diff options
Diffstat (limited to 'src/debug/dwarf/line.go')
| -rw-r--r-- | src/debug/dwarf/line.go | 852 |
1 files changed, 852 insertions, 0 deletions
diff --git a/src/debug/dwarf/line.go b/src/debug/dwarf/line.go new file mode 100644 index 0000000..4df4a17 --- /dev/null +++ b/src/debug/dwarf/line.go @@ -0,0 +1,852 @@ +// Copyright 2015 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package dwarf + +import ( + "errors" + "fmt" + "io" + "path" + "strings" +) + +// 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 { + buf buf + + // Original .debug_line section data. Used by Seek. + section []byte + + str []byte // .debug_str + lineStr []byte // .debug_line_str + + // Header information + version uint16 + addrsize int + segmentSelectorSize int + minInstructionLength int + maxOpsPerInstruction int + defaultIsStmt bool + lineBase int + lineRange int + opcodeBase int + opcodeLengths []int + directories []string + fileEntries []*LineFile + + programOffset Offset // section offset of line number program + endOffset Offset // section offset of byte following program + + initialFileEntries int // initial length of fileEntries + + // Current line number program state machine registers + state LineEntry // public state + fileIndex int // private state +} + +// 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 + + // 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 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) { + if d.line == nil { + // No line tables available. + return nil, nil + } + + // Get line table information from cu. + off, ok := cu.Val(AttrStmtList).(int64) + if !ok { + // cu has no line table. + return nil, nil + } + if off < 0 || off > int64(len(d.line)) { + return nil, errors.New("AttrStmtList value out of range") + } + // AttrCompDir is optional if all file names are absolute. Use + // the empty string if it's not present. + compDir, _ := cu.Val(AttrCompDir).(string) + + // Create the LineReader. + u := &d.unit[d.offsetToUnit(cu.Offset)] + buf := makeBuf(d, u, "line", Offset(off), d.line[off:]) + // The compilation directory is implicitly directories[0]. + r := LineReader{ + buf: buf, + section: d.line, + str: d.str, + lineStr: d.lineStr, + } + + // Read the header. + if err := r.readHeader(compDir); err != nil { + return nil, err + } + + // Initialize line reader state. + r.Reset() + + return &r, nil +} + +// readHeader reads the line number program header from r.buf and sets +// all of the header fields in r. +func (r *LineReader) readHeader(compDir string) error { + buf := &r.buf + + // Read basic header fields [DWARF2 6.2.4]. + hdrOffset := buf.off + unitLength, dwarf64 := buf.unitLength() + r.endOffset = buf.off + unitLength + if r.endOffset > buf.off+Offset(len(buf.data)) { + return DecodeError{"line", hdrOffset, fmt.Sprintf("line table end %d exceeds section size %d", r.endOffset, buf.off+Offset(len(buf.data)))} + } + r.version = buf.uint16() + if buf.err == nil && (r.version < 2 || r.version > 5) { + // DWARF goes to all this effort to make new opcodes + // backward-compatible, and then adds fields right in + // the middle of the header in new versions, so we're + // picky about only supporting known line table + // versions. + return DecodeError{"line", hdrOffset, fmt.Sprintf("unknown line table version %d", r.version)} + } + if r.version >= 5 { + r.addrsize = int(buf.uint8()) + r.segmentSelectorSize = int(buf.uint8()) + } else { + r.addrsize = buf.format.addrsize() + r.segmentSelectorSize = 0 + } + var headerLength Offset + if dwarf64 { + headerLength = Offset(buf.uint64()) + } else { + headerLength = Offset(buf.uint32()) + } + programOffset := buf.off + headerLength + if programOffset > r.endOffset { + return DecodeError{"line", hdrOffset, fmt.Sprintf("malformed line table: program offset %d exceeds end offset %d", programOffset, r.endOffset)} + } + r.programOffset = programOffset + r.minInstructionLength = int(buf.uint8()) + if r.version >= 4 { + // [DWARF4 6.2.4] + r.maxOpsPerInstruction = int(buf.uint8()) + } else { + r.maxOpsPerInstruction = 1 + } + r.defaultIsStmt = buf.uint8() != 0 + r.lineBase = int(int8(buf.uint8())) + r.lineRange = int(buf.uint8()) + + // Validate header. + if buf.err != nil { + return buf.err + } + if r.maxOpsPerInstruction == 0 { + return DecodeError{"line", hdrOffset, "invalid maximum operations per instruction: 0"} + } + if r.lineRange == 0 { + return DecodeError{"line", hdrOffset, "invalid line range: 0"} + } + + // Read standard opcode length table. This table starts with opcode 1. + r.opcodeBase = int(buf.uint8()) + r.opcodeLengths = make([]int, r.opcodeBase) + for i := 1; i < r.opcodeBase; i++ { + r.opcodeLengths[i] = int(buf.uint8()) + } + + // Validate opcode lengths. + if buf.err != nil { + return buf.err + } + for i, length := range r.opcodeLengths { + if known, ok := knownOpcodeLengths[i]; ok && known != length { + return DecodeError{"line", hdrOffset, fmt.Sprintf("opcode %d expected to have length %d, but has length %d", i, known, length)} + } + } + + if r.version < 5 { + // Read include directories table. + r.directories = []string{compDir} + for { + directory := buf.string() + if buf.err != nil { + return buf.err + } + if len(directory) == 0 { + break + } + if !pathIsAbs(directory) { + // Relative paths are implicitly relative to + // the compilation directory. + directory = pathJoin(compDir, directory) + } + r.directories = append(r.directories, directory) + } + + // Read file name list. File numbering starts with 1, + // so leave the first entry nil. + r.fileEntries = make([]*LineFile, 1) + for { + if done, err := r.readFileEntry(); err != nil { + return err + } else if done { + break + } + } + } else { + dirFormat := r.readLNCTFormat() + c := buf.uint() + r.directories = make([]string, c) + for i := range r.directories { + dir, _, _, err := r.readLNCT(dirFormat, dwarf64) + if err != nil { + return err + } + r.directories[i] = dir + } + fileFormat := r.readLNCTFormat() + c = buf.uint() + r.fileEntries = make([]*LineFile, c) + for i := range r.fileEntries { + name, mtime, size, err := r.readLNCT(fileFormat, dwarf64) + if err != nil { + return err + } + r.fileEntries[i] = &LineFile{name, mtime, int(size)} + } + } + + r.initialFileEntries = len(r.fileEntries) + + return buf.err +} + +// lnctForm is a pair of an LNCT code and a form. This represents an +// entry in the directory name or file name description in the DWARF 5 +// line number program header. +type lnctForm struct { + lnct int + form format +} + +// readLNCTFormat reads an LNCT format description. +func (r *LineReader) readLNCTFormat() []lnctForm { + c := r.buf.uint8() + ret := make([]lnctForm, c) + for i := range ret { + ret[i].lnct = int(r.buf.uint()) + ret[i].form = format(r.buf.uint()) + } + return ret +} + +// readLNCT reads a sequence of LNCT entries and returns path information. +func (r *LineReader) readLNCT(s []lnctForm, dwarf64 bool) (path string, mtime uint64, size uint64, err error) { + var dir string + for _, lf := range s { + var str string + var val uint64 + switch lf.form { + case formString: + str = r.buf.string() + case formStrp, formLineStrp: + var off uint64 + if dwarf64 { + off = r.buf.uint64() + } else { + off = uint64(r.buf.uint32()) + } + if uint64(int(off)) != off { + return "", 0, 0, DecodeError{"line", r.buf.off, "strp/line_strp offset out of range"} + } + var b1 buf + if lf.form == formStrp { + b1 = makeBuf(r.buf.dwarf, r.buf.format, "str", 0, r.str) + } else { + b1 = makeBuf(r.buf.dwarf, r.buf.format, "line_str", 0, r.lineStr) + } + b1.skip(int(off)) + str = b1.string() + if b1.err != nil { + return "", 0, 0, DecodeError{"line", r.buf.off, b1.err.Error()} + } + case formStrpSup: + // Supplemental sections not yet supported. + if dwarf64 { + r.buf.uint64() + } else { + r.buf.uint32() + } + case