{simple,shoddy,smart} minsize-oriented linker
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# stolen from the contrib folder in https://github.com/blackle/LZMA-Vizualizer
# (i.e. I'm stealing it from myself)
# custom elf parser because a standard one wouldn't be trustable because the
# ELFs we're parsing will be a bit wonky anyway
from struct import unpack
from typing import *
ELFCLASS32 = 1
ELFCLASS64 = 2
EM_386 = 3
EM_X86_64 = 62
PT_NULL = 0
PT_LOAD = 1
PT_DYNAMIC = 2
PT_INTERP = 3
DT_NULL = 0
DT_NEEDED = 1
DT_STRTAB = 5
DT_SYMTAB = 6
class Phdr(NamedTuple):
ptype: int
off : int
vaddr: int
paddr: int
filesz: int
memsz: int
flags: int
align: int
class Dyn(NamedTuple):
tag: int
val: int
class ELF(NamedTuple):
data : bytes
ident : bytes
eclass: int
mach : int
entry : int
phdrs : Sequence[Phdr]
dyn : Sequence[Dyn]
is32bit: bool
# yeah, there's some code duplication here
# idgaf
def parse_phdr32(data: bytes, phoff:int, phentsz:int, phnum:int) -> Sequence[Phdr]:
ps = []
for off in range(phoff, phoff+phentsz*phnum, phentsz):
ptype, off, vaddr, paddr, filesz, memsz, flags, align = \
unpack('<IIIIIIII', data[off:off+8*4])
p = Phdr(ptype, off, vaddr, paddr, filesz, memsz, flags, align)
ps.append(p)
return ps
def parse_dyn32(data: bytes, dynp: Phdr) -> Dyn:
ds = []
off = dynp.off
while True:
tag, val = unpack('<II', data[off:off+2*4])
ds.append(Dyn(tag, val))
if tag == DT_NULL: break
off = off + 2*4
return ds
def parse_32(data: bytes) -> ELF:
ident = data[:16]
eclass = data[4]
mach = unpack('<H', data[18:18+2])[0]
entry = unpack('<I', data[24:24+4])[0]
phoff = unpack('<I', data[28:28+4])[0]
phentsz = unpack('<H', data[42:42+2])[0]
phnum = unpack('<H', data[44:44+2])[0]
phdrs = parse_phdr32(data, phoff, phentsz, phnum)
dyn = None
for p in phdrs:
if p.ptype == PT_DYNAMIC:
dyn = parse_dyn32(data, p)
break
return ELF(data, ident, eclass, mach, entry, phdrs, dyn, True)
def parse_phdr64(data: bytes, phoff:int, phentsz:int, phnum:int) -> Sequence[Phdr]:
ps = []
for off in range(phoff, phoff+phentsz*phnum, phentsz):
# TODO
ptype, flags, off, vaddr, paddr, filesz, memsz, align = \
unpack('<IIQQQQQQ', data[off:off+2*4+6*8])
p = Phdr(ptype, off, vaddr, paddr, filesz, memsz, flags, align)
ps.append(p)
return ps
def parse_dyn64(data: bytes, dynp: Phdr) -> Dyn:
ds = []
off = dynp.off
while True:
tag, val = unpack('<QQ', data[off:off+2*8])
ds.append(Dyn(tag, val))
if tag == DT_NULL: break
off = off + 2*8
return ds
def parse_64(data: bytes) -> ELF:
ident = data[:16]
eclass = data[4]
mach = unpack('<H', data[18:18+2])[0]
entry = unpack('<Q', data[24:24+8])[0]
phoff = unpack('<Q', data[32:32+8])[0]
phentsz = unpack('<H', data[54:54+2])[0]
phnum = unpack('<H', data[56:56+2])[0]
phdrs = parse_phdr64(data, phoff, phentsz, phnum)
dyn = None
for p in phdrs:
if p.ptype == PT_DYNAMIC:
dyn = parse_dyn64(data, p)
break
return ELF(data, ident, eclass, mach, entry, phdrs, dyn, False)
def parse(data: bytes) -> ELF:
assert data[:4] == b'\x7FELF', "Not a valid ELF file" # good enough
ecls = data[4]
if ecls == ELFCLASS32: return parse_32(data)
elif ecls == ELFCLASS64: return parse_64(data)
else:
emch = unpack('<H', data[18:18+2])[0]
if emch == EM_386: return parse_32(data)
elif emch == EM_X86_64: return parse_64(data)
assert False, "bad E_CLASS %d" % ecls