{
	      /* This is a new opcode the generator but not we know about.
		 Read the parameters associated with it but then discard
		 everything.  Read all the parameters for this opcode.  */
	      for (int n = standard_opcode_lengths[opcode]; n > 0; --n)
		get_uleb128 (u128, linep);

	      /* Next round, ignore this opcode.  */
	      continue;
	    }
	}

      /* Put all the files in an array.  */
      Dwarf_Files *files = libdw_alloc (dbg, Dwarf_Files,
					sizeof (Dwarf_Files)
					+ nfilelist * sizeof (Dwarf_Fileinfo)
					+ (ndirlist + 1) * sizeof (char *),
					1);
      const char **dirs = (void *) &files->info[nfilelist];

      files->nfiles = nfilelist;
      while (nfilelist-- > 0)
	{
	  files->info[nfilelist] = filelist->info;
	  filelist = filelist->next;
	}
      assert (filelist == NULL);

      /* Put all the directory strings in an array.  */
      files->ndirs = ndirlist;
      for (unsigned int i = 0; i < ndirlist; ++i)
예제 #2
0
int
dwarf_getlocation_implicit_value (Dwarf_Attribute *attr, const Dwarf_Op *op,
				  Dwarf_Block *return_block)
{
  if (attr == NULL)
    return -1;

  struct loc_block_s fake = { .addr = (void *) op };
  struct loc_block_s **found = tfind (&fake, &attr->cu->locs, loc_compare);
  if (unlikely (found == NULL))
    {
      __libdw_seterrno (DWARF_E_NO_BLOCK);
      return -1;
    }

  return_block->length = (*found)->length;
  return_block->data = (*found)->data;
  return 0;
}

/* DW_AT_data_member_location can be a constant as well as a loclistptr.
   Only data[48] indicate a loclistptr.  */
static int
check_constant_offset (Dwarf_Attribute *attr,
		       Dwarf_Op **llbuf, size_t *listlen)
{
  if (attr->code != DW_AT_data_member_location)
    return 1;

  switch (attr->form)
    {
      /* Punt for any non-constant form.  */
    default:
      return 1;

    case DW_FORM_data1:
    case DW_FORM_data2:
    case DW_FORM_data4:
    case DW_FORM_data8:
    case DW_FORM_sdata:
    case DW_FORM_udata:
      break;
    }

  /* Check whether we already cached this location.  */
  struct loc_s fake = { .addr = attr->valp };
  struct loc_s **found = tfind (&fake, &attr->cu->locs, loc_compare);

  if (found == NULL)
    {
      Dwarf_Word offset;
      if (INTUSE(dwarf_formudata) (attr, &offset) != 0)
	return -1;

      Dwarf_Op *result = libdw_alloc (attr->cu->dbg,
				      Dwarf_Op, sizeof (Dwarf_Op), 1);

      result->atom = DW_OP_plus_uconst;
      result->number = offset;
      result->number2 = 0;
      result->offset = 0;

      /* Insert a record in the search tree so we can find it again later.  */
      struct loc_s *newp = libdw_alloc (attr->cu->dbg,
					struct loc_s, sizeof (struct loc_s),
					1);
      newp->addr = attr->valp;
      newp->loc = result;
      newp->nloc = 1;

      found = tsearch (newp, &attr->cu->locs, loc_compare);
    }

  assert ((*found)->nloc == 1);

  if (llbuf != NULL)
    {
      *llbuf = (*found)->loc;
      *listlen = 1;
    }

  return 0;
}

int
internal_function
__libdw_intern_expression (Dwarf *dbg, bool other_byte_order,
			   unsigned int address_size, unsigned int ref_size,
			   void **cache, const Dwarf_Block *block,
			   bool cfap, bool valuep,
			   Dwarf_Op **llbuf, size_t *listlen, int sec_index)
{
  /* Empty location expressions don't have any ops to intern.  */
  if (block->length == 0)
    {
      *listlen = 0;
      return 0;
    }

