/* Subroutines needed for unwinding stack frames for exception handling.  */

/* Copyright (C) 1997-2018 Free Software Foundation, Inc.

   Contributed by Jason Merrill <jason@cygnus.com>.

   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

   <http://www.gnu.org/licenses/>.  */

#ifdef _LIBC

# include <shlib-compat.h>

#endif

#if !defined _LIBC || SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2_5)

#ifdef _LIBC

#include <stdlib.h>

#include <string.h>

#include <libc-lock.h>

#include <dwarf2.h>

#include <unwind.h>

#define NO_BASE_OF_ENCODED_VALUE

#include <unwind-pe.h>

#include <unwind-dw2-fde.h>

#else

#ifndef _Unwind_Find_FDE

#include "tconfig.h"

#include "tsystem.h"

#include "dwarf2.h"

#include "unwind.h"

#define NO_BASE_OF_ENCODED_VALUE

#include "unwind-pe.h"

#include "unwind-dw2-fde.h"

#include "gthr.h"

#endif

#endif

/* The unseen_objects list contains objects that have been registered

   but not yet categorized in any way.  The seen_objects list has had

   it's pc_begin and count fields initialized at minimum, and is sorted

   by decreasing value of pc_begin.  */

static struct object *unseen_objects;

static struct object *seen_objects;

#ifdef _LIBC

__libc_lock_define_initialized (static, object_mutex)

#define init_object_mutex_once()

#define __gthread_mutex_lock(m) __libc_lock_lock (*(m))

#define __gthread_mutex_unlock(m) __libc_lock_unlock (*(m))

void __register_frame_info_bases (void *begin, struct object *ob,

				  void *tbase, void *dbase);

hidden_proto (__register_frame_info_bases)

void __register_frame_info_table_bases (void *begin,

					struct object *ob,

					void *tbase, void *dbase);

hidden_proto (__register_frame_info_table_bases)

void *__deregister_frame_info_bases (void *begin);

hidden_proto (__deregister_frame_info_bases)

#else

#ifdef __GTHREAD_MUTEX_INIT

static __gthread_mutex_t object_mutex = __GTHREAD_MUTEX_INIT;

#else

static __gthread_mutex_t object_mutex;

#endif

#ifdef __GTHREAD_MUTEX_INIT_FUNCTION

static void

init_object_mutex (void)

{

  __GTHREAD_MUTEX_INIT_FUNCTION (&object_mutex);

}

static void

init_object_mutex_once (void)

{

  static __gthread_once_t once = __GTHREAD_ONCE_INIT;

  __gthread_once (&once, init_object_mutex);

}

#else

#define init_object_mutex_once()

#endif

#endif /* _LIBC */

/* Called from crtbegin.o to register the unwind info for an object.  */

void

__register_frame_info_bases (void *begin, struct object *ob,

			     void *tbase, void *dbase)

{

  /* If .eh_frame is empty, don't register at all.  */

  if (*(uword *) begin == 0)

    return;

  ob->pc_begin = (void *)-1;

  ob->tbase = tbase;

  ob->dbase = dbase;

  ob->u.single = begin;

  ob->s.i = 0;

  ob->s.b.encoding = DW_EH_PE_omit;

#ifdef DWARF2_OBJECT_END_PTR_EXTENSION

  ob->fde_end = NULL;

#endif

  init_object_mutex_once ();

  __gthread_mutex_lock (&object_mutex);

  ob->next = unseen_objects;

  unseen_objects = ob;

  __gthread_mutex_unlock (&object_mutex);

}

hidden_def (__register_frame_info_bases)

void

__register_frame_info (void *begin, struct object *ob)

{

  __register_frame_info_bases (begin, ob, 0, 0);

}

void

__register_frame (void *begin)

{

  struct object *ob;

  /* If .eh_frame is empty, don't register at all.  */

  if (*(uword *) begin == 0)

    return;

  ob = (struct object *) malloc (sizeof (struct object));

  __register_frame_info_bases (begin, ob, 0, 0);

}

/* Similar, but BEGIN is actually a pointer to a table of unwind entries

   for different translation units.  Called from the file generated by

   collect2.  */

void

__register_frame_info_table_bases (void *begin, struct object *ob,

				   void *tbase, void *dbase)

{

  ob->pc_begin = (void *)-1;

  ob->tbase = tbase;

  ob->dbase = dbase;

  ob->u.array = begin;

  ob->s.i = 0;

  ob->s.b.from_array = 1;

  ob->s.b.encoding = DW_EH_PE_omit;

  init_object_mutex_once ();

