7eddfb77b9
It was reading all the way to the end of the debug_info section, slowing down stacktraces substantially. Benchmark before: BenchmarkConditionalBreakpoints-4 1 80344642562 ns/op Benchmark after: BenchmarkConditionalBreakpoints-4 1 22218288218 ns/op i.e. a reduction of the cost of a breakpoint hit from 8ms to 2.2ms Updates #1549
480 lines
12 KiB
Go
480 lines
12 KiB
Go
package reader
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import (
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"debug/dwarf"
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"errors"
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"fmt"
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"github.com/go-delve/delve/pkg/dwarf/op"
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)
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type Reader struct {
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*dwarf.Reader
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depth int
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}
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// New returns a reader for the specified dwarf data.
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func New(data *dwarf.Data) *Reader {
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return &Reader{data.Reader(), 0}
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}
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// Seek moves the reader to an arbitrary offset.
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func (reader *Reader) Seek(off dwarf.Offset) {
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reader.depth = 0
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reader.Reader.Seek(off)
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}
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// SeekToEntry moves the reader to an arbitrary entry.
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func (reader *Reader) SeekToEntry(entry *dwarf.Entry) error {
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reader.Seek(entry.Offset)
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// Consume the current entry so .Next works as intended
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_, err := reader.Next()
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return err
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}
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// SeekToFunctionEntry moves the reader to the function that includes the
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// specified program counter.
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func (reader *Reader) SeekToFunction(pc RelAddr) (*dwarf.Entry, error) {
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reader.Seek(0)
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for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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if entry.Tag != dwarf.TagSubprogram {
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continue
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}
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lowpc, ok := entry.Val(dwarf.AttrLowpc).(uint64)
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if !ok {
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continue
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}
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highpc, ok := entry.Val(dwarf.AttrHighpc).(uint64)
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if !ok {
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continue
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}
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if lowpc <= uint64(pc) && highpc > uint64(pc) {
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return entry, nil
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}
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}
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return nil, fmt.Errorf("unable to find function context")
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}
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// Returns the address for the named entry.
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func (reader *Reader) AddrFor(name string, staticBase uint64) (uint64, error) {
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entry, err := reader.FindEntryNamed(name, false)
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if err != nil {
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return 0, err
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}
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instructions, ok := entry.Val(dwarf.AttrLocation).([]byte)
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if !ok {
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return 0, fmt.Errorf("type assertion failed")
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}
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addr, _, err := op.ExecuteStackProgram(op.DwarfRegisters{StaticBase: staticBase}, instructions)
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if err != nil {
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return 0, err
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}
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return uint64(addr), nil
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}
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// Returns the address for the named struct member. Expects the reader to be at the parent entry
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// or one of the parents children, thus does not seek to parent by itself.
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func (reader *Reader) AddrForMember(member string, initialInstructions []byte) (uint64, error) {
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for {
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entry, err := reader.NextMemberVariable()
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if err != nil {
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return 0, err
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}
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if entry == nil {
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return 0, fmt.Errorf("nil entry for member named %s", member)
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}
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name, ok := entry.Val(dwarf.AttrName).(string)
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if !ok || name != member {
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continue
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}
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instructions, ok := entry.Val(dwarf.AttrDataMemberLoc).([]byte)
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if !ok {
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continue
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}
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addr, _, err := op.ExecuteStackProgram(op.DwarfRegisters{}, append(initialInstructions, instructions...))
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return uint64(addr), err
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}
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}
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var TypeNotFoundErr = errors.New("no type entry found, use 'types' for a list of valid types")
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// SeekToType moves the reader to the type specified by the entry,
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// optionally resolving typedefs and pointer types. If the reader is set
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// to a struct type the NextMemberVariable call can be used to walk all member data.
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func (reader *Reader) SeekToType(entry *dwarf.Entry, resolveTypedefs bool, resolvePointerTypes bool) (*dwarf.Entry, error) {
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offset, ok := entry.Val(dwarf.AttrType).(dwarf.Offset)
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if !ok {
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return nil, fmt.Errorf("entry does not have a type attribute")
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}
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// Seek to the first type offset
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reader.Seek(offset)
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// Walk the types to the base
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for typeEntry, err := reader.Next(); typeEntry != nil; typeEntry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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if typeEntry.Tag == dwarf.TagTypedef && !resolveTypedefs {
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return typeEntry, nil
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}
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if typeEntry.Tag == dwarf.TagPointerType && !resolvePointerTypes {
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return typeEntry, nil
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}
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offset, ok = typeEntry.Val(dwarf.AttrType).(dwarf.Offset)
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if !ok {
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return typeEntry, nil
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}
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reader.Seek(offset)
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}
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return nil, TypeNotFoundErr
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}
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func (reader *Reader) NextType() (*dwarf.Entry, error) {
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for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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switch entry.Tag {
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case dwarf.TagArrayType, dwarf.TagBaseType, dwarf.TagClassType, dwarf.TagStructType, dwarf.TagUnionType, dwarf.TagConstType, dwarf.TagVolatileType, dwarf.TagRestrictType, dwarf.TagEnumerationType, dwarf.TagPointerType, dwarf.TagSubroutineType, dwarf.TagTypedef, dwarf.TagUnspecifiedType:
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return entry, nil
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}
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}
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return nil, nil
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}
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// SeekToTypeNamed moves the reader to the type specified by the name.