  /* Check whether we already looked at this list.  */
  struct loc_s fake = { .addr = block->data };
  struct loc_s **found = tfind (&fake, cache, loc_compare);
  if (found != NULL)
    {
      /* We already saw it.  */
      *llbuf = (*found)->loc;
      *listlen = (*found)->nloc;

      if (valuep)
	{
	  assert (*listlen > 1);
	  assert ((*llbuf)[*listlen - 1].atom == DW_OP_stack_value);
	}

      return 0;
    }

  const unsigned char *data = block->data;
  const unsigned char *const end_data = data + block->length;

  const struct { bool other_byte_order; } bo = { other_byte_order };

  struct loclist *loclist = NULL;
  unsigned int n = 0;

  /* Stack allocate at most this many locs.  */
#define MAX_STACK_LOCS 256
  struct loclist stack_locs[MAX_STACK_LOCS];
#define NEW_LOC() ({ struct loclist *ll;			\
		     ll = (likely (n < MAX_STACK_LOCS)		\
			   ? &stack_locs[n]			\
			   : malloc (sizeof (struct loclist)));	\
		     if (unlikely (ll == NULL))			\
		       goto nomem;				\
		     n++;					\
		     ll->next = loclist;			\
		     loclist = ll;				\
		     ll; })

  if (cfap)
    {
      /* Synthesize the operation to push the CFA before the expression.  */
      struct loclist *newloc = NEW_LOC ();
      newloc->atom = DW_OP_call_frame_cfa;
      newloc->number = 0;
      newloc->number2 = 0;
      newloc->offset = -1;
    }

  /* Decode the opcodes.  It is possible in some situations to have a
     block of size zero.  */
  while (data < end_data)
    {
      struct loclist *newloc;
      newloc = NEW_LOC ();
      newloc->number = 0;
      newloc->number2 = 0;
      newloc->offset = data - block->data;

      switch ((newloc->atom = *data++))
	{
	case DW_OP_addr:
	  /* Address, depends on address size of CU.  */
	  if (dbg == NULL)
	    {
	      // XXX relocation?
	      if (address_size == 4)
		{
		  if (unlikely (data + 4 > end_data))
		    goto invalid;
		  else
		    newloc->number = read_4ubyte_unaligned_inc (&bo, data);
		}
	      else
		{
		  if (unlikely (data + 8 > end_data))
		    goto invalid;
		  else
		    newloc->number = read_8ubyte_unaligned_inc (&bo, data);
		}
	    }
	  else if (__libdw_read_address_inc (dbg, sec_index, &data,
					     address_size, &newloc->number))
	    goto invalid;
	  break;

	case DW_OP_call_ref:
	  /* DW_FORM_ref_addr, depends on offset size of CU.  */
	  if (dbg == NULL || __libdw_read_offset_inc (dbg, sec_index, &data,
						      ref_size,
						      &newloc->number,
						      IDX_debug_info, 0))
	    goto invalid;
	  break;

	case DW_OP_deref:
	case DW_OP_dup:
	case DW_OP_drop:
	case DW_OP_over:
	case DW_OP_swap:
	case DW_OP_rot:
	case DW_OP_xderef:
	case DW_OP_abs:
	case DW_OP_and:
	case DW_OP_div:
	case DW_OP_minus:
	case DW_OP_mod:
	case DW_OP_mul:
	case DW_OP_neg:
	case DW_OP_not:
	case DW_OP_or:
	case DW_OP_plus:
	case DW_OP_shl:
	case DW_OP_shr:
	case DW_OP_shra:
	case DW_OP_xor:
	case DW_OP_eq:
	case DW_OP_ge:
	case DW_OP_gt:
	case DW_OP_le:
	case DW_OP_lt:
	case DW_OP_ne:
	case DW_OP_lit0 ... DW_OP_lit31:
	case DW_OP_reg0 ... DW_OP_reg31:
	case DW_OP_nop:
	case DW_OP_push_object_address:
	case DW_OP_call_frame_cfa:
	case DW_OP_form_tls_address:
	case DW_OP_GNU_push_tls_address:
	case DW_OP_stack_value:
	  /* No operand.  */
	  break;

