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dl-tls.c

/* Thread-local storage handling in the ELF dynamic linker.  Generic version.
   Copyright (C) 2002, 2003 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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/param.h>

#include <tls.h>

/* We don't need any of this if TLS is not supported.  */
#ifdef USE_TLS

# include <dl-tls.h>
# include <ldsodefs.h>

/* Amount of excess space to allocate in the static TLS area
   to allow dynamic loading of modules defining IE-model TLS data.  */
# define TLS_STATIC_SURPLUS   64

/* Value used for dtv entries for which the allocation is delayed.  */
# define TLS_DTV_UNALLOCATED  ((void *) -1l)


/* Out-of-memory handler.  */
# ifdef SHARED
static void
__attribute__ ((__noreturn__))
oom (void)
{
  _dl_fatal_printf ("cannot allocate memory for thread-local data: ABORT\n");
}
# endif



size_t
internal_function
_dl_next_tls_modid (void)
{
  size_t result;

  if (__builtin_expect (GL(dl_tls_dtv_gaps), false))
    {
      size_t disp = 0;
      struct dtv_slotinfo_list *runp = GL(dl_tls_dtv_slotinfo_list);

      /* Note that this branch will never be executed during program
       start since there are no gaps at that time.  Therefore it
       does not matter that the dl_tls_dtv_slotinfo is not allocated
       yet when the function is called for the first times.  */
      result = GL(dl_tls_static_nelem) + 1;
      /* If the following would not be true we mustn't have assumed
       there is a gap.  */
      assert (result <= GL(dl_tls_max_dtv_idx));
      do
      {
        while (result - disp < runp->len)
          {
            if (runp->slotinfo[result - disp].map == NULL)
            break;

            ++result;
            assert (result <= GL(dl_tls_max_dtv_idx) + 1);
          }

        if (result - disp < runp->len)
          break;

        disp += runp->len;
      }
      while ((runp = runp->next) != NULL);

      if (result >= GL(dl_tls_max_dtv_idx))
      {
        /* The new index must indeed be exactly one higher than the
           previous high.  */
        assert (result == GL(dl_tls_max_dtv_idx));

        /* There is no gap anymore.  */
        GL(dl_tls_dtv_gaps) = false;

        goto nogaps;
      }
    }
  else
    {
      /* No gaps, allocate a new entry.  */
    nogaps:
      result = ++GL(dl_tls_max_dtv_idx);
    }

  return result;
}

# ifdef SHARED

void
internal_function
_dl_determine_tlsoffset (void)
{
  struct dtv_slotinfo *slotinfo;
  size_t max_align = __alignof__ (void *);
  size_t offset;
  size_t cnt;

  /* The first element of the dtv slot info list is allocated.  */
  assert (GL(dl_tls_dtv_slotinfo_list) != NULL);
  /* There is at this point only one element in the
     dl_tls_dtv_slotinfo_list list.  */
  assert (GL(dl_tls_dtv_slotinfo_list)->next == NULL);

# if TLS_TCB_AT_TP
  /* We simply start with zero.  */
  offset = 0;

  slotinfo = GL(dl_tls_dtv_slotinfo_list)->slotinfo;
  for (cnt = 1; slotinfo[cnt].map != NULL; ++cnt)
    {
      assert (cnt < GL(dl_tls_dtv_slotinfo_list)->len);

      max_align = MAX (max_align, slotinfo[cnt].map->l_tls_align);

      /* Compute the offset of the next TLS block.  */
      offset = roundup (offset + slotinfo[cnt].map->l_tls_blocksize,
                  slotinfo[cnt].map->l_tls_align);

      /* XXX For some architectures we perhaps should store the
       negative offset.  */
      slotinfo[cnt].map->l_tls_offset = offset;
    }

  /* The thread descriptor (pointed to by the thread pointer) has its
     own alignment requirement.  Adjust the static TLS size
     and TLS offsets appropriately.  */
  // XXX How to deal with this.  We cannot simply add zero bytes
  // XXX after the first (closest to the TCB) TLS block since this
  // XXX would invalidate the offsets the linker creates for the LE
  // XXX model.

