DWO file format: tags, attributes and forms

.debug_info.dwo holds a full tree of debugging information entries (DIEs), so any DWARF tag, attribute and form may appear in it. This page lists them all, from tables 7.2 to 7.6 of DWARF Version 5. Codes marked 5 are new in version 5. The codes of expressions, base types, languages and the line-number program are in the standard’s other tables and are not repeated here.

Unit types

Value	Name	Meaning
`0x01`	`DW_UT_compile`	Full compilation unit (not split).
`0x02`	`DW_UT_type`	Type unit (not split).
`0x03`	`DW_UT_partial`	Partial compilation unit.
`0x04`	`DW_UT_skeleton`	Skeleton unit, in the program.
`0x05`	`DW_UT_split_compile`	Split compilation unit, in the `.dwo`.
`0x06`	`DW_UT_split_type`	Split type unit, in the `.dwo`.
`0x80`–`0xFF`	`DW_UT_lo_user`–`DW_UT_hi_user`	Vendor unit types.

Abbreviations and entries

Each DIE in .debug_info.dwo starts with a ULEB128 abbreviation code (0 is a null entry, which ends a list of siblings), followed by its attribute values in the order its abbreviation gives. An abbreviation in .debug_abbrev.dwo is:

Field	Encoding	Meaning
code	ULEB128	The abbreviation code; 0 ends the unit’s table.
tag	ULEB128	A `DW_TAG` value.
children	1 byte	`0x00` `DW_CHILDREN_no`: the next entry is a sibling. `0x01` `DW_CHILDREN_yes`: the next entry is its first child.
attribute specifications	pairs of ULEB128	An `DW_AT` name and a `DW_FORM`; for `DW_FORM_implicit_const` a SLEB128 value follows, and no value is stored in the DIE. A pair of 0, 0 ends the list.

With DW_FORM_indirect the value in the DIE starts with a ULEB128 form code, then the value in that form.

Value	Name	Value	Name
`0x01`	`DW_TAG_array_type`	`0x27`	`DW_TAG_constant`
`0x02`	`DW_TAG_class_type`	`0x28`	`DW_TAG_enumerator`
`0x03`	`DW_TAG_entry_point`	`0x29`	`DW_TAG_file_type`
`0x04`	`DW_TAG_enumeration_type`	`0x2a`	`DW_TAG_friend`
`0x05`	`DW_TAG_formal_parameter`	`0x2b`	`DW_TAG_namelist`
`0x06`, `0x07`	reserved	`0x2c`	`DW_TAG_namelist_item`
`0x08`	`DW_TAG_imported_declaration`	`0x2d`	`DW_TAG_packed_type`
`0x09`	reserved	`0x2e`	`DW_TAG_subprogram`
`0x0a`	`DW_TAG_label`	`0x2f`	`DW_TAG_template_type_parameter`
`0x0b`	`DW_TAG_lexical_block`	`0x30`	`DW_TAG_template_value_parameter`
`0x0c`	reserved	`0x31`	`DW_TAG_thrown_type`
`0x0d`	`DW_TAG_member`	`0x32`	`DW_TAG_try_block`
`0x0e`	reserved	`0x33`	`DW_TAG_variant_part`
`0x0f`	`DW_TAG_pointer_type`	`0x34`	`DW_TAG_variable`
`0x10`	`DW_TAG_reference_type`	`0x35`	`DW_TAG_volatile_type`
`0x11`	`DW_TAG_compile_unit`	`0x36`	`DW_TAG_dwarf_procedure`
`0x12`	`DW_TAG_string_type`	`0x37`	`DW_TAG_restrict_type`
`0x13`	`DW_TAG_structure_type`	`0x38`	`DW_TAG_interface_type`
`0x14`	reserved	`0x39`	`DW_TAG_namespace`
`0x15`	`DW_TAG_subroutine_type`	`0x3a`	`DW_TAG_imported_module`
`0x16`	`DW_TAG_typedef`	`0x3b`	`DW_TAG_unspecified_type`
`0x17`	`DW_TAG_union_type`	`0x3c`	`DW_TAG_partial_unit`
`0x18`	`DW_TAG_unspecified_parameters`	`0x3d`	`DW_TAG_imported_unit`
`0x19`	`DW_TAG_variant`	`0x3e`	reserved (was `DW_TAG_mutable_type` in DWARF 3)
`0x1a`	`DW_TAG_common_block`	`0x3f`	`DW_TAG_condition`
`0x1b`	`DW_TAG_common_inclusion`	`0x40`	`DW_TAG_shared_type`
`0x1c`	`DW_TAG_inheritance`	`0x41`	`DW_TAG_type_unit`
`0x1d`	`DW_TAG_inlined_subroutine`	`0x42`	`DW_TAG_rvalue_reference_type`
`0x1e`	`DW_TAG_module`	`0x43`	`DW_TAG_template_alias`
`0x1f`	`DW_TAG_ptr_to_member_type`	`0x44`	`DW_TAG_coarray_type` 5
`0x20`	`DW_TAG_set_type`	`0x45`	`DW_TAG_generic_subrange` 5
`0x21`	`DW_TAG_subrange_type`	`0x46`	`DW_TAG_dynamic_type` 5
`0x22`	`DW_TAG_with_stmt`	`0x47`	`DW_TAG_atomic_type` 5
`0x23`	`DW_TAG_access_declaration`	`0x48`	`DW_TAG_call_site` 5
`0x24`	`DW_TAG_base_type`	`0x49`	`DW_TAG_call_site_parameter` 5
`0x25`	`DW_TAG_catch_block`	`0x4a`	`DW_TAG_skeleton_unit` 5
`0x26`	`DW_TAG_const_type`	`0x4b`	`DW_TAG_immutable_type` 5
		`0x4080`–`0xffff`	`DW_TAG_lo_user`–`DW_TAG_hi_user` (vendor tags)