formStrx: + // .debug_line.dwo sections not yet supported. + r.buf.uint() + case formStrx1: + r.buf.uint8() + case formStrx2: + r.buf.uint16() + case formStrx3: + r.buf.uint24() + case formStrx4: + r.buf.uint32() + case formData1: + val = uint64(r.buf.uint8()) + case formData2: + val = uint64(r.buf.uint16()) + case formData4: + val = uint64(r.buf.uint32()) + case formData8: + val = r.buf.uint64() + case formData16: + r.buf.bytes(16) + case formDwarfBlock: + r.buf.bytes(int(r.buf.uint())) + case formUdata: + val = r.buf.uint() + } + + switch lf.lnct { + case lnctPath: + path = str + case lnctDirectoryIndex: + if val >= uint64(len(r.directories)) { + return "", 0, 0, DecodeError{"line", r.buf.off, "directory index out of range"} + } + dir = r.directories[val] + case lnctTimestamp: + mtime = val + case lnctSize: + size = val + case lnctMD5: + // Ignored. + } + } + + if dir != "" && path != "" { + path = pathJoin(dir, path) + } + + return path, mtime, size, nil +} + +// readFileEntry reads a file entry from either the header or a +// DW_LNE_define_file extended opcode and adds it to r.fileEntries. A +// true return value indicates that there are no more entries to read. +func (r *LineReader) readFileEntry() (bool, error) { + name := r.buf.string() + if r.buf.err != nil { + return false, r.buf.err + } + if len(name) == 0 { + return true, nil + } + off := r.buf.off + dirIndex := int(r.buf.uint()) + if !pathIsAbs(name) { + if dirIndex >= len(r.directories) { + return false, DecodeError{"line", off, "directory index too large"} + } + name = pathJoin(r.directories[dirIndex], name) + } + mtime := r.buf.uint() + length := int(r.buf.uint()) + + // If this is a dynamically added path and the cursor was + // backed up, we may have already added this entry. Avoid + // updating existing line table entries in this case. This + // avoids an allocation and potential racy access to the slice + // backing store if the user called Files. + if len(r.fileEntries) < cap(r.fileEntries) { + fe := r.fileEntries[:len(r.fileEntries)+1] + if fe[len(fe)-1] != nil { + // We already processed this addition. + r.fileEntries = fe + return false, nil + } + } + r.fileEntries = append(r.fileEntries, &LineFile{name, mtime, length}) + return false, nil +} + +// updateFile updates r.state.File after r.fileIndex has +// changed or r.fileEntries has changed. +func (r *LineReader) updateFile() { + if r.fileIndex < len(r.fileEntries) { + r.state.File = r.fileEntries[r.fileIndex] + } else { + r.state.File = nil + } +} + +// 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 (r *LineReader) Next(entry *LineEntry) error { + if r.buf.err != nil { + return r.buf.err + } + + // Execute opcodes until we reach an opcode that emits a line + // table entry. + for { + if len(r.buf.data) == 0 { + return io.EOF + } + emit := r.step(entry) + if r.buf.err != nil { + return r.buf.err + } + if emit { + return nil + } + } +} + +// knownOpcodeLengths gives the opcode lengths (in varint arguments) +// of known standard opcodes. +var knownOpcodeLengths = map[int]int{ + lnsCopy: 0, + lnsAdvancePC: 1, + lnsAdvanceLine: 1, + lnsSetFile: 1, + lnsNegateStmt: 0, + lnsSetBasicBlock: 0, + lnsConstAddPC: 0, + lnsSetPrologueEnd: 0, + lnsSetEpilogueBegin: 0, + lnsSetISA: 1, + // lnsFixedAdvancePC takes a uint8 rather than a varint; it's + // unclear what length the header is supposed to claim, so + // ignore it. +} + +// step processes the next opcode and updates r.state. If the opcode +// emits a row in the line table, this updates *entry and returns +// true. +func (r *LineReader) step(entry *LineEntry) bool { + opcode := int(r.buf.uint8()) + + if opcode >= r.opcodeBase { + // Special opcode [DWARF2 6.2.5.1, DWARF4 6.2.5.1] + adjustedOpcode := opcode - r.opcodeBase + r.advancePC(adjustedOpcode / r.lineRange) + lineDelta := r.lineBase + adjustedOpcode%r.lineRange + r.state.Line += lineDelta + goto emit + } + + switch opcode { + case 0: + // Extended opcode [DWARF2 6.2.5.3] + length := Offset(r.buf.uint()) + startOff := r.buf.off + opcode := r.buf.uint8() + + switch opcode { + case lneEndSequence: + r.state.EndSequence = true + *entry = r.state + r.resetState() + + case lneSetAddress: + switch r.addrsize { + case 1: + r.state.Address = uint64(r.buf.uint8()) + case 2: + r.state.Address = uint64(r.buf.uint16()) + case 4: + r.state.Address = uint64(r.buf.uint32()) + case 8: + r.state.Address = r.buf.uint64() + default: + r.buf.error("unknown address size") + } + + case lneDefineFile: + if done, err := r.readFileEntry(); err != nil { + r.buf.err = err + return false + } else if done { + r.buf.err = DecodeError{"line", startOff, "malformed DW_LNE_define_file operation"} + return false + } + r.updateFile() + + case lneSetDiscriminator: + // [DWARF4 6.2.5.3] + r.state.Discriminator = int(r.buf.uint()) + } + + r.buf.skip(int(startOff + length - r.buf.off)) + + if opcode == lneEndSequence { + return true + } + + // Standard opcodes [DWARF2 6.2.5.2] + case lnsCopy: + goto emit + + case lnsAdvancePC: + r.advancePC(int(r.buf.uint())) + + case lnsAdvanceLine: + r.state.Line += int(r.buf.int()) + + case lnsSetFile: + r.fileIndex = int(r.buf.uint()) + r.updateFile() + + case lnsSetColumn: + r.state.Column = int(r.buf.uint()) + + case lnsNegateStmt: + r.state.IsStmt = !r.state.IsStmt + + case lnsSetBasicBlock: + r.state.BasicBlock = true + + case lnsConstAddPC: + r.advancePC((255 - r.opcodeBase) / r.lineRange) + + case lnsFixedAdvancePC: + r.state.Address += uint64(r.buf.uint16()) + + // DWARF3 standard opcodes [DWARF3 6.2.5.2] + case lnsSetPrologueEnd: + r.state.PrologueEnd = true + + case lnsSetEpilogueBegin: + r.state.EpilogueBegin = true + + case lnsSetISA: + r.state.ISA = int(r.buf.uint()) + + default: + // Unhandled standard opcode. Skip the number of + // arguments that the prologue says this opcode has. + for i := 0; i < r.opcodeLengths[opcode]; i++ { + r.buf.uint() + } + } + return false + +emit: + *entry = r.state + r.state.BasicBlock = false + r.state.PrologueEnd = false + r.state.EpilogueBegin = false + r.state.Discriminator = 0 + return true +} + +// advancePC advances "operation pointer" (the combination of Address +// and OpIndex) in r.state by opAdvance steps. +func (r *LineReader) advancePC(opAdvance int) { + opIndex := r.state.OpIndex + opAdvance + r.state.Address += uint64(r.minInstructionLength * (opIndex / r.maxOpsPerInstruction)) + r.state.OpIndex = opIndex % r.maxOpsPerInstruction +} + +// A LineReaderPos represents a position in a line table. +type LineReaderPos struct { + // off is the current offset in the DWARF line section. + off Offset + // numFileEntries is the length of fileEntries. + numFileEntries int + // state and fileIndex are the statement machine state at + // offset off. + state LineEntry + fileIndex int +} + +// Tell returns the current position in the line table. +func (r *LineReader) Tell() LineReaderPos { + return LineReaderPos{r.buf.off, len(r.fileEntries), r.state, r.fileIndex} +} + +// 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 (r *LineReader) Seek(pos LineReaderPos) { + r.buf.off = pos.off + r.buf.data = r.section[r.buf.off:r.endOffset] + r.fileEntries = r.fileEntries[:pos.numFileEntries] + r.state = pos.state + r.fileIndex = pos.fileIndex +} + +// Reset repositions the line table reader at the beginning of the +// line table. +func (r *LineReader) Reset() { + // Reset buffer to the line number program offset. + r.buf.off = r.programOffset + r.buf.data = r.section[r.buf.off:r.endOffset] + + // Reset file entries list. + r.fileEntries = r.fileEntries[:r.initialFileEntries] + + // Reset line number program state. + r.resetState() +} + +// resetState resets r.state to its default values +func (r *LineReader) resetState() { + // Reset the state machine registers to the defaults