dwarf

package
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 Go to latest Published: May 19, 2023 License: BSD-3-Clause Imports: 9 Imported by: 0

Documentation

Overview

Package dwarf provides access to DWARF debugging information loaded from executable files, as defined in the DWARF 2.0 Standard at http://dwarfstd.org/doc/dwarf-2.0.0.pdf.

Security

This package is not designed to be hardened against adversarial inputs, and is outside the scope of https://go.dev/security/policy. In particular, only basic validation is done when parsing object files. As such, care should be taken when parsing untrusted inputs, as parsing malformed files may consume significant resources, or cause panics.

Index

Constants

This section is empty.

Variables

View Source 
var ErrUnknownPC = errors.New("ErrUnknownPC")

ErrUnknownPC is the error returned by LineReader.ScanPC when the seek PC is not covered by any entry in the line table.

Functions

This section is empty.

Types

type AddrType 

type AddrType struct {
	BasicType
}

An AddrType represents a machine address type.

type ArrayType 

type ArrayType struct {
	CommonType
	Type          Type
	StrideBitSize int64 // if > 0, number of bits to hold each element
	Count         int64 // if == -1, an incomplete array, like char x[].
}

An ArrayType represents a fixed size array type.

func (*ArrayType) Size 

func (t *ArrayType) Size() int64

func (*ArrayType) String 

func (t *ArrayType) String() string

type Attr 

type Attr uint32

An Attr identifies the attribute type in a DWARF Entry's Field. 