	case DW_OP_const1u:
	case DW_OP_pick:
	case DW_OP_deref_size:
	case DW_OP_xderef_size:
	  if (unlikely (data >= end_data))
	    {
	    invalid:
	      __libdw_seterrno (DWARF_E_INVALID_DWARF);
	    returnmem:
	      /* Free any dynamicly allocated loclists, if any.  */
	      while (n > MAX_STACK_LOCS)
		{
		  struct loclist *loc = loclist;
		  loclist = loc->next;
		  free (loc);
		  n--;
		}
	      return -1;
	    }

	  newloc->number = *data++;
	  break;

	case DW_OP_const1s:
	  if (unlikely (data >= end_data))
	    goto invalid;

	  newloc->number = *((int8_t *) data);
	  ++data;
	  break;

	case DW_OP_const2u:
	  if (unlikely (data + 2 > end_data))
	    goto invalid;

	  newloc->number = read_2ubyte_unaligned_inc (&bo, data);
	  break;

	case DW_OP_const2s:
	case DW_OP_skip:
	case DW_OP_bra:
	case DW_OP_call2:
	  if (unlikely (data + 2 > end_data))
	    goto invalid;

	  newloc->number = read_2sbyte_unaligned_inc (&bo, data);
	  break;

	case DW_OP_const4u:
	  if (unlikely (data + 4 > end_data))
	    goto invalid;

	  newloc->number = read_4ubyte_unaligned_inc (&bo, data);
	  break;

	case DW_OP_const4s:
	case DW_OP_call4:
	case DW_OP_GNU_parameter_ref:
	  if (unlikely (data + 4 > end_data))
	    goto invalid;

	  newloc->number = read_4sbyte_unaligned_inc (&bo, data);
	  break;

	case DW_OP_const8u:
	  if (unlikely (data + 8 > end_data))
	    goto invalid;

	  newloc->number = read_8ubyte_unaligned_inc (&bo, data);
	  break;

	case DW_OP_const8s:
	  if (unlikely (data + 8 > end_data))
	    goto invalid;

	  newloc->number = read_8sbyte_unaligned_inc (&bo, data);
	  break;

	case DW_OP_constu:
	case DW_OP_plus_uconst:
	case DW_OP_regx:
	case DW_OP_piece:
	case DW_OP_GNU_convert:
	case DW_OP_GNU_reinterpret:
	  get_uleb128 (newloc->number, data, end_data);
	  break;

	case DW_OP_consts:
	case DW_OP_breg0 ... DW_OP_breg31:
	case DW_OP_fbreg:
	  get_sleb128 (newloc->number, data, end_data);
	  break;

	case DW_OP_bregx:
	  get_uleb128 (newloc->number, data, end_data);
	  if (unlikely (data >= end_data))
	    goto invalid;
	  get_sleb128 (newloc->number2, data, end_data);
	  break;

	case DW_OP_bit_piece:
	case DW_OP_GNU_regval_type:
	  get_uleb128 (newloc->number, data, end_data);
	  if (unlikely (data >= end_data))
	    goto invalid;
	  get_uleb128 (newloc->number2, data, end_data);
	  break;

	case DW_OP_implicit_value:
	case DW_OP_GNU_entry_value:
	  /* This cannot be used in a CFI expression.  */
	  if (unlikely (dbg == NULL))
	    goto invalid;

	  /* start of block inc. len.  */
	  newloc->number2 = (Dwarf_Word) (uintptr_t) data;
	  get_uleb128 (newloc->number, data, end_data); /* Block length.  */
	  if (unlikely ((Dwarf_Word) (end_data - data) < newloc->number))
	    goto invalid;
	  data += newloc->number;		/* Skip the block.  */
	  break;

	case DW_OP_GNU_implicit_pointer:
	  /* DW_FORM_ref_addr, depends on offset size of CU.  */
	  if (dbg == NULL || __libdw_read_offset_inc (dbg, sec_index, &data,
						      ref_size,
						      &newloc->number,
						      IDX_debug_info, 0))
	    goto invalid;
	  if (unlikely (data >= end_data))
	    goto invalid;
	  get_uleb128 (newloc->number2, data, end_data); /* Byte offset.  */
	  break;

	case DW_OP_GNU_deref_type:
	  if (unlikely (data + 1 >= end_data))
	    goto invalid;
	  newloc->number = *data++;
	  get_uleb128 (newloc->number2, data, end_data);
	  break;

	case DW_OP_GNU_const_type:
	  {
	    size_t size;
	    get_uleb128 (newloc->number, data, end_data);
	    if (unlikely (data >= end_data))
	      goto invalid;

