src

symtab.go (18365B)

---

 // Copyright 2009 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 gosym implements access to the Go symbol
 // and line number tables embedded in Go binaries generated
 // by the gc compilers.
 package gosym
 
 import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
 	"strconv"
 	"strings"
 )
 
 /*
  * Symbols
  */
 
 // A Sym represents a single symbol table entry.
 type Sym struct {
 	Value  uint64
 	Type   byte
 	Name   string
 	GoType uint64
 	// If this symbol is a function symbol, the corresponding Func
 	Func *Func
 
 	goVersion version
 }
 
 // Static reports whether this symbol is static (not visible outside its file).
 func (s *Sym) Static() bool { return s.Type >= 'a' }
 
 // nameWithoutInst returns s.Name if s.Name has no brackets (does not reference an
 // instantiated type, function, or method). If s.Name contains brackets, then it
 // returns s.Name with all the contents between (and including) the outermost left
 // and right bracket removed. This is useful to ignore any extra slashes or dots
 // inside the brackets from the string searches below, where needed.
 func (s *Sym) nameWithoutInst() string {
 	start := strings.Index(s.Name, "[")
 	if start < 0 {
 		return s.Name
 	}
 	end := strings.LastIndex(s.Name, "]")
 	if end < 0 {
 		// Malformed name, should contain closing bracket too.
 		return s.Name
 	}
 	return s.Name[0:start] + s.Name[end+1:]
 }
 
 // PackageName returns the package part of the symbol name,
 // or the empty string if there is none.
 func (s *Sym) PackageName() string {
 	name := s.nameWithoutInst()
 
 	// Since go1.20, a prefix of "type:" and "go:" is a compiler-generated symbol,
 	// they do not belong to any package.
 	//
 	// See cmd/compile/internal/base/link.go:ReservedImports variable.
 	if s.goVersion >= ver120 && (strings.HasPrefix(name, "go:") || strings.HasPrefix(name, "type:")) {
 		return ""
 	}
 
 	// For go1.18 and below, the prefix are "type." and "go." instead.
 	if s.goVersion <= ver118 && (strings.HasPrefix(name, "go.") || strings.HasPrefix(name, "type.")) {
 		return ""
 	}
 
 	pathend := strings.LastIndex(name, "/")
 	if pathend < 0 {
 		pathend = 0
 	}
 
 	if i := strings.Index(name[pathend:], "."); i != -1 {
 		return name[:pathend+i]
 	}
 	return ""
 }
 
 // ReceiverName returns the receiver type name of this symbol,
 // or the empty string if there is none.  A receiver name is only detected in
 // the case that s.Name is fully-specified with a package name.
 func (s *Sym) ReceiverName() string {
 	name := s.nameWithoutInst()
 	// If we find a slash in name, it should precede any bracketed expression
 	// that was removed, so pathend will apply correctly to name and s.Name.
 	pathend := strings.LastIndex(name, "/")
 	if pathend < 0 {
 		pathend = 0
 	}
 	// Find the first dot after pathend (or from the beginning, if there was
 	// no slash in name).
 	l := strings.Index(name[pathend:], ".")
 	// Find the last dot after pathend (or the beginning).
 	r := strings.LastIndex(name[pathend:], ".")
 	if l == -1 || r == -1 || l == r {
 		// There is no receiver if we didn't find two distinct dots after pathend.
 		return ""
 	}
 	// Given there is a trailing '.' that is in name, find it now in s.Name.
 	// pathend+l should apply to s.Name, because it should be the dot in the
 	// package name.
 	r = strings.LastIndex(s.Name[pathend:], ".")
 	return s.Name[pathend+l+1 : pathend+r]
 }
 