const (
	AttrSibling        Attr = 0x01
	AttrLocation       Attr = 0x02
	AttrName           Attr = 0x03
	AttrOrdering       Attr = 0x09
	AttrByteSize       Attr = 0x0B
	AttrBitOffset      Attr = 0x0C
	AttrBitSize        Attr = 0x0D
	AttrStmtList       Attr = 0x10
	AttrLowpc          Attr = 0x11
	AttrHighpc         Attr = 0x12
	AttrLanguage       Attr = 0x13
	AttrDiscr          Attr = 0x15
	AttrDiscrValue     Attr = 0x16
	AttrVisibility     Attr = 0x17
	AttrImport         Attr = 0x18
	AttrStringLength   Attr = 0x19
	AttrCommonRef      Attr = 0x1A
	AttrCompDir        Attr = 0x1B
	AttrConstValue     Attr = 0x1C
	AttrContainingType Attr = 0x1D
	AttrDefaultValue   Attr = 0x1E
	AttrInline         Attr = 0x20
	AttrIsOptional     Attr = 0x21
	AttrLowerBound     Attr = 0x22
	AttrProducer       Attr = 0x25
	AttrPrototyped     Attr = 0x27
	AttrReturnAddr     Attr = 0x2A
	AttrStartScope     Attr = 0x2C
	AttrStrideSize     Attr = 0x2E
	AttrUpperBound     Attr = 0x2F
	AttrAbstractOrigin Attr = 0x31
	AttrAccessibility  Attr = 0x32
	AttrAddrClass      Attr = 0x33
	AttrArtificial     Attr = 0x34
	AttrBaseTypes      Attr = 0x35
	AttrCalling        Attr = 0x36
	AttrCount          Attr = 0x37
	AttrDataMemberLoc  Attr = 0x38
	AttrDeclColumn     Attr = 0x39
	AttrDeclFile       Attr = 0x3A
	AttrDeclLine       Attr = 0x3B
	AttrDeclaration    Attr = 0x3C
	AttrDiscrList      Attr = 0x3D
	AttrEncoding       Attr = 0x3E
	AttrExternal       Attr = 0x3F
	AttrFrameBase      Attr = 0x40
	AttrFriend         Attr = 0x41
	AttrIdentifierCase Attr = 0x42
	AttrMacroInfo      Attr = 0x43
	AttrNamelistItem   Attr = 0x44
	AttrPriority       Attr = 0x45
	AttrSegment        Attr = 0x46
	AttrSpecification  Attr = 0x47
	AttrStaticLink     Attr = 0x48
	AttrType           Attr = 0x49
	AttrUseLocation    Attr = 0x4A
	AttrVarParam       Attr = 0x4B
	AttrVirtuality     Attr = 0x4C
	AttrVtableElemLoc  Attr = 0x4D
	// The following are new in DWARF 3.
	AttrAllocated     Attr = 0x4E
	AttrAssociated    Attr = 0x4F
	AttrDataLocation  Attr = 0x50
	AttrStride        Attr = 0x51
	AttrEntrypc       Attr = 0x52
	AttrUseUTF8       Attr = 0x53
	AttrExtension     Attr = 0x54
	AttrRanges        Attr = 0x55
	AttrTrampoline    Attr = 0x56
	AttrCallColumn    Attr = 0x57
	AttrCallFile      Attr = 0x58
	AttrCallLine      Attr = 0x59
	AttrDescription   Attr = 0x5A
	AttrBinaryScale   Attr = 0x5B
	AttrDecimalScale  Attr = 0x5C
	AttrSmall         Attr = 0x5D
	AttrDecimalSign   Attr = 0x5E
	AttrDigitCount    Attr = 0x5F
	AttrPictureString Attr = 0x60
	AttrMutable       Attr = 0x61
	AttrThreadsScaled Attr = 0x62
	AttrExplicit      Attr = 0x63
	AttrObjectPointer Attr = 0x64
	AttrEndianity     Attr = 0x65
	AttrElemental     Attr = 0x66
	AttrPure          Attr = 0x67
	AttrRecursive     Attr = 0x68
	// The following are new in DWARF 4.
	AttrSignature      Attr = 0x69
	AttrMainSubprogram Attr = 0x6A
	AttrDataBitOffset  Attr = 0x6B
	AttrConstExpr      Attr = 0x6C
	AttrEnumClass      Attr = 0x6D
	AttrLinkageName    Attr = 0x6E
	// The following are new in DWARF 5.
	AttrStringLengthBitSize  Attr = 0x6F
	AttrStringLengthByteSize Attr = 0x70
	AttrRank                 Attr = 0x71
	AttrStrOffsetsBase       Attr = 0x72
	AttrAddrBase             Attr = 0x73
	AttrRnglistsBase         Attr = 0x74
	AttrDwoName              Attr = 0x76
	AttrReference            Attr = 0x77
	AttrRvalueReference      Attr = 0x78
	AttrMacros               Attr = 0x79
	AttrCallAllCalls         Attr = 0x7A
	AttrCallAllSourceCalls   Attr = 0x7B
	AttrCallAllTailCalls     Attr = 0x7C
	AttrCallReturnPC         Attr = 0x7D
	AttrCallValue            Attr = 0x7E
	AttrCallOrigin           Attr = 0x7F
	AttrCallParameter        Attr = 0x80
	AttrCallPC               Attr = 0x81
	AttrCallTailCall         Attr = 0x82
	AttrCallTarget           Attr = 0x83
	AttrCallTargetClobbered  Attr = 0x84
	AttrCallDataLocation     Attr = 0x85
	AttrCallDataValue        Attr = 0x86
	AttrNoreturn             Attr = 0x87
	AttrAlignment            Attr = 0x88
	AttrExportSymbols        Attr = 0x89
	AttrDeleted              Attr = 0x8A
	AttrDefaulted            Attr = 0x8B
	AttrLoclistsBase         Attr = 0x8C
)

func (Attr) GoString 

func (a Attr) GoString() string

func (Attr) String 

func (i Attr) String() string

type BasicType 

type BasicType struct {
	CommonType
	BitSize       int64
	BitOffset     int64
	DataBitOffset int64
}

A BasicType holds fields common to all basic types.

See the documentation for StructField for more info on the interpretation of the BitSize/BitOffset/DataBitOffset fields.

func (*BasicType) Basic 

func (b *BasicType) Basic() *BasicType

func (*BasicType) String 

func (t *BasicType) String() string

type BoolType 

type BoolType struct {
	BasicType
}

A BoolType represents a boolean type.

type CharType 

type CharType struct {
	BasicType
}

A CharType represents a signed character type.

type Class 

type Class int

A Class is the DWARF 4 class of an attribute value.

In general, a given attribute's value may take on one of several possible classes defined by DWARF, each of which leads to a slightly different interpretation of the attribute.