	    /* start of block inc. len.  */
	    newloc->number2 = (Dwarf_Word) (uintptr_t) data;
	    size = *data++;
	    if (unlikely ((Dwarf_Word) (end_data - data) < size))
	      goto invalid;
	    data += size;		/* Skip the block.  */
	  }
	  break;

	default:
	  goto invalid;
	}
    }

  if (unlikely (n == 0))
    {
      /* This is not allowed.
	 It would mean an empty location expression, which we handled
	 already as a special case above.  */
      goto invalid;
    }

  if (valuep)
    {
      struct loclist *newloc = NEW_LOC ();
      newloc->atom = DW_OP_stack_value;
      newloc->number = 0;
      newloc->number2 = 0;
      newloc->offset = data - block->data;
    }

  /* Allocate the array.  */
  Dwarf_Op *result;
  if (dbg != NULL)
    result = libdw_alloc (dbg, Dwarf_Op, sizeof (Dwarf_Op), n);
  else
    {
      result = malloc (sizeof *result * n);
      if (result == NULL)
	{
	nomem:
	  __libdw_seterrno (DWARF_E_NOMEM);
	  goto returnmem;
	}
    }

  /* Store the result.  */
  *llbuf = result;
  *listlen = n;

  do
    {
      /* We populate the array from the back since the list is backwards.  */
      --n;
      result[n].atom = loclist->atom;
      result[n].number = loclist->number;
      result[n].number2 = loclist->number2;
      result[n].offset = loclist->offset;

      if (result[n].atom == DW_OP_implicit_value)
	store_implicit_value (dbg, cache, &result[n]);

      struct loclist *loc = loclist;
      loclist = loclist->next;
      if (unlikely (n + 1 > MAX_STACK_LOCS))
	free (loc);
    }
  while (n > 0);

  /* Insert a record in the search tree so that we can find it again later.  */
  struct loc_s *newp;
  if (dbg != NULL)
    newp = libdw_alloc (dbg, struct loc_s, sizeof (struct loc_s), 1);
  else
    {
      newp = malloc (sizeof *newp);
      if (newp == NULL)
	{
	  free (result);
	  goto nomem;
	}
    }

  newp->addr = block->data;
  newp->loc = result;
  newp->nloc = *listlen;
  (void) tsearch (newp, cache, loc_compare);

  /* We did it.  */
  return 0;
}

static int
getlocation (struct Dwarf_CU *cu, const Dwarf_Block *block,
	     Dwarf_Op **llbuf, size_t *listlen, int sec_index)
{
  /* Empty location expressions don't have any ops to intern.
     Note that synthetic empty_cu doesn't have an associated DWARF dbg.  */
  if (block->length == 0)
    {
      *listlen = 0;
      return 0;
    }

  return __libdw_intern_expression (cu->dbg, cu->dbg->other_byte_order,
				    cu->address_size, (cu->version == 2
						       ? cu->address_size
						       : cu->offset_size),
				    &cu->locs, block,
				    false, false,
				    llbuf, listlen, sec_index);
}

int
dwarf_getlocation (Dwarf_Attribute *attr, Dwarf_Op **llbuf, size_t *listlen)
{
  if (! attr_ok (attr))
    return -1;

  int result = check_constant_offset (attr, llbuf, listlen);
  if (result != 1)
    return result;

  /* If it has a block form, it's a single location expression.  */
  Dwarf_Block block;
  if (INTUSE(dwarf_formblock) (attr, &block) != 0)
    return -1;

  return getlocation (attr->cu, &block, llbuf, listlen, cu_sec_idx (attr->cu));
}

static int
attr_base_address (Dwarf_Attribute *attr, Dwarf_Addr *basep)
{
  /* Fetch the CU's base address.  */
  Dwarf_Die cudie = CUDIE (attr->cu);

