Exemplo n.º 1
0
/**
 * die_get_data_member_location - Get the data-member offset
 * @mb_die: a DIE of a member of a data structure
 * @offs: The offset of the member in the data structure
 *
 * Get the offset of @mb_die in the data structure including @mb_die, and
 * stores result offset to @offs. If any error occurs this returns errno.
 */
int die_get_data_member_location(Dwarf_Die *mb_die, Dwarf_Word *offs)
{
	Dwarf_Attribute attr;
	Dwarf_Op *expr;
	size_t nexpr;
	int ret;

	if (dwarf_attr(mb_die, DW_AT_data_member_location, &attr) == NULL)
		return -ENOENT;

	if (dwarf_formudata(&attr, offs) != 0) {
		/* DW_AT_data_member_location should be DW_OP_plus_uconst */
		ret = dwarf_getlocation(&attr, &expr, &nexpr);
		if (ret < 0 || nexpr == 0)
			return -ENOENT;

		if (expr[0].atom != DW_OP_plus_uconst || nexpr != 1) {
			pr_debug("Unable to get offset:Unexpected OP %x (%zd)\n",
				 expr[0].atom, nexpr);
			return -ENOTSUP;
		}
		*offs = (Dwarf_Word)expr[0].number;
	}
	return 0;
}
Exemplo n.º 2
0
/** \brief Initialize the location of a member of a type
 * (DW_AT_data_member_location of a DW_TAG_member).
 *
 *  \param  type   a type (struct, class)
 *  \param  member the member of the type
 *  \param  child  DIE of the member (DW_TAG_member)
 */
static void MC_dwarf_fill_member_location(
  simgrid::mc::Type* type, simgrid::mc::Member* member, Dwarf_Die * child)
{
  if (dwarf_hasattr(child, DW_AT_data_bit_offset))
    xbt_die("Can't groke DW_AT_data_bit_offset.");

  if (not dwarf_hasattr_integrate(child, DW_AT_data_member_location)) {
    if (type->type == DW_TAG_union_type)
      return;
    xbt_die
        ("Missing DW_AT_data_member_location field in DW_TAG_member %s of type <%"
         PRIx64 ">%s", member->name.c_str(),
         (uint64_t) type->id, type->name.c_str());
  }

  Dwarf_Attribute attr;
  dwarf_attr_integrate(child, DW_AT_data_member_location, &attr);
  int form = dwarf_whatform(&attr);
  simgrid::dwarf::FormClass form_class = simgrid::dwarf::classify_form(form);
  switch (form_class) {
  case simgrid::dwarf::FormClass::ExprLoc:
  case simgrid::dwarf::FormClass::Block:
    // Location expression:
    {
      Dwarf_Op *expr;
      size_t len;
      if (dwarf_getlocation(&attr, &expr, &len))
        xbt_die
            ("Could not read location expression DW_AT_data_member_location in DW_TAG_member %s of type <%"
             PRIx64 ">%s", MC_dwarf_attr_integrate_string(child, DW_AT_name),
             (uint64_t) type->id, type->name.c_str());
      member->location_expression = simgrid::dwarf::DwarfExpression(expr, expr+len);
      break;
    }
  case simgrid::dwarf::FormClass::Constant:
    // Offset from the base address of the object:
    {
      Dwarf_Word offset;
      if (not dwarf_formudata(&attr, &offset))
        member->offset(offset);
      else
        xbt_die("Cannot get %s location <%" PRIx64 ">%s",
                MC_dwarf_attr_integrate_string(child, DW_AT_name),
                (uint64_t) type->id, type->name.c_str());
      break;
    }

  default:
    // includes FormClass::LocListPtr (reference to a location list: TODO) and FormClass::Reference (it's supposed to be
    // possible in DWARF2 but I couldn't find its semantic in the spec)
    xbt_die("Can't handle form class (%d) / form 0x%x as DW_AT_member_location", (int)form_class, (unsigned)form);
  }