  GL(dl_tls_static_used) = offset;
  GL(dl_tls_static_size) = roundup (offset + TLS_STATIC_SURPLUS + TLS_TCB_SIZE,
                            TLS_TCB_ALIGN);
# elif TLS_DTV_AT_TP
  /* The TLS blocks start right after the TCB.  */
  offset = TLS_TCB_SIZE;

  /* The first block starts right after the TCB.  */
  slotinfo = GL(dl_tls_dtv_slotinfo_list)->slotinfo;
  if (slotinfo[1].map != NULL)
    {
      size_t prev_size;

      offset = roundup (offset, slotinfo[1].map->l_tls_align);
      slotinfo[1].map->l_tls_offset = offset;
      max_align = slotinfo[1].map->l_tls_align;
      prev_size = slotinfo[1].map->l_tls_blocksize;

      for (cnt = 2; slotinfo[cnt].map != NULL; ++cnt)
      {
        assert (cnt < GL(dl_tls_dtv_slotinfo_list)->len);

        max_align = MAX (max_align, slotinfo[cnt].map->l_tls_align);

        /* Compute the offset of the next TLS block.  */
        offset = roundup (offset + prev_size,
                      slotinfo[cnt].map->l_tls_align);

        /* XXX For some architectures we perhaps should store the
           negative offset.  */
        slotinfo[cnt].map->l_tls_offset = offset;

        prev_size = slotinfo[cnt].map->l_tls_blocksize;
      }

      offset += prev_size;
    }

  GL(dl_tls_static_used) = offset;
  GL(dl_tls_static_size) = roundup (offset + TLS_STATIC_SURPLUS,
                            TLS_TCB_ALIGN);
# else
#  error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
# endif

  /* The alignment requirement for the static TLS block.  */
  GL(dl_tls_static_align) = MAX (TLS_TCB_ALIGN, max_align);
}


/* This is called only when the data structure setup was skipped at startup,
   when there was no need for it then.  Now we have dynamically loaded
   something needing TLS, or libpthread needs it.  */
int
internal_function
_dl_tls_setup (void)
{
  assert (GL(dl_tls_dtv_slotinfo_list) == NULL);
  assert (GL(dl_tls_max_dtv_idx) == 0);

  const size_t nelem = 2 + TLS_SLOTINFO_SURPLUS;

  GL(dl_tls_dtv_slotinfo_list)
    = calloc (1, (sizeof (struct dtv_slotinfo_list)
              + nelem * sizeof (struct dtv_slotinfo)));
  if (GL(dl_tls_dtv_slotinfo_list) == NULL)
    return -1;

  GL(dl_tls_dtv_slotinfo_list)->len = nelem;

  /* Number of elements in the static TLS block.  It can't be zero
     because of various assumptions.  The one element is null.  */
  GL(dl_tls_static_nelem) = GL(dl_tls_max_dtv_idx) = 1;

  /* This initializes more variables for us.  */
  _dl_determine_tlsoffset ();

  return 0;
}
rtld_hidden_def (_dl_tls_setup)
# endif

static void *
internal_function
allocate_dtv (void *result)
{
  dtv_t *dtv;
  size_t dtv_length;

  /* We allocate a few more elements in the dtv than are needed for the
     initial set of modules.  This should avoid in most cases expansions
     of the dtv.  */
  dtv_length = GL(dl_tls_max_dtv_idx) + DTV_SURPLUS;
  dtv = calloc (dtv_length + 2, sizeof (dtv_t));
  if (dtv != NULL)
    {
      /* This is the initial length of the dtv.  */
      dtv[0].counter = dtv_length;

      /* The rest of the dtv (including the generation counter) is
       Initialize with zero to indicate nothing there.  */

      /* Add the dtv to the thread data structures.  */
      INSTALL_DTV (result, dtv);
    }
  else
    result = NULL;

  return result;
}


/* Get size and alignment requirements of the static TLS block.  */
void
internal_function
_dl_get_tls_static_info (size_t *sizep, size_t *alignp)
{
  *sizep = GL(dl_tls_static_size);
  *alignp = GL(dl_tls_static_align);
}


void *
internal_function
_dl_allocate_tls_storage (void)
{
  void *result;
  size_t size = GL(dl_tls_static_size);

