Here summarizes the supports provided by golang/debug package.
debug/dwarf
const.go
// An Attr identifies the attribute type in a DWARF Entry's Field.
type Attr uint32
const (
AttrSibling Attr = 0x01
AttrLocation Attr = 0x02
AttrName Attr = 0x03
AttrOrdering Attr = 0x09
AttrByteSize Attr = 0x0B
AttrBitOffset Attr = 0x0C
...
)
// A format is a DWARF data encoding format.
type format uint32
const (
// value formats
formAddr format = 0x01
formDwarfBlock2 format = 0x03
formDwarfBlock4 format = 0x04
formData2 format = 0x05
formData4 format = 0x06
...
)
// A Tag is the classification (the type) of an Entry.
type Tag uint32
const (
TagArrayType Tag = 0x01
TagClassType Tag = 0x02
TagEntryPoint Tag = 0x03
TagEnumerationType Tag = 0x04
TagFormalParameter Tag = 0x05
...
)
// Location expression operators.
// The debug info encodes value locations like 8(R3)
// as a sequence of these op codes.
// This package does not implement full expressions;
// the opPlusUconst operator is expected by the type parser.
const (
opAddr = 0x03 /* 1 op, const addr */
opDeref = 0x06
opConst1u = 0x08 /* 1 op, 1 byte const */
opConst1s = 0x09 /* " signed */
...
opDup = 0x12
opDrop = 0x13
opOver = 0x14
...
)
...
attr_string.go
const _Attr_name = "SiblingLocationNameOrderingByteSizeBitOffsetBitSizeStmtListLowpcHighpcLanguageDiscrDiscrValueVisibilityImportStringLengthCommonRefCompDirConstValueContainingTypeDefaultValueInlineIsOptionalLowerBoundProducerPrototypedReturnAddrStartScopeStrideSizeUpperBoundAbstractOriginAccessibilityAddrClassArtificialBaseTypesCallingCountDataMemberLocDeclColumnDeclFileDeclLineDeclarationDiscrListEncodingExternalFrameBaseFriendIdentifierCaseMacroInfoNamelistItemPrioritySegmentSpecificationStaticLinkTypeUseLocationVarParamVirtualityVtableElemLocAllocatedAssociatedDataLocationStrideEntrypcUseUTF8ExtensionRangesTrampolineCallColumnCallFileCallLineDescription"
var _Attr_map = map[Attr]string{
1: _Attr_name[0:7],
2: _Attr_name[7:15],
3: _Attr_name[15:19],
9: _Attr_name[19:27],
11: _Attr_name[27:35],
12: _Attr_name[35:44],
...
}
func (i Attr) String() string {
if str, ok := _Attr_map[i]; ok {
return str
}
return "Attr(" + strconv.FormatInt(int64(i), 10) + ")"
}
entry.go
DWARF debug information entry (DIE) parser. An entry is a sequence of data items of a given format. The first word in the entry is an index into what DWARF calls the abbreviation table. An abbreviation is really just a type descriptor: it’s an array of attribute tag/value format pairs
// An entry is a sequence of attribute/value pairs.
type Entry struct {
Offset Offset // offset of Entry in DWARF info
Tag Tag // tag (kind of Entry)
Children bool // whether Entry is followed by children
Field []Field
}
// An Offset represents the location of an Entry within the DWARF info.
// (See Reader.Seek.)
type Offset uint32
// A Field is a single attribute/value pair in an Entry.
//
// A value can be one of several "attribute classes" defined by DWARF.
// The Go types corresponding to each class are:
//
// DWARF class Go type Class
// ----------- ------- -----
// address uint64 ClassAddress
// block []byte ClassBlock
// constant int64 ClassConstant
// flag bool ClassFlag
// reference
// to info dwarf.Offset ClassReference
// to type unit uint64 ClassReferenceSig
// string string ClassString
// exprloc []byte ClassExprLoc
// lineptr int64 ClassLinePtr
// loclistptr int64 ClassLocListPtr
// macptr int64 ClassMacPtr
// rangelistptr int64 ClassRangeListPtr
//
// For unrecognized or vendor-defined attributes, Class may be
// ClassUnknown.
type Field struct {
Attr Attr
Val interface{}
Class Class
}
// A Class is the DWARF 4 class of an attribute value.
type Class int
const (
// ClassUnknown represents values of unknown DWARF class.
ClassUnknown Class = iota
// ClassAddress represents values of type uint64 that are
// addresses on the target machine.
ClassAddress
// ClassBlock represents values of type []byte whose
// interpretation depends on the attribute.
ClassBlock
...