  /* Find the base address of the compilation unit.  It will
     normally be specified by DW_AT_low_pc.  In DWARF-3 draft 4,
     the base address could be overridden by DW_AT_entry_pc.  It's
     been removed, but GCC emits DW_AT_entry_pc and not DW_AT_lowpc
     for compilation units with discontinuous ranges.  */
  Dwarf_Attribute attr_mem;
  if (unlikely (INTUSE(dwarf_lowpc) (&cudie, basep) != 0)
      && INTUSE(dwarf_formaddr) (INTUSE(dwarf_attr) (&cudie,
						     DW_AT_entry_pc,
						     &attr_mem),
				 basep) != 0)
    {
      if (INTUSE(dwarf_errno) () != 0)
	return -1;

      /* The compiler provided no base address when it should
	 have.  Buggy GCC does this when it used absolute
	 addresses in the location list and no DW_AT_ranges.  */
      *basep = 0;
    }
  return 0;
}
static int
getlocation (struct Dwarf_CU *cu, const Dwarf_Block *block,
	     Dwarf_Op **llbuf, size_t *listlen)
{
  Dwarf *dbg = cu->dbg;

  /* Check whether we already looked at this list.  */
  struct loc_s fake = { .addr = block->data };
  struct loc_s **found = tfind (&fake, &cu->locs, loc_compare);
  if (found != NULL)
    {
      /* We already saw it.  */
      *llbuf = (*found)->loc;
      *listlen = (*found)->nloc;

      return 0;
    }

  const unsigned char *data = block->data;
  const unsigned char *const end_data = data + block->length;

  struct loclist *loclist = NULL;
  unsigned int n = 0;
  /* Decode the opcodes.  It is possible in some situations to have a
     block of size zero.  */
  while (data < end_data)
    {
      struct loclist *newloc;
      newloc = (struct loclist *) alloca (sizeof (struct loclist));
      newloc->number = 0;
      newloc->number2 = 0;
      newloc->offset = data - block->data;
      newloc->next = loclist;
      loclist = newloc;
      ++n;

      switch ((newloc->atom = *data++))
	{
	case DW_OP_addr:
	  /* Address, depends on address size of CU.  */
	  if (cu->address_size == 4)
	    {
	      if (unlikely (data + 4 > end_data))
		{
		invalid:
		  __libdw_seterrno (DWARF_E_INVALID_DWARF);
		  return -1;
		}

	      newloc->number = read_4ubyte_unaligned_inc (dbg, data);
	    }
	  else
	    {
	      if (unlikely (data + 8 > end_data))
		goto invalid;

	      newloc->number = read_8ubyte_unaligned_inc (dbg, data);
	    }
	  break;

	case DW_OP_deref:
	case DW_OP_dup:
	case DW_OP_drop:
	case DW_OP_over:
	case DW_OP_swap:
	case DW_OP_rot:
	case DW_OP_xderef:
	case DW_OP_abs:
	case DW_OP_and:
	case DW_OP_div:
	case DW_OP_minus:
	case DW_OP_mod:
	case DW_OP_mul:
	case DW_OP_neg:
	case DW_OP_not:
	case DW_OP_or:
	case DW_OP_plus:
	case DW_OP_shl:
	case DW_OP_shr:
	case DW_OP_shra:
	case DW_OP_xor:
	case DW_OP_eq:
	case DW_OP_ge:
	case DW_OP_gt:
	case DW_OP_le:
	case DW_OP_lt:
	case DW_OP_ne:
	case DW_OP_lit0 ... DW_OP_lit31:
	case DW_OP_reg0 ... DW_OP_reg31:
	case DW_OP_nop:
	case DW_OP_push_object_address:
	case DW_OP_call_ref:
	  /* No operand.  */
	  break;

	case DW_OP_const1u:
	case DW_OP_pick:
	case DW_OP_deref_size:
	case DW_OP_xderef_size:
	  if (unlikely (data >= end_data))
	    goto invalid;

	  newloc->number = *data++;
	  break;

	case DW_OP_const1s:
	  if (unlikely (data >= end_data))
	    goto invalid;

