csu/libc-tls.c

   1 /* Initialization code for TLS in statically linked application.
   2    Copyright (C) 2002-2024 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 #include <pthreadP.h>
  28 #include <dl-call_tls_init_tp.h>
  29
  30 #ifdef SHARED
  31  #error makefile bug, this file is for static only
  32 #endif
  33
  34 dtv_t _dl_static_dtv[2 + TLS_SLOTINFO_SURPLUS];
  35
  36
  37 static struct dtv_slotinfo_list static_slotinfo =
  38   {
  39    /* Allocate an array of 2 + TLS_SLOTINFO_SURPLUS elements.  */
  40    .slotinfo =  { [array_length (_dl_static_dtv) - 1] = { 0 } },
  41   };
  42
  43 /* Highest dtv index currently needed.  */
  44 size_t _dl_tls_max_dtv_idx;
  45 /* Flag signalling whether there are gaps in the module ID allocation.  */
  46 bool _dl_tls_dtv_gaps;
  47 /* Information about the dtv slots.  */
  48 struct dtv_slotinfo_list *_dl_tls_dtv_slotinfo_list;
  49 /* Number of modules in the static TLS block.  */
  50 size_t _dl_tls_static_nelem;
  51 /* Size of the static TLS block.  */
  52 size_t _dl_tls_static_size;
  53 /* Size actually allocated in the static TLS block.  */
  54 size_t _dl_tls_static_used;
  55 /* Alignment requirement of the static TLS block.  */
  56 size_t _dl_tls_static_align;
  57 /* Size of surplus space in the static TLS area for dynamically
  58    loaded modules with IE-model TLS or for TLSDESC optimization.
  59    See comments in elf/dl-tls.c where it is initialized.  */
  60 size_t _dl_tls_static_surplus;
  61 /* Remaining amount of static TLS that may be used for optimizing
  62    dynamic TLS access (e.g. with TLSDESC).  */
  63 size_t _dl_tls_static_optional;
  64
  65 /* Generation counter for the dtv.  */
  66 size_t _dl_tls_generation;
  67
  68
  69 /* Additional definitions needed by TLS initialization.  */
  70 #ifdef TLS_INIT_HELPER
  71 TLS_INIT_HELPER
  72 #endif
  73
  74 static void
  75 init_slotinfo (void)
  76 {
  77   /* Create the slotinfo list.  Note that the type of static_slotinfo
  78      has effectively a zero-length array, so we cannot use the size of
  79      static_slotinfo to determine the array length.  */
  80   static_slotinfo.len = array_length (_dl_static_dtv);
  81   /* static_slotinfo.next = NULL; -- Already zero.  */
  82
  83   /* The slotinfo list.  Will be extended by the code doing dynamic
  84      linking.  */
  85   GL(dl_tls_max_dtv_idx) = 1;
  86   GL(dl_tls_dtv_slotinfo_list) = &static_slotinfo;
  87 }
  88
  89 static void
  90 init_static_tls (size_t memsz, size_t align)
  91 {
  92   /* That is the size of the TLS memory for this object.  */
  93   GL(dl_tls_static_size) = roundup (memsz + GLRO(dl_tls_static_surplus),
  94                                     TCB_ALIGNMENT);
  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   __tls_pre_init_tp ();
 120
 121   /* Look through the TLS segment if there is any.  */
 122   for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
 123     if (phdr->p_type == PT_TLS)
 124       {
 125         /* Remember the values we need.  */
 126         memsz = phdr->p_memsz;
 127         filesz = phdr->p_filesz;
 128         initimage = (void *) phdr->p_vaddr + main_map->l_addr;
 129         align = phdr->p_align;
 130         if (phdr->p_align > max_align)
 131           max_align = phdr->p_align;
 132         break;
 133       }
 134
 135   /* Calculate the size of the static TLS surplus, with 0 auditors.  */
 136   _dl_tls_static_surplus_init (0);
 137
 138   /* We have to set up the TCB block which also (possibly) contains
 139      'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
 140      Instead we use 'sbrk' which would only uses 'errno' if it fails.
 141      In this case we are right away out of memory and the user gets
 142      what she/he deserves.  */
 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 + GLRO(dl_tls_static_surplus), max_align);
 148   tlsblock = _dl_early_allocate (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
 149   if (tlsblock == NULL)
 150     _startup_fatal_tls_error ();
 151 #elif TLS_DTV_AT_TP
 152   tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
 153   tlsblock = _dl_early_allocate (tcb_offset + memsz + max_align
 154                                  + TLS_PRE_TCB_SIZE
 155                                  + GLRO(dl_tls_static_surplus));
 156   if (tlsblock == NULL)
 157     _startup_fatal_tls_error ();
 158   tlsblock += TLS_PRE_TCB_SIZE;
 159 #else
 160   /* In case a model with a different layout for the TCB and DTV
 161      is defined add another #elif here and in the following #ifs.  */
 162 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 163 #endif
 164
 165   /* Align the TLS block.  */
 166   tlsblock = (void *) (((uintptr_t) tlsblock + max_align - 1)
 167                        & ~(max_align - 1));
 168
 169   /* Initialize the dtv.  [0] is the length, [1] the generation counter.  */
 170   _dl_static_dtv[0].counter = (sizeof (_dl_static_dtv) / sizeof (_dl_static_dtv[0])) - 2;
 171   // _dl_static_dtv[1].counter = 0;             would be needed if not already done
 172
 173   /* Initialize the TLS block.  */
 174 #if TLS_TCB_AT_TP
 175   _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
 176                                - roundup (memsz, align ?: 1));
 177   main_map->l_tls_offset = roundup (memsz, align ?: 1);
 178 #elif TLS_DTV_AT_TP
 179   _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
 180   main_map->l_tls_offset = tcb_offset;
 181 #else
 182 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 183 #endif
 184   _dl_static_dtv[2].pointer.to_free = NULL;
 185   /* sbrk gives us zero'd memory, so we don't need to clear the remainder.  */
 186   memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz);
 187
 188   /* Install the pointer to the dtv.  */
 189
 190   /* Initialize the thread pointer.  */
 191 #if TLS_TCB_AT_TP
 192   INSTALL_DTV ((char *) tlsblock + tcb_offset, _dl_static_dtv);
 193
 194   call_tls_init_tp ((char *) tlsblock + tcb_offset);
 195 #elif TLS_DTV_AT_TP
 196   INSTALL_DTV (tlsblock, _dl_static_dtv);
 197   call_tls_init_tp (tlsblock);
 198 #endif
 199
 200   /* Update the executable's link map with enough information to make
 201      the TLS routines happy.  */
 202   main_map->l_tls_align = align;
 203   main_map->l_tls_blocksize = memsz;
 204   main_map->l_tls_initimage = initimage;
 205   main_map->l_tls_initimage_size = filesz;
 206   main_map->l_tls_modid = 1;
 207
 208   init_slotinfo ();
 209   /* static_slotinfo.slotinfo[1].gen = 0; -- Already zero.  */
 210   static_slotinfo.slotinfo[1].map = main_map;
 211
 212   memsz = roundup (memsz, align ?: 1);
 213
 214 #if TLS_DTV_AT_TP
 215   memsz += tcb_offset;
 216 #endif
 217
 218   init_static_tls (memsz, MAX (TCB_ALIGNMENT, max_align));
 219 }