}
Exemplo n.º 3
0
static std::unique_ptr<simgrid::mc::Variable> MC_die_to_variable(
  simgrid::mc::ObjectInformation* info, Dwarf_Die * die,
  Dwarf_Die * unit, simgrid::mc::Frame* frame,
  const char *ns)
{
  // Skip declarations:
  if (MC_dwarf_attr_flag(die, DW_AT_declaration, false))
    return nullptr;

  // Skip compile time constants:
  if (dwarf_hasattr(die, DW_AT_const_value))
    return nullptr;

  Dwarf_Attribute attr_location;
  if (dwarf_attr(die, DW_AT_location, &attr_location) == nullptr)
    // No location: do not add it ?
    return nullptr;

  std::unique_ptr<simgrid::mc::Variable> variable =
    std::unique_ptr<simgrid::mc::Variable>(new simgrid::mc::Variable());
  variable->id = dwarf_dieoffset(die);
  variable->global = frame == nullptr;     // Can be override base on DW_AT_location
  variable->object_info = info;

  const char *name = MC_dwarf_attr_integrate_string(die, DW_AT_name);
  if (name)
    variable->name = name;
  variable->type_id = MC_dwarf_at_type(die);

  int form = dwarf_whatform(&attr_location);
  simgrid::dwarf::FormClass form_class;
  if (form == DW_FORM_sec_offset)
    form_class = simgrid::dwarf::FormClass::Constant;
  else
    form_class = simgrid::dwarf::classify_form(form);
  switch (form_class) {
  case simgrid::dwarf::FormClass::ExprLoc:
  case simgrid::dwarf::FormClass::Block:
    // Location expression:
    {
      Dwarf_Op *expr;
      size_t len;
      if (dwarf_getlocation(&attr_location, &expr, &len)) {
        xbt_die(
          "Could not read location expression in DW_AT_location "
          "of variable <%" PRIx64 ">%s",
          (uint64_t) variable->id,
          variable->name.c_str());
      }

      if (len == 1 && expr[0].atom == DW_OP_addr) {
        variable->global = true;
        uintptr_t offset = (uintptr_t) expr[0].number;
        uintptr_t base = (uintptr_t) info->base_address();
        variable->address = (void *) (base + offset);
      } else
        variable->location_list = {
            simgrid::dwarf::LocationListEntry(simgrid::dwarf::DwarfExpression(expr, expr + len))};

      break;
    }

  case simgrid::dwarf::FormClass::LocListPtr:
  case simgrid::dwarf::FormClass::Constant:
    // Reference to location list:
    variable->location_list = simgrid::dwarf::location_list(
      *info, attr_location);
    break;

  default:
    xbt_die("Unexpected form 0x%x (%i), class 0x%x (%i) list for location in <%" PRIx64 ">%s", (unsigned)form, form,
            (unsigned)form_class, (int)form_class, (uint64_t)variable->id, variable->name.c_str());
  }

  // Handle start_scope:
  if (dwarf_hasattr(die, DW_AT_start_scope)) {
    Dwarf_Attribute attr;
    dwarf_attr(die, DW_AT_start_scope, &attr);
    int form = dwarf_whatform(&attr);
    simgrid::dwarf::FormClass form_class = simgrid::dwarf::classify_form(form);
    if (form_class == simgrid::dwarf::FormClass::Constant) {
      Dwarf_Word value;
      variable->start_scope = dwarf_formudata(&attr, &value) == 0 ? (size_t)value : 0;
    } else {
      // TODO: FormClass::RangeListPtr
      xbt_die("Unhandled form 0x%x, class 0x%X for DW_AT_start_scope of variable %s", (unsigned)form,
              (unsigned)form_class, name == nullptr ? "?" : name);
    }
  }

  if (ns && variable->global)
    variable->name =
      std::string(ns) + "::" + variable->name;