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// If the reader is set to a struct type the NextMemberVariable call
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// can be used to walk all member data.
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func (reader *Reader) SeekToTypeNamed(name string) (*dwarf.Entry, error) {
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// Walk the types to the base
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for entry, err := reader.NextType(); entry != nil; entry, err = reader.NextType() {
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if err != nil {
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return nil, err
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}
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n, ok := entry.Val(dwarf.AttrName).(string)
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if !ok {
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continue
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}
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if n == name {
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return entry, nil
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}
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}
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return nil, TypeNotFoundErr
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}
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// Finds the entry for 'name'.
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func (reader *Reader) FindEntryNamed(name string, member bool) (*dwarf.Entry, error) {
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depth := 1
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for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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if entry.Children {
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depth++
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}
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if entry.Tag == 0 {
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depth--
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if depth <= 0 {
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return nil, fmt.Errorf("could not find symbol value for %s", name)
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}
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}
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if member {
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if entry.Tag != dwarf.TagMember {
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continue
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}
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} else {
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if entry.Tag != dwarf.TagVariable && entry.Tag != dwarf.TagFormalParameter && entry.Tag != dwarf.TagStructType {
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continue
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}
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}
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n, ok := entry.Val(dwarf.AttrName).(string)
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if !ok || n != name {
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continue
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}
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return entry, nil
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}
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return nil, fmt.Errorf("could not find symbol value for %s", name)
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}
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func (reader *Reader) InstructionsForEntryNamed(name string, member bool) ([]byte, error) {
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entry, err := reader.FindEntryNamed(name, member)
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if err != nil {
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return nil, err
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}
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var attr dwarf.Attr
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if member {
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attr = dwarf.AttrDataMemberLoc
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} else {
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attr = dwarf.AttrLocation
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}
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instr, ok := entry.Val(attr).([]byte)
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if !ok {
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return nil, errors.New("invalid typecast for Dwarf instructions")
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}
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return instr, nil
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}
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func (reader *Reader) InstructionsForEntry(entry *dwarf.Entry) ([]byte, error) {
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if entry.Tag == dwarf.TagMember {
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instructions, ok := entry.Val(dwarf.AttrDataMemberLoc).([]byte)
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if !ok {
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return nil, fmt.Errorf("member data has no data member location attribute")
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}
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// clone slice to prevent stomping on the dwarf data
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return append([]byte{}, instructions...), nil
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}
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// non-member
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instructions, ok := entry.Val(dwarf.AttrLocation).([]byte)
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if !ok {
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return nil, fmt.Errorf("entry has no location attribute")
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}
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// clone slice to prevent stomping on the dwarf data
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return append([]byte{}, instructions...), nil
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}
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// NextMemberVariable moves the reader to the next debug entry that describes a member variable and returns the entry.
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func (reader *Reader) NextMemberVariable() (*dwarf.Entry, error) {
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for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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// All member variables will be at the same depth
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reader.SkipChildren()
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// End of the current depth
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if entry.Tag == 0 {
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break
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}
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if entry.Tag == dwarf.TagMember {
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return entry, nil
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}
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}
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// No more items
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return nil, nil
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}
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// NextPackageVariable moves the reader to the next debug entry that describes a package variable.
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// Any TagVariable entry that is not inside a sub prgram entry and is marked external is considered a package variable.
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func (reader *Reader) NextPackageVariable() (*dwarf.Entry, error) {
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for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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if entry.Tag == dwarf.TagVariable {
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ext, ok := entry.Val(dwarf.AttrExternal).(bool)
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if ok && ext {
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return entry, nil
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}
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}
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// Ignore everything inside sub programs
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if entry.Tag == dwarf.TagSubprogram {
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reader.SkipChildren()
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}
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}
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// No more items
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return nil, nil
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}
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func (reader *Reader) NextCompileUnit() (*dwarf.Entry, error) {
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for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
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if err != nil {
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return nil, err
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}
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if entry.Tag == dwarf.TagCompileUnit {
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return entry, nil
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}
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}
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return nil, nil
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}
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// Entry represents a debug_info entry.
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// When calling Val, if the entry does not have the specified attribute, the
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// entry specified by DW_AT_abstract_origin will be searched recursively.