DWARF version 4 distinguishes attribute value classes more finely than previous versions of DWARF. The reader will disambiguate coarser classes from earlier versions of DWARF into the appropriate DWARF 4 class. For example, DWARF 2 uses "constant" for constants as well as all types of section offsets, but the reader will canonicalize attributes in DWARF 2 files that refer to section offsets to one of the Class*Ptr classes, even though these classes were only defined in DWARF 3. 

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

	// ClassConstant represents values of type int64 that are
	// constants. The interpretation of this constant depends on
	// the attribute.
	ClassConstant

	// ClassExprLoc represents values of type []byte that contain
	// an encoded DWARF expression or location description.
	ClassExprLoc

	// ClassFlag represents values of type bool.
	ClassFlag

	// ClassLinePtr represents values that are an int64 offset
	// into the "line" section.
	ClassLinePtr

	// ClassLocListPtr represents values that are an int64 offset
	// into the "loclist" section.
	ClassLocListPtr

	// ClassMacPtr represents values that are an int64 offset into
	// the "mac" section.
	ClassMacPtr

	// ClassRangeListPtr represents values that are an int64 offset into
	// the "rangelist" section.
	ClassRangeListPtr

	// ClassReference represents values that are an Offset offset
	// of an Entry in the info section (for use with Reader.Seek).
	// The DWARF specification combines ClassReference and
	// ClassReferenceSig into class "reference".
	ClassReference

	// ClassReferenceSig represents values that are a uint64 type
	// signature referencing a type Entry.
	ClassReferenceSig

	// ClassString represents values that are strings. If the
	// compilation unit specifies the AttrUseUTF8 flag (strongly
	// recommended), the string value will be encoded in UTF-8.
	// Otherwise, the encoding is unspecified.
	ClassString

	// ClassReferenceAlt represents values of type int64 that are
	// an offset into the DWARF "info" section of an alternate
	// object file.
	ClassReferenceAlt

	// ClassStringAlt represents values of type int64 that are an
	// offset into the DWARF string section of an alternate object
	// file.
	ClassStringAlt

	// ClassAddrPtr represents values that are an int64 offset
	// into the "addr" section.
	ClassAddrPtr

	// ClassLocList represents values that are an int64 offset
	// into the "loclists" section.
	ClassLocList

	// ClassRngList represents values that are a uint64 offset
	// from the base of the "rnglists" section.
	ClassRngList

	// ClassRngListsPtr represents values that are an int64 offset
	// into the "rnglists" section. These are used as the base for
	// ClassRngList values.
	ClassRngListsPtr

	// ClassStrOffsetsPtr represents values that are an int64
	// offset into the "str_offsets" section.
	ClassStrOffsetsPtr
)

func (Class) GoString 

func (i Class) GoString() string

func (Class) String 

func (i Class) String() string

type CommonType 

type CommonType struct {
	ByteSize int64  // size of value of this type, in bytes
	Name     string // name that can be used to refer to type
}

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.

func (*CommonType) Common 

func (c *CommonType) Common() *CommonType

func (*CommonType) Size 

func (c *CommonType) Size() int64

type ComplexType 

type ComplexType struct {
	BasicType
}

A ComplexType represents a complex floating point type.

type Data 

type Data struct {
	// contains filtered or unexported fields
}

Data represents the DWARF debugging information loaded from an executable file (for example, an ELF or Mach-O executable).

func New 

func New(abbrev, aranges, frame, info, line, pubnames, ranges, str []byte) (*Data, error)

New returns a new Data object initialized from the given parameters. Rather than calling this function directly, clients should typically use the DWARF method of the File type of the appropriate package debug/elf, debug/macho, or debug/pe.