  // The current code needs a variable name,
  // generate a fake one:
  if (variable->name.empty()) {
    variable->name = "@anonymous#" + std::to_string(mc_anonymous_variable_index);
    mc_anonymous_variable_index++;
  }
  return variable;
}
Exemplo n.º 4
0
/* Get all variables and print their value expressions. */
static void
print_varlocs (Dwarf_Die *funcdie)
{
  // Display frame base for function if it exists.
  // Should be used for DW_OP_fbreg.
  has_frame_base = dwarf_hasattr (funcdie, DW_AT_frame_base);
  if (has_frame_base)
    {
      Dwarf_Attribute fb_attr;
      if (dwarf_attr (funcdie, DW_AT_frame_base, &fb_attr) == NULL)
	error (EXIT_FAILURE, 0, "dwarf_attr fb: %s", dwarf_errmsg (-1));

      Dwarf_Op *fb_expr;
      size_t fb_exprlen;
      if (dwarf_getlocation (&fb_attr, &fb_expr, &fb_exprlen) == 0)
	{
	  // Covers all of function.
	  Dwarf_Addr entrypc;
	  if (dwarf_entrypc (funcdie, &entrypc) != 0)
	    error (EXIT_FAILURE, 0, "dwarf_entrypc: %s", dwarf_errmsg (-1));

	  printf ("    frame_base: ");
	  if (entrypc == 0)
	    printf ("XXX zero address"); // XXX bad DWARF?
	  else
	    print_expr_block (&fb_attr, fb_expr, fb_exprlen, entrypc);
	  printf ("\n");
	}
      else
	{
	  Dwarf_Addr base, start, end;
	  ptrdiff_t off = 0;
	  printf ("    frame_base:\n");
          while ((off = dwarf_getlocations (&fb_attr, off, &base,
					    &start, &end,
					    &fb_expr, &fb_exprlen)) > 0)
	    {
	      printf ("      (%" PRIx64 ",%" PRIx64 ") ", start, end);
	      print_expr_block (&fb_attr, fb_expr, fb_exprlen, start);
	      printf ("\n");
	    }

	  if (off < 0)
	    error (EXIT_FAILURE, 0, "dwarf_getlocations fb: %s",
		   dwarf_errmsg (-1));
	}
    }
  else if (dwarf_tag (funcdie) == DW_TAG_inlined_subroutine)
    {
      // See whether the subprogram we are inlined into has a frame
      // base we should use.
      Dwarf_Die *scopes;
      int n = dwarf_getscopes_die (funcdie, &scopes);
      if (n <= 0)
	error (EXIT_FAILURE, 0, "dwarf_getscopes_die: %s", dwarf_errmsg (-1));

      while (n-- > 0)
	if (dwarf_tag (&scopes[n]) == DW_TAG_subprogram
	    && dwarf_hasattr (&scopes[n], DW_AT_frame_base))
	  {
	    has_frame_base = true;
	    break;
	  }
      free (scopes);
    }

  if (! dwarf_haschildren (funcdie))
    return;

  Dwarf_Die child;
  int res = dwarf_child (funcdie, &child);
  if (res < 0)
    error (EXIT_FAILURE, 0, "dwarf_child: %s", dwarf_errmsg (-1));

  /* We thought there was a child, but the child list was actually
     empty. This isn't technically an error in the DWARF, but it is
     certainly non-optimimal.  */
  if (res == 1)
    return;

  do
    {
      int tag = dwarf_tag (&child);
      if (tag == DW_TAG_variable || tag == DW_TAG_formal_parameter)
	{
	  const char *what = tag == DW_TAG_variable ? "variable" : "parameter";
	  print_die (&child, what, 2);

	  if (dwarf_hasattr (&child, DW_AT_location))
	    {
	      Dwarf_Attribute attr;
	      if (dwarf_attr (&child, DW_AT_location, &attr) == NULL)
		error (EXIT_FAILURE, 0, "dwarf_attr: %s", dwarf_errmsg (-1));