# if TLS_DTV_AT_TP
  /* Memory layout is:
     [ TLS_PRE_TCB_SIZE ] [ TLS_TCB_SIZE ] [ TLS blocks ]
                    ^ This should be returned.  */
  size += (TLS_PRE_TCB_SIZE + GL(dl_tls_static_align) - 1)
        & ~(GL(dl_tls_static_align) - 1);
# endif

  /* Allocate a correctly aligned chunk of memory.  */
  result = __libc_memalign (GL(dl_tls_static_align), size);
  if (__builtin_expect (result != NULL, 0))
    {
      /* Allocate the DTV.  */
      void *allocated = result;

# if TLS_TCB_AT_TP
      /* The TCB follows the TLS blocks.  */
      result = (char *) result + size - TLS_TCB_SIZE;

      /* Clear the TCB data structure.  We can't ask the caller (i.e.
       libpthread) to do it, because we will initialize the DTV et al.  */
      memset (result, 0, TLS_TCB_SIZE);
# elif TLS_DTV_AT_TP
      result = (char *) result + size - GL(dl_tls_static_size);

      /* Clear the TCB data structure and TLS_PRE_TCB_SIZE bytes before it.
       We can't ask the caller (i.e. libpthread) to do it, because we will
       initialize the DTV et al.  */
      memset ((char *) result - TLS_PRE_TCB_SIZE, 0,
            TLS_PRE_TCB_SIZE + TLS_TCB_SIZE);
# endif

      result = allocate_dtv (result);
      if (result == NULL)
      free (allocated);
    }

  return result;
}


void *
internal_function
_dl_allocate_tls_init (void *result)
{
  if (result == NULL)
    /* The memory allocation failed.  */
    return NULL;

  dtv_t *dtv = GET_DTV (result);
  struct dtv_slotinfo_list *listp;
  size_t total = 0;

  /* We have to look prepare the dtv for all currently loaded
     modules using TLS.  For those which are dynamically loaded we
     add the values indicating deferred allocation.  */
  listp = GL(dl_tls_dtv_slotinfo_list);
  while (1)
    {
      size_t cnt;

      for (cnt = total == 0 ? 1 : 0; cnt < listp->len; ++cnt)
      {
        struct link_map *map;
        void *dest;

        /* Check for the total number of used slots.  */
        if (total + cnt > GL(dl_tls_max_dtv_idx))
          break;

        map = listp->slotinfo[cnt].map;
        if (map == NULL)
          /* Unused entry.  */
          continue;

        if (map->l_tls_offset == 0)
          {
            /* For dynamically loaded modules we simply store
             the value indicating deferred allocation.  */
            dtv[map->l_tls_modid].pointer = TLS_DTV_UNALLOCATED;
            continue;
          }

        assert (map->l_tls_modid == cnt);
        assert (map->l_tls_blocksize >= map->l_tls_initimage_size);
# if TLS_TCB_AT_TP
        assert (map->l_tls_offset >= map->l_tls_blocksize);
        dest = (char *) result - map->l_tls_offset;
# elif TLS_DTV_AT_TP
        dest = (char *) result + map->l_tls_offset;
# else
#  error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
# endif

        /* Copy the initialization image and clear the BSS part.  */
        dtv[map->l_tls_modid].pointer = dest;
        memset (__mempcpy (dest, map->l_tls_initimage,
                       map->l_tls_initimage_size), '\0',
              map->l_tls_blocksize - map->l_tls_initimage_size);
      }

      total += cnt;
      if (total >= GL(dl_tls_max_dtv_idx))
      break;

      listp = listp->next;
      assert (listp != NULL);
    }

  return result;
}
rtld_hidden_def (_dl_allocate_tls_init)

void *
internal_function
_dl_allocate_tls (void *mem)
{
  return _dl_allocate_tls_init (mem == NULL
                        ? _dl_allocate_tls_storage ()
                        : allocate_dtv (mem));
}
rtld_hidden_def (_dl_allocate_tls)


void
internal_function
_dl_deallocate_tls (void *tcb, bool dealloc_tcb)
{
  dtv_t *dtv = GET_DTV (tcb);