  __gthread_mutex_lock (&object_mutex);

  ob->next = unseen_objects;

  unseen_objects = ob;

  __gthread_mutex_unlock (&object_mutex);

}

hidden_def (__register_frame_info_table_bases)

void

__register_frame_info_table (void *begin, struct object *ob)

{

  __register_frame_info_table_bases (begin, ob, 0, 0);

}

void

__register_frame_table (void *begin)

{

  struct object *ob = (struct object *) malloc (sizeof (struct object));

  __register_frame_info_table_bases (begin, ob, 0, 0);

}

/* Called from crtbegin.o to deregister the unwind info for an object.  */

/* ??? Glibc has for a while now exported __register_frame_info and

   __deregister_frame_info.  If we call __register_frame_info_bases

   from crtbegin (wherein it is declared weak), and this object does

   not get pulled from libgcc.a for other reasons, then the

   invocation of __deregister_frame_info will be resolved from glibc.

   Since the registration did not happen there, we'll abort.

   Therefore, declare a new deregistration entry point that does the

   exact same thing, but will resolve to the same library as

   implements __register_frame_info_bases.  */

void *

__deregister_frame_info_bases (void *begin)

{

  struct object **p;

  struct object *ob = 0;

  struct fde_vector *tofree = NULL;

  /* If .eh_frame is empty, we haven't registered.  */

  if (*(uword *) begin == 0)

    return ob;

  init_object_mutex_once ();

  __gthread_mutex_lock (&object_mutex);

  for (p = &unseen_objects; *p ; p = &(*p)->next)

    if ((*p)->u.single == begin)

      {

	ob = *p;

	*p = ob->next;

	goto out;

      }

  for (p = &seen_objects; *p ; p = &(*p)->next)

    if ((*p)->s.b.sorted)

      {

	if ((*p)->u.sort->orig_data == begin)

	  {

	    ob = *p;

	    *p = ob->next;

	    tofree = ob->u.sort;

	    goto out;

	  }

      }

    else

      {

	if ((*p)->u.single == begin)

	  {

	    ob = *p;

	    *p = ob->next;

	    goto out;

	  }

      }

  __gthread_mutex_unlock (&object_mutex);

  abort ();

 out:

  __gthread_mutex_unlock (&object_mutex);

  free (tofree);

  return (void *) ob;

}

hidden_def (__deregister_frame_info_bases)

void *

__deregister_frame_info (void *begin)

{

  return __deregister_frame_info_bases (begin);

}

void

__deregister_frame (void *begin)

{

  /* If .eh_frame is empty, we haven't registered.  */

  if (*(uword *) begin != 0)

    free (__deregister_frame_info_bases (begin));

}

/* Like base_of_encoded_value, but take the base from a struct object

   instead of an _Unwind_Context.  */

static _Unwind_Ptr

base_from_object (unsigned char encoding, struct object *ob)

{

  if (encoding == DW_EH_PE_omit)

    return 0;

  switch (encoding & 0x70)

    {

    case DW_EH_PE_absptr:

    case DW_EH_PE_pcrel:

    case DW_EH_PE_aligned:

      return 0;

    case DW_EH_PE_textrel:

      return (_Unwind_Ptr) ob->tbase;

    case DW_EH_PE_datarel:

      return (_Unwind_Ptr) ob->dbase;

    }

  abort ();

}

/* Return the FDE pointer encoding from the CIE.  */

/* ??? This is a subset of extract_cie_info from unwind-dw2.c.  */

static int

get_cie_encoding (struct dwarf_cie *cie)

{

  const unsigned char *aug, *p;

  _Unwind_Ptr dummy;

  _Unwind_Word utmp;

  _Unwind_Sword stmp;

  aug = cie->augmentation;

  if (aug[0] != 'z')

    return DW_EH_PE_absptr;

  /* Skip the augmentation string.  */

  p = aug + strlen ((const char *) aug) + 1;

  p = read_uleb128 (p, &utmp);		/* Skip code alignment.  */

  p = read_sleb128 (p, &stmp);		/* Skip data alignment.  */

  p++;					/* Skip return address column.  */

  aug++;				/* Skip 'z' */

  p = read_uleb128 (p, &utmp);		/* Skip augmentation length.  */

  while (1)

    {

      /* This is what we're looking for.  */

      if (*aug == 'R')

	return *p;