)
// a single entry's description: a sequence of attributes
type abbrev struct {
tag Tag
children bool
field []afield
}
type afield struct {
attr Attr
fmt format
class Class
}
// a map from entry format ids to their descriptions
type abbrevTable map[uint32]abbrev
// ParseAbbrev returns the abbreviation table that starts at byte off
// in the .debug_abbrev section.
func (d *Data) parseAbbrev(off uint64, vers int) (abbrevTable, error) {
if m, ok := d.abbrevCache[off]; ok {
return m, nil
}
data := d.abbrev
...
b := makeBuf(d, unknownFormat{}, "abbrev", 0, data)
...
}
class_string.go
const _Class_name = "ClassUnknownClassAddressClassBlockClassConstantClassExprLocClassFlagClassLinePtrClassLocListPtrClassMacPtrClassRangeListPtrClassReferenceClassReferenceSigClassStringClassReferenceAltClassStringAlt"
var _Class_index = [...]uint8{0, 12, 24, 34, 47, 59, 68, 80, 95, 106, 123, 137, 154, 165, 182, 196}
func (i Class) String() string {
if i < 0 || i >= Class(len(_Class_index)-1) {
return "Class(" + strconv.FormatInt(int64(i), 10) + ")"
}
return _Class_name[_Class_index[i]:_Class_index[i+1]]
}
open.go
// Data represents the DWARF debugging information
// loaded from an executable file (for example, an ELF or Mach-O executable).
type Data struct {
// raw data
abbrev []byte
aranges []byte
frame []byte
info []byte
line []byte
pubnames []byte
ranges []byte
str []byte
// parsed data
abbrevCache map[uint64]abbrevTable
order binary.ByteOrder
typeCache map[Offset]Type
typeSigs map[uint64]*typeUnit
unit []unit
}
.debug_info of 32-bit DWARF differs from the one of 64-bit DWARF:
- 32-bit DWARF: 4 byte length, 2 byte version
- 64-bit DWARF: 4 bytes of 0xff, 8 byte length, 2 byte version
Compiler generates debug information for each compilation unit. Linker will merge them into section .debug_info into executable file, like ELF executable file.
Data.parseUnits() parses the .debug_info section in executable file, it works as following:
func (d *Data) parseUnits() ([]unit, error) {
// Count units.
nunit := 0
b := makeBuf(d, unknownFormat{}, "info", 0, d.info)
// all compilation units' debug info is merged by linker into executable file,
// here counts the number of compilation unit.
for len(b.data) > 0 {
len, _ := b.unitLength()
if len != Offset(uint32(len)) {
b.error("unit length overflow")
break
}
b.skip(int(len))
nunit++
}
if b.err != nil {
return nil, b.err
}
// Again, this time writing them down.
b = makeBuf(d, unknownFormat{}, "info", 0, d.info)
units := make([]unit, nunit)
for i := range units {
u := &units[i]
u.base = b.off
// parse .debug_info and build the struct `unit` for each compilation unit
...
}
return units, nil
}
unit.go
DWARF debug info is split into a sequence of compilation units. Each unit has its own abbreviation table and address size.
// unit a unit represents a compilation unit
type unit struct {
base Offset // byte offset of header within the aggregate info
off Offset // byte offset of data within the aggregate info
data []byte
atable abbrevTable
asize int
vers int
is64 bool // True for 64-bit DWARF format
}
buf.go
Buffered reading and decoding of DWARF data streams.
// Data buffer being decoded.
type buf struct {
dwarf *Data
order binary.ByteOrder
format dataFormat
name string
off Offset
data []byte
err error
}
line.go
// A LineReader reads a sequence of LineEntry structures from a DWARF
// "line" section for a single compilation unit. LineEntries occur in
// order of increasing PC and each LineEntry gives metadata for the
// instructions from that LineEntry's PC to just before the next
// LineEntry's PC. The last entry will have its EndSequence field set.
type LineReader struct {
...
}
// A LineEntry is a row in a DWARF line table.
type LineEntry struct {
// Address is the program-counter value of a machine
// instruction generated by the compiler. This LineEntry
// applies to each instruction from Address to just before the
// Address of the next LineEntry.
Address uint64
// OpIndex is the index of an operation within a VLIW
// instruction. The index of the first operation is 0. For
// non-VLIW architectures, it will always be 0. Address and
// OpIndex together form an operation pointer that can
// reference any individual operation within the instruction
// stream.
OpIndex int
// File is the source file corresponding to these
// instructions.
File *LineFile
// Line is the source code line number corresponding to these
// instructions. Lines are numbered beginning at 1. It may be
// 0 if these instructions cannot be attributed to any source
// line.