Attributes

The classes say which kinds of form an attribute may use (see classes).

Value	Name	Classes
`0x01`	`DW_AT_sibling`	reference
`0x02`	`DW_AT_location`	exprloc, loclist
`0x03`	`DW_AT_name`	string
`0x04`–`0x08`	reserved	–
`0x09`	`DW_AT_ordering`	constant
`0x0a`	reserved	–
`0x0b`	`DW_AT_byte_size`	constant, exprloc, reference
`0x0c`	reserved (was `DW_AT_bit_offset` in DWARF 3 and earlier)	constant, exprloc, reference
`0x0d`	`DW_AT_bit_size`	constant, exprloc, reference
`0x0e`, `0x0f`	reserved	–
`0x10`	`DW_AT_stmt_list`	lineptr
`0x11`	`DW_AT_low_pc`	address
`0x12`	`DW_AT_high_pc`	address, constant
`0x13`	`DW_AT_language`	constant
`0x14`	reserved	–
`0x15`	`DW_AT_discr`	reference
`0x16`	`DW_AT_discr_value`	constant
`0x17`	`DW_AT_visibility`	constant
`0x18`	`DW_AT_import`	reference
`0x19`	`DW_AT_string_length`	exprloc, loclist, reference
`0x1a`	`DW_AT_common_reference`	reference
`0x1b`	`DW_AT_comp_dir`	string
`0x1c`	`DW_AT_const_value`	block, constant, string
`0x1d`	`DW_AT_containing_type`	reference
`0x1e`	`DW_AT_default_value`	constant, reference, flag
`0x1f`	reserved	–
`0x20`	`DW_AT_inline`	constant
`0x21`	`DW_AT_is_optional`	flag
`0x22`	`DW_AT_lower_bound`	constant, exprloc, reference
`0x23`, `0x24`	reserved	–
`0x25`	`DW_AT_producer`	string
`0x26`	reserved	–
`0x27`	`DW_AT_prototyped`	flag
`0x28`, `0x29`	reserved	–
`0x2a`	`DW_AT_return_addr`	exprloc, loclist
`0x2b`	reserved	–
`0x2c`	`DW_AT_start_scope`	constant, rnglist
`0x2d`	reserved	–
`0x2e`	`DW_AT_bit_stride`	constant, exprloc, reference
`0x2f`	`DW_AT_upper_bound`	constant, exprloc, reference
`0x30`	reserved	–
`0x31`	`DW_AT_abstract_origin`	reference
`0x32`	`DW_AT_accessibility`	constant
`0x33`	`DW_AT_address_class`	constant
`0x34`	`DW_AT_artificial`	flag
`0x35`	`DW_AT_base_types`	reference
`0x36`	`DW_AT_calling_convention`	constant
`0x37`	`DW_AT_count`	constant, exprloc, reference
`0x38`	`DW_AT_data_member_location`	constant, exprloc, loclist
`0x39`	`DW_AT_decl_column`	constant
`0x3a`	`DW_AT_decl_file`	constant
`0x3b`	`DW_AT_decl_line`	constant
`0x3c`	`DW_AT_declaration`	flag
`0x3d`	`DW_AT_discr_list`	block
`0x3e`	`DW_AT_encoding`	constant
`0x3f`	`DW_AT_external`	flag
`0x40`	`DW_AT_frame_base`	exprloc, loclist
`0x41`	`DW_AT_friend`	reference
`0x42`	`DW_AT_identifier_case`	constant
`0x43`	reserved (was `DW_AT_macro_info` in DWARF 4 and earlier)	macptr
`0x44`	`DW_AT_namelist_item`	reference
`0x45`	`DW_AT_priority`	reference
`0x46`	`DW_AT_segment`	exprloc, loclist
`0x47`	`DW_AT_specification`	reference
`0x48`	`DW_AT_static_link`	exprloc, loclist
`0x49`	`DW_AT_type`	reference
`0x4a`	`DW_AT_use_location`	exprloc, loclist