      /* Personality encoding and pointer.  */

      else if (*aug == 'P')

	{

	  /* ??? Avoid dereferencing indirect pointers, since we're

	     faking the base address.  Gotta keep DW_EH_PE_aligned

	     intact, however.  */

	  p = read_encoded_value_with_base (*p & 0x7F, 0, p + 1, &dummy);

	}

      /* LSDA encoding.  */

      else if (*aug == 'L')

	p++;

      /* Otherwise end of string, or unknown augmentation.  */

      else

	return DW_EH_PE_absptr;

      aug++;

    }

}

static inline int

get_fde_encoding (struct dwarf_fde *f)

{

  return get_cie_encoding (get_cie (f));

}

/* Sorting an array of FDEs by address.

   (Ideally we would have the linker sort the FDEs so we don't have to do

   it at run time. But the linkers are not yet prepared for this.)  */

/* Return the Nth pc_begin value from FDE x.  */

static inline _Unwind_Ptr

get_pc_begin (fde *x, size_t n)

{

  _Unwind_Ptr p;

  memcpy (&p, x->pc_begin + n * sizeof (_Unwind_Ptr), sizeof (_Unwind_Ptr));

  return p;

}

/* Comparison routines.  Three variants of increasing complexity.  */

static int

fde_unencoded_compare (struct object *ob __attribute__((unused)),

		       fde *x, fde *y)

{

  _Unwind_Ptr x_ptr = get_pc_begin (x, 0);

  _Unwind_Ptr y_ptr = get_pc_begin (y, 0);

  if (x_ptr > y_ptr)

    return 1;

  if (x_ptr < y_ptr)

    return -1;

  return 0;

}

static int

fde_single_encoding_compare (struct object *ob, fde *x, fde *y)

{

  _Unwind_Ptr base, x_ptr, y_ptr;

  base = base_from_object (ob->s.b.encoding, ob);

  read_encoded_value_with_base (ob->s.b.encoding, base, x->pc_begin, &x_ptr);

  read_encoded_value_with_base (ob->s.b.encoding, base, y->pc_begin, &y_ptr);

  if (x_ptr > y_ptr)

    return 1;

  if (x_ptr < y_ptr)

    return -1;

  return 0;

}

static int

fde_mixed_encoding_compare (struct object *ob, fde *x, fde *y)

{

  int x_encoding, y_encoding;

  _Unwind_Ptr x_ptr, y_ptr;

  x_encoding = get_fde_encoding (x);

  read_encoded_value_with_base (x_encoding, base_from_object (x_encoding, ob),

				x->pc_begin, &x_ptr);

  y_encoding = get_fde_encoding (y);

  read_encoded_value_with_base (y_encoding, base_from_object (y_encoding, ob),

				y->pc_begin, &y_ptr);

  if (x_ptr > y_ptr)

    return 1;

  if (x_ptr < y_ptr)

    return -1;

  return 0;

}

typedef int (*fde_compare_t) (struct object *, fde *, fde *);

/* This is a special mix of insertion sort and heap sort, optimized for

   the data sets that actually occur. They look like

   101 102 103 127 128 105 108 110 190 111 115 119 125 160 126 129 130.

   I.e. a linearly increasing sequence (coming from functions in the text

   section), with additionally a few unordered elements (coming from functions

   in gnu_linkonce sections) whose values are higher than the values in the

   surrounding linear sequence (but not necessarily higher than the values

   at the end of the linear sequence!).

   The worst-case total run time is O(N) + O(n log (n)), where N is the

   total number of FDEs and n is the number of erratic ones.  */

struct fde_accumulator

{

  struct fde_vector *linear;

  struct fde_vector *erratic;

};

static int

start_fde_sort (struct fde_accumulator *accu, size_t count)

{

  size_t size;

  if (! count)

    return 0;

  size = sizeof (struct fde_vector) + sizeof (fde *) * count;

  if ((accu->linear = (struct fde_vector *) malloc (size)))

    {

      accu->linear->count = 0;

      if ((accu->erratic = (struct fde_vector *) malloc (size)))

	accu->erratic->count = 0;

      return 1;

    }

  else

    return 0;

}

static inline void

fde_insert (struct fde_accumulator *accu, fde *this_fde)

{

  if (accu->linear)

    accu->linear->array[accu->linear->count++] = this_fde;

}

/* Split LINEAR into a linear sequence with low values and an erratic

   sequence with high values, put the linear one (of longest possible

   length) into LINEAR and the erratic one into ERRATIC. This is O(N).