The []byte arguments are the data from the corresponding debug section in the object file; for example, for an ELF object, abbrev is the contents of the ".debug_abbrev" section.

func (*Data) AddSection 

func (d *Data) AddSection(name string, contents []byte) error

AddSection adds another DWARF section by name. The name should be a DWARF section name such as ".debug_addr", ".debug_str_offsets", and so forth. This approach is used for new DWARF sections added in DWARF 5 and later.

func (*Data) AddTypes 

func (d *Data) AddTypes(name string, types []byte) error

AddTypes will add one .debug_types section to the DWARF data. A typical object with DWARF version 4 debug info will have multiple .debug_types sections. The name is used for error reporting only, and serves to distinguish one .debug_types section from another.

func (*Data) LineReader 

func (d *Data) LineReader(cu *Entry) (*LineReader, error)

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 (*Data) Ranges 

func (d *Data) Ranges(e *Entry) ([][2]uint64, error)

Ranges returns the PC ranges covered by e, a slice of [low,high) pairs. Only some entry types, such as TagCompileUnit or TagSubprogram, have PC ranges; for others, this will return nil with no error.

func (*Data) Reader 

func (d *Data) Reader() *Reader

Reader returns a new Reader for Data. The reader is positioned at byte offset 0 in the DWARF “info” section.

func (*Data) Type 

func (d *Data) Type(off Offset) (Type, error)

Type reads the type at off in the DWARF “info” section.

type DecodeError 

type DecodeError struct {
	Name   string
	Offset Offset
	Err    string
}

func (DecodeError) Error 

func (e DecodeError) Error() string

type DotDotDotType 

type DotDotDotType struct {
	CommonType
}

A DotDotDotType represents the variadic ... function parameter.

func (*DotDotDotType) String 

func (t *DotDotDotType) String() string

type Entry 

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 entry is a sequence of attribute/value pairs.

func (*Entry) AttrField 

func (e *Entry) AttrField(a Attr) *Field

AttrField returns the Field associated with attribute Attr in Entry, or nil if there is no such attribute.

func (*Entry) Val 

func (e *Entry) Val(a Attr) any

Val returns the value associated with attribute Attr in Entry, or nil if there is no such attribute.

A common idiom is to merge the check for nil return with the check that the value has the expected dynamic type, as in: 

v, ok := e.Val(AttrSibling).(int64)

type EnumType 

type EnumType struct {
	CommonType
	EnumName string
	Val      []*EnumValue
}

An EnumType represents an enumerated type. The only indication of its native integer type is its ByteSize (inside CommonType).

func (*EnumType) String 

func (t *EnumType) String() string

type EnumValue 

type EnumValue struct {
	Name string
	Val  int64
}

An EnumValue represents a single enumeration value.

type Field 

type Field struct {
	Attr  Attr
	Val   any
	Class Class
}

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 FloatType 

type FloatType struct {
	BasicType
}

A FloatType represents a floating point type.

type FuncType 

type FuncType struct {
	CommonType
	ReturnType Type
	ParamType  []Type
}

A FuncType represents a function type.

func (*FuncType) String 

func (t *FuncType) String() string

type IntType 

type IntType struct {
	BasicType
}

An IntType represents a signed integer type.

type LineEntry 

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

	// IsStmt indicates that Address is a recommended breakpoint
	// location, such as the beginning of a line, statement, or a
	// distinct subpart of a statement.
	IsStmt bool

	// BasicBlock indicates that Address is the beginning of a
	// basic block.
	BasicBlock bool

	// PrologueEnd indicates that Address is one (of possibly
	// many) PCs where execution should be suspended for a
	// breakpoint on entry to the containing function.
	//
	// Added in DWARF 3.
	PrologueEnd bool

	// EpilogueBegin indicates that Address is one (of possibly
	// many) PCs where execution should be suspended for a
	// breakpoint on exit from this function.
	//
	// Added in DWARF 3.
	EpilogueBegin bool

	// ISA is the instruction set architecture for these
	// instructions. Possible ISA values should be defined by the
	// applicable ABI specification.
	//
	// Added in DWARF 3.
	ISA int

	// Discriminator is an arbitrary integer indicating the block
	// to which these instructions belong. It serves to
	// distinguish among multiple blocks that may all have with
	// the same source file, line, and column. Where only one
	// block exists for a given source position, it should be 0.
	//
	// Added in DWARF 3.
	Discriminator int

	// EndSequence indicates that Address is the first byte after
	// the end of a sequence of target machine instructions. If it
	// is set, only this and the Address field are meaningful. A
	// line number table may contain information for multiple
	// potentially disjoint instruction sequences. The last entry
	// in a line table should always have EndSequence set.
	EndSequence bool
}

A LineEntry is a row in a DWARF line table.

type LineFile 

type LineFile struct {
	Name   string
	Mtime  uint64 // Implementation defined modification time, or 0 if unknown
	Length int    // File length, or 0 if unknown
}

A LineFile is a source file referenced by a DWARF line table entry.

type LineReader 

type LineReader struct {
	// contains filtered or unexported fields
}

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.

func (*LineReader) Files 

func (r *LineReader) Files() []*LineFile

Files returns the file name table of this compilation unit as of the current position in the line table. The file name table may be referenced from attributes in this compilation unit such as AttrDeclFile.