	      Dwarf_Op *expr;
	      size_t exprlen;
	      if (dwarf_getlocation (&attr, &expr, &exprlen) == 0)
		{
		  // Covers all ranges of the function.
		  // Evaluate the expression block for each range.
		  ptrdiff_t offset = 0;
		  Dwarf_Addr base, begin, end;
		  do
		    {
		      offset = dwarf_ranges (funcdie, offset, &base,
					     &begin, &end);
		      if (offset < 0)
			error (EXIT_FAILURE, 0, "dwarf_ranges: %s",
			       dwarf_errmsg (-1));

		      if (offset > 0)
			{
			  if (exprlen == 0)
			    printf ("      (%"
				    PRIx64 ",%" PRIx64
				    ") <empty expression>\n", begin, end);
			  else
			    print_expr_block_addrs (&attr, begin, end,
						    expr, exprlen);
			}
		    }
		  while (offset > 0);

		  if (offset < 0)
		    error (EXIT_FAILURE, 0, "dwarf_ranges: %s",
			   dwarf_errmsg (-1));
		}
	      else
		{
		  Dwarf_Addr base, begin, end;
		  ptrdiff_t offset = 0;
		  while ((offset = dwarf_getlocations (&attr, offset,
						       &base, &begin, &end,
						       &expr, &exprlen)) > 0)
		    if (begin >= end)
		      printf ("      (%" PRIx64 ",%" PRIx64
			      ") <empty range>\n", begin, end); // XXX report?
		    else
		      {
			print_expr_block_addrs (&attr, begin, end,
						expr, exprlen);

			// Extra sanity check for dwarf_getlocation_addr
			// Must at least find one range for begin and end-1.
			Dwarf_Op *expraddr;
			size_t expraddr_len;
			int locs = dwarf_getlocation_addr (&attr, begin,
							   &expraddr,
							   &expraddr_len, 1);
			assert (locs == 1);
			locs = dwarf_getlocation_addr (&attr, end - 1,
						       &expraddr,
						       &expraddr_len, 1);
			assert (locs == 1);
		      }

		  if (offset < 0)
		    error (EXIT_FAILURE, 0, "dwarf_getlocations: %s",
			   dwarf_errmsg (-1));
		}
	    }
	  else if (dwarf_hasattr (&child, DW_AT_const_value))
	    {
	      printf ("      <constant value>\n"); // Lookup type and print.
	    }
	  else
	    {
	      printf ("      <no value>\n");
	    }
	}
    }
  while (dwarf_siblingof (&child, &child) == 0);
}
Exemplo n.º 5
0
static void
print_expr (Dwarf_Attribute *attr, Dwarf_Op *expr, Dwarf_Addr addr)
{
  uint8_t atom = expr->atom;
  const char *opname = dwarf_opcode_string (atom);
  assert (opname != NULL);

  switch (atom)
    {
    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_stack_value:
      /* No arguments. */
      printf ("%s", opname);
      break;

    case DW_OP_form_tls_address:
      /* No arguments. Special. Pops an address and pushes the
	 corresponding address in the current thread local
	 storage. Uses the thread local storage block of the defining
	 module (executable, shared library). */
      printf ("%s", opname);
      break;

    case DW_OP_GNU_push_tls_address:
      /* No arguments. Special. Not the same as DW_OP_form_tls_address.
	 Pops an offset into the current thread local strorage and
	 pushes back the actual address. */
      printf ("%s", opname);
      break;

    case DW_OP_call_frame_cfa:
      /* No arguments. Special. Pushes Call Frame Address as computed
	 by CFI data (dwarf_cfi_addrframe will fetch that info (either from
	 the .eh_frame or .debug_frame CFI) and dwarf_frame_cfa translatesr
         the CFI instructions into a plain DWARF expression.
	 Never used in CFI itself. */

      if (attr == NULL)
	error (EXIT_FAILURE, 0, "%s used in CFI", opname);

      printf ("%s ", opname);
      if (cfi_eh == NULL && cfi_debug == NULL)
	error (EXIT_FAILURE, 0, "DW_OP_call_frame_cfa used but no cfi found.");

      Dwarf_Frame *frame;
      if (dwarf_cfi_addrframe (cfi_eh, addr + cfi_eh_bias, &frame) != 0
	  && dwarf_cfi_addrframe (cfi_debug, addr, &frame) != 0)
	error (EXIT_FAILURE, 0, "dwarf_cfi_addrframe 0x%" PRIx64 ": %s",
	       addr, dwarf_errmsg (-1));

