Exemplo n.º 1
0
/* Call probe_finder callback with scope DIE */
static int call_probe_finder(Dwarf_Die *sc_die, struct probe_finder *pf)
{
	Dwarf_Attribute fb_attr;
	size_t nops;
	int ret;

	if (!sc_die) {
		pr_err("Caller must pass a scope DIE. Program error.\n");
		return -EINVAL;
	}

	/* If not a real subprogram, find a real one */
	if (!die_is_func_def(sc_die)) {
		if (!die_find_realfunc(&pf->cu_die, pf->addr, &pf->sp_die)) {
			pr_warning("Failed to find probe point in any "
				   "functions.\n");
			return -ENOENT;
		}
	} else
		memcpy(&pf->sp_die, sc_die, sizeof(Dwarf_Die));

	/* Get the frame base attribute/ops from subprogram */
	dwarf_attr(&pf->sp_die, DW_AT_frame_base, &fb_attr);
	ret = dwarf_getlocation_addr(&fb_attr, pf->addr, &pf->fb_ops, &nops, 1);
	if (ret <= 0 || nops == 0) {
		pf->fb_ops = NULL;
#if _ELFUTILS_PREREQ(0, 142)
	} else if (nops == 1 && pf->fb_ops[0].atom == DW_OP_call_frame_cfa &&
		   pf->cfi != NULL) {
		Dwarf_Frame *frame;
		if (dwarf_cfi_addrframe(pf->cfi, pf->addr, &frame) != 0 ||
		    dwarf_frame_cfa(frame, &pf->fb_ops, &nops) != 0) {
			pr_warning("Failed to get call frame on 0x%jx\n",
				   (uintmax_t)pf->addr);
			return -ENOENT;
		}
#endif
	}

	/* Call finder's callback handler */
	ret = pf->callback(sc_die, pf);

	/* *pf->fb_ops will be cached in libdw. Don't free it. */
	pf->fb_ops = NULL;

	return ret;
}
static int call_probe_finder(Dwarf_Die *sc_die, struct probe_finder *pf)
{
	Dwarf_Attribute fb_attr;
	size_t nops;
	int ret;

	if (!sc_die) {
		pr_err("Caller must pass a scope DIE. Program error.\n");
		return -EINVAL;
	}

	
	if (dwarf_tag(sc_die) != DW_TAG_subprogram) {
		if (!die_find_realfunc(&pf->cu_die, pf->addr, &pf->sp_die)) {
			pr_warning("Failed to find probe point in any "
				   "functions.\n");
			return -ENOENT;
		}
	} else
		memcpy(&pf->sp_die, sc_die, sizeof(Dwarf_Die));

	
	dwarf_attr(&pf->sp_die, DW_AT_frame_base, &fb_attr);
	ret = dwarf_getlocation_addr(&fb_attr, pf->addr, &pf->fb_ops, &nops, 1);
	if (ret <= 0 || nops == 0) {
		pf->fb_ops = NULL;
#if _ELFUTILS_PREREQ(0, 142)
	} else if (nops == 1 && pf->fb_ops[0].atom == DW_OP_call_frame_cfa &&
		   pf->cfi != NULL) {
		Dwarf_Frame *frame;
		if (dwarf_cfi_addrframe(pf->cfi, pf->addr, &frame) != 0 ||
		    dwarf_frame_cfa(frame, &pf->fb_ops, &nops) != 0) {
			pr_warning("Failed to get call frame on 0x%jx\n",
				   (uintmax_t)pf->addr);
			return -ENOENT;
		}
#endif
	}

	
	ret = pf->callback(sc_die, pf);

	
	pf->fb_ops = NULL;

	return ret;
}
Exemplo n.º 3
0
/*
 * Use the DWARF expression for the Call-frame-address and determine
 * if return address is in LR and if a new frame was allocated.
 */
static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
{
	Dwarf_Op ops_mem[2];
	Dwarf_Op dummy;
	Dwarf_Op *ops = &dummy;
	size_t nops;
	int result;

	result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
	if (result < 0) {
		pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1));
		return -1;
	}

	/*
	 * Check if return address is on the stack. If return address
	 * is in a register (typically R0), it is yet to be saved on
	 * the stack.
	 */
	if ((nops != 0 || ops != NULL) &&
		!(nops == 1 && ops[0].atom == DW_OP_regx &&
			ops[0].number2 == 0 && ops[0].offset == 0))
		return 0;

	/*
	 * Return address is in LR. Check if a frame was allocated
	 * but not-yet used.
	 */
	result = dwarf_frame_cfa(frame, &ops, &nops);
	if (result < 0) {
		pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,
					dwarf_errmsg(-1));
		return -1;
	}

	/*
	 * If call frame address is in r1, no new frame was allocated.
	 */
	if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&
				ops[0].number2 == 0)
		return 1;

	/*
	 * A new frame was allocated but has not yet been used.
	 */
	return 2;
}
Exemplo n.º 4
0
/* Call probe_finder callback with real subprogram DIE */
static int call_probe_finder(Dwarf_Die *sp_die, struct probe_finder *pf)
{
	Dwarf_Die die_mem;
	Dwarf_Attribute fb_attr;
	size_t nops;
	int ret;

	/* If no real subprogram, find a real one */
	if (!sp_die || dwarf_tag(sp_die) != DW_TAG_subprogram) {
		sp_die = die_find_real_subprogram(&pf->cu_die,
						  pf->addr, &die_mem);
		if (!sp_die) {
			pr_warning("Failed to find probe point in any "
				   "functions.\n");
			return -ENOENT;
		}
	}

