Source file src/pkg/cmd/internal/objfile/disasm.go

     1	// Copyright 2014 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package objfile
     6	
     7	import (
     8		"bufio"
     9		"bytes"
    10		"cmd/internal/src"
    11		"container/list"
    12		"debug/gosym"
    13		"encoding/binary"
    14		"fmt"
    15		"io"
    16		"io/ioutil"
    17		"os"
    18		"path/filepath"
    19		"regexp"
    20		"sort"
    21		"strings"
    22		"text/tabwriter"
    23	
    24		"golang.org/x/arch/arm/armasm"
    25		"golang.org/x/arch/arm64/arm64asm"
    26		"golang.org/x/arch/ppc64/ppc64asm"
    27		"golang.org/x/arch/x86/x86asm"
    28	)
    29	
    30	// Disasm is a disassembler for a given File.
    31	type Disasm struct {
    32		syms      []Sym            //symbols in file, sorted by address
    33		pcln      Liner            // pcln table
    34		text      []byte           // bytes of text segment (actual instructions)
    35		textStart uint64           // start PC of text
    36		textEnd   uint64           // end PC of text
    37		goarch    string           // GOARCH string
    38		disasm    disasmFunc       // disassembler function for goarch
    39		byteOrder binary.ByteOrder // byte order for goarch
    40	}
    41	
    42	// Disasm returns a disassembler for the file f.
    43	func (e *Entry) Disasm() (*Disasm, error) {
    44		syms, err := e.Symbols()
    45		if err != nil {
    46			return nil, err
    47		}
    48	
    49		pcln, err := e.PCLineTable()
    50		if err != nil {
    51			return nil, err
    52		}
    53	
    54		textStart, textBytes, err := e.Text()
    55		if err != nil {
    56			return nil, err
    57		}
    58	
    59		goarch := e.GOARCH()
    60		disasm := disasms[goarch]
    61		byteOrder := byteOrders[goarch]
    62		if disasm == nil || byteOrder == nil {
    63			return nil, fmt.Errorf("unsupported architecture")
    64		}
    65	
    66		// Filter out section symbols, overwriting syms in place.
    67		keep := syms[:0]
    68		for _, sym := range syms {
    69			switch sym.Name {
    70			case "runtime.text", "text", "_text", "runtime.etext", "etext", "_etext":
    71				// drop
    72			default:
    73				keep = append(keep, sym)
    74			}
    75		}
    76		syms = keep
    77		d := &Disasm{
    78			syms:      syms,
    79			pcln:      pcln,
    80			text:      textBytes,
    81			textStart: textStart,
    82			textEnd:   textStart + uint64(len(textBytes)),
    83			goarch:    goarch,
    84			disasm:    disasm,
    85			byteOrder: byteOrder,
    86		}
    87	
    88		return d, nil
    89	}
    90	
    91	// lookup finds the symbol name containing addr.
    92	func (d *Disasm) lookup(addr uint64) (name string, base uint64) {
    93		i := sort.Search(len(d.syms), func(i int) bool { return addr < d.syms[i].Addr })
    94		if i > 0 {
    95			s := d.syms[i-1]
    96			if s.Addr != 0 && s.Addr <= addr && addr < s.Addr+uint64(s.Size) {
    97				return s.Name, s.Addr
    98			}
    99		}
   100		return "", 0
   101	}
   102	
   103	// base returns the final element in the path.
   104	// It works on both Windows and Unix paths,
   105	// regardless of host operating system.
   106	func base(path string) string {
   107		path = path[strings.LastIndex(path, "/")+1:]
   108		path = path[strings.LastIndex(path, `\`)+1:]
   109		return path
   110	}
   111	
   112	// CachedFile contains the content of a file split into lines.
   113	type CachedFile struct {
   114		FileName string
   115		Lines    [][]byte
   116	}
   117	
   118	// FileCache is a simple LRU cache of file contents.
   119	type FileCache struct {
   120		files  *list.List
   121		maxLen int
   122	}
   123	
   124	// NewFileCache returns a FileCache which can contain up to maxLen cached file contents.
   125	func NewFileCache(maxLen int) *FileCache {
   126		return &FileCache{
   127			files:  list.New(),
   128			maxLen: maxLen,
   129		}
   130	}
   131	
   132	// Line returns the source code line for the given file and line number.
   133	// If the file is not already cached, reads it, inserts it into the cache,
   134	// and removes the least recently used file if necessary.
   135	// If the file is in cache, it is moved to the front of the list.
   136	func (fc *FileCache) Line(filename string, line int) ([]byte, error) {
   137		if filepath.Ext(filename) != ".go" {
   138			return nil, nil
   139		}
   140	
   141		// Clean filenames returned by src.Pos.SymFilename()
   142		// or src.PosBase.SymFilename() removing
   143		// the leading src.FileSymPrefix.