`0x4b`	`DW_AT_variable_parameter`	flag
`0x4c`	`DW_AT_virtuality`	constant
`0x4d`	`DW_AT_vtable_elem_location`	exprloc, loclist
`0x4e`	`DW_AT_allocated`	constant, exprloc, reference
`0x4f`	`DW_AT_associated`	constant, exprloc, reference
`0x50`	`DW_AT_data_location`	exprloc
`0x51`	`DW_AT_byte_stride`	constant, exprloc, reference
`0x52`	`DW_AT_entry_pc`	address, constant
`0x53`	`DW_AT_use_UTF8`	flag
`0x54`	`DW_AT_extension`	reference
`0x55`	`DW_AT_ranges`	rnglist
`0x56`	`DW_AT_trampoline`	address, flag, reference, string
`0x57`	`DW_AT_call_column`	constant
`0x58`	`DW_AT_call_file`	constant
`0x59`	`DW_AT_call_line`	constant
`0x5a`	`DW_AT_description`	string
`0x5b`	`DW_AT_binary_scale`	constant
`0x5c`	`DW_AT_decimal_scale`	constant
`0x5d`	`DW_AT_small`	reference
`0x5e`	`DW_AT_decimal_sign`	constant
`0x5f`	`DW_AT_digit_count`	constant
`0x60`	`DW_AT_picture_string`	string
`0x61`	`DW_AT_mutable`	flag
`0x62`	`DW_AT_threads_scaled`	flag
`0x63`	`DW_AT_explicit`	flag
`0x64`	`DW_AT_object_pointer`	reference
`0x65`	`DW_AT_endianity`	constant
`0x66`	`DW_AT_elemental`	flag
`0x67`	`DW_AT_pure`	flag
`0x68`	`DW_AT_recursive`	flag
`0x69`	`DW_AT_signature`	reference
`0x6a`	`DW_AT_main_subprogram`	flag
`0x6b`	`DW_AT_data_bit_offset`	constant
`0x6c`	`DW_AT_const_expr`	flag
`0x6d`	`DW_AT_enum_class`	flag
`0x6e`	`DW_AT_linkage_name`	string
`0x6f`	`DW_AT_string_length_bit_size` 5	constant
`0x70`	`DW_AT_string_length_byte_size` 5	constant
`0x71`	`DW_AT_rank` 5	constant, exprloc
`0x72`	`DW_AT_str_offsets_base` 5	stroffsetsptr
`0x73`	`DW_AT_addr_base` 5	addrptr
`0x74`	`DW_AT_rnglists_base` 5	rnglistsptr
`0x75`	reserved (unused)	–
`0x76`	`DW_AT_dwo_name` 5	string
`0x77`	`DW_AT_reference` 5	flag
`0x78`	`DW_AT_rvalue_reference` 5	flag
`0x79`	`DW_AT_macros` 5	macptr
`0x7a`	`DW_AT_call_all_calls` 5	flag
`0x7b`	`DW_AT_call_all_source_calls` 5	flag
`0x7c`	`DW_AT_call_all_tail_calls` 5	flag
`0x7d`	`DW_AT_call_return_pc` 5	address
`0x7e`	`DW_AT_call_value` 5	exprloc
`0x7f`	`DW_AT_call_origin` 5	exprloc
`0x80`	`DW_AT_call_parameter` 5	reference
`0x81`	`DW_AT_call_pc` 5	address
`0x82`	`DW_AT_call_tail_call` 5	flag
`0x83`	`DW_AT_call_target` 5	exprloc
`0x84`	`DW_AT_call_target_clobbered` 5	exprloc
`0x85`	`DW_AT_call_data_location` 5	exprloc
`0x86`	`DW_AT_call_data_value` 5	exprloc
`0x87`	`DW_AT_noreturn` 5	flag
`0x88`	`DW_AT_alignment` 5	constant
`0x89`	`DW_AT_export_symbols` 5	flag
`0x8a`	`DW_AT_deleted` 5	flag
`0x8b`	`DW_AT_defaulted` 5	constant
`0x8c`	`DW_AT_loclists_base` 5	loclistsptr
`0x2000`–`0x3fff`	`DW_AT_lo_user`–`DW_AT_hi_user` (vendor attributes, e.g. the GNU split-DWARF ones at `0x2130`–`0x2135`)	–