   Because the longest linear sequence we are trying to locate within the

   incoming LINEAR array can be interspersed with (high valued) erratic

   entries.  We construct a chain indicating the sequenced entries.

   To avoid having to allocate this chain, we overlay it onto the space of

   the ERRATIC array during construction.  A final pass iterates over the

   chain to determine what should be placed in the ERRATIC array, and

   what is the linear sequence.  This overlay is safe from aliasing.  */

static void

fde_split (struct object *ob, fde_compare_t fde_compare,

	   struct fde_vector *linear, struct fde_vector *erratic)

{

  static fde *marker;

  size_t count = linear->count;

  fde **chain_end = ▮

  size_t i, j, k;

  /* This should optimize out, but it is wise to make sure this assumption

     is correct. Should these have different sizes, we cannot cast between

     them and the overlaying onto ERRATIC will not work.  */

  if (sizeof (fde *) != sizeof (fde **))

    abort ();

  for (i = 0; i < count; i++)

    {

      fde **probe;

      for (probe = chain_end;

	   probe != &marker && fde_compare (ob, linear->array[i], *probe) < 0;

	   probe = chain_end)

	{

	  chain_end = (fde **) erratic->array[probe - linear->array];

	  erratic->array[probe - linear->array] = NULL;

	}

      erratic->array[i] = (fde *) chain_end;

      chain_end = &linear->array[i];

    }

  /* Each entry in LINEAR which is part of the linear sequence we have

     discovered will correspond to a non-NULL entry in the chain we built in

     the ERRATIC array.  */

  for (i = j = k = 0; i < count; i++)

    if (erratic->array[i])

      linear->array[j++] = linear->array[i];

    else

      erratic->array[k++] = linear->array[i];

  linear->count = j;

  erratic->count = k;

}

/* This is O(n log(n)).  BSD/OS defines heapsort in stdlib.h, so we must

   use a name that does not conflict.  */

static void

frame_heapsort (struct object *ob, fde_compare_t fde_compare,

		struct fde_vector *erratic)

{

  /* For a description of this algorithm, see:

     Samuel P. Harbison, Guy L. Steele Jr.: C, a reference manual, 2nd ed.,

     p. 60-61.  */

  fde ** a = erratic->array;

  /* A portion of the array is called a "heap" if for all i>=0:

     If i and 2i+1 are valid indices, then a[i] >= a[2i+1].

     If i and 2i+2 are valid indices, then a[i] >= a[2i+2].  */

#define SWAP(x,y) do { fde * tmp = x; x = y; y = tmp; } while (0)

  size_t n = erratic->count;

  size_t m = n;

  size_t i;

  while (m > 0)

    {

      /* Invariant: a[m..n-1] is a heap.  */

      m--;

      for (i = m; 2*i+1 < n; )

	{

	  if (2*i+2 < n

	      && fde_compare (ob, a[2*i+2], a[2*i+1]) > 0

	      && fde_compare (ob, a[2*i+2], a[i]) > 0)

	    {

	      SWAP (a[i], a[2*i+2]);

	      i = 2*i+2;

	    }

	  else if (fde_compare (ob, a[2*i+1], a[i]) > 0)

	    {

	      SWAP (a[i], a[2*i+1]);

	      i = 2*i+1;

	    }

	  else

	    break;

	}

    }

  while (n > 1)

    {

      /* Invariant: a[0..n-1] is a heap.  */

      n--;

      SWAP (a[0], a[n]);

      for (i = 0; 2*i+1 < n; )

	{

	  if (2*i+2 < n

	      && fde_compare (ob, a[2*i+2], a[2*i+1]) > 0

	      && fde_compare (ob, a[2*i+2], a[i]) > 0)

	    {

	      SWAP (a[i], a[2*i+2]);

	      i = 2*i+2;

	    }

	  else if (fde_compare (ob, a[2*i+1], a[i]) > 0)

	    {

	      SWAP (a[i], a[2*i+1]);

	      i = 2*i+1;

	    }

	  else

	    break;

	}

    }

#undef SWAP

}

/* Merge V1 and V2, both sorted, and put the result into V1.  */

static void

fde_merge (struct object *ob, fde_compare_t fde_compare,

	   struct fde_vector *v1, struct fde_vector *v2)

{

  size_t i1, i2;

  fde * fde2;

  i2 = v2->count;

  if (i2 > 0)