	  newloc->number = *((int8_t *) data);
	  ++data;
	  break;

	case DW_OP_const2u:
	  if (unlikely (data + 2 > end_data))
	    goto invalid;

	  newloc->number = read_2ubyte_unaligned_inc (dbg, data);
	  break;

	case DW_OP_const2s:
	case DW_OP_skip:
	case DW_OP_bra:
	case DW_OP_call2:
	  if (unlikely (data + 2 > end_data))
	    goto invalid;

	  newloc->number = read_2sbyte_unaligned_inc (dbg, data);
	  break;

	case DW_OP_const4u:
	  if (unlikely (data + 4 > end_data))
	    goto invalid;

	  newloc->number = read_4ubyte_unaligned_inc (dbg, data);
	  break;

	case DW_OP_const4s:
	case DW_OP_call4:
	  if (unlikely (data + 4 > end_data))
	    goto invalid;

	  newloc->number = read_4sbyte_unaligned_inc (dbg, data);
	  break;

	case DW_OP_const8u:
	  if (unlikely (data + 8 > end_data))
	    goto invalid;

	  newloc->number = read_8ubyte_unaligned_inc (dbg, data);
	  break;

	case DW_OP_const8s:
	  if (unlikely (data + 8 > end_data))
	    goto invalid;

	  newloc->number = read_8sbyte_unaligned_inc (dbg, data);
	  break;

	case DW_OP_constu:
	case DW_OP_plus_uconst:
	case DW_OP_regx:
	case DW_OP_piece:
	  /* XXX Check size.  */
	  get_uleb128 (newloc->number, data);
	  break;

	case DW_OP_consts:
	case DW_OP_breg0 ... DW_OP_breg31:
	case DW_OP_fbreg:
	  /* XXX Check size.  */
	  get_sleb128 (newloc->number, data);
	  break;

	case DW_OP_bregx:
	  /* XXX Check size.  */
	  get_uleb128 (newloc->number, data);
	  get_sleb128 (newloc->number2, data);
	  break;

	default:
	  goto invalid;
	}
    }

  if (unlikely (n == 0))
    {
      /* This is not allowed.

	 XXX Is it?  */
      goto invalid;
    }

  /* Allocate the array.  */
  Dwarf_Op *result = libdw_alloc (dbg, Dwarf_Op, sizeof (Dwarf_Op), n);

  /* Store the result.  */
  *llbuf = result;
  *listlen = n;

  do
    {
      /* We populate the array from the back since the list is
         backwards.  */
      --n;
      result[n].atom = loclist->atom;
      result[n].number = loclist->number;
      result[n].number2 = loclist->number2;
      result[n].offset = loclist->offset;

      loclist = loclist->next;
    }
  while (n > 0);

  /* Insert a record in the search tree so that we can find it again
     later.  */
  struct loc_s *newp = libdw_alloc (dbg, struct loc_s, sizeof (struct loc_s),
				    1);
  newp->addr = block->data;
  newp->loc = result;
  newp->nloc = *listlen;
  (void) tsearch (newp, &cu->locs, loc_compare);

  /* We did it.  */
  return 0;
}

int
dwarf_getlocation (attr, llbuf, listlen)
     Dwarf_Attribute *attr;
     Dwarf_Op **llbuf;
     size_t *listlen;
{
  if (! attr_ok (attr))
    return -1;

  /* If it has a block form, it's a single location expression.  */
  Dwarf_Block block;
  if (INTUSE(dwarf_formblock) (attr, &block) != 0)
    return -1;

  return getlocation (attr->cu, &block, llbuf, listlen);
}

int
dwarf_getlocation_addr (attr, address, llbufs, listlens, maxlocs)
     Dwarf_Attribute *attr;
     Dwarf_Addr address;
     Dwarf_Op **llbufs;
     size_t *listlens;
     size_t maxlocs;
{
  if (! attr_ok (attr))
    return -1;

  if (llbufs == NULL)
    maxlocs = SIZE_MAX;