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type Entry interface {
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Val(dwarf.Attr) interface{}
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}
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type compositeEntry []*dwarf.Entry
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func (ce compositeEntry) Val(attr dwarf.Attr) interface{} {
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for _, e := range ce {
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if r := e.Val(attr); r != nil {
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return r
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}
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}
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return nil
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}
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// LoadAbstractOrigin loads the entry corresponding to the
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// DW_AT_abstract_origin of entry and returns a combination of entry and its
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// abstract origin.
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func LoadAbstractOrigin(entry *dwarf.Entry, aordr *dwarf.Reader) (Entry, dwarf.Offset) {
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ao, ok := entry.Val(dwarf.AttrAbstractOrigin).(dwarf.Offset)
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if !ok {
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return entry, entry.Offset
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}
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r := []*dwarf.Entry{entry}
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for {
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aordr.Seek(ao)
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e, _ := aordr.Next()
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if e == nil {
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break
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}
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r = append(r, e)
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ao, ok = e.Val(dwarf.AttrAbstractOrigin).(dwarf.Offset)
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if !ok {
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break
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}
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}
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return compositeEntry(r), entry.Offset
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}
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// InlineStackReader provides a way to read the stack of inlined calls at a
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// specified PC address.
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type InlineStackReader struct {
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dwarf *dwarf.Data
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reader *dwarf.Reader
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pc uint64
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entry *dwarf.Entry
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err error
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// stack contains the list of DIEs that will be returned by Next.
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stack []*dwarf.Entry
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}
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// InlineStack returns an InlineStackReader for the specified function and
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// PC address.
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// If pc is 0 then all inlined calls will be returned.
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func InlineStack(dw *dwarf.Data, fnoff dwarf.Offset, pc RelAddr) *InlineStackReader {
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reader := dw.Reader()
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reader.Seek(fnoff)
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r := &InlineStackReader{dwarf: dw, reader: reader, pc: uint64(pc)}
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r.precalcStack(nil)
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return r
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}
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// precalcStack precalculates the inlined call stack for irdr.pc.
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// If irdr.pc == 0 then all inlined calls will be saved in irdr.stack.
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// Otherwise an inlined call will be saved in irdr.stack if its range, or
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// the range of one of its child entries contains irdr.pc.
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// The recursive calculation of range inclusion is necessary because
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// sometimes when doing midstack inlining the Go compiler emits the toplevel
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// inlined call with ranges that do not cover the inlining of nested inlined
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// calls.
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// For example if a function A calls B which calls C and both the calls to
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// B and C are inlined the DW_AT_inlined_subroutine entry for A might have
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// ranges that do not cover the ranges of the inlined call to C.
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// This is probably a violation of the DWARF standard (it's unclear) but we
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// might as well support it as best as possible anyway.
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func (irdr *InlineStackReader) precalcStack(rentry *dwarf.Entry) bool {
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var contains bool
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childLoop:
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for {
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if irdr.err != nil {
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return contains
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}
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e2, err := irdr.reader.Next()
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if e2 == nil || err != nil {
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break
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}
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switch e2.Tag {
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case 0:
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break childLoop
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case dwarf.TagLexDwarfBlock, dwarf.TagSubprogram, dwarf.TagInlinedSubroutine:
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if irdr.precalcStack(e2) {
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contains = true
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}
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default:
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irdr.reader.SkipChildren()
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}
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if rentry == nil {
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break
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}
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}
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if rentry != nil && rentry.Tag == dwarf.TagInlinedSubroutine {
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if !contains {
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if irdr.pc != 0 {
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contains, irdr.err = entryRangesContains(irdr.dwarf, rentry, irdr.pc)
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} else {
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contains = true
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}
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}
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if contains {
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irdr.stack = append(irdr.stack, rentry)
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}
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}
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return contains
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}
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// Next reads next inlined call in the stack, returns false if there aren't any.
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// Next reads the inlined stack of calls backwards, starting with the
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// deepest inlined call and moving back out, like a normal stacktrace works.
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func (irdr *InlineStackReader) Next() bool {
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if irdr.err != nil {
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return false
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}
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if len(irdr.stack) == 0 {
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return false
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}
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irdr.entry = irdr.stack[0]
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irdr.stack = irdr.stack[1:]
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return true
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}
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// Entry returns the DIE for the current inlined call.
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func (irdr *InlineStackReader) Entry() *dwarf.Entry {
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return irdr.entry
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}
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// Err returns an error, if any was encountered.
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func (irdr *InlineStackReader) Err() error {
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return irdr.err
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}
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// SkipChildren skips all children of the current inlined call.
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func (irdr *InlineStackReader) SkipChildren() {
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irdr.reader.SkipChildren()
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}
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