      Dwarf_Op *cfa_ops;
      size_t cfa_nops;
      if (dwarf_frame_cfa (frame, &cfa_ops, &cfa_nops) != 0)
	error (EXIT_FAILURE, 0, "dwarf_frame_cfa 0x%" PRIx64 ": %s",
	       addr, dwarf_errmsg (-1));
      if (cfa_nops < 1)
	error (EXIT_FAILURE, 0, "dwarf_frame_cfa no ops");
      print_expr_block (NULL, cfa_ops, cfa_nops, 0);
      free (frame);
      break;

    case DW_OP_push_object_address:
      /* No arguments. Special. Pushes object address explicitly.
       Normally only done implicitly by DW_AT_data_member_location.
       Never used in CFI. */
      if (attr == NULL)
	error (EXIT_FAILURE, 0, "%s used in CFI", opname);
      printf ("%s", opname);
      break;

    case DW_OP_addr:
      /* 1 address argument. */
      printf ("%s(0x%" PRIx64 ")", opname, (Dwarf_Addr) expr->number);
      break;

    case DW_OP_const1u:
    case DW_OP_const2u:
    case DW_OP_const4u:
    case DW_OP_const8u:
    case DW_OP_constu:
    case DW_OP_pick:
    case DW_OP_plus_uconst:
    case DW_OP_regx:
    case DW_OP_piece:
    case DW_OP_deref_size:
    case DW_OP_xderef_size:
      /* 1 numeric unsigned argument. */
      printf ("%s(%" PRIu64 ")", opname, expr->number);
      break;

    case DW_OP_call2:
    case DW_OP_call4:
    case DW_OP_call_ref:
      /* 1 DIE offset argument for more ops in location attribute of DIE.
         Never used in CFI.  */
      {
	if (attr == NULL)
	  error (EXIT_FAILURE, 0, "%s used in CFI", opname);

	Dwarf_Attribute call_attr;
	if (dwarf_getlocation_attr (attr, expr, &call_attr) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_attr for %s error %s",
		 opname, dwarf_errmsg (-1));

	Dwarf_Die call_die;
	if (dwarf_getlocation_die (attr, expr, &call_die) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_die for %s error %s",
		 opname, dwarf_errmsg (-1));

	Dwarf_Op *call_ops;
	size_t call_len;
	if (dwarf_getlocation (&call_attr, &call_ops, &call_len) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation for entry: %s",
		 dwarf_errmsg (-1));

	printf ("%s([%" PRIx64 "]) ", opname, dwarf_dieoffset (&call_die));
	print_expr_block (&call_attr, call_ops, call_len, addr);
      }
      break;

    case DW_OP_const1s:
    case DW_OP_const2s:
    case DW_OP_const4s:
    case DW_OP_const8s:
    case DW_OP_consts:
    case DW_OP_skip:
    case DW_OP_bra:
    case DW_OP_breg0 ... DW_OP_breg31:
      /* 1 numeric signed argument. */
      printf ("%s(%" PRId64 ")", opname, (Dwarf_Sword) expr->number);
      break;

    case DW_OP_fbreg:
      /* 1 numeric signed argument. Offset from frame base. */
      if (attr == NULL)
	  error (EXIT_FAILURE, 0, "%s used in CFI", opname);

      if (! has_frame_base)
	error (EXIT_FAILURE, 0, "DW_OP_fbreg used without a frame base");

      printf ("%s(%" PRId64 ")", opname, (Dwarf_Sword) expr->number);
      break;

    case DW_OP_bregx:
      /* 2 arguments, unsigned register number, signed offset. */
      printf ("%s(%" PRIu64 ",%" PRId64 ")", opname,
	      expr->number, (Dwarf_Sword) expr->number2);
      break;

    case DW_OP_bit_piece:
      /* 2 arguments, unsigned size, unsigned offset. */
      printf ("%s(%" PRIu64 ",%" PRIu64 ")", opname,
	      expr->number, expr->number2);
      break;

    case DW_OP_implicit_value:
      /* Special, unsigned size plus block. */
      {
	Dwarf_Attribute const_attr;
	Dwarf_Block block;
	if (dwarf_getlocation_attr (attr, expr, &const_attr) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_attr: %s",
		 dwarf_errmsg (-1));

	if (dwarf_formblock (&const_attr, &block) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_formblock: %s",
		 dwarf_errmsg (-1));