 // BaseName returns the symbol name without the package or receiver name.
 func (s *Sym) BaseName() string {
 	name := s.nameWithoutInst()
 	if i := strings.LastIndex(name, "."); i != -1 {
 		if s.Name != name {
 			brack := strings.Index(s.Name, "[")
 			if i > brack {
 				// BaseName is a method name after the brackets, so
 				// recalculate for s.Name. Otherwise, i applies
 				// correctly to s.Name, since it is before the
 				// brackets.
 				i = strings.LastIndex(s.Name, ".")
 			}
 		}
 		return s.Name[i+1:]
 	}
 	return s.Name
 }
 
 // A Func collects information about a single function.
 type Func struct {
 	Entry uint64
 	*Sym
 	End       uint64
 	Params    []*Sym // nil for Go 1.3 and later binaries
 	Locals    []*Sym // nil for Go 1.3 and later binaries
 	FrameSize int
 	LineTable *LineTable
 	Obj       *Obj
 	// Addition: extra data to support inlining.
 	inlTree
 }
 
 // An Obj represents a collection of functions in a symbol table.
 //
 // The exact method of division of a binary into separate Objs is an internal detail
 // of the symbol table format.
 //
 // In early versions of Go each source file became a different Obj.
 //
 // In Go 1 and Go 1.1, each package produced one Obj for all Go sources
 // and one Obj per C source file.
 //
 // In Go 1.2, there is a single Obj for the entire program.
 type Obj struct {
 	// Funcs is a list of functions in the Obj.
 	Funcs []Func
 
 	// In Go 1.1 and earlier, Paths is a list of symbols corresponding
 	// to the source file names that produced the Obj.
 	// In Go 1.2, Paths is nil.
 	// Use the keys of Table.Files to obtain a list of source files.
 	Paths []Sym // meta
 }
 
 /*
  * Symbol tables
  */
 
 // Table represents a Go symbol table. It stores all of the
 // symbols decoded from the program and provides methods to translate
 // between symbols, names, and addresses.
 type Table struct {
 	Syms  []Sym // nil for Go 1.3 and later binaries
 	Funcs []Func
 	Files map[string]*Obj // for Go 1.2 and later all files map to one Obj
 	Objs  []Obj           // for Go 1.2 and later only one Obj in slice
 
 	go12line *LineTable // Go 1.2 line number table
 }
 
 type sym struct {
 	value  uint64
 	gotype uint64
 	typ    byte
 	name   []byte
 }
 
 var (
 	littleEndianSymtab    = []byte{0xFD, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00}
 	bigEndianSymtab       = []byte{0xFF, 0xFF, 0xFF, 0xFD, 0x00, 0x00, 0x00}
 	oldLittleEndianSymtab = []byte{0xFE, 0xFF, 0xFF, 0xFF, 0x00, 0x00}
 )
 