  /* The array starts with dtv[-1].  */
  free (dtv - 1);

  if (dealloc_tcb)
    {
# if TLS_TCB_AT_TP
      /* The TCB follows the TLS blocks.  Back up to free the whole block.  */
      tcb -= GL(dl_tls_static_size) - TLS_TCB_SIZE;
# elif TLS_DTV_AT_TP
      /* Back up the TLS_PRE_TCB_SIZE bytes.  */
      tcb -= (TLS_PRE_TCB_SIZE + GL(dl_tls_static_align) - 1)
           & ~(GL(dl_tls_static_align) - 1);
# endif
      free (tcb);
    }
}
rtld_hidden_def (_dl_deallocate_tls)


# ifdef SHARED
/* The __tls_get_addr function has two basic forms which differ in the
   arguments.  The IA-64 form takes two parameters, the module ID and
   offset.  The form used, among others, on IA-32 takes a reference to
   a special structure which contain the same information.  The second
   form seems to be more often used (in the moment) so we default to
   it.  Users of the IA-64 form have to provide adequate definitions
   of the following macros.  */
#  ifndef GET_ADDR_ARGS
#   define GET_ADDR_ARGS tls_index *ti
#  endif
#  ifndef GET_ADDR_MODULE
#   define GET_ADDR_MODULE ti->ti_module
#  endif
#  ifndef GET_ADDR_OFFSET
#   define GET_ADDR_OFFSET ti->ti_offset
#  endif
/* Systems which do not have tls_index also probably have to define
   DONT_USE_TLS_INDEX.  */

#  ifndef __TLS_GET_ADDR
#   define __TLS_GET_ADDR __tls_get_addr
#  endif


/* Return the symbol address given the map of the module it is in and
   the symbol record.  This is used in dl-sym.c.  */
void *
internal_function
_dl_tls_symaddr (struct link_map *map, const ElfW(Sym) *ref)
{
#  ifndef DONT_USE_TLS_INDEX
  tls_index tmp =
    {
      .ti_module = map->l_tls_modid,
      .ti_offset = ref->st_value
    };

  return __TLS_GET_ADDR (&tmp);
#  else
  return __TLS_GET_ADDR (map->l_tls_modid, ref->st_value);
#  endif
}


static void *
allocate_and_init (struct link_map *map)
{
  void *newp;

  newp = __libc_memalign (map->l_tls_align, map->l_tls_blocksize);
  if (newp == NULL)
    oom ();

  /* Initialize the memory.  */
  memset (__mempcpy (newp, map->l_tls_initimage, map->l_tls_initimage_size),
        '\0', map->l_tls_blocksize - map->l_tls_initimage_size);

  return newp;
}


/* The generic dynamic and local dynamic model cannot be used in
   statically linked applications.  */
void *
__tls_get_addr (GET_ADDR_ARGS)
{
  dtv_t *dtv = THREAD_DTV ();
  struct link_map *the_map = NULL;
  void *p;

  if (__builtin_expect (dtv[0].counter != GL(dl_tls_generation), 0))
    {
      struct dtv_slotinfo_list *listp;
      size_t idx;

      /* The global dl_tls_dtv_slotinfo array contains for each module
       index the generation counter current when the entry was
       created.  This array never shrinks so that all module indices
       which were valid at some time can be used to access it.
       Before the first use of a new module index in this function
       the array was extended appropriately.  Access also does not
       have to be guarded against modifications of the array.  It is
       assumed that pointer-size values can be read atomically even
       in SMP environments.  It is possible that other threads at
       the same time dynamically load code and therefore add to the
       slotinfo list.  This is a problem since we must not pick up
       any information about incomplete work.  The solution to this
       is to ignore all dtv slots which were created after the one
       we are currently interested.  We know that dynamic loading
       for this module is completed and this is the last load
       operation we know finished.  */
      idx = GET_ADDR_MODULE;
      listp = GL(dl_tls_dtv_slotinfo_list);
      while (idx >= listp->len)
      {
        idx -= listp->len;
        listp = listp->next;
      }

      if (dtv[0].counter < listp->slotinfo[idx].gen)
      {
        /* The generation counter for the slot is higher than what
           the current dtv implements.  We have to update the whole
           dtv but only those entries with a generation counter <=
           the one for the entry we need.  */
        size_t new_gen = listp->slotinfo[idx].gen;
        size_t total = 0;