Forms

“Offset size” is 4 bytes in the 32-bit DWARF format and 8 in the 64-bit format.

Value	Name	Class	Encoding in the DIE
`0x01`	`DW_FORM_addr`	address	An address of `address_size` bytes, relocated by the linker.
`0x02`	reserved	–	–
`0x03`	`DW_FORM_block2`	block	2-byte length, then that many bytes.
`0x04`	`DW_FORM_block4`	block	4-byte length, then that many bytes.
`0x05`	`DW_FORM_data2`	constant	2 bytes.
`0x06`	`DW_FORM_data4`	constant	4 bytes.
`0x07`	`DW_FORM_data8`	constant	8 bytes.
`0x08`	`DW_FORM_string`	string	The string itself, ending in a 0 byte.
`0x09`	`DW_FORM_block`	block	ULEB128 length, then that many bytes.
`0x0a`	`DW_FORM_block1`	block	1-byte length, then that many bytes.
`0x0b`	`DW_FORM_data1`	constant	1 byte.
`0x0c`	`DW_FORM_flag`	flag	1 byte: 0 false, other values true.
`0x0d`	`DW_FORM_sdata`	constant	SLEB128.
`0x0e`	`DW_FORM_strp`	string	Offset-size offset into `.debug_str`.
`0x0f`	`DW_FORM_udata`	constant	ULEB128.
`0x10`	`DW_FORM_ref_addr`	reference	Offset-size offset from the start of `.debug_info`.
`0x11`	`DW_FORM_ref1`	reference	1-byte offset from the start of the unit header.
`0x12`	`DW_FORM_ref2`	reference	2-byte unit offset.
`0x13`	`DW_FORM_ref4`	reference	4-byte unit offset.
`0x14`	`DW_FORM_ref8`	reference	8-byte unit offset.
`0x15`	`DW_FORM_ref_udata`	reference	ULEB128 unit offset.
`0x16`	`DW_FORM_indirect`	(any)	ULEB128 form code, then a value in that form.
`0x17`	`DW_FORM_sec_offset`	addrptr, lineptr, loclist, loclistsptr, macptr, rnglist, rnglistsptr, stroffsetsptr	Offset-size offset into the section the attribute’s class names.
`0x18`	`DW_FORM_exprloc`	exprloc	ULEB128 length, then a DWARF expression.
`0x19`	`DW_FORM_flag_present`	flag	Nothing: the attribute is present and true.
`0x1a`	`DW_FORM_strx` 5	string	ULEB128 index into the string offsets table.
`0x1b`	`DW_FORM_addrx` 5	address	ULEB128 index into `.debug_addr`.
`0x1c`	`DW_FORM_ref_sup4` 5	reference	4-byte offset into a supplementary file’s `.debug_info`.
`0x1d`	`DW_FORM_strp_sup` 5	string	Offset-size offset into a supplementary file’s `.debug_str`.
`0x1e`	`DW_FORM_data16` 5	constant	16 bytes.
`0x1f`	`DW_FORM_line_strp` 5	string	Offset-size offset into `.debug_line_str`.
`0x20`	`DW_FORM_ref_sig8`	reference	8-byte type signature of a type unit.
`0x21`	`DW_FORM_implicit_const` 5	constant	Nothing: the value is the SLEB128 stored in the abbreviation.
`0x22`	`DW_FORM_loclistx` 5	loclist	ULEB128 index into the location list offsets.
`0x23`	`DW_FORM_rnglistx` 5	rnglist	ULEB128 index into the range list offsets.
`0x24`	`DW_FORM_ref_sup8` 5	reference	8-byte offset into a supplementary file’s `.debug_info`.
`0x25`	`DW_FORM_strx1` 5	string	1-byte string index.
`0x26`	`DW_FORM_strx2` 5	string	2-byte string index.
`0x27`	`DW_FORM_strx3` 5	string	3-byte string index.
`0x28`	`DW_FORM_strx4` 5	string	4-byte string index.
`0x29`	`DW_FORM_addrx1` 5	address	1-byte address index.
`0x2a`	`DW_FORM_addrx2` 5	address	2-byte address index.
`0x2b`	`DW_FORM_addrx3` 5	address	3-byte address index.
`0x2c`	`DW_FORM_addrx4` 5	address	4-byte address index.

