disasm.go

Documentation: cmd/internal/objfile

     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  	"container/list"
    11  	"debug/gosym"
    12  	"encoding/binary"
    13  	"fmt"
    14  	"io"
    15  	"os"
    16  	"path/filepath"
    17  	"regexp"
    18  	"sort"
    19  	"strings"
    20  	"text/tabwriter"
    21  
    22  	"cmd/internal/src"
    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 := os.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  	// because //line directives can be out-of-range. (#36683)
   179  	if line-1 >= len(cf.Lines) || line-1 < 0 {
   180  		return nil, nil
   181  	}
   182  
   183  	return cf.Lines[line-1], nil
   184  }
   185  
   186  // Print prints a disassembly of the file to w.
   187  // If filter is non-nil, the disassembly only includes functions with names matching filter.
   188  // If printCode is true, the disassembly includs corresponding source lines.
   189  // The disassembly only includes functions that overlap the range [start, end).
   190  func (d *Disasm) Print(w io.Writer, filter *regexp.Regexp, start, end uint64, printCode bool, gnuAsm bool) {
   191  	if start < d.textStart {
   192  		start = d.textStart
   193  	}
   194  	if end > d.textEnd {
   195  		end = d.textEnd
   196  	}
   197  	printed := false
   198  	bw := bufio.NewWriter(w)
   199  
   200  	var fc *FileCache
   201  	if printCode {
   202  		fc = NewFileCache(8)
   203  	}
   204  
   205  	tw := tabwriter.NewWriter(bw, 18, 8, 1, '\t', tabwriter.StripEscape)
   206  	for _, sym := range d.syms {
   207  		symStart := sym.Addr
   208  		symEnd := sym.Addr + uint64(sym.Size)
   209  		relocs := sym.Relocs
   210  		if sym.Code != 'T' && sym.Code != 't' ||
   211  			symStart < d.textStart ||
   212  			symEnd <= start || end <= symStart ||
   213  			filter != nil && !filter.MatchString(sym.Name) {
   214  			continue
   215  		}
   216  		if printed {
   217  			fmt.Fprintf(bw, "\n")
   218  		}
   219  		printed = true
   220  
   221  		file, _, _ := d.pcln.PCToLine(sym.Addr)
   222  		fmt.Fprintf(bw, "TEXT %s(SB) %s\n", sym.Name, file)
   223  
   224  		if symEnd > end {
   225  			symEnd = end
   226  		}
   227  		code := d.text[:end-d.textStart]
   228  
   229  		var lastFile string
   230  		var lastLine int
   231  
   232  		d.Decode(symStart, symEnd, relocs, gnuAsm, func(pc, size uint64, file string, line int, text string) {
   233  			i := pc - d.textStart
   234  
   235  			if printCode {
   236  				if file != lastFile || line != lastLine {
   237  					if srcLine, err := fc.Line(file, line); err == nil {
   238  						fmt.Fprintf(tw, "%s%s%s\n", []byte{tabwriter.Escape}, srcLine, []byte{tabwriter.Escape})
   239  					}
   240  
   241  					lastFile, lastLine = file, line
   242  				}
   243  
   244  				fmt.Fprintf(tw, "  %#x\t", pc)
   245  			} else {
   246  				fmt.Fprintf(tw, "  %s:%d\t%#x\t", base(file), line, pc)
   247  			}
   248  
   249  			if size%4 != 0 || d.goarch == "386" || d.goarch == "amd64" {
   250  				// Print instruction as bytes.
   251  				fmt.Fprintf(tw, "%x", code[i:i+size])
   252  			} else {
   253  				// Print instruction as 32-bit words.
   254  				for j := uint64(0); j < size; j += 4 {
   255  					if j > 0 {
   256  						fmt.Fprintf(tw, " ")
   257  					}
   258  					fmt.Fprintf(tw, "%08x", d.byteOrder.Uint32(code[i+j:]))
   259  				}
   260  			}
   261  			fmt.Fprintf(tw, "\t%s\t\n", text)
   262  		})
   263  		tw.Flush()
   264  	}
   265  	bw.Flush()
   266  }
   267  
   268  // Decode disassembles the text segment range [start, end), calling f for each instruction.