	/* This is the "old" way. Check they result in the same.  */
	Dwarf_Block block_impl;
	if (dwarf_getlocation_implicit_value (attr, expr, &block_impl) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_implicit_value: %s",
		 dwarf_errmsg (-1));

	assert (expr->number == block.length);
	assert (block.length == block_impl.length);
	printf ("%s(%" PRIu64 "){", opname, block.length);
	for (size_t i = 0; i < block.length; i++)
	  {
	    printf ("%02x", block.data[i]);
	    assert (block.data[i] == block_impl.data[i]);
	  }
	printf("}");
      }
      break;

    case DW_OP_GNU_implicit_pointer:
      /* Special, DIE offset, signed offset. Referenced DIE has a
	 location or const_value attribute. */
      {
	if (attr == NULL)
	  error (EXIT_FAILURE, 0, "%s used in CFI", opname);

	Dwarf_Attribute attrval;
	if (dwarf_getlocation_implicit_pointer (attr, expr, &attrval) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_implicit_pointer: %s",
		 dwarf_errmsg (-1));

	// Sanity check, results should be the same.
	Dwarf_Attribute attrval2;
	if (dwarf_getlocation_attr (attr, expr, &attrval2) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_attr: %s",
		 dwarf_errmsg (-1));

	assert (dwarf_whatattr (&attrval) == dwarf_whatattr (&attrval2));
	assert (dwarf_whatform (&attrval) == dwarf_whatform (&attrval2));
	// In theory two different valp pointers could point to the same
	// value. But here we really expect them to be the equal.
	assert (attrval.valp == attrval2.valp);

	Dwarf_Die impl_die;
	if (dwarf_getlocation_die (attr, expr, &impl_die) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_due: %s",
		 dwarf_errmsg (-1));

	printf ("%s([%" PRIx64 "],%" PRId64 ") ", opname,
		dwarf_dieoffset (&impl_die), expr->number2);

	if (dwarf_whatattr (&attrval) == DW_AT_const_value)
	  printf ("<constant value>"); // Lookup type...
	else
	  {
	    // Lookup the location description at the current address.
	    Dwarf_Op *exprval;
	    size_t exprval_len;
	    int locs = dwarf_getlocation_addr (&attrval, addr,
					       &exprval, &exprval_len, 1);
	    if (locs == 0)
	      printf ("<no location>"); // This means "optimized out".
	    else if (locs == 1)
	      print_expr_block (&attrval, exprval, exprval_len, addr);
	    else
	      error (EXIT_FAILURE, 0,
		     "dwarf_getlocation_addr attrval at addr 0x%" PRIx64
		     ", locs (%d): %s", addr, locs, dwarf_errmsg (-1));
	  }
      }
      break;

    case DW_OP_GNU_entry_value:
      /* Special, unsigned size plus expression block. All registers
	 inside the block should be interpreted as they had on
	 entering the function. dwarf_getlocation_attr will return an
	 attribute containing the block as locexpr which can be
	 retrieved with dwarf_getlocation.  */
      {
	Dwarf_Attribute entry_attr;
	if (dwarf_getlocation_attr (attr, expr, &entry_attr) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_attr: %s",
		 dwarf_errmsg (-1));