 func walksymtab(data []byte, fn func(sym) error) error {
 	if len(data) == 0 { // missing symtab is okay
 		return nil
 	}
 	var order binary.ByteOrder = binary.BigEndian
 	newTable := false
 	switch {
 	case bytes.HasPrefix(data, oldLittleEndianSymtab):
 		// Same as Go 1.0, but little endian.
 		// Format was used during interim development between Go 1.0 and Go 1.1.
 		// Should not be widespread, but easy to support.
 		data = data[6:]
 		order = binary.LittleEndian
 	case bytes.HasPrefix(data, bigEndianSymtab):
 		newTable = true
 	case bytes.HasPrefix(data, littleEndianSymtab):
 		newTable = true
 		order = binary.LittleEndian
 	}
 	var ptrsz int
 	if newTable {
 		if len(data) < 8 {
 			return &DecodingError{len(data), "unexpected EOF", nil}
 		}
 		ptrsz = int(data[7])
 		if ptrsz != 4 && ptrsz != 8 {
 			return &DecodingError{7, "invalid pointer size", ptrsz}
 		}
 		data = data[8:]
 	}
 	var s sym
 	p := data
 	for len(p) >= 4 {
 		var typ byte
 		if newTable {
 			// Symbol type, value, Go type.
 			typ = p[0] & 0x3F
 			wideValue := p[0]&0x40 != 0
 			goType := p[0]&0x80 != 0
 			if typ < 26 {
 				typ += 'A'
 			} else {
 				typ += 'a' - 26
 			}
 			s.typ = typ
 			p = p[1:]
 			if wideValue {
 				if len(p) < ptrsz {
 					return &DecodingError{len(data), "unexpected EOF", nil}
 				}
 				// fixed-width value
 				if ptrsz == 8 {
 					s.value = order.Uint64(p[0:8])
 					p = p[8:]
 				} else {
 					s.value = uint64(order.Uint32(p[0:4]))
 					p = p[4:]
 				}
 			} else {
 				// varint value
 				s.value = 0
 				shift := uint(0)
 				for len(p) > 0 && p[0]&0x80 != 0 {
 					s.value |= uint64(p[0]&0x7F) << shift
 					shift += 7
 					p = p[1:]
 				}
 				if len(p) == 0 {
 					return &DecodingError{len(data), "unexpected EOF", nil}
 				}
 				s.value |= uint64(p[0]) << shift
 				p = p[1:]
 			}
 			if goType {
 				if len(p) < ptrsz {
 					return &DecodingError{len(data), "unexpected EOF", nil}
 				}
 				// fixed-width go type
 				if ptrsz == 8 {
 					s.gotype = order.Uint64(p[0:8])
 					p = p[8:]
 				} else {
 					s.gotype = uint64(order.Uint32(p[0:4]))
 					p = p[4:]
 				}
 			}
 		} else {
 			// Value, symbol type.
 			s.value = uint64(order.Uint32(p[0:4]))
 			if len(p) < 5 {
 				return &DecodingError{len(data), "unexpected EOF", nil}
 			}
 			typ = p[4]
 			if typ&0x80 == 0 {
 				return &DecodingError{len(data) - len(p) + 4, "bad symbol type", typ}
 			}
 			typ &^= 0x80
 			s.typ = typ
 			p = p[5:]
 		}
 
 		// Name.
 		var i int
 		var nnul int
 		for i = 0; i < len(p); i++ {
 			if p[i] == 0 {
 				nnul = 1
 				break
 			}
 		}
 		switch typ {
 		case 'z', 'Z':
 			p = p[i+nnul:]
 			for i = 0; i+2 <= len(p); i += 2 {
 				if p[i] == 0 && p[i+1] == 0 {
 					nnul = 2
 					break
 				}
 			}
 		}
 		if len(p) < i+nnul {
 			return &DecodingError{len(data), "unexpected EOF", nil}
 		}
 		s.name = p[0:i]
 		i += nnul
 		p = p[i:]
 
 		if !newTable {
 			if len(p) < 4 {
 				return &DecodingError{len(data), "unexpected EOF", nil}
 			}
 			// Go type.
 			s.gotype = uint64(order.Uint32(p[:4]))
 			p = p[4:]
 		}
 		_ = fn(s)
 	}
 	return nil
 }
 
 // NewTable decodes the Go symbol table (the ".gosymtab" section in ELF),
 // returning an in-memory representation.
 // Starting with Go 1.3, the Go symbol table no longer includes symbol data.
 func NewTable(symtab []byte, pcln *LineTable) (*Table, error) {
 	var n int
 	err := walksymtab(symtab, func(s sym) error {
 		n++
 		return nil
 	})
 	if err != nil {
 		return nil, err
 	}
 
