignment, as
 139      _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
 140      and dl_tls_static_align.  */
 141   tcb_offset = roundup (memsz + GL(dl_tls_static_size), max_align);
 142   tlsblock = __sbrk (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
 143 #elif TLS_DTV_AT_TP
 144   tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
 145   tlsblock = __sbrk (tcb_offset + memsz + max_align
 146                      + TLS_PRE_TCB_SIZE + GL(dl_tls_static_size));
 147   tlsblock += TLS_PRE_TCB_SIZE;
 148 #else
 149   /* In case a model with a different layout for the TCB and DTV
 150      is defined add another #elif here and in the following #ifs.  */
 151 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 152 #endif
 153
 154   /* Align the TLS block.  */
 155   tlsblock = (void *) (((uintptr_t) tlsblock + max_align - 1)
 156                        & ~(max_align - 1));
 157
 158   /* Initialize the dtv.  [0] is the length, [1] the generation counter.  */
 159   _dl_static_dtv[0].counter = (sizeof (_dl_static_dtv) / sizeof (_dl_static_dtv[0])) - 2;
 160   // _dl_static_dtv[1].counter = 0;             would be needed if not already done
 161
 162   /* Initialize the TLS block.  */
 163 #if TLS_TCB_AT_TP
 164   _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
 165                                - roundup (memsz, align ?: 1));
 166   main_map->l_tls_offset = roundup (memsz, align ?: 1);
 167 #elif TLS_DTV_AT_TP
 168   _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
 169   main_map->l_tls_offset = tcb_offset;
 170 #else
 171 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 172 #endif
 173   _dl_static_dtv[2].pointer.to_free = NULL;
 174   /* sbrk gives us zero'd memory, so we don't need to clear the remainder.  */
 175   memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz);
 176
 177   /* Install the pointer to the dtv.  */
 178
 179   /* Initialize the thread pointer.  */
 180 #if TLS_TCB_AT_TP
 181   INSTALL_DTV ((char *) tlsblock + tcb_offset, _dl_static_dtv);
 182
 183   const char *lossage = TLS_INIT_TP ((char *) tlsblock + tcb_offset);
 184 #elif TLS_DTV_AT_TP
 185   INSTALL_DTV (tlsblock, _dl_static_dtv);
 186   const char *lossage = TLS_INIT_TP (tlsblock);
 187 #else
 188 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 189 #endif
 190   if (__builtin_expect (lossage != NULL, 0))
 191     _startup_fatal (lossage);
 192
 193   /* Update the executable's link map with enough information to make
 194      the TLS routines happy.  */
 195   main_map->l_tls_align = align;
 196   main_map->l_tls_blocksize = memsz;
 197   main_map->l_tls_initimage = initimage;
 198   main_map->l_tls_initimage_size = filesz;
 199   main_map->l_tls_modid = 1;
 200
 201   init_slotinfo ();
 202   /* static_slotinfo.slotinfo[1].gen = 0; -- Already zero.  */
 203   static_slotinfo.slotinfo[1].map = main_map;
 204
 205   memsz = roundup (memsz, align ?: 1);
 206
 207 #if TLS_DTV_AT_TP
 208   memsz += tcb_offset;
 209 #endif
 210
 211   init_static_tls (memsz, MAX (TLS_TCB_ALIGN, max_align));
 212 }