	/* Get the frame base attribute/ops */
	dwarf_attr(sp_die, DW_AT_frame_base, &fb_attr);
	ret = dwarf_getlocation_addr(&fb_attr, pf->addr, &pf->fb_ops, &nops, 1);
	if (ret <= 0 || nops == 0) {
		pf->fb_ops = NULL;
#if _ELFUTILS_PREREQ(0, 142)
	} else if (nops == 1 && pf->fb_ops[0].atom == DW_OP_call_frame_cfa &&
		   pf->cfi != NULL) {
		Dwarf_Frame *frame;
		if (dwarf_cfi_addrframe(pf->cfi, pf->addr, &frame) != 0 ||
		    dwarf_frame_cfa(frame, &pf->fb_ops, &nops) != 0) {
			pr_warning("Failed to get call frame on 0x%jx\n",
				   (uintmax_t)pf->addr);
			return -ENOENT;
		}
#endif
	}

	/* Call finder's callback handler */
	ret = pf->callback(sp_die, pf);

	/* *pf->fb_ops will be cached in libdw. Don't free it. */
	pf->fb_ops = NULL;

	return ret;
}
Exemplo n.º 5
0
static int
handle_cfi (Dwfl *dwfl, const char *which, Dwarf_CFI *cfi,
	    GElf_Addr pc, struct stuff *stuff)
{
  int result = dwarf_cfi_addrframe (cfi, pc - stuff->bias, &stuff->frame);
  if (result != 0)
    {
      error (0, 0, "dwarf_addrframe (%s): %s", which, dwfl_errmsg (-1));
      return 1;
    }

  Dwarf_Addr start = pc;
  Dwarf_Addr end = pc;
  bool signalp;
  int ra_regno = dwarf_frame_info (stuff->frame, &start, &end, &signalp);
  if (ra_regno >= 0)
    {
      start += stuff->bias;
      end += stuff->bias;
    }

  printf ("%s has %#" PRIx64 " => [%#" PRIx64 ", %#" PRIx64 "):\n",
	  which, pc, start, end);

  if (ra_regno < 0)
    printf ("\treturn address register unavailable (%s)\n",
	    dwarf_errmsg (0));
  else
    printf ("\treturn address in reg%u%s\n",
	    ra_regno, signalp ? " (signal frame)" : "");

  Dwarf_Op *cfa_ops;
  size_t cfa_nops;
  result = dwarf_frame_cfa (stuff->frame, &cfa_ops, &cfa_nops);

  printf ("\tCFA ");
  print_detail (result, cfa_ops, cfa_nops, stuff->bias);

  (void) dwfl_module_register_names (dwfl_addrmodule (dwfl, pc),
				     &print_register, stuff);

  return 0;
}
Exemplo n.º 6
0
/* Show a probe point to output buffer */
static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
{
	struct kprobe_trace_event *tev;
	Dwarf_Addr eaddr;
	Dwarf_Die die_mem;
	const char *name;
	int ret, i;
	Dwarf_Attribute fb_attr;
	size_t nops;

	if (pf->ntevs == pf->max_tevs) {
		pr_warning("Too many( > %d) probe point found.\n",
			   pf->max_tevs);
		return -ERANGE;
	}
	tev = &pf->tevs[pf->ntevs++];

	/* If no real subprogram, find a real one */
	if (!sp_die || dwarf_tag(sp_die) != DW_TAG_subprogram) {
		sp_die = die_find_real_subprogram(&pf->cu_die,
						 pf->addr, &die_mem);
		if (!sp_die) {
			pr_warning("Failed to find probe point in any "
				   "functions.\n");
			return -ENOENT;
		}
	}

	/* Copy the name of probe point */
	name = dwarf_diename(sp_die);
	if (name) {
		if (dwarf_entrypc(sp_die, &eaddr) != 0) {
			pr_warning("Failed to get entry pc of %s\n",
				   dwarf_diename(sp_die));
			return -ENOENT;
		}
		tev->point.symbol = strdup(name);
		if (tev->point.symbol == NULL)
			return -ENOMEM;
		tev->point.offset = (unsigned long)(pf->addr - eaddr);
	} else
		/* This function has no name. */
		tev->point.offset = (unsigned long)pf->addr;

	pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
		 tev->point.offset);

	/* Get the frame base attribute/ops */
	dwarf_attr(sp_die, DW_AT_frame_base, &fb_attr);
	ret = dwarf_getlocation_addr(&fb_attr, pf->addr, &pf->fb_ops, &nops, 1);
	if (ret <= 0 || nops == 0) {
		pf->fb_ops = NULL;
#if _ELFUTILS_PREREQ(0, 142)
	} else if (nops == 1 && pf->fb_ops[0].atom == DW_OP_call_frame_cfa &&
		   pf->cfi != NULL) {
		Dwarf_Frame *frame;
		if (dwarf_cfi_addrframe(pf->cfi, pf->addr, &frame) != 0 ||
		    dwarf_frame_cfa(frame, &pf->fb_ops, &nops) != 0) {
			pr_warning("Failed to get CFA on 0x%jx\n",
				   (uintmax_t)pf->addr);
			return -ENOENT;
		}
#endif
	}

	/* Find each argument */
	tev->nargs = pf->pev->nargs;
	tev->args = zalloc(sizeof(struct kprobe_trace_arg) * tev->nargs);
	if (tev->args == NULL)
		return -ENOMEM;
	for (i = 0; i < pf->pev->nargs; i++) {
		pf->pvar = &pf->pev->args[i];
		pf->tvar = &tev->args[i];
		ret = find_variable(sp_die, pf);
		if (ret != 0)
			return ret;
	}

	/* *pf->fb_ops will be cached in libdw. Don't free it. */
	pf->fb_ops = NULL;
	return 0;
}
Exemplo n.º 7
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);
    }
}