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elf.go
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elf.go
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package loader
import (
"bytes"
"debug/dwarf"
"debug/elf"
"encoding/binary"
"github.com/pkg/errors"
"io"
"io/ioutil"
"strings"
"github.com/lunixbochs/usercorn/go/models"
)
var machineMap = map[elf.Machine]string{
elf.EM_386: "x86",
elf.EM_AARCH64: "arm64",
elf.EM_ARM: "arm",
elf.EM_MIPS: "mips",
elf.EM_PPC64: "ppc64",
elf.EM_PPC: "ppc",
elf.EM_SPARC: "sparc",
elf.EM_X86_64: "x86_64",
}
type ElfLoader struct {
LoaderBase
file *elf.File
phoff, shoff uint64
phentsize, phnum int
shentsize, shnum int
shstrndx int
phdr []byte
}
var elfMagic = []byte{0x7f, 0x45, 0x4c, 0x46}
func MatchElf(r io.ReaderAt) bool {
return bytes.Equal(getMagic(r), elfMagic)
}
func NewElfLoader(r io.ReaderAt, arch string) (models.Loader, error) {
file, err := elf.NewFile(r)
if err != nil {
return nil, err
}
machineName, ok := machineMap[file.Machine]
if !ok {
return nil, errors.Errorf("Unsupported machine: %s", file.Machine)
}
l := &ElfLoader{
LoaderBase: LoaderBase{
arch: machineName,
os: "linux",
entry: file.Entry,
byteOrder: file.ByteOrder,
},
file: file,
}
sr := io.NewSectionReader(r, 0, 1<<63-1)
switch file.Class {
case elf.ELFCLASS32:
l.bits = 32
var hdr elf.Header32
if err := binary.Read(sr, file.ByteOrder, &hdr); err != nil {
return nil, errors.Wrap(err, "failed to read file header")
}
l.phoff, l.phentsize, l.phnum = uint64(hdr.Phoff), int(hdr.Phentsize), int(hdr.Phnum)
l.shoff, l.shentsize, l.shnum = uint64(hdr.Shoff), int(hdr.Shentsize), int(hdr.Shnum)
l.shstrndx = int(hdr.Shstrndx)
case elf.ELFCLASS64:
l.bits = 64
var hdr elf.Header64
if err := binary.Read(sr, file.ByteOrder, &hdr); err != nil {
return nil, errors.Wrap(err, "failed to read file header")
}
l.phoff, l.phentsize, l.phnum = uint64(hdr.Phoff), int(hdr.Phentsize), int(hdr.Phnum)
l.shoff, l.shentsize, l.shnum = uint64(hdr.Shoff), int(hdr.Shentsize), int(hdr.Shnum)
default:
return nil, errors.New("Unknown ELF class.")
}
l.phdr = make([]byte, l.phentsize*l.phnum)
r.ReadAt(l.phdr, int64(l.phoff))
return l, nil
}
func (e *ElfLoader) Interp() string {
for _, prog := range e.file.Progs {
if prog.Type == elf.PT_INTERP {
data, _ := ioutil.ReadAll(prog.Open())
return strings.TrimRight(string(data), "\x00")
}
}
return ""
}
func (e *ElfLoader) Header() (uint64, []byte, int) {
return e.phoff, e.phdr, e.phnum
}
func (e *ElfLoader) Type() int {
switch e.file.Type {
case elf.ET_EXEC:
return EXEC
case elf.ET_DYN:
return DYN
default:
return UNKNOWN
}
}
func (e *ElfLoader) DataSegment() (start, end uint64) {
sec := e.file.Section(".data")
if sec != nil {
return sec.Addr, sec.Addr + sec.Size
}
return 0, 0
}
func (e *ElfLoader) Segments() ([]models.SegmentData, error) {
ret := make([]models.SegmentData, 0, len(e.file.Progs))
for _, prog := range e.file.Progs {
if prog.Type != elf.PT_LOAD {
continue
}
filesz := prog.Filesz
stream := prog.Open()
prot := 0
if prog.Flags&elf.PF_R != 0 {
prot |= 1
}
if prog.Flags&elf.PF_W != 0 {
prot |= 2
}
if prog.Flags&elf.PF_X != 0 {
prot |= 4
}
ret = append(ret, models.SegmentData{
Off: prog.Off,
Addr: prog.Vaddr,
Size: prog.Memsz,
Prot: prot,
DataFunc: func() ([]byte, error) {
data := make([]byte, filesz)
_, err := stream.Read(data)
// swallow EOF so we can still load broken binaries
if err == io.EOF {
err = nil
}
return data, err
},
})
}
return ret, nil
}
func (e *ElfLoader) getSymbols() ([]models.Symbol, error) {
syms, err := e.file.Symbols()
if err != nil {
return []models.Symbol{}, err
}
symbols := make([]models.Symbol, 0, len(syms))
for _, s := range syms {
symbols = append(symbols, models.Symbol{
Name: s.Name,
Start: s.Value,
End: s.Value + s.Size,
Dynamic: false,
})
}
// don't care about missing dyn symtab
dyn, _ := e.file.DynamicSymbols()
for _, s := range dyn {
symbols = append(symbols, models.Symbol{
Name: s.Name,
Start: s.Value,
End: s.Value + s.Size,
Dynamic: true,
})
}
return symbols, nil
}
func (e *ElfLoader) Symbols() ([]models.Symbol, error) {
var err error
if e.symCache == nil {
e.symCache, err = e.getSymbols()
}
return e.symCache, err
}
func (e *ElfLoader) DWARF() (*dwarf.Data, error) {
return e.file.DWARF()
}