	Dwarf_Op *entry_ops;
	size_t entry_len;
	if (dwarf_getlocation (&entry_attr, &entry_ops, &entry_len) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation for entry: %s",
		 dwarf_errmsg (-1));

	printf ("%s(%zd) ", opname, entry_len);
	print_expr_block (attr, entry_ops, entry_len, addr);
      }
      break;

    case DW_OP_GNU_parameter_ref:
      /* Special, unsigned CU relative DIE offset pointing to a
	 DW_TAG_formal_parameter. The value that parameter had at the
	 call site of the current function will be put on the DWARF
	 stack. The value can be retrieved by finding the
	 DW_TAG_GNU_call_site_parameter which has as
	 DW_AT_abstract_origin the same formal parameter DIE. */
      {
	Dwarf_Die param;
	if (dwarf_getlocation_die (attr, expr, &param) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_die: %s",
		 dwarf_errmsg (-1));
	// XXX actually lookup DW_TAG_GNU_call_site_parameter
	printf ("%s[%" PRIx64 "]", opname, dwarf_dieoffset (&param));
	assert (expr->number == dwarf_cuoffset (&param));
	assert (dwarf_tag (&param) == DW_TAG_formal_parameter);
      }
      break;

    case DW_OP_GNU_convert:
    case DW_OP_GNU_reinterpret:
      /* Special, unsigned CU relative DIE offset pointing to a
	 DW_TAG_base_type. Pops a value, converts or reinterprets the
	 value to the given type. When the argument is zero the value
	 becomes untyped again. */
      {
	Dwarf_Die type;
	Dwarf_Off off = expr->number;
	if (off != 0)
	  {
	    if (dwarf_getlocation_die (attr, expr, &type) != 0)
	      error (EXIT_FAILURE, 0, "dwarf_getlocation_die: %s",
		     dwarf_errmsg (-1));
	    off = dwarf_dieoffset (&type);
	    assert (expr->number == dwarf_cuoffset (&type));
	    printf ("%s", opname);
	    print_base_type (&type);
	  }
	else
	  printf ("%s[%" PRIu64 "]", opname, off);

      }
      break;

    case DW_OP_GNU_regval_type:
      /* Special, unsigned register number plus unsigned CU relative
         DIE offset pointing to a DW_TAG_base_type. */
      {
	Dwarf_Die type;
	if (dwarf_getlocation_die (attr, expr, &type) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_die: %s",
		 dwarf_errmsg (-1));
	assert (expr->number2 == dwarf_cuoffset (&type));
	// XXX check size against base_type size?
	printf ("%s(reg%" PRIu64 ")", opname, expr->number);
	print_base_type (&type);
      }
      break;

    case DW_OP_GNU_deref_type:
      /* Special, unsigned size plus unsigned CU relative DIE offset
	 pointing to a DW_TAG_base_type. */ 
      {
	Dwarf_Die type;
	if (dwarf_getlocation_die (attr, expr, &type) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_die: %s",
		 dwarf_errmsg (-1));
	assert (expr->number2 == dwarf_cuoffset (&type));
	// XXX check size against base_type size?
	printf ("%s(%" PRIu64 ")", opname, expr->number);
	print_base_type (&type);
      }
      break;

    case DW_OP_GNU_const_type:
      /* Special, unsigned CU relative DIE offset pointing to a
	 DW_TAG_base_type, an unsigned size length plus a block with
	 the constant value. */
      {
	Dwarf_Die type;
	if (dwarf_getlocation_die (attr, expr, &type) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_die: %s",
		 dwarf_errmsg (-1));
	assert (expr->number == dwarf_cuoffset (&type));

	Dwarf_Attribute const_attr;
	if (dwarf_getlocation_attr (attr, expr, &const_attr) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_getlocation_attr for type: %s",
		 dwarf_errmsg (-1));
	  
	Dwarf_Block block;
	if (dwarf_formblock (&const_attr, &block) != 0)
	  error (EXIT_FAILURE, 0, "dwarf_formblock for type: %s",
		 dwarf_errmsg (-1));

	printf ("%s", opname);
	print_base_type (&type);
	printf ("(%" PRIu64 ")[", block.length);
	for (size_t i = 0; i < block.length; i++)
	  printf ("%02x", block.data[i]);
	printf("]");
      }
      break;

    default:
      error (EXIT_FAILURE, 0, "unhandled opcode: DW_OP_%s (0x%x)",
	     opname, atom);
    }
}