// readELFGoBuildID the Go build ID string from an ELF binary.
// The Go build ID is stored in a note described by an ELF PT_NOTE prog header.
// The caller has already opened filename, to get f, and read the first 4 kB out, in data.
func readELFGoBuildID(filename string, f *os.File, data []byte) (buildid string, err error) {
// Assume the note content is in the first 4 kB, already read.
// Rewrite the ELF header to set shnum to 0, so that we can pass
// the data to elf.NewFile and it will decode the Prog list but not
// try to read the section headers and the string table from disk.
// That's a waste of I/O when all we care about is the Prog list
// and the one ELF note.
switch elf.Class(data[elf.EI_CLASS]) {
case elf.ELFCLASS32:
data[48] = 0
data[49] = 0
case elf.ELFCLASS64:
data[60] = 0
data[61] = 0
}
const elfGoBuildIDTag = 4
ef, err := elf.NewFile(bytes.NewReader(data))
if err != nil {
return "", &os.PathError{Path: filename, Op: "parse", Err: err}
}
for _, p := range ef.Progs {
if p.Type != elf.PT_NOTE || p.Off >= uint64(len(data)) || p.Off+p.Filesz >= uint64(len(data)) || p.Filesz < 16 {
continue
}
note := data[p.Off : p.Off+p.Filesz]
nameSize := ef.ByteOrder.Uint32(note)
valSize := ef.ByteOrder.Uint32(note[4:])
tag := ef.ByteOrder.Uint32(note[8:])
name := note[12:16]
if nameSize != 4 || 16+valSize > uint32(len(note)) || tag != elfGoBuildIDTag || !bytes.Equal(name, elfGoNote) {
continue
}
return string(note[16 : 16+valSize]), nil
}
// No note. Treat as successful but build ID empty.
return "", nil
}
func ReadElfHeader(buf []byte) ElfFileHeader {
class := elf.Class(buf[4])
data := elf.Data(buf[5])
ei_ver := elf.Version(buf[6])
osabi := elf.OSABI(buf[7])
abi_ver := uint8(buf[8])
byte_order := ToByteOrder(data)
// Initialize part of the struct for now (the non-byte-order dependent bits)
header := ElfFileHeader{
Class: class,
Data: data,
EI_Version: ei_ver,
OSABI: osabi,
ABIVersion: abi_ver}
byte_reader := bytes.NewReader(buf[16:])
err1 := binary.Read(byte_reader, byte_order, &header.Type)
err2 := binary.Read(byte_reader, byte_order, &header.Machine)
err3 := binary.Read(byte_reader, byte_order, &header.E_Version)
if err1 != nil || err2 != nil || err3 != nil {
panic("Failed to read ELF machine")
}
header.Entry, header.Phoff, header.Shoff = ReadElfHeaderWithClass(
byte_reader, class, byte_order)
err1 = binary.Read(byte_reader, byte_order, &header.Flags)
err2 = binary.Read(byte_reader, byte_order, &header.FileHeaderSize)
err3 = binary.Read(byte_reader, byte_order, &header.Phentsize)
if err1 != nil || err2 != nil || err3 != nil {
panic("Failed to read ELF machine")
}
err1 = binary.Read(byte_reader, byte_order, &header.Phnum)
err2 = binary.Read(byte_reader, byte_order, &header.Shentsize)
err3 = binary.Read(byte_reader, byte_order, &header.Shnum)
err4 := binary.Read(byte_reader, byte_order, &header.Shstrndx)
if err1 != nil || err2 != nil || err3 != nil || err4 != nil {
panic("Failed to read ELF machine")
}
return header
}
// The Go build ID is stored in a note described by an ELF PT_NOTE prog
// header. The caller has already opened filename, to get f, and read
// at least 4 kB out, in data.
func readELFGoBuildID(filename string, f *os.File, data []byte) (buildid string, err error) {
// Assume the note content is in the data, already read.
// Rewrite the ELF header to set shnum to 0, so that we can pass
// the data to elf.NewFile and it will decode the Prog list but not
// try to read the section headers and the string table from disk.
// That's a waste of I/O when all we care about is the Prog list
// and the one ELF note.
switch elf.Class(data[elf.EI_CLASS]) {
case elf.ELFCLASS32:
data[48] = 0
data[49] = 0
case elf.ELFCLASS64:
data[60] = 0
data[61] = 0
}
const elfGoBuildIDTag = 4
ef, err := elf.NewFile(bytes.NewReader(data))
if err != nil {
return "", &os.PathError{Path: filename, Op: "parse", Err: err}
}
for _, p := range ef.Progs {
if p.Type != elf.PT_NOTE || p.Filesz < 16 {
continue
}
var note []byte
if p.Off+p.Filesz < uint64(len(data)) {
note = data[p.Off : p.Off+p.Filesz]
} else {
// For some linkers, such as the Solaris linker,
// the buildid may not be found in data (which
// likely contains the first 16kB of the file)
// or even the first few megabytes of the file
// due to differences in note segment placement;
// in that case, extract the note data manually.
_, err = f.Seek(int64(p.Off), 0)
if err != nil {
return "", err
}
note = make([]byte, p.Filesz)
_, err = io.ReadFull(f, note)
if err != nil {
return "", err
}
}
nameSize := ef.ByteOrder.Uint32(note)
valSize := ef.ByteOrder.Uint32(note[4:])
tag := ef.ByteOrder.Uint32(note[8:])
name := note[12:16]
if nameSize != 4 || 16+valSize > uint32(len(note)) || tag != elfGoBuildIDTag || !bytes.Equal(name, elfGoNote) {
continue
}
return string(note[16 : 16+valSize]), nil
}
// No note. Treat as successful but build ID empty.
return "", nil
}