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package hemfix
/*
goupx: Fix compiled go binaries so that they can be packed by
the universal packer for executables (upx)
Copyright (c) 2012 Peter Waller <[email protected]>
All rights reserved.
Based on code found at http://sourceforge.net/tracker/?func=detail&atid=102331&aid=3408066&group_id=2331
Based on hemfix.c Copyright (C) 2012 John Reiser, BitWagon Software LLC
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
import (
ELF "debug/elf"
"encoding/binary"
"errors"
"io"
"log"
"os"
)
// The functions gethdr and writephdr are heavily influenced by code found at
// http://golang.org/src/pkg/debug/elf/file.go
// Returns the Prog header offset and size
func gethdr(f *ELF.File, sr io.ReadSeeker) (int64, int, error) {
sr.Seek(0, os.SEEK_SET)
switch f.Class {
case ELF.ELFCLASS32:
hdr := new(ELF.Header32)
if err := binary.Read(sr, f.ByteOrder, hdr); err != nil {
return 0, 0, err
}
return int64(hdr.Phoff), int(hdr.Phentsize), nil
case ELF.ELFCLASS64:
hdr := new(ELF.Header64)
if err := binary.Read(sr, f.ByteOrder, hdr); err != nil {
return 0, 0, err
}
return int64(hdr.Phoff), int(hdr.Phentsize), nil
}
return 0, 0, errors.New("Unexpected ELF class")
}
// Write out a Prog header to an elf with a given destination
// Writes out `p` to `sw` at `dst` using information from `f`
func writephdr(f *ELF.File, dst int64, sw io.WriteSeeker, p *ELF.Prog) error {
sw.Seek(dst, os.SEEK_SET)
switch f.Class {
case ELF.ELFCLASS32:
hdr := ELF.Prog32{
Type: uint32(p.Type),
Flags: uint32(p.Flags),
Off: uint32(p.Off),
Vaddr: uint32(p.Vaddr),
Paddr: uint32(p.Paddr),
Filesz: uint32(p.Filesz),
Memsz: uint32(p.Memsz),
Align: uint32(p.Align),
}
if err := binary.Write(sw, f.ByteOrder, hdr); err != nil {
return err
}
case ELF.ELFCLASS64:
hdr := ELF.Prog64{
Type: uint32(p.Type),
Flags: uint32(p.Flags),
Off: p.Off,
Vaddr: p.Vaddr,
Paddr: p.Paddr,
Filesz: p.Filesz,
Memsz: p.Memsz,
Align: p.Align,
}
if err := binary.Write(sw, f.ByteOrder, hdr); err != nil {
return err
}
}
return nil
}
func fixelf(elf *ELF.File, fd io.ReadWriteSeeker) error {
// Determine where to write header (need
off, sz, err := gethdr(elf, fd)
if err != nil {
return err
}
for i := range elf.Progs {
p := elf.Progs[i]
if p.ProgHeader.Type != ELF.PT_LOAD {
// Only consider PT_LOAD sections
continue
}
if p.Flags&ELF.PF_X != ELF.PF_X {
continue
}
mask := -p.Align
if ^mask&p.Vaddr != 0 && (^mask&(p.Vaddr-p.Off)) == 0 {
log.Printf("Hemming PT_LOAD section")
hem := ^mask & p.Off
p.Off -= hem
p.Vaddr -= hem
if p.Paddr != 0 {
p.Paddr -= hem
}
p.Filesz += hem
p.Memsz += hem
dst := off + int64(sz*i)
writephdr(elf, dst, fd, p)
break
}
}
return nil
}
func FixFile(filename string) error {
fd, err := os.OpenFile(filename, os.O_RDWR, 0)
if err != nil {
return err
}
defer fd.Close()
elf, err := ELF.NewFile(fd)
if err != nil {
log.Print("Failed to parse ELF. This can happen if the binary is already packed.")
return err
}
defer elf.Close()
log.Printf("%+v", elf.FileHeader)
err = fixelf(elf, fd)
if err != nil {
log.Fatal("Failure to read ELF header")
return err
}
return nil
}
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