   144		filename = strings.TrimPrefix(filename, src.FileSymPrefix)
   145	
   146		// Expand literal "$GOROOT" rewritten by obj.AbsFile()
   147		filename = filepath.Clean(os.ExpandEnv(filename))
   148	
   149		var cf *CachedFile
   150		var e *list.Element
   151	
   152		for e = fc.files.Front(); e != nil; e = e.Next() {
   153			cf = e.Value.(*CachedFile)
   154			if cf.FileName == filename {
   155				break
   156			}
   157		}
   158	
   159		if e == nil {
   160			content, err := ioutil.ReadFile(filename)
   161			if err != nil {
   162				return nil, err
   163			}
   164	
   165			cf = &CachedFile{
   166				FileName: filename,
   167				Lines:    bytes.Split(content, []byte{'\n'}),
   168			}
   169			fc.files.PushFront(cf)
   170	
   171			if fc.files.Len() >= fc.maxLen {
   172				fc.files.Remove(fc.files.Back())
   173			}
   174		} else {
   175			fc.files.MoveToFront(e)
   176		}
   177	
   178		return cf.Lines[line-1], nil
   179	}
   180	
   181	// Print prints a disassembly of the file to w.
   182	// If filter is non-nil, the disassembly only includes functions with names matching filter.
   183	// If printCode is true, the disassembly includs corresponding source lines.
   184	// The disassembly only includes functions that overlap the range [start, end).
   185	func (d *Disasm) Print(w io.Writer, filter *regexp.Regexp, start, end uint64, printCode bool) {
   186		if start < d.textStart {
   187			start = d.textStart
   188		}
   189		if end > d.textEnd {
   190			end = d.textEnd
   191		}
   192		printed := false
   193		bw := bufio.NewWriter(w)
   194	
   195		var fc *FileCache
   196		if printCode {
   197			fc = NewFileCache(8)
   198		}
   199	
   200		tw := tabwriter.NewWriter(bw, 18, 8, 1, '\t', tabwriter.StripEscape)
   201		for _, sym := range d.syms {
   202			symStart := sym.Addr
   203			symEnd := sym.Addr + uint64(sym.Size)
   204			relocs := sym.Relocs
   205			if sym.Code != 'T' && sym.Code != 't' ||
   206				symStart < d.textStart ||
   207				symEnd <= start || end <= symStart ||
   208				filter != nil && !filter.MatchString(sym.Name) {
   209				continue
   210			}
   211			if printed {
   212				fmt.Fprintf(bw, "\n")
   213			}
   214			printed = true
   215	
   216			file, _, _ := d.pcln.PCToLine(sym.Addr)
   217			fmt.Fprintf(bw, "TEXT %s(SB) %s\n", sym.Name, file)
   218	
   219			if symEnd > end {
   220				symEnd = end
   221			}
   222			code := d.text[:end-d.textStart]
   223	
   224			var lastFile string
   225			var lastLine int
   226	
   227			d.Decode(symStart, symEnd, relocs, func(pc, size uint64, file string, line int, text string) {
   228				i := pc - d.textStart
   229	
   230				if printCode {
   231					if file != lastFile || line != lastLine {
   232						if srcLine, err := fc.Line(file, line); err == nil {
   233							fmt.Fprintf(tw, "%s%s%s\n", []byte{tabwriter.Escape}, srcLine, []byte{tabwriter.Escape})
   234						}
   235	
   236						lastFile, lastLine = file, line
   237					}
   238	
   239					fmt.Fprintf(tw, "  %#x\t", pc)
   240				} else {
   241					fmt.Fprintf(tw, "  %s:%d\t%#x\t", base(file), line, pc)
   242				}
   243	
   244				if size%4 != 0 || d.goarch == "386" || d.goarch == "amd64" || d.goarch == "amd64p32" {
   245					// Print instruction as bytes.
   246					fmt.Fprintf(tw, "%x", code[i:i+size])
   247				} else {
   248					// Print instruction as 32-bit words.
   249					for j := uint64(0); j < size; j += 4 {
   250						if j > 0 {
   251							fmt.Fprintf(tw, " ")
   252						}
   253						fmt.Fprintf(tw, "%08x", d.byteOrder.Uint32(code[i+j:]))
   254					}
   255				}
   256				fmt.Fprintf(tw, "\t%s\t\n", text)
   257			})
   258			tw.Flush()
   259		}
   260		bw.Flush()
   261	}
   262	
   263	// Decode disassembles the text segment range [start, end), calling f for each instruction.
