elf-multilib-id.py: reference implementation for generating a multilib identifier

elf-multilib-id.py (text/x-python), 4.58 KB, created by Zac Medico on 2015-01-03 08:45:44 UTC

#!/usr/bin/env python
#
# Compute a multilib ABI identifier, as discussed here:
#
# 	https://bugs.gentoo.org/show_bug.cgi?id=534206
#
# Supported identifiers:
#
#	alpha_{32,64}
#	arm_{32,64}
#	hppa_{32,64}
#	ia_{32,64}
#	m68k_{32,64}
#	mips_{eabi32,eabi64,n32,n64,o32,o64}
#	ppc_{32,64}
#	s390_{32,64}
#	sh_{32,64}
#	sparc_{32,64}
#	x86_{32,64,x64}
#
# NOTES:
#
# * The ABIs referenced by some of the above *_32 and *_64 identifiers
#   may be imaginary, but they are listed anyway, since the goal is to
#   establish a naming convention that is as consistent and uniform as
#   possible.
#
# * The Elf header's e_ident[EI_OSABI] byte is completely ignored,
#   since OS-independence is one of the goals. The assumption is that,
#   for given installation, we are only interested in tracking multilib
#   ABIs for a single OS.

from __future__ import print_function

import collections
import os
import sys

USAGE = "%s <filename>\n"

EI_CLASS           = 4
ELFCLASS32         = 1
ELFCLASS64         = 2

EI_DATA = 5
ELFDATA2LSB = 1
ELFDATA2MSB = 2

E_MACHINE          = 18
EM_SPARC           = 2
EM_386             = 3
EM_68K             = 4
EM_MIPS            = 8
EM_PARISC          = 15
EM_SPARC32PLUS     = 18
EM_PPC             = 20
EM_PPC64           = 21
EM_S390            = 22
EM_ARM             = 40
EM_ALPHA           = 41
EM_SH              = 42
EM_SPARCV9         = 43
EM_IA_64           = 50
EM_X86_64          = 62
EM_AARCH64         = 183

E_ENTRY            = 24
EF_MIPS_ABI        = 0x0000F000
EF_MIPS_ABI2       = 0x00000020
E_MIPS_ABI_O32     = 0x00001000
E_MIPS_ABI_O64     = 0x00002000
E_MIPS_ABI_EABI32  = 0x00003000
E_MIPS_ABI_EABI64  = 0x00004000

machine_prefix_map = {
	EM_386:           "x86",
	EM_68K:           "m68k",
	EM_AARCH64:       "arm",
	EM_ALPHA:         "alpha",
	EM_ARM:           "arm",
	EM_IA_64:         "ia",
	EM_MIPS:          "mips",
	EM_PARISC:        "hppa",
	EM_PPC:           "ppc",
	EM_PPC64:         "ppc",
	EM_S390:          "s390",
	EM_SH:            "sh",
	EM_SPARC:         "sparc",
	EM_SPARC32PLUS:   "sparc",
	EM_SPARCV9:       "sparc",
	EM_X86_64:        "x86",
}

_elf_header = collections.namedtuple('_elf_header',
	('ei_class', 'ei_data', 'e_machine', 'e_flags'))

def compute_suffix_mips(elf_header):

	name = None
	mips_abi = elf_header.e_flags & EF_MIPS_ABI

	if mips_abi:
		if mips_abi == E_MIPS_ABI_O32:
			name = "o32"
		elif mips_abi == E_MIPS_ABI_O64:
			name = "o64"
		elif mips_abi == E_MIPS_ABI_EABI32:
			name = "eabi32"
		elif mips_abi == E_MIPS_ABI_EABI64:
			name = "eabi64"

	elif elf_header.e_flags & EF_MIPS_ABI2:
		name = "n32"
	elif elf_header.ei_class == ELFCLASS64:
		name = "n64"

	return name

def compute_multilib_id(elf_header):

	prefix = machine_prefix_map.get(elf_header.e_machine)
	suffix = None

	if prefix == "mips":
		suffix = compute_suffix_mips(elf_header)
	elif elf_header.ei_class == ELFCLASS64:
		suffix = "64"
	elif elf_header.ei_class == ELFCLASS32:
		if elf_header.e_machine == EM_X86_64:
			suffix = "x32"
		else:
			suffix = "32"

	if prefix is None or suffix is None:
		multilib_id = None
	else:
		multilib_id = "%s_%s" % (prefix, suffix)

	return multilib_id

def uint16_be(data):
	return (ord(data[0:1]) << 8) + ord(data[1:2])

def uint16_le(data):
	return ord(data[0:1]) + (ord(data[1:2]) << 8)

def uint32_be(data):
	return (
		(ord(data[0:1]) << 24) +
		(ord(data[1:2]) << 16) +
		(ord(data[2:3]) << 8) +
		ord(data[3:4])
	)

def uint32_le(data):
	return (
		ord(data[0:1]) +
		(ord(data[1:2]) << 8) +
		(ord(data[2:3]) << 16) +
		(ord(data[3:4]) << 24)
	)

def read_elf_header(f):

	f.seek(EI_CLASS)
	ei_class = ord(f.read(1))
	ei_data = ord(f.read(1))

	if ei_class == ELFCLASS32:
		width = 32
	elif ei_class == ELFCLASS64:
		width = 64
	else:
		width = None

	if ei_data == ELFDATA2LSB:
		uint16 = uint16_le
		uint32 = uint32_le
	elif ei_data == ELFDATA2MSB:
		uint16 = uint16_be
		uint32 = uint32_be
	else:
		uint16 = None
		uint32 = None

	if width is None or uint16 is None:
		e_machine = None
		e_flags = None
	else:
		f.seek(E_MACHINE)
		e_machine = uint16(f.read(2))

		# E_ENTRY + 3 * sizeof(uintN)
		e_flags_offset = E_ENTRY + 3 * width // 8
		f.seek(e_flags_offset)
		e_flags = uint32(f.read(4))

	return _elf_header(ei_class, ei_data, e_machine, e_flags)

def main(argv):

	if len(argv) != 2 or not os.path.isfile(argv[1]):
		sys.stderr.write(USAGE % argv[0])
		return 1

	with open(argv[1], 'rb') as f:
		elf_header = read_elf_header(f)

	if elf_header.e_machine is None:
		multilib_id = None
	else:
		multilib_id = compute_multilib_id(elf_header)

	print(multilib_id)
	return multilib_id is None and 1 or os.EX_OK

if __name__ == "__main__":
	sys.exit(main(sys.argv))