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// Copyright 2013 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.
// Parsing of ELF executables (Linux, FreeBSD, and so on).
package objfile
import (
"debug/dwarf"
"debug/elf"
"encoding/binary"
"fmt"
"io"
)
type elfFile struct {
elf *elf.File
}
func openElf(r io.ReaderAt) (rawFile, error) {
f, err := elf.NewFile(r)
if err != nil {
return nil, err
}
return &elfFile{f}, nil
}
func (f *elfFile) symbols() ([]Sym, error) {
elfSyms, err := f.elf.Symbols()
if err != nil {
return nil, err
}
var syms []Sym
for _, s := range elfSyms {
sym := Sym{Addr: s.Value, Name: s.Name, Size: int64(s.Size), Code: '?'}
switch s.Section {
case elf.SHN_UNDEF:
sym.Code = 'U'
case elf.SHN_COMMON:
sym.Code = 'B'
default:
i := int(s.Section)
if i < 0 || i >= len(f.elf.Sections) {
break
}
sect := f.elf.Sections[i]
switch sect.Flags & (elf.SHF_WRITE | elf.SHF_ALLOC | elf.SHF_EXECINSTR) {
case elf.SHF_ALLOC | elf.SHF_EXECINSTR:
sym.Code = 'T'
case elf.SHF_ALLOC:
sym.Code = 'R'
case elf.SHF_ALLOC | elf.SHF_WRITE:
sym.Code = 'D'
}
}
if elf.ST_BIND(s.Info) == elf.STB_LOCAL {
sym.Code += 'a' - 'A'
}
syms = append(syms, sym)
}
return syms, nil
}
func (f *elfFile) pcln() (textStart uint64, symtab, pclntab []byte, err error) {
if sect := f.elf.Section(".text"); sect != nil {
textStart = sect.Addr
}
sect := f.elf.Section(".gosymtab")
if sect == nil {
// try .data.rel.ro.gosymtab, for PIE binaries
sect = f.elf.Section(".data.rel.ro.gosymtab")
}
if sect != nil {
if symtab, err = sect.Data(); err != nil {
return 0, nil, nil, err
}
} else {
// if both sections failed, try the symbol
symtab = f.symbolData("runtime.symtab", "runtime.esymtab")
}
sect = f.elf.Section(".gopclntab")
if sect == nil {
// try .data.rel.ro.gopclntab, for PIE binaries
sect = f.elf.Section(".data.rel.ro.gopclntab")
}
if sect != nil {
if pclntab, err = sect.Data(); err != nil {
return 0, nil, nil, err
}
} else {
// if both sections failed, try the symbol
pclntab = f.symbolData("runtime.pclntab", "runtime.epclntab")
}
return textStart, symtab, pclntab, nil
}
func (f *elfFile) text() (textStart uint64, text []byte, err error) {
sect := f.elf.Section(".text")
if sect == nil {
return 0, nil, fmt.Errorf("text section not found")
}
textStart = sect.Addr
text, err = sect.Data()
return
}
func (f *elfFile) goarch() string {
switch f.elf.Machine {
case elf.EM_386:
return "386"
case elf.EM_X86_64:
return "amd64"
case elf.EM_ARM:
return "arm"
case elf.EM_AARCH64:
return "arm64"
case elf.EM_PPC64:
if f.elf.ByteOrder == binary.LittleEndian {
return "ppc64le"
}
return "ppc64"
case elf.EM_S390:
return "s390x"
}
return ""
}
func (f *elfFile) loadAddress() (uint64, error) {
for _, p := range f.elf.Progs {
if p.Type == elf.PT_LOAD && p.Flags&elf.PF_X != 0 {
return p.Vaddr, nil
}
}
return 0, fmt.Errorf("unknown load address")
}
func (f *elfFile) dwarf() (*dwarf.Data, error) {
return f.elf.DWARF()
}
func (f *elfFile) symbolData(start, end string) []byte {
elfSyms, err := f.elf.Symbols()
if err != nil {
return nil
}
var addr, eaddr uint64
for _, s := range elfSyms {
if s.Name == start {
addr = s.Value
} else if s.Name == end {
eaddr = s.Value
}
if addr != 0 && eaddr != 0 {
break
}
}
if addr == 0 || eaddr < addr {
return nil
}
size := eaddr - addr
data := make([]byte, size)
for _, prog := range f.elf.Progs {
if prog.Vaddr <= addr && addr+size-1 <= prog.Vaddr+prog.Filesz-1 {
if _, err := prog.ReadAt(data, int64(addr-prog.Vaddr)); err != nil {
return nil
}
return data
}
}
return nil
}
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