   264	func (d *Disasm) Decode(start, end uint64, relocs []Reloc, f func(pc, size uint64, file string, line int, text string)) {
   265		if start < d.textStart {
   266			start = d.textStart
   267		}
   268		if end > d.textEnd {
   269			end = d.textEnd
   270		}
   271		code := d.text[:end-d.textStart]
   272		lookup := d.lookup
   273		for pc := start; pc < end; {
   274			i := pc - d.textStart
   275			text, size := d.disasm(code[i:], pc, lookup, d.byteOrder)
   276			file, line, _ := d.pcln.PCToLine(pc)
   277			sep := "\t"
   278			for len(relocs) > 0 && relocs[0].Addr < i+uint64(size) {
   279				text += sep + relocs[0].Stringer.String(pc-start)
   280				sep = " "
   281				relocs = relocs[1:]
   282			}
   283			f(pc, uint64(size), file, line, text)
   284			pc += uint64(size)
   285		}
   286	}
   287	
   288	type lookupFunc = func(addr uint64) (sym string, base uint64)
   289	type disasmFunc func(code []byte, pc uint64, lookup lookupFunc, ord binary.ByteOrder) (text string, size int)
   290	
   291	func disasm_386(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder) (string, int) {
   292		return disasm_x86(code, pc, lookup, 32)
   293	}
   294	
   295	func disasm_amd64(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder) (string, int) {
   296		return disasm_x86(code, pc, lookup, 64)
   297	}
   298	
   299	func disasm_x86(code []byte, pc uint64, lookup lookupFunc, arch int) (string, int) {
   300		inst, err := x86asm.Decode(code, arch)
   301		var text string
   302		size := inst.Len
   303		if err != nil || size == 0 || inst.Op == 0 {
   304			size = 1
   305			text = "?"
   306		} else {
   307			text = x86asm.GoSyntax(inst, pc, lookup)
   308		}
   309		return text, size
   310	}
   311	
   312	type textReader struct {
   313		code []byte
   314		pc   uint64
   315	}
   316	
   317	func (r textReader) ReadAt(data []byte, off int64) (n int, err error) {
   318		if off < 0 || uint64(off) < r.pc {
   319			return 0, io.EOF
   320		}
   321		d := uint64(off) - r.pc
   322		if d >= uint64(len(r.code)) {
   323			return 0, io.EOF
   324		}
   325		n = copy(data, r.code[d:])
   326		if n < len(data) {
   327			err = io.ErrUnexpectedEOF
   328		}
   329		return
   330	}
   331	
   332	func disasm_arm(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder) (string, int) {
   333		inst, err := armasm.Decode(code, armasm.ModeARM)
   334		var text string
   335		size := inst.Len
   336		if err != nil || size == 0 || inst.Op == 0 {
   337			size = 4
   338			text = "?"
   339		} else {
   340			text = armasm.GoSyntax(inst, pc, lookup, textReader{code, pc})
   341		}
   342		return text, size
   343	}
   344	
   345	func disasm_arm64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder) (string, int) {
   346		inst, err := arm64asm.Decode(code)
   347		var text string
   348		if err != nil || inst.Op == 0 {
   349			text = "?"
   350		} else {
   351			text = arm64asm.GoSyntax(inst, pc, lookup, textReader{code, pc})
   352		}
   353		return text, 4
   354	}
   355	
   356	func disasm_ppc64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder) (string, int) {
   357		inst, err := ppc64asm.Decode(code, byteOrder)
   358		var text string
   359		size := inst.Len
   360		if err != nil || size == 0 {
   361			size = 4
   362			text = "?"
   363		} else {
   364			text = ppc64asm.GoSyntax(inst, pc, lookup)
   365		}
   366		return text, size
   367	}
   368	
   369	var disasms = map[string]disasmFunc{
   370		"386":      disasm_386,
   371		"amd64":    disasm_amd64,
   372		"amd64p32": disasm_amd64,
   373		"arm":      disasm_arm,
   374		"arm64":    disasm_arm64,
   375		"ppc64":    disasm_ppc64,
   376		"ppc64le":  disasm_ppc64,
   377	}
   378	
   379	var byteOrders = map[string]binary.ByteOrder{
   380		"386":      binary.LittleEndian,
   381		"amd64":    binary.LittleEndian,
   382		"amd64p32": binary.LittleEndian,
   383		"arm":      binary.LittleEndian,
   384		"arm64":    binary.LittleEndian,
   385		"ppc64":    binary.BigEndian,
   386		"ppc64le":  binary.LittleEndian,
   387		"s390x":    binary.BigEndian,
   388	}
   389	
   390	type Liner interface {
   391		// Given a pc, returns the corresponding file, line, and function data.
   392		// If unknown, returns "",0,nil.
   393		PCToLine(uint64) (string, int, *gosym.Func)
   394	}
   395	

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