glibc/csu/libc-tls.c

/* Initialization code for TLS in statically linked application.
   Copyright (C) 2002-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <startup.h>
#include <errno.h>
#include <ldsodefs.h>
#include <tls.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/param.h>
#include <array_length.h>

#ifdef SHARED
 #error makefile bug, this file is for static only
#endif

dtv_t _dl_static_dtv[2 + TLS_SLOTINFO_SURPLUS];


static struct dtv_slotinfo_list static_slotinfo =
  {
   /* Allocate an array of 2 + TLS_SLOTINFO_SURPLUS elements.  */
   .slotinfo =  { [array_length (_dl_static_dtv) - 1] = { 0 } },
  };

/* Highest dtv index currently needed.  */
size_t _dl_tls_max_dtv_idx;
/* Flag signalling whether there are gaps in the module ID allocation.  */
bool _dl_tls_dtv_gaps;
/* Information about the dtv slots.  */
struct dtv_slotinfo_list *_dl_tls_dtv_slotinfo_list;
/* Number of modules in the static TLS block.  */
size_t _dl_tls_static_nelem;
/* Size of the static TLS block.  */
size_t _dl_tls_static_size;
/* Size actually allocated in the static TLS block.  */
size_t _dl_tls_static_used;
/* Alignment requirement of the static TLS block.  */
size_t _dl_tls_static_align;
/* Size of surplus space in the static TLS area for dynamically
   loaded modules with IE-model TLS or for TLSDESC optimization.
   See comments in elf/dl-tls.c where it is initialized.  */
size_t _dl_tls_static_surplus;
/* Remaining amount of static TLS that may be used for optimizing
   dynamic TLS access (e.g. with TLSDESC).  */
size_t _dl_tls_static_optional;

/* Generation counter for the dtv.  */
size_t _dl_tls_generation;


/* Additional definitions needed by TLS initialization.  */
#ifdef TLS_INIT_HELPER
TLS_INIT_HELPER
#endif

static void
init_slotinfo (void)
{
  /* Create the slotinfo list.  Note that the type of static_slotinfo
     has effectively a zero-length array, so we cannot use the size of
     static_slotinfo to determine the array length.  */
  static_slotinfo.len = array_length (_dl_static_dtv);
  /* static_slotinfo.next = NULL; -- Already zero.  */

  /* The slotinfo list.  Will be extended by the code doing dynamic
     linking.  */
  GL(dl_tls_max_dtv_idx) = 1;
  GL(dl_tls_dtv_slotinfo_list) = &static_slotinfo;
}

static void
init_static_tls (size_t memsz, size_t align)
{
  /* That is the size of the TLS memory for this object.  */
  GL(dl_tls_static_size) = roundup (memsz + GLRO(dl_tls_static_surplus),
				    TLS_TCB_ALIGN);
#if TLS_TCB_AT_TP
  GL(dl_tls_static_size) += TLS_TCB_SIZE;
#endif
  GL(dl_tls_static_used) = memsz;
  /* The alignment requirement for the static TLS block.  */
  GL(dl_tls_static_align) = align;
  /* Number of elements in the static TLS block.  */
  GL(dl_tls_static_nelem) = GL(dl_tls_max_dtv_idx);
}

void
__libc_setup_tls (void)
{
  void *tlsblock;
  size_t memsz = 0;
  size_t filesz = 0;
  void *initimage = NULL;
  size_t align = 0;
  size_t max_align = TCB_ALIGNMENT;
  size_t tcb_offset;
  const ElfW(Phdr) *phdr;

  struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;

  __tls_pre_init_tp ();

  /* Look through the TLS segment if there is any.  */
  if (_dl_phdr != NULL)
    for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
      if (phdr->p_type == PT_TLS)
	{
	  /* Remember the values we need.  */
	  memsz = phdr->p_memsz;
	  filesz = phdr->p_filesz;
	  initimage = (void *) phdr->p_vaddr + main_map->l_addr;
	  align = phdr->p_align;
	  if (phdr->p_align > max_align)
	    max_align = phdr->p_align;
	  break;
	}

  /* Calculate the size of the static TLS surplus, with 0 auditors.  */
  _dl_tls_static_surplus_init (0);

  /* We have to set up the TCB block which also (possibly) contains
     'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
     Instead we use 'sbrk' which would only uses 'errno' if it fails.
     In this case we are right away out of memory and the user gets
     what she/he deserves.  */
#if TLS_TCB_AT_TP
  /* Align the TCB offset to the maximum alignment, as
     _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
     and dl_tls_static_align.  */
  tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
  tlsblock = __sbrk (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
#elif TLS_DTV_AT_TP
  tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
  tlsblock = __sbrk (tcb_offset + memsz + max_align
		     + TLS_PRE_TCB_SIZE + GLRO(dl_tls_static_surplus));
  tlsblock += TLS_PRE_TCB_SIZE;
#else
  /* In case a model with a different layout for the TCB and DTV
     is defined add another #elif here and in the following #ifs.  */
# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
#endif

  /* Align the TLS block.  */
  tlsblock = (void *) (((uintptr_t) tlsblock + max_align - 1)
		       & ~(max_align - 1));

  /* Initialize the dtv.  [0] is the length, [1] the generation counter.  */
  _dl_static_dtv[0].counter = (sizeof (_dl_static_dtv) / sizeof (_dl_static_dtv[0])) - 2;
  // _dl_static_dtv[1].counter = 0;		would be needed if not already done

  /* Initialize the TLS block.  */
#if TLS_TCB_AT_TP
  _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
			       - roundup (memsz, align ?: 1));
  main_map->l_tls_offset = roundup (memsz, align ?: 1);
#elif TLS_DTV_AT_TP
  _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
  main_map->l_tls_offset = tcb_offset;
#else
# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
#endif
  _dl_static_dtv[2].pointer.to_free = NULL;
  /* sbrk gives us zero'd memory, so we don't need to clear the remainder.  */
  memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz);

  /* Install the pointer to the dtv.  */

  /* Initialize the thread pointer.  */
#if TLS_TCB_AT_TP
  INSTALL_DTV ((char *) tlsblock + tcb_offset, _dl_static_dtv);

  const char *lossage = TLS_INIT_TP ((char *) tlsblock + tcb_offset);
#elif TLS_DTV_AT_TP
  INSTALL_DTV (tlsblock, _dl_static_dtv);
  const char *lossage = TLS_INIT_TP (tlsblock);
#else
# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
#endif
  if (__builtin_expect (lossage != NULL, 0))
    _startup_fatal (lossage);
  __tls_init_tp ();

  /* Update the executable's link map with enough information to make
     the TLS routines happy.  */
  main_map->l_tls_align = align;
  main_map->l_tls_blocksize = memsz;
  main_map->l_tls_initimage = initimage;
  main_map->l_tls_initimage_size = filesz;
  main_map->l_tls_modid = 1;

  init_slotinfo ();
  /* static_slotinfo.slotinfo[1].gen = 0; -- Already zero.  */
  static_slotinfo.slotinfo[1].map = main_map;

  memsz = roundup (memsz, align ?: 1);

#if TLS_DTV_AT_TP
  memsz += tcb_offset;
#endif

  init_static_tls (memsz, MAX (TLS_TCB_ALIGN, max_align));
}