  /* If it has a block form, it's a single location expression.  */
  Dwarf_Block block;
  if (INTUSE(dwarf_formblock) (attr, &block) == 0)
    {
      if (maxlocs == 0)
	return 0;
      if (llbufs != NULL &&
	  getlocation (attr->cu, &block, &llbufs[0], &listlens[0]) != 0)
	return -1;
      return listlens[0] == 0 ? 0 : 1;
    }

  int error = INTUSE(dwarf_errno) ();
  if (unlikely (error != DWARF_E_NO_BLOCK))
    {
      __libdw_seterrno (error);
      return -1;
    }

  /* Must have the form data4 or data8 which act as an offset.  */
  Dwarf_Word offset;
  if (unlikely (INTUSE(dwarf_formudata) (attr, &offset) != 0))
    return -1;

  const Elf_Data *d = attr->cu->dbg->sectiondata[IDX_debug_loc];
  if (unlikely (d == NULL))
    {
      __libdw_seterrno (DWARF_E_NO_LOCLIST);
      return -1;
    }

  Dwarf_Addr base = (Dwarf_Addr) -1;
  unsigned char *readp = d->d_buf + offset;
  size_t got = 0;
  while (got < maxlocs)
    {
      if ((unsigned char *) d->d_buf + d->d_size - readp
	  < attr->cu->address_size * 2)
	{
	invalid:
	  __libdw_seterrno (DWARF_E_INVALID_DWARF);
	  return -1;
	}

      Dwarf_Addr begin;
      Dwarf_Addr end;
      if (attr->cu->address_size == 8)
	{
	  begin = read_8ubyte_unaligned_inc (attr->cu->dbg, readp);
	  end = read_8ubyte_unaligned_inc (attr->cu->dbg, readp);

	  if (begin == (Elf64_Addr) -1l) /* Base address entry.  */
	    {
	      base = end;
	      if (unlikely (base == (Dwarf_Addr) -1))
		goto invalid;
	      continue;
	    }
	}
      else
	{
	  begin = read_4ubyte_unaligned_inc (attr->cu->dbg, readp);
	  end = read_4ubyte_unaligned_inc (attr->cu->dbg, readp);

	  if (begin == (Elf32_Addr) -1) /* Base address entry.  */
	    {
	      base = end;
	      continue;
	    }
	}

      if (begin == 0 && end == 0) /* End of list entry.  */
	break;

      if ((unsigned char *) d->d_buf + d->d_size - readp < 2)
	goto invalid;

      /* We have a location expression.  */
      block.length = read_2ubyte_unaligned_inc (attr->cu->dbg, readp);
      block.data = readp;
      if ((unsigned char *) d->d_buf + d->d_size - readp
	  < (ptrdiff_t) block.length)
	goto invalid;
      readp += block.length;

      if (base == (Dwarf_Addr) -1)
	{
	  /* Fetch the CU's base address.  */
	  Dwarf_Die cudie = CUDIE (attr->cu);

	  /* Find the base address of the compilation unit.  It will
	     normally be specified by DW_AT_low_pc.  In DWARF-3 draft 4,
	     the base address could be overridden by DW_AT_entry_pc.  It's
	     been removed, but GCC emits DW_AT_entry_pc and not DW_AT_lowpc
	     for compilation units with discontinuous ranges.  */
	  Dwarf_Attribute attr_mem;
	  if (unlikely (INTUSE(dwarf_lowpc) (&cudie, &base) != 0)
	      && INTUSE(dwarf_formaddr) (INTUSE(dwarf_attr) (&cudie,
							     DW_AT_entry_pc,
							     &attr_mem),
					 &base) != 0)
	    {
	      if (INTUSE(dwarf_errno) () != 0)
		return -1;

	      /* The compiler provided no base address when it should
		 have.  Buggy GCC does this when it used absolute
		 addresses in the location list and no DW_AT_ranges.  */
	      base = 0;
	    }
	}

      if (address >= base + begin && address < base + end)
	{
	  /* This one matches the address.  */
	  if (llbufs != NULL
	      && unlikely (getlocation (attr->cu, &block,
					&llbufs[got], &listlens[got]) != 0))
	    return -1;
	  ++got;
	}
    }

  return got;
}