 	var t Table
 	if pcln.isGo12() {
 		t.go12line = pcln
 	}
 	fname := make(map[uint16]string)
 	t.Syms = make([]Sym, 0, n)
 	nf := 0
 	nz := 0
 	lasttyp := uint8(0)
 	err = walksymtab(symtab, func(s sym) error {
 		n := len(t.Syms)
 		t.Syms = t.Syms[0 : n+1]
 		ts := &t.Syms[n]
 		ts.Type = s.typ
 		ts.Value = s.value
 		ts.GoType = s.gotype
 		ts.goVersion = pcln.version
 		switch s.typ {
 		default:
 			// rewrite name to use . instead of · (c2 b7)
 			w := 0
 			b := s.name
 			for i := 0; i < len(b); i++ {
 				if b[i] == 0xc2 && i+1 < len(b) && b[i+1] == 0xb7 {
 					i++
 					b[i] = '.'
 				}
 				b[w] = b[i]
 				w++
 			}
 			ts.Name = string(s.name[0:w])
 		case 'z', 'Z':
 			if lasttyp != 'z' && lasttyp != 'Z' {
 				nz++
 			}
 			for i := 0; i < len(s.name); i += 2 {
 				eltIdx := binary.BigEndian.Uint16(s.name[i : i+2])
 				elt, ok := fname[eltIdx]
 				if !ok {
 					return &DecodingError{-1, "bad filename code", eltIdx}
 				}
 				if n := len(ts.Name); n > 0 && ts.Name[n-1] != '/' {
 					ts.Name += "/"
 				}
 				ts.Name += elt
 			}
 		}
 		switch s.typ {
 		case 'T', 't', 'L', 'l':
 			nf++
 		case 'f':
 			fname[uint16(s.value)] = ts.Name
 		}
 		lasttyp = s.typ
 		return nil
 	})
 	if err != nil {
 		return nil, err
 	}
 
 	t.Funcs = make([]Func, 0, nf)
 	t.Files = make(map[string]*Obj)
 
 	var obj *Obj
 	if t.go12line != nil {
 		// Put all functions into one Obj.
 		t.Objs = make([]Obj, 1)
 		obj = &t.Objs[0]
 		t.go12line.go12MapFiles(t.Files, obj)
 	} else {
 		t.Objs = make([]Obj, 0, nz)
 	}
 
 	// Count text symbols and attach frame sizes, parameters, and
 	// locals to them. Also, find object file boundaries.
 	lastf := 0
 	for i := 0; i < len(t.Syms); i++ {
 		sym := &t.Syms[i]
 		switch sym.Type {
 		case 'Z', 'z': // path symbol
 			if t.go12line != nil {
 				// Go 1.2 binaries have the file information elsewhere. Ignore.
 				break
 			}
 			// Finish the current object
 			if obj != nil {
 				obj.Funcs = t.Funcs[lastf:]
 			}
 			lastf = len(t.Funcs)
 
 			// Start new object
 			n := len(t.Objs)
 			t.Objs = t.Objs[0 : n+1]
 			obj = &t.Objs[n]
 
 			// Count & copy path symbols
 			var end int
 			for end = i + 1; end < len(t.Syms); end++ {
 				if c := t.Syms[end].Type; c != 'Z' && c != 'z' {
 					break
 				}
 			}
 			obj.Paths = t.Syms[i:end]
 			i = end - 1 // loop will i++
 
 			// Record file names
 			depth := 0
 			for j := range obj.Paths {
 				s := &obj.Paths[j]
 				if s.Name == "" {
 					depth--
 				} else {
 					if depth == 0 {
 						t.Files[s.Name] = obj
 					}
 					depth++
 				}
 			}
 
 		case 'T', 't', 'L', 'l': // text symbol
 			if n := len(t.Funcs); n > 0 {
 				t.Funcs[n-1].End = sym.Value
 			}
 			if sym.Name == "runtime.etext" || sym.Name == "etext" {
 				continue
 			}
 
 			// Count parameter and local (auto) syms
 			var np, na int
 			var end int
 		countloop:
 			for end = i + 1; end < len(t.Syms); end++ {
 				switch t.Syms[end].Type {
 				case 'T', 't', 'L', 'l', 'Z', 'z':
 					break countloop
 				case 'p':
 					np++
 				case 'a':
 					na++
 				}
 			}
 