Entry 0 is always nil, since file index 0 represents "no file".

The file name table of a compilation unit is not fixed. Files returns the file table as of the current position in the line table. This may contain more entries than the file table at an earlier position in the line table, though existing entries never change.

func (*LineReader) Next 

func (r *LineReader) Next(entry *LineEntry) error

Next sets *entry to the next row in this line table and moves to the next row. If there are no more entries and the line table is properly terminated, it returns io.EOF.

Rows are always in order of increasing entry.Address, but entry.Line may go forward or backward.

func (*LineReader) Reset 

func (r *LineReader) Reset()

Reset repositions the line table reader at the beginning of the line table.

func (*LineReader) Seek 

func (r *LineReader) Seek(pos LineReaderPos)

Seek restores the line table reader to a position returned by Tell.

The argument pos must have been returned by a call to Tell on this line table.

func (*LineReader) SeekPC 

func (r *LineReader) SeekPC(pc uint64, entry *LineEntry) error

SeekPC sets *entry to the LineEntry that includes pc and positions the reader on the next entry in the line table. If necessary, this will seek backwards to find pc.

If pc is not covered by any entry in this line table, SeekPC returns ErrUnknownPC. In this case, *entry and the final seek position are unspecified.

Note that DWARF line tables only permit sequential, forward scans. Hence, in the worst case, this takes time linear in the size of the line table. If the caller wishes to do repeated fast PC lookups, it should build an appropriate index of the line table.

func (*LineReader) Tell 

func (r *LineReader) Tell() LineReaderPos

Tell returns the current position in the line table.

type LineReaderPos 

type LineReaderPos struct {
	// contains filtered or unexported fields
}

A LineReaderPos represents a position in a line table.

type Offset 

type Offset uint32

An Offset represents the location of an Entry within the DWARF info. (See Reader.Seek.)

type PtrType 

type PtrType struct {
	CommonType
	Type Type
}

A PtrType represents a pointer type.

func (*PtrType) String 

func (t *PtrType) String() string

type QualType 

type QualType struct {
	CommonType
	Qual string
	Type Type
}

A QualType represents a type that has the C/C++ "const", "restrict", or "volatile" qualifier.

func (*QualType) Size 

func (t *QualType) Size() int64

func (*QualType) String 

func (t *QualType) String() string

type Reader 

type Reader struct {
	// contains filtered or unexported fields
}

A Reader allows reading Entry structures from a DWARF “info” section. The Entry structures are arranged in a tree. The Reader's Next function return successive entries from a pre-order traversal of the tree. If an entry has children, its Children field will be true, and the children follow, terminated by an Entry with Tag 0.

func (*Reader) AddressSize 

func (r *Reader) AddressSize() int

AddressSize returns the size in bytes of addresses in the current compilation unit.

func (*Reader) ByteOrder 

func (r *Reader) ByteOrder() binary.ByteOrder

ByteOrder returns the byte order in the current compilation unit.

func (*Reader) Next 

func (r *Reader) Next() (*Entry, error)

Next reads the next entry from the encoded entry stream. It returns nil, nil when it reaches the end of the section. It returns an error if the current offset is invalid or the data at the offset cannot be decoded as a valid Entry.

func (*Reader) Seek 

func (r *Reader) Seek(off Offset)

Seek positions the Reader at offset off in the encoded entry stream. Offset 0 can be used to denote the first entry.

func (*Reader) SeekPC 

func (r *Reader) SeekPC(pc uint64) (*Entry, error)

SeekPC returns the Entry for the compilation unit that includes pc, and positions the reader to read the children of that unit. If pc is not covered by any unit, SeekPC returns ErrUnknownPC and the position of the reader is undefined.