Line int
// Column is the column number within the source line of these
// instructions. Columns are numbered beginning at 1. It may
// be 0 to indicate the "left edge" of the line.
Column int
...
}
// A LineFile is a source file referenced by a DWARF line table entry.
type LineFile struct {
Name string
Mtime uint64 // Implementation defined modification time, or 0 if unknown
Length int // File length, or 0 if unknown
}
// LineReader returns a new reader for the line table of compilation
// unit cu, which must be an Entry with tag TagCompileUnit.
//
// If this compilation unit has no line table, it returns nil, nil.
func (d *Data) LineReader(cu *Entry) (*LineReader, error) {
...
}
tag_string.go
const (
_Tag_name_0 = "ArrayTypeClassTypeEntryPointEnumerationTypeFormalParameter"
_Tag_name_1 = "ImportedDeclaration"
_Tag_name_2 = "LabelLexDwarfBlock"
_Tag_name_3 = "Member"
_Tag_name_4 = "PointerTypeReferenceTypeCompileUnitStringTypeStructType"
_Tag_name_5 = "SubroutineTypeTypedefUnionTypeUnspecifiedParametersVariantCommonDwarfBlockCommonInclusionInheritanceInlinedSubroutineModulePtrToMemberTypeSetTypeSubrangeTypeWithStmtAccessDeclarationBaseTypeCatchDwarfBlockConstTypeConstantEnumeratorFileTypeFriendNamelistNamelistItemPackedTypeSubprogramTemplateTypeParameterTemplateValueParameterThrownTypeTryDwarfBlockVariantPartVariableVolatileTypeDwarfProcedureRestrictTypeInterfaceTypeNamespaceImportedModuleUnspecifiedTypePartialUnitImportedUnitMutableTypeConditionSharedTypeTypeUnitRvalueReferenceTypeTemplateAlias"
)
var (
_Tag_index_0 = [...]uint8{0, 9, 18, 28, 43, 58}
_Tag_index_2 = [...]uint8{0, 5, 18}
_Tag_index_4 = [...]uint8{0, 11, 24, 35, 45, 55}
_Tag_index_5 = [...]uint16{0, 14, 21, 30, 51, 58, 74, 89, 100, 117, 123, 138, 145, 157, 165, 182, 190, 205, 214, 222, 232, 240, 246, 254, 266, 276, 286, 307, 329, 339, 352, 363, 371, 383, 397, 409, 422, 431, 445, 460, 471, 483, 494, 503, 513, 521, 540, 553}
)
func (i Tag) String() string {
switch {
case 1 <= i && i <= 5:
i -= 1
...
}
}
type
DWARF type information structures. The format is heavily biased toward C, but for simplicity the String methods use a pseudo-Go syntax.
// A Type conventionally represents a pointer to any of the
// specific Type structures (CharType, StructType, etc.).
type Type interface {
Common() *CommonType
String() string
Size() int64
}
// A CommonType holds fields common to multiple types.
// If a field is not known or not applicable for a given type,
// the zero value is used.
type CommonType struct {
ByteSize int64 // size of value of this type, in bytes
Name string // name that can be used to refer to type
}
...
// Basic types
// A BasicType holds fields common to all basic types.
type BasicType struct {
CommonType
BitSize int64
BitOffset int64
}
// A CharType represents a signed character type
type CharType struct{
BasicType
}
type UcharType{...}
type IntType struct{...}
...
type AddrType struct{...}
type UnspecifiedType struct{...}
type QualType struct{...}
type ArrayType struct{...}
type VoidType struct{...}
type PtrType struct{...}
type StructType struct{...}
type StructField struct{...}
type FuncType struct{...}
type DotDotDotType struct{...}
type TypedefType struct{...}
...
typeunit.go
// Parse the type units stored in a DWARF4 .debug_types section. Each
// type unit defines a single primary type and an 8-byte signature.
// Other sections may then use formRefSig8 to refer to the type.
// The typeUnit format is a single type with a signature. It holds
// the same data as a compilation unit.
type typeUnit struct {
unit
toff Offset // Offset to signature type within data.
name string // Name of .debug_type section.
cache Type // Cache the type, nil to start.
}
// Parse a .debug_types section.
func (d *Data) parseTypes(name string, types []byte) error {
b := makeBuf(d, unknownFormat{}, name, 0, types)
for len(b.data) > 0 {
...
}
// typeUnitReader is a typeReader for a tagTypeUnit.
type typeUnitReader struct {
d *Data
tu *typeUnit
b buf
err error
...
)