 			// Fill in the function symbol
 			n := len(t.Funcs)
 			t.Funcs = t.Funcs[0 : n+1]
 			fn := &t.Funcs[n]
 			sym.Func = fn
 			fn.Params = make([]*Sym, 0, np)
 			fn.Locals = make([]*Sym, 0, na)
 			fn.Sym = sym
 			fn.Entry = sym.Value
 			fn.Obj = obj
 			if t.go12line != nil {
 				// All functions share the same line table.
 				// It knows how to narrow down to a specific
 				// function quickly.
 				fn.LineTable = t.go12line
 			} else if pcln != nil {
 				fn.LineTable = pcln.slice(fn.Entry)
 				pcln = fn.LineTable
 			}
 			for j := i; j < end; j++ {
 				s := &t.Syms[j]
 				switch s.Type {
 				case 'm':
 					fn.FrameSize = int(s.Value)
 				case 'p':
 					n := len(fn.Params)
 					fn.Params = fn.Params[0 : n+1]
 					fn.Params[n] = s
 				case 'a':
 					n := len(fn.Locals)
 					fn.Locals = fn.Locals[0 : n+1]
 					fn.Locals[n] = s
 				}
 			}
 			i = end - 1 // loop will i++
 		}
 	}
 
 	if t.go12line != nil && nf == 0 {
 		t.Funcs = t.go12line.go12Funcs()
 	}
 	if obj != nil {
 		obj.Funcs = t.Funcs[lastf:]
 	}
 	return &t, nil
 }
 
 // PCToFunc returns the function containing the program counter pc,
 // or nil if there is no such function.
 func (t *Table) PCToFunc(pc uint64) *Func {
 	funcs := t.Funcs
 	for len(funcs) > 0 {
 		m := len(funcs) / 2
 		fn := &funcs[m]
 		switch {
 		case pc < fn.Entry:
 			funcs = funcs[0:m]
 		case fn.Entry <= pc && pc < fn.End:
 			return fn
 		default:
 			funcs = funcs[m+1:]
 		}
 	}
 	return nil
 }
 
 // PCToLine looks up line number information for a program counter.
 // If there is no information, it returns fn == nil.
 func (t *Table) PCToLine(pc uint64) (file string, line int, fn *Func) {
 	if fn = t.PCToFunc(pc); fn == nil {
 		return
 	}
 	if t.go12line != nil {
 		file = t.go12line.go12PCToFile(pc)
 		line = t.go12line.go12PCToLine(pc)
 	} else {
 		file, line = fn.Obj.lineFromAline(fn.LineTable.PCToLine(pc))
 	}
 	return
 }
 
 // LineToPC looks up the first program counter on the given line in
 // the named file. It returns UnknownPathError or UnknownLineError if
 // there is an error looking up this line.
 func (t *Table) LineToPC(file string, line int) (pc uint64, fn *Func, err error) {
 	obj, ok := t.Files[file]
 	if !ok {
 		return 0, nil, UnknownFileError(file)
 	}
 
 	if t.go12line != nil {
 		pc := t.go12line.go12LineToPC(file, line)
 		if pc == 0 {
 			return 0, nil, &UnknownLineError{file, line}
 		}
 		return pc, t.PCToFunc(pc), nil
 	}
 
 	abs, err := obj.alineFromLine(file, line)
 	if err != nil {
 		return
 	}
 	for i := range obj.Funcs {
 		f := &obj.Funcs[i]
 		pc := f.LineTable.LineToPC(abs, f.End)
 		if pc != 0 {
 			return pc, f, nil
 		}
 	}
 	return 0, nil, &UnknownLineError{file, line}
 }
 
 // LookupSym returns the text, data, or bss symbol with the given name,
 // or nil if no such symbol is found.
 func (t *Table) LookupSym(name string) *Sym {
 	// TODO(austin) Maybe make a map
 	for i := range t.Syms {
 		s := &t.Syms[i]
 		switch s.Type {
 		case 'T', 't', 'L', 'l', 'D', 'd', 'B', 'b':
 			if s.Name == name {
 				return s
 			}
 		}
 	}
 	return nil
 }
 