Because compilation units can describe multiple regions of the executable, in the worst case SeekPC must search through all the ranges in all the compilation units. Each call to SeekPC starts the search at the compilation unit of the last call, so in general looking up a series of PCs will be faster if they are sorted. If the caller wishes to do repeated fast PC lookups, it should build an appropriate index using the Ranges method.

func (*Reader) SkipChildren 

func (r *Reader) SkipChildren()

SkipChildren skips over the child entries associated with the last Entry returned by Next. If that Entry did not have children or Next has not been called, SkipChildren is a no-op.

type StructField 

type StructField struct {
	Name          string
	Type          Type
	ByteOffset    int64
	ByteSize      int64 // usually zero; use Type.Size() for normal fields
	BitOffset     int64
	DataBitOffset int64
	BitSize       int64 // zero if not a bit field
}

A StructField represents a field in a struct, union, or C++ class type.

Bit Fields

The BitSize, BitOffset, and DataBitOffset fields describe the bit size and offset of data members declared as bit fields in C/C++ struct/union/class types.

BitSize is the number of bits in the bit field.

DataBitOffset, if non-zero, is the number of bits from the start of the enclosing entity (e.g. containing struct/class/union) to the start of the bit field. This corresponds to the DW_AT_data_bit_offset DWARF attribute that was introduced in DWARF 4.

BitOffset, if non-zero, is the number of bits between the most significant bit of the storage unit holding the bit field to the most significant bit of the bit field. Here "storage unit" is the type name before the bit field (for a field "unsigned x:17", the storage unit is "unsigned"). BitOffset values can vary depending on the endianness of the system. BitOffset corresponds to the DW_AT_bit_offset DWARF attribute that was deprecated in DWARF 4 and removed in DWARF 5.

At most one of DataBitOffset and BitOffset will be non-zero; DataBitOffset/BitOffset will only be non-zero if BitSize is non-zero. Whether a C compiler uses one or the other will depend on compiler vintage and command line options.

Here is an example of C/C++ bit field use, along with what to expect in terms of DWARF bit offset info. Consider this code: 

struct S {
	int q;
	int j:5;
	int k:6;
	int m:5;
	int n:8;
} s;

For the code above, one would expect to see the following for DW_AT_bit_offset values (using GCC 8): 

       Little   |     Big
       Endian   |    Endian
                |
"j":     27     |     0
"k":     21     |     5
"m":     16     |     11
"n":     8      |     16

Note that in the above the offsets are purely with respect to the containing storage unit for j/k/m/n -- these values won't vary based on the size of prior data members in the containing struct.

If the compiler emits DW_AT_data_bit_offset, the expected values would be: 

"j":     32
"k":     37
"m":     43
"n":     48

Here the value 32 for "j" reflects the fact that the bit field is preceded by other data members (recall that DW_AT_data_bit_offset values are relative to the start of the containing struct). Hence DW_AT_data_bit_offset values can be quite large for structs with many fields.

DWARF also allow for the possibility of base types that have non-zero bit size and bit offset, so this information is also captured for base types, but it is worth noting that it is not possible to trigger this behavior using mainstream languages.

type StructType 

type StructType struct {
	CommonType
	StructName string
	Kind       string // "struct", "union", or "class".
	Field      []*StructField
	Incomplete bool // if true, struct, union, class is declared but not defined
}

A StructType represents a struct, union, or C++ class type.

func (*StructType) Defn 

func (t *StructType) Defn() string

func (*StructType) String 

func (t *StructType) String() string

type Tag 

type Tag uint32

A Tag is the classification (the type) of an Entry. 

