objfile.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 implements portable access to OS-specific executable files.
     6  package objfile
     7  
     8  import (
     9  	"cmd/internal/archive"
    10  	"debug/dwarf"
    11  	"debug/gosym"
    12  	"fmt"
    13  	"io"
    14  	"os"
    15  	"sort"
    16  )
    17  
    18  type rawFile interface {
    19  	symbols() (syms []Sym, err error)
    20  	pcln() (textStart uint64, symtab, pclntab []byte, err error)
    21  	text() (textStart uint64, text []byte, err error)
    22  	goarch() string
    23  	loadAddress() (uint64, error)
    24  	dwarf() (*dwarf.Data, error)
    25  }
    26  
    27  // A File is an opened executable file.
    28  type File struct {
    29  	r       *os.File
    30  	entries []*Entry
    31  }
    32  
    33  type Entry struct {
    34  	name string
    35  	raw  rawFile
    36  }
    37  
    38  // A Sym is a symbol defined in an executable file.
    39  type Sym struct {
    40  	Name   string  // symbol name
    41  	Addr   uint64  // virtual address of symbol
    42  	Size   int64   // size in bytes
    43  	Code   rune    // nm code (T for text, D for data, and so on)
    44  	Type   string  // XXX?
    45  	Relocs []Reloc // in increasing Addr order
    46  }
    47  
    48  type Reloc struct {
    49  	Addr     uint64 // Address of first byte that reloc applies to.
    50  	Size     uint64 // Number of bytes
    51  	Stringer RelocStringer
    52  }
    53  
    54  type RelocStringer interface {
    55  	// insnOffset is the offset of the instruction containing the relocation
    56  	// from the start of the symbol containing the relocation.
    57  	String(insnOffset uint64) string
    58  }
    59  
    60  var openers = []func(io.ReaderAt) (rawFile, error){
    61  	openElf,
    62  	openMacho,
    63  	openPE,
    64  	openPlan9,
    65  	openXcoff,
    66  }
    67  
    68  // Open opens the named file.
    69  // The caller must call f.Close when the file is no longer needed.
    70  func Open(name string) (*File, error) {
    71  	r, err := os.Open(name)
    72  	if err != nil {
    73  		return nil, err
    74  	}
    75  	if f, err := openGoFile(r); err == nil {
    76  		return f, nil
    77  	} else if _, ok := err.(archive.ErrGoObjOtherVersion); ok {
    78  		return nil, fmt.Errorf("open %s: %v", name, err)
    79  	}
    80  	for _, try := range openers {
    81  		if raw, err := try(r); err == nil {
    82  			return &File{r, []*Entry{{raw: raw}}}, nil
    83  		}
    84  	}
    85  	r.Close()
    86  	return nil, fmt.Errorf("open %s: unrecognized object file", name)
    87  }
    88  
    89  func (f *File) Close() error {
    90  	return f.r.Close()
    91  }
    92  
    93  func (f *File) Entries() []*Entry {
    94  	return f.entries
    95  }
    96  
    97  func (f *File) Symbols() ([]Sym, error) {
    98  	return f.entries[0].Symbols()
    99  }
   100  
   101  func (f *File) PCLineTable() (Liner, error) {
   102  	return f.entries[0].PCLineTable()
   103  }
   104  
   105  func (f *File) Text() (uint64, []byte, error) {
   106  	return f.entries[0].Text()
   107  }
   108  
   109  func (f *File) GOARCH() string {
   110  	return f.entries[0].GOARCH()
   111  }
   112  
   113  func (f *File) LoadAddress() (uint64, error) {
   114  	return f.entries[0].LoadAddress()
   115  }
   116  
   117  func (f *File) DWARF() (*dwarf.Data, error) {
   118  	return f.entries[0].DWARF()
   119  }
   120  
   121  func (f *File) Disasm() (*Disasm, error) {
   122  	return f.entries[0].Disasm()
   123  }
   124  
   125  func (e *Entry) Name() string {
   126  	return e.name
   127  }
   128  
   129  func (e *Entry) Symbols() ([]Sym, error) {
   130  	syms, err := e.raw.symbols()
   131  	if err != nil {
   132  		return nil, err
   133  	}
   134  	sort.Sort(byAddr(syms))
   135  	return syms, nil
   136  }
   137  
   138  type byAddr []Sym
   139  
   140  func (x byAddr) Less(i, j int) bool { return x[i].Addr < x[j].Addr }
   141  func (x byAddr) Len() int           { return len(x) }
   142  func (x byAddr) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
   143  
   144  func (e *Entry) PCLineTable() (Liner, error) {
   145  	// If the raw file implements Liner directly, use that.
   146  	// Currently, only Go intermediate objects and archives (goobj) use this path.
   147  	if pcln, ok := e.raw.(Liner); ok {
   148  		return pcln, nil
   149  	}
   150  	// Otherwise, read the pcln tables and build a Liner out of that.
   151  	textStart, symtab, pclntab, err := e.raw.pcln()
   152  	if err != nil {
   153  		return nil, err
   154  	}
   155  	syms, err := e.raw.symbols()
   156  	if err == nil {
   157  		for _, s := range syms {
   158  			if s.Name == "runtime.text" {
   159  				textStart = s.Addr
   160  				break
   161  			}
   162  		}
   163  	}
   164  	return gosym.NewTable(symtab, gosym.NewLineTable(pclntab, textStart))
   165  }
   166  
   167  func (e *Entry) Text() (uint64, []byte, error) {
   168  	return e.raw.text()
   169  }
   170  
   171  func (e *Entry) GOARCH() string {
   172  	return e.raw.goarch()
   173  }
   174  
   175  // LoadAddress returns the expected load address of the file.
   176  // This differs from the actual load address for a position-independent
   177  // executable.
   178  func (e *Entry) LoadAddress() (uint64, error) {
   179  	return e.raw.loadAddress()
   180  }
   181  
   182  // DWARF returns DWARF debug data for the file, if any.
   183  // This is for cmd/pprof to locate cgo functions.
   184  func (e *Entry) DWARF() (*dwarf.Data, error) {
   185  	return e.raw.dwarf()
   186  }
   187
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