   269  func (d *Disasm) Decode(start, end uint64, relocs []Reloc, gnuAsm bool, f func(pc, size uint64, file string, line int, text string)) {
   270  	if start < d.textStart {
   271  		start = d.textStart
   272  	}
   273  	if end > d.textEnd {
   274  		end = d.textEnd
   275  	}
   276  	code := d.text[:end-d.textStart]
   277  	lookup := d.lookup
   278  	for pc := start; pc < end; {
   279  		i := pc - d.textStart
   280  		text, size := d.disasm(code[i:], pc, lookup, d.byteOrder, gnuAsm)
   281  		file, line, _ := d.pcln.PCToLine(pc)
   282  		sep := "\t"
   283  		for len(relocs) > 0 && relocs[0].Addr < i+uint64(size) {
   284  			text += sep + relocs[0].Stringer.String(pc-start)
   285  			sep = " "
   286  			relocs = relocs[1:]
   287  		}
   288  		f(pc, uint64(size), file, line, text)
   289  		pc += uint64(size)
   290  	}
   291  }
   292  
   293  type lookupFunc = func(addr uint64) (sym string, base uint64)
   294  type disasmFunc func(code []byte, pc uint64, lookup lookupFunc, ord binary.ByteOrder, _ bool) (text string, size int)
   295  
   296  func disasm_386(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
   297  	return disasm_x86(code, pc, lookup, 32, gnuAsm)
   298  }
   299  
   300  func disasm_amd64(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
   301  	return disasm_x86(code, pc, lookup, 64, gnuAsm)
   302  }
   303  
   304  func disasm_x86(code []byte, pc uint64, lookup lookupFunc, arch int, gnuAsm bool) (string, int) {
   305  	inst, err := x86asm.Decode(code, arch)
   306  	var text string
   307  	size := inst.Len
   308  	if err != nil || size == 0 || inst.Op == 0 {
   309  		size = 1
   310  		text = "?"
   311  	} else {
   312  		if gnuAsm {
   313  			text = fmt.Sprintf("%-36s // %s", x86asm.GoSyntax(inst, pc, lookup), x86asm.GNUSyntax(inst, pc, nil))
   314  		} else {
   315  			text = x86asm.GoSyntax(inst, pc, lookup)
   316  		}
   317  	}
   318  	return text, size
   319  }
   320  
   321  type textReader struct {
   322  	code []byte
   323  	pc   uint64
   324  }
   325  
   326  func (r textReader) ReadAt(data []byte, off int64) (n int, err error) {
   327  	if off < 0 || uint64(off) < r.pc {
   328  		return 0, io.EOF
   329  	}
   330  	d := uint64(off) - r.pc
   331  	if d >= uint64(len(r.code)) {
   332  		return 0, io.EOF
   333  	}
   334  	n = copy(data, r.code[d:])
   335  	if n < len(data) {
   336  		err = io.ErrUnexpectedEOF
   337  	}
   338  	return
   339  }
   340  
   341  func disasm_arm(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
   342  	inst, err := armasm.Decode(code, armasm.ModeARM)
   343  	var text string
   344  	size := inst.Len
   345  	if err != nil || size == 0 || inst.Op == 0 {
   346  		size = 4
   347  		text = "?"
   348  	} else if gnuAsm {
   349  		text = fmt.Sprintf("%-36s // %s", armasm.GoSyntax(inst, pc, lookup, textReader{code, pc}), armasm.GNUSyntax(inst))
   350  	} else {
   351  		text = armasm.GoSyntax(inst, pc, lookup, textReader{code, pc})
   352  	}
   353  	return text, size
   354  }
   355  
   356  func disasm_arm64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder, gnuAsm bool) (string, int) {
   357  	inst, err := arm64asm.Decode(code)
   358  	var text string
   359  	if err != nil || inst.Op == 0 {
   360  		text = "?"
   361  	} else if gnuAsm {
   362  		text = fmt.Sprintf("%-36s // %s", arm64asm.GoSyntax(inst, pc, lookup, textReader{code, pc}), arm64asm.GNUSyntax(inst))
   363  	} else {
   364  		text = arm64asm.GoSyntax(inst, pc, lookup, textReader{code, pc})
   365  	}
   366  	return text, 4
   367  }
   368  
   369  func disasm_ppc64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder, gnuAsm bool) (string, int) {
   370  	inst, err := ppc64asm.Decode(code, byteOrder)
   371  	var text string
   372  	size := inst.Len
   373  	if err != nil || size == 0 {
   374  		size = 4
   375  		text = "?"
   376  	} else {
   377  		if gnuAsm {
   378  			text = fmt.Sprintf("%-36s // %s", ppc64asm.GoSyntax(inst, pc, lookup), ppc64asm.GNUSyntax(inst, pc))
   379  		} else {
   380  			text = ppc64asm.GoSyntax(inst, pc, lookup)
   381  		}
   382  	}
   383  	return text, size
   384  }
   385  
   386  var disasms = map[string]disasmFunc{
   387  	"386":     disasm_386,
   388  	"amd64":   disasm_amd64,
   389  	"arm":     disasm_arm,
   390  	"arm64":   disasm_arm64,
   391  	"ppc64":   disasm_ppc64,
   392  	"ppc64le": disasm_ppc64,
   393  }
   394  
   395  var byteOrders = map[string]binary.ByteOrder{
   396  	"386":     binary.LittleEndian,
   397  	"amd64":   binary.LittleEndian,
   398  	"arm":     binary.LittleEndian,
   399  	"arm64":   binary.LittleEndian,
   400  	"ppc64":   binary.BigEndian,
   401  	"ppc64le": binary.LittleEndian,
   402  	"s390x":   binary.BigEndian,
   403  }
   404  
   405  type Liner interface {
   406  	// Given a pc, returns the corresponding file, line, and function data.
   407  	// If unknown, returns "",0,nil.
   408  	PCToLine(uint64) (string, int, *gosym.Func)
   409  }
   410
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