    {

      i1 = v1->count;

      do

	{

	  i2--;

	  fde2 = v2->array[i2];

	  while (i1 > 0 && fde_compare (ob, v1->array[i1-1], fde2) > 0)

	    {

	      v1->array[i1+i2] = v1->array[i1-1];

	      i1--;

	    }

	  v1->array[i1+i2] = fde2;

	}

      while (i2 > 0);

      v1->count += v2->count;

    }

}

static void

end_fde_sort (struct object *ob, struct fde_accumulator *accu, size_t count)

{

  fde_compare_t fde_compare;

  if (accu->linear->count != count)

    abort ();

  if (ob->s.b.mixed_encoding)

    fde_compare = fde_mixed_encoding_compare;

  else if (ob->s.b.encoding == DW_EH_PE_absptr)

    fde_compare = fde_unencoded_compare;

  else

    fde_compare = fde_single_encoding_compare;

  if (accu->erratic)

    {

      fde_split (ob, fde_compare, accu->linear, accu->erratic);

      if (accu->linear->count + accu->erratic->count != count)

	abort ();

      frame_heapsort (ob, fde_compare, accu->erratic);

      fde_merge (ob, fde_compare, accu->linear, accu->erratic);

      free (accu->erratic);

    }

  else

    {

      /* We've not managed to malloc an erratic array,

	 so heap sort in the linear one.  */

      frame_heapsort (ob, fde_compare, accu->linear);

    }

}

/* Update encoding, mixed_encoding, and pc_begin for OB for the

   fde array beginning at THIS_FDE.  Return the number of fdes

   encountered along the way.  */

static size_t

classify_object_over_fdes (struct object *ob, fde *this_fde)

{

  struct dwarf_cie *last_cie = 0;

  size_t count = 0;

  int encoding = DW_EH_PE_absptr;

  _Unwind_Ptr base = 0;

  for (; ! last_fde (ob, this_fde); this_fde = next_fde (this_fde))

    {

      struct dwarf_cie *this_cie;

      _Unwind_Ptr mask, pc_begin;

      /* Skip CIEs.  */

      if (this_fde->CIE_delta == 0)

	continue;

      /* Determine the encoding for this FDE.  Note mixed encoded

	 objects for later.  */

      this_cie = get_cie (this_fde);

      if (this_cie != last_cie)

	{

	  last_cie = this_cie;

	  encoding = get_cie_encoding (this_cie);

	  base = base_from_object (encoding, ob);

	  if (ob->s.b.encoding == DW_EH_PE_omit)

	    ob->s.b.encoding = encoding;

	  else if (ob->s.b.encoding != encoding)

	    ob->s.b.mixed_encoding = 1;

	}

      read_encoded_value_with_base (encoding, base, this_fde->pc_begin,

				    &pc_begin);

      /* Take care to ignore link-once functions that were removed.

	 In these cases, the function address will be NULL, but if

	 the encoding is smaller than a pointer a true NULL may not

	 be representable.  Assume 0 in the representable bits is NULL.  */

      mask = size_of_encoded_value (encoding);

      if (mask < sizeof (void *))

	mask = (1L << (mask << 3)) - 1;

      else

	mask = -1;

      if ((pc_begin & mask) == 0)

	continue;

      count += 1;

      if ((void *) pc_begin < ob->pc_begin)

	ob->pc_begin = (void *) pc_begin;

    }

  return count;

}

static void

add_fdes (struct object *ob, struct fde_accumulator *accu, fde *this_fde)

{

  struct dwarf_cie *last_cie = 0;

  int encoding = ob->s.b.encoding;

  _Unwind_Ptr base = base_from_object (ob->s.b.encoding, ob);

  for (; ! last_fde (ob, this_fde); this_fde = next_fde (this_fde))

    {

      struct dwarf_cie *this_cie;

      /* Skip CIEs.  */

      if (this_fde->CIE_delta == 0)

	continue;

      if (ob->s.b.mixed_encoding)

	{

	  /* Determine the encoding for this FDE.  Note mixed encoded

	     objects for later.  */

	  this_cie = get_cie (this_fde);

	  if (this_cie != last_cie)

	    {

	      last_cie = this_cie;

	      encoding = get_cie_encoding (this_cie);

	      base = base_from_object (encoding, ob);

	    }

	}

      if (encoding == DW_EH_PE_absptr)

	{

	  if (get_pc_begin (this_fde, 0) == 0)

	    continue;

	}

      else

	{

	  _Unwind_Ptr pc_begin, mask;

	  read_encoded_value_with_base (encoding, base, this_fde->pc_begin,

					&pc_begin);

	  /* Take care to ignore link-once functions that were removed.

