elf.go

Documentation: cmd/internal/objfile

     1  // Copyright 2013 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  // Parsing of ELF executables (Linux, FreeBSD, and so on).
     6  
     7  package objfile
     8  
     9  import (
    10  	"debug/dwarf"
    11  	"debug/elf"
    12  	"encoding/binary"
    13  	"fmt"
    14  	"io"
    15  )
    16  
    17  type elfFile struct {
    18  	elf *elf.File
    19  }
    20  
    21  func openElf(r io.ReaderAt) (rawFile, error) {
    22  	f, err := elf.NewFile(r)
    23  	if err != nil {
    24  		return nil, err
    25  	}
    26  	return &elfFile{f}, nil
    27  }
    28  
    29  func (f *elfFile) symbols() ([]Sym, error) {
    30  	elfSyms, err := f.elf.Symbols()
    31  	if err != nil {
    32  		return nil, err
    33  	}
    34  
    35  	var syms []Sym
    36  	for _, s := range elfSyms {
    37  		sym := Sym{Addr: s.Value, Name: s.Name, Size: int64(s.Size), Code: '?'}
    38  		switch s.Section {
    39  		case elf.SHN_UNDEF:
    40  			sym.Code = 'U'
    41  		case elf.SHN_COMMON:
    42  			sym.Code = 'B'
    43  		default:
    44  			i := int(s.Section)
    45  			if i < 0 || i >= len(f.elf.Sections) {
    46  				break
    47  			}
    48  			sect := f.elf.Sections[i]
    49  			switch sect.Flags & (elf.SHF_WRITE | elf.SHF_ALLOC | elf.SHF_EXECINSTR) {
    50  			case elf.SHF_ALLOC | elf.SHF_EXECINSTR:
    51  				sym.Code = 'T'
    52  			case elf.SHF_ALLOC:
    53  				sym.Code = 'R'
    54  			case elf.SHF_ALLOC | elf.SHF_WRITE:
    55  				sym.Code = 'D'
    56  			}
    57  		}
    58  		if elf.ST_BIND(s.Info) == elf.STB_LOCAL {
    59  			sym.Code += 'a' - 'A'
    60  		}
    61  		syms = append(syms, sym)
    62  	}
    63  
    64  	return syms, nil
    65  }
    66  
    67  func (f *elfFile) pcln() (textStart uint64, symtab, pclntab []byte, err error) {
    68  	if sect := f.elf.Section(".text"); sect != nil {
    69  		textStart = sect.Addr
    70  	}
    71  	if sect := f.elf.Section(".gosymtab"); sect != nil {
    72  		if symtab, err = sect.Data(); err != nil {
    73  			return 0, nil, nil, err
    74  		}
    75  	}
    76  	if sect := f.elf.Section(".gopclntab"); sect != nil {
    77  		if pclntab, err = sect.Data(); err != nil {
    78  			return 0, nil, nil, err
    79  		}
    80  	}
    81  	return textStart, symtab, pclntab, nil
    82  }
    83  
    84  func (f *elfFile) text() (textStart uint64, text []byte, err error) {
    85  	sect := f.elf.Section(".text")
    86  	if sect == nil {
    87  		return 0, nil, fmt.Errorf("text section not found")
    88  	}
    89  	textStart = sect.Addr
    90  	text, err = sect.Data()
    91  	return
    92  }
    93  
    94  func (f *elfFile) goarch() string {
    95  	switch f.elf.Machine {
    96  	case elf.EM_386:
    97  		return "386"
    98  	case elf.EM_X86_64:
    99  		return "amd64"
   100  	case elf.EM_ARM:
   101  		return "arm"
   102  	case elf.EM_AARCH64:
   103  		return "arm64"
   104  	case elf.EM_PPC64:
   105  		if f.elf.ByteOrder == binary.LittleEndian {
   106  			return "ppc64le"
   107  		}
   108  		return "ppc64"
   109  	case elf.EM_S390:
   110  		return "s390x"
   111  	}
   112  	return ""
   113  }
   114  
   115  func (f *elfFile) loadAddress() (uint64, error) {
   116  	for _, p := range f.elf.Progs {
   117  		if p.Type == elf.PT_LOAD && p.Flags&elf.PF_X != 0 {
   118  			return p.Vaddr, nil
   119  		}
   120  	}
   121  	return 0, fmt.Errorf("unknown load address")
   122  }
   123  
   124  func (f *elfFile) dwarf() (*dwarf.Data, error) {
   125  	return f.elf.DWARF()
   126  }
   127
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