 // LookupFunc returns the text, data, or bss symbol with the given name,
 // or nil if no such symbol is found.
 func (t *Table) LookupFunc(name string) *Func {
 	for i := range t.Funcs {
 		f := &t.Funcs[i]
 		if f.Sym.Name == name {
 			return f
 		}
 	}
 	return nil
 }
 
 // SymByAddr returns the text, data, or bss symbol starting at the given address.
 func (t *Table) SymByAddr(addr uint64) *Sym {
 	for i := range t.Syms {
 		s := &t.Syms[i]
 		switch s.Type {
 		case 'T', 't', 'L', 'l', 'D', 'd', 'B', 'b':
 			if s.Value == addr {
 				return s
 			}
 		}
 	}
 	return nil
 }
 
 /*
  * Object files
  */
 
 // This is legacy code for Go 1.1 and earlier, which used the
 // Plan 9 format for pc-line tables. This code was never quite
 // correct. It's probably very close, and it's usually correct, but
 // we never quite found all the corner cases.
 //
 // Go 1.2 and later use a simpler format, documented at golang.org/s/go12symtab.
 
 func (o *Obj) lineFromAline(aline int) (string, int) {
 	type stackEnt struct {
 		path   string
 		start  int
 		offset int
 		prev   *stackEnt
 	}
 
 	noPath := &stackEnt{"", 0, 0, nil}
 	tos := noPath
 
 pathloop:
 	for _, s := range o.Paths {
 		val := int(s.Value)
 		switch {
 		case val > aline:
 			break pathloop
 
 		case val == 1:
 			// Start a new stack
 			tos = &stackEnt{s.Name, val, 0, noPath}
 
 		case s.Name == "":
 			// Pop
 			if tos == noPath {
 				return "<malformed symbol table>", 0
 			}
 			tos.prev.offset += val - tos.start
 			tos = tos.prev
 
 		default:
 			// Push
 			tos = &stackEnt{s.Name, val, 0, tos}
 		}
 	}
 
 	if tos == noPath {
 		return "", 0
 	}
 	return tos.path, aline - tos.start - tos.offset + 1
 }
 
 func (o *Obj) alineFromLine(path string, line int) (int, error) {
 	if line < 1 {
 		return 0, &UnknownLineError{path, line}
 	}
 
 	for i, s := range o.Paths {
 		// Find this path
 		if s.Name != path {
 			continue
 		}
 
 		// Find this line at this stack level
 		depth := 0
 		var incstart int
 		line += int(s.Value)
 	pathloop:
 		for _, s := range o.Paths[i:] {
 			val := int(s.Value)
 			switch {
 			case depth == 1 && val >= line:
 				return line - 1, nil
 
 			case s.Name == "":
 				depth--
 				if depth == 0 {
 					break pathloop
 				} else if depth == 1 {
 					line += val - incstart
 				}
 
 			default:
 				if depth == 1 {
 					incstart = val
 				}
 				depth++
 			}
 		}
 		return 0, &UnknownLineError{path, line}
 	}
 	return 0, UnknownFileError(path)
 }
 
 /*
  * Errors
  */
 
 // UnknownFileError represents a failure to find the specific file in
 // the symbol table.
 type UnknownFileError string
 
 func (e UnknownFileError) Error() string { return "unknown file: " + string(e) }
 
 // UnknownLineError represents a failure to map a line to a program
 // counter, either because the line is beyond the bounds of the file
 // or because there is no code on the given line.
 type UnknownLineError struct {
 	File string
 	Line int
 }
 
 func (e *UnknownLineError) Error() string {
 	return "no code at " + e.File + ":" + strconv.Itoa(e.Line)
 }
 
 // DecodingError represents an error during the decoding of
 // the symbol table.
 type DecodingError struct {
 	off int
 	msg string
 	val any
 }
 
 func (e *DecodingError) Error() string {
 	msg := e.msg
 	if e.val != nil {
 		msg += fmt.Sprintf(" '%v'", e.val)
 	}
 	msg += fmt.Sprintf(" at byte %#x", e.off)
 	return msg
 }