	     In these cases, the function address will be NULL, but if

	     the encoding is smaller than a pointer a true NULL may not

	     be representable.  Assume 0 in the representable bits is NULL.  */

	  mask = size_of_encoded_value (encoding);

	  if (mask < sizeof (void *))

	    mask = (1L << (mask << 3)) - 1;

	  else

	    mask = -1;

	  if ((pc_begin & mask) == 0)

	    continue;

	}

      fde_insert (accu, this_fde);

    }

}

/* Set up a sorted array of pointers to FDEs for a loaded object.  We

   count up the entries before allocating the array because it's likely to

   be faster.  We can be called multiple times, should we have failed to

   allocate a sorted fde array on a previous occasion.  */

static void

init_object (struct object* ob)

{

  struct fde_accumulator accu;

  size_t count;

  count = ob->s.b.count;

  if (count == 0)

    {

      if (ob->s.b.from_array)

	{

	  fde **p = ob->u.array;

	  for (count = 0; *p; ++p)

	    count += classify_object_over_fdes (ob, *p);

	}

      else

	count = classify_object_over_fdes (ob, ob->u.single);

      /* The count field we have in the main struct object is somewhat

	 limited, but should suffice for virtually all cases.  If the

	 counted value doesn't fit, re-write a zero.  The worst that

	 happens is that we re-count next time -- admittedly non-trivial

	 in that this implies some 2M fdes, but at least we function.  */

      ob->s.b.count = count;

      if (ob->s.b.count != count)

	ob->s.b.count = 0;

    }

  if (!start_fde_sort (&accu, count))

    return;

  if (ob->s.b.from_array)

    {

      fde **p;

      for (p = ob->u.array; *p; ++p)

	add_fdes (ob, &accu, *p);

    }

  else

    add_fdes (ob, &accu, ob->u.single);

  end_fde_sort (ob, &accu, count);

  /* Save the original fde pointer, since this is the key by which the

     DSO will deregister the object.  */

  accu.linear->orig_data = ob->u.single;

  ob->u.sort = accu.linear;

  ob->s.b.sorted = 1;

}

/* A linear search through a set of FDEs for the given PC.  This is

   used when there was insufficient memory to allocate and sort an

   array.  */

static fde *

linear_search_fdes (struct object *ob, fde *this_fde, void *pc)

{

  struct dwarf_cie *last_cie = 0;

  int encoding = ob->s.b.encoding;

  _Unwind_Ptr base = base_from_object (ob->s.b.encoding, ob);

  for (; ! last_fde (ob, this_fde); this_fde = next_fde (this_fde))

    {

      struct dwarf_cie *this_cie;

      _Unwind_Ptr pc_begin, pc_range;

      /* Skip CIEs.  */

      if (this_fde->CIE_delta == 0)

	continue;

      if (ob->s.b.mixed_encoding)

	{

	  /* Determine the encoding for this FDE.  Note mixed encoded

	     objects for later.  */

	  this_cie = get_cie (this_fde);

	  if (this_cie != last_cie)

	    {

	      last_cie = this_cie;

	      encoding = get_cie_encoding (this_cie);

	      base = base_from_object (encoding, ob);

	    }

	}

      if (encoding == DW_EH_PE_absptr)

	{

	  pc_begin = get_pc_begin (this_fde, 0);

	  pc_range = get_pc_begin (this_fde, 1);

	  if (pc_begin == 0)

	    continue;

	}

      else

	{

	  _Unwind_Ptr mask;

	  const unsigned char *p;

	  p = read_encoded_value_with_base (encoding, base,

					    this_fde->pc_begin, &pc_begin);

	  read_encoded_value_with_base (encoding & 0x0F, 0, p, &pc_range);

	  /* Take care to ignore link-once functions that were removed.

	     In these cases, the function address will be NULL, but if

	     the encoding is smaller than a pointer a true NULL may not

	     be representable.  Assume 0 in the representable bits is NULL.  */

	  mask = size_of_encoded_value (encoding);

	  if (mask < sizeof (void *))

	    mask = (1L << (mask << 3)) - 1;

	  else

	    mask = -1;

	  if ((pc_begin & mask) == 0)

	    continue;

	}

      if ((_Unwind_Ptr) pc - pc_begin < pc_range)

	return this_fde;

    }

  return NULL;

}