given in + // [DWARF4 6.2.2]. + r.state = LineEntry{ + Address: 0, + OpIndex: 0, + File: nil, + Line: 1, + Column: 0, + IsStmt: r.defaultIsStmt, + BasicBlock: false, + PrologueEnd: false, + EpilogueBegin: false, + ISA: 0, + Discriminator: 0, + } + r.fileIndex = 1 + r.updateFile() +} + +// 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 (r *LineReader) Files() []*LineFile { + return r.fileEntries +} + +// ErrUnknownPC is the error returned by LineReader.ScanPC when the +// seek PC is not covered by any entry in the line table. +var ErrUnknownPC = errors.New("ErrUnknownPC") + +// 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 (r *LineReader) SeekPC(pc uint64, entry *LineEntry) error { + if err := r.Next(entry); err != nil { + return err + } + if entry.Address > pc { + // We're too far. Start at the beginning of the table. + r.Reset() + if err := r.Next(entry); err != nil { + return err + } + if entry.Address > pc { + // The whole table starts after pc. + r.Reset() + return ErrUnknownPC + } + } + + // Scan until we pass pc, then back up one. + for { + var next LineEntry + pos := r.Tell() + if err := r.Next(&next); err != nil { + if err == io.EOF { + return ErrUnknownPC + } + return err + } + if next.Address > pc { + if entry.EndSequence { + // pc is in a hole in the table. + return ErrUnknownPC + } + // entry is the desired entry. Back up the + // cursor to "next" and return success. + r.Seek(pos) + return nil + } + *entry = next + } +} + +// pathIsAbs reports whether path is an absolute path (or "full path +// name" in DWARF parlance). This is in "whatever form makes sense for +// the host system", so this accepts both UNIX-style and DOS-style +// absolute paths. We avoid the filepath package because we want this +// to behave the same regardless of our host system and because we +// don't know what system the paths came from. +func pathIsAbs(path string) bool { + _, path = splitDrive(path) + return len(path) > 0 && (path[0] == '/' || path[0] == '\\') +} + +// pathJoin joins dirname and filename. filename must be relative. +// DWARF paths can be UNIX-style or DOS-style, so this handles both. +func pathJoin(dirname, filename string) string { + if len(dirname) == 0 { + return filename + } + // dirname should be absolute, which means we can determine + // whether it's a DOS path reasonably reliably by looking for + // a drive letter or UNC path. + drive, dirname := splitDrive(dirname) + if drive == "" { + // UNIX-style path. + return path.Join(dirname, filename) + } + // DOS-style path. + drive2, filename := splitDrive(filename) + if drive2 != "" { + if !strings.EqualFold(drive, drive2) { + // Different drives. There's not much we can + // do here, so just ignore the directory. + return drive2 + filename + } + // Drives are the same. Ignore drive on filename. + } + if !(strings.HasSuffix(dirname, "/") || strings.HasSuffix(dirname, `\`)) && dirname != "" { + sep := `\` + if strings.HasPrefix(dirname, "/") { + sep = `/` + } + dirname += sep + } + return drive + dirname + filename +} + +// splitDrive splits the DOS drive letter or UNC share point from +// path, if any. path == drive + rest +func splitDrive(path string) (drive, rest string) { + if len(path) >= 2 && path[1] == ':' { + if c := path[0]; 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' { + return path[:2], path[2:] + } + } + if len(path) > 3 && (path[0] == '\\' || path[0] == '/') && (path[1] == '\\' || path[1] == '/') { + // Normalize the path so we can search for just \ below. + npath := strings.Replace(path, "/", `\`, -1) + // Get the host part, which must be non-empty. + slash1 := strings.IndexByte(npath[2:], '\\') + 2 + if slash1 > 2 { + // Get the mount-point part, which must be non-empty. + slash2 := strings.IndexByte(npath[slash1+1:], '\\') + slash1 + 1 + if slash2 > slash1 { + return path[:slash2], path[slash2:] + } + } + } + return "", path +} |