const (
	TagArrayType              Tag = 0x01
	TagClassType              Tag = 0x02
	TagEntryPoint             Tag = 0x03
	TagEnumerationType        Tag = 0x04
	TagFormalParameter        Tag = 0x05
	TagImportedDeclaration    Tag = 0x08
	TagLabel                  Tag = 0x0A
	TagLexDwarfBlock          Tag = 0x0B
	TagMember                 Tag = 0x0D
	TagPointerType            Tag = 0x0F
	TagReferenceType          Tag = 0x10
	TagCompileUnit            Tag = 0x11
	TagStringType             Tag = 0x12
	TagStructType             Tag = 0x13
	TagSubroutineType         Tag = 0x15
	TagTypedef                Tag = 0x16
	TagUnionType              Tag = 0x17
	TagUnspecifiedParameters  Tag = 0x18
	TagVariant                Tag = 0x19
	TagCommonDwarfBlock       Tag = 0x1A
	TagCommonInclusion        Tag = 0x1B
	TagInheritance            Tag = 0x1C
	TagInlinedSubroutine      Tag = 0x1D
	TagModule                 Tag = 0x1E
	TagPtrToMemberType        Tag = 0x1F
	TagSetType                Tag = 0x20
	TagSubrangeType           Tag = 0x21
	TagWithStmt               Tag = 0x22
	TagAccessDeclaration      Tag = 0x23
	TagBaseType               Tag = 0x24
	TagCatchDwarfBlock        Tag = 0x25
	TagConstType              Tag = 0x26
	TagConstant               Tag = 0x27
	TagEnumerator             Tag = 0x28
	TagFileType               Tag = 0x29
	TagFriend                 Tag = 0x2A
	TagNamelist               Tag = 0x2B
	TagNamelistItem           Tag = 0x2C
	TagPackedType             Tag = 0x2D
	TagSubprogram             Tag = 0x2E
	TagTemplateTypeParameter  Tag = 0x2F
	TagTemplateValueParameter Tag = 0x30
	TagThrownType             Tag = 0x31
	TagTryDwarfBlock          Tag = 0x32
	TagVariantPart            Tag = 0x33
	TagVariable               Tag = 0x34
	TagVolatileType           Tag = 0x35
	// The following are new in DWARF 3.
	TagDwarfProcedure  Tag = 0x36
	TagRestrictType    Tag = 0x37
	TagInterfaceType   Tag = 0x38
	TagNamespace       Tag = 0x39
	TagImportedModule  Tag = 0x3A
	TagUnspecifiedType Tag = 0x3B
	TagPartialUnit     Tag = 0x3C
	TagImportedUnit    Tag = 0x3D
	TagMutableType     Tag = 0x3E // Later removed from DWARF.
	TagCondition       Tag = 0x3F
	TagSharedType      Tag = 0x40
	// The following are new in DWARF 4.
	TagTypeUnit            Tag = 0x41
	TagRvalueReferenceType Tag = 0x42
	TagTemplateAlias       Tag = 0x43
	// The following are new in DWARF 5.
	TagCoarrayType       Tag = 0x44
	TagGenericSubrange   Tag = 0x45
	TagDynamicType       Tag = 0x46
	TagAtomicType        Tag = 0x47
	TagCallSite          Tag = 0x48
	TagCallSiteParameter Tag = 0x49
	TagSkeletonUnit      Tag = 0x4A
	TagImmutableType     Tag = 0x4B
)

func (Tag) GoString 

func (t Tag) GoString() string

func (Tag) String 

func (i Tag) String() string

type Type 

type Type interface {
	Common() *CommonType
	String() string
	Size() int64
}

A Type conventionally represents a pointer to any of the specific Type structures (CharType, StructType, etc.).

type TypedefType 

type TypedefType struct {
	CommonType
	Type Type
}

A TypedefType represents a named type.

func (*TypedefType) Size 

func (t *TypedefType) Size() int64

func (*TypedefType) String 

func (t *TypedefType) String() string

type UcharType 

type UcharType struct {
	BasicType
}

A UcharType represents an unsigned character type.

type UintType 

type UintType struct {
	BasicType
}

A UintType represents an unsigned integer type.

type UnspecifiedType 

type UnspecifiedType struct {
	BasicType
}

An UnspecifiedType represents an implicit, unknown, ambiguous or nonexistent type.

type UnsupportedType 

type UnsupportedType struct {
	CommonType
	Tag Tag
}

An UnsupportedType is a placeholder returned in situations where we encounter a type that isn't supported.

func (*UnsupportedType) String 

func (t *UnsupportedType) String() string

type VoidType 

type VoidType struct {
	CommonType
}

A VoidType represents the C void type.

func (*VoidType) String 

func (t *VoidType) String() string

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