A .dwo is never relocated, so its producers avoid forms that would need relocation: strings use the strx forms rather than DW_FORM_strp, addresses the addrx forms, and references stay inside the unit or name a type unit with DW_FORM_ref_sig8.

Classes

Class	Forms	Meaning
address	`addr`, `addrx`, `addrx1`–`addrx4`	A machine address, direct or by index.
addrptr	`sec_offset`	Offset into `.debug_addr`.
block	`block1`, `block2`, `block4`, `block`	Uninterpreted bytes.
constant	`data1`, `data2`, `data4`, `data8`, `data16`, `sdata`, `udata`, `implicit_const`	A number or other fixed data, in target byte order.
exprloc	`exprloc`	A DWARF expression or location description.
flag	`flag`, `flag_present`	True or false.
lineptr	`sec_offset`	Offset into `.debug_line` or `.debug_line.dwo`.
loclist	`loclistx`, `sec_offset`	A location list.
loclistsptr	`sec_offset`	Offset into `.debug_loclists`.
macptr	`sec_offset`	Offset into `.debug_macro` or `.debug_macro.dwo`.
reference	`ref1`, `ref2`, `ref4`, `ref8`, `ref_udata`, `ref_addr`, `ref_sig8`, `ref_sup4`, `ref_sup8`	Another DIE.
rnglist	`rnglistx`, `sec_offset`	A range list.
rnglistsptr	`sec_offset`	Offset into `.debug_rnglists`.
string	`string`, `strp`, `line_strp`, `strp_sup`, `strx`, `strx1`–`strx4`	A string, inline or by offset or index.
stroffsetsptr	`sec_offset`	Offset into `.debug_str_offsets`.

Sources

DWARF Debugging Information Format, Version 5: section 7.5.1 and table 7.2 (unit types), 7.5.2 and 7.5.3 (entries and abbreviations), table 7.3 (tags), table 7.4 (children), table 7.5 (attributes and classes), 7.5.5 and table 7.6 (classes and forms). The note on GNU vendor attributes is from LLVM’s BinaryFormat/Dwarf.def.

.DWO File Format – Tags, attributes and forms