        /* We have to look through the entire dtv slotinfo list.  */
        listp =  GL(dl_tls_dtv_slotinfo_list);
        do
          {
            size_t cnt;

            for (cnt = total = 0 ? 1 : 0; cnt < listp->len; ++cnt)
            {
              size_t gen = listp->slotinfo[cnt].gen;
              struct link_map *map;
              size_t modid;

              if (gen > new_gen)
                /* This is a slot for a generation younger than
                   the one we are handling now.  It might be
                   incompletely set up so ignore it.  */
                continue;

              /* If the entry is older than the current dtv layout
                 we know we don't have to handle it.  */
              if (gen <= dtv[0].counter)
                continue;

              /* If there is no map this means the entry is empty.  */
              map = listp->slotinfo[cnt].map;
              if (map == NULL)
                {
                  /* If this modid was used at some point the memory
                   might still be allocated.  */
                  if (dtv[total + cnt].pointer != TLS_DTV_UNALLOCATED)
                  {
                    free (dtv[total + cnt].pointer);
                    dtv[total + cnt].pointer = TLS_DTV_UNALLOCATED;
                  }

                  continue;
                }

              /* Check whether the current dtv array is large enough.  */
              modid = map->l_tls_modid;
              assert (total + cnt == modid);
              if (dtv[-1].counter < modid)
                {
                  /* Reallocate the dtv.  */
                  dtv_t *newp;
                  size_t newsize = GL(dl_tls_max_dtv_idx) + DTV_SURPLUS;
                  size_t oldsize = dtv[-1].counter;

                  assert (map->l_tls_modid <= newsize);

                  if (dtv == GL(dl_initial_dtv))
                  {
                    /* This is the initial dtv that was allocated
                       during rtld startup using the dl-minimal.c
                       malloc instead of the real malloc.  We can't
                       free it, we have to abandon the old storage.  */

                    newp = malloc ((2 + newsize) * sizeof (dtv_t));
                    if (newp == NULL)
                      oom ();
                    memcpy (newp, &dtv[-1], oldsize * sizeof (dtv_t));
                  }
                  else
                  {
                    newp = realloc (&dtv[-1],
                                (2 + newsize) * sizeof (dtv_t));
                    if (newp == NULL)
                      oom ();
                  }

                  newp[0].counter = newsize;

                  /* Clear the newly allocated part.  */
                  memset (newp + 2 + oldsize, '\0',
                        (newsize - oldsize) * sizeof (dtv_t));

                  /* Point dtv to the generation counter.  */
                  dtv = &newp[1];

                  /* Install this new dtv in the thread data
                   structures.  */
                  INSTALL_NEW_DTV (dtv);
                }

              /* If there is currently memory allocate for this
                 dtv entry free it.  */
              /* XXX Ideally we will at some point create a memory
                 pool.  */
              if (dtv[modid].pointer != TLS_DTV_UNALLOCATED)
                /* Note that free is called for NULL is well.  We
                   deallocate even if it is this dtv entry we are
                   supposed to load.  The reason is that we call
                   memalign and not malloc.  */
                free (dtv[modid].pointer);

              /* This module is loaded dynamically- We defer
                 memory allocation.  */
              dtv[modid].pointer = TLS_DTV_UNALLOCATED;

              if (modid == GET_ADDR_MODULE)
                the_map = map;
            }

            total += listp->len;
          }
        while ((listp = listp->next) != NULL);

        /* This will be the new maximum generation counter.  */
        dtv[0].counter = new_gen;
      }
    }

  p = dtv[GET_ADDR_MODULE].pointer;

  if (__builtin_expect (p == TLS_DTV_UNALLOCATED, 0))
    {
      /* The allocation was deferred.  Do it now.  */
      if (the_map == NULL)
      {
        /* Find the link map for this module.  */
        size_t idx = GET_ADDR_MODULE;
        struct dtv_slotinfo_list *listp = GL(dl_tls_dtv_slotinfo_list);

        while (idx >= listp->len)
          {
            idx -= listp->len;
            listp = listp->next;
          }

        the_map = listp->slotinfo[idx].map;
      }

      p = dtv[GET_ADDR_MODULE].pointer = allocate_and_init (the_map);
    }

  return (char *) p + GET_ADDR_OFFSET;
}
# endif

#endif      /* use TLS */

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