{simple,shoddy,smart} minsize-oriented linker
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#!/usr/bin/env python3
import argparse
import glob
import itertools
import os, os.path
import shutil
import subprocess
import sys
import tempfile
from smol.shared import *
from smol.parse import *
from smol.emit import *
from smol.cnl import *
def main():
parser = argparse.ArgumentParser()
parser.add_argument('-m', '--target', default='', \
help='architecture to generate asm code for (default: auto)')
parser.add_argument('-l', '--library', default=[], metavar='LIB', action='append', \
help='libraries to link against')
parser.add_argument('-L', '--libdir', default=[], metavar='DIR', action='append', \
help="directories to search libraries in")
parser.add_argument('-s', '--hash16', default=False, action='store_true', \
help="Use 16-bit (BSD) hashes instead of 32-bit djb2 hashes. "+\
"Implies -fuse-dnload-loader")
parser.add_argument('-n', '--nx', default=False, action='store_true', \
help="Use NX (i.e. don't use RWE pages). Costs the size of one phdr, "+\
"plus some extra bytes on i386.")
parser.add_argument('-d', '--det', default=False, action='store_true', \
help="Make the order of imports deterministic (default: just use " + \
"whatever binutils throws at us)")
parser.add_argument('-fuse-interp', default=False, action='store_true', \
help="Include a program interpreter header (PT_INTERP). If not " +\
"enabled, ld.so has to be invoked manually by the end user.")
parser.add_argument('-falign-stack', default=False, action='store_true', \
help="Align the stack before running user code (_start). If not " + \
"enabled, this has to be done manually. Costs 1 byte.")
parser.add_argument('-fuse-nx', default=False, action='store_true', \
help="Don't use one big RWE segment, but use separate RW and RE ones."+\
" Use this to keep strict kernels (PaX/grsec) happy. Costs at "+\
"least the size of one program header entry.")
parser.add_argument('-fuse-dnload-loader', default=False, action='store_true', \
help="Use a dnload-style loader for resolving symbols, which doesn't "+\
"depend on nonstandard/undocumented ELF and ld.so features, but "+\
"is slightly larger. If not enabled, a smaller custom loader is "+\
"used which assumes glibc.")
parser.add_argument('-fskip-zero-value', default=False, action='store_true', \
help="Skip an ELF symbol with a zero address (a weak symbol) when "+\
"parsing libraries at runtime. Try enabling this if you're "+\
"experiencing sudden breakage. However, many libraries don't use "+\
"weak symbols, so this doesn't often pose a problem. Costs ~5 bytes.")
parser.add_argument('-fuse-dt-debug', default=False, action='store_true', \
help="Use the DT_DEBUG Dyn header to access the link_map, which doesn't"+\
" depend on nonstandard/undocumented ELF and ld.so features. If "+\
"not enabled, the link_map is accessed using data leaked to the "+\
"entrypoint by ld.so, which assumes glibc. Costs ~10 bytes.")
parser.add_argument('-fuse-dl-fini', default=False, action='store_true', \
help="Pass _dl_fini to the user entrypoint, which should be done to "+\
"properly comply with all standards, but is very often not "+\
"needed at all. Costs 2 bytes.")
parser.add_argument('-fskip-entries', default=False, action='store_true', \
help="Skip the first two entries in the link map (resp. ld.so and "+\
"the vDSO). Speeds up symbol resolving, but costs ~5 bytes.")
parser.add_argument('-fno-start-arg', default=False, action='store_true', \
help="Don't pass a pointer to argc/argv/envp to the entrypoint using "+\
"the standard calling convention. This means you need to read "+\
"these yourself in assembly if you want to use them! (envp is "+\
"a preprequisite for X11, because it needs $DISPLAY.) Frees 3 bytes.")
parser.add_argument('-funsafe-dynamic', default=False, action='store_true', \
help="Don't end the ELF Dyn table with a DT_NULL entry. This might "+\
"cause ld.so to interpret the entire binary as the Dyn table, "+\
"so only enable this if you're sure this won't break things!")
parser.add_argument('--nasm', default=os.getenv('NASM') or shutil.which('nasm'), \
help="which nasm binary to use")
parser.add_argument('--cc', default=os.getenv('CC') or shutil.which('cc'), \
help="which cc binary to use (MUST BE GCC!)")
parser.add_argument('--scanelf', default=os.getenv('SCANELF') or shutil.which('scanelf'), \
help="which scanelf binary to use")
parser.add_argument('--readelf', default=os.getenv('READELF') or shutil.which('readelf'), \
help="which readelf binary to use")
parser.add_argument('--cflags', default=[], metavar='CFLAGS', action='append',
help="Flags to pass to the C compiler for the relinking step")
parser.add_argument('--asflags', default=[], metavar='ASFLAGS', action='append',
help="Flags to pass to the assembler when creating the ELF header and runtime startup code")
parser.add_argument('--ldflags', default=[], metavar='LDFLAGS', action='append',
help="Flags to pass to the linker for the final linking step")
parser.add_argument('--smolrt', default=os.getcwd()+"/rt",
help="Directory containing the smol runtime sources")
parser.add_argument('--smolld', default=os.getcwd()+"/ld",
help="Directory containing the smol linker scripts")
parser.add_argument('--verbose', default=False, action='store_true', \
help="Be verbose about what happens and which subcommands are invoked")
parser.add_argument('--keeptmp', default=False, action='store_true', \
help="Keep temp files (only useful for debugging)")
parser.add_argument('input', nargs='+', help="input object file")
parser.add_argument('output', type=str, help="output binary")
args = parser.parse_args()
if args.hash16:
args.fuse_dnload_loader = True
if args.fskip_zero_value: args.asflags.insert(0, "-DSKIP_ZERO_VALUE")
if args.fuse_nx: args.asflags.insert(0, "-DUSE_NX")
if args.fskip_entries: args.asflags.insert(0, "-DSKIP_ENTRIES")
if args.funsafe_dynamic: args.asflags.insert(0, "-DUNSAFE_DYNAMIC")
if args.fno_start_arg: args.asflags.insert(0, "-DNO_START_ARG")
if args.fuse_dl_fini: args.asflags.insert(0, "-DUSE_DL_FINI")
if args.fuse_dt_debug: args.asflags.insert(0, "-DUSE_DT_DEBUG")
if args.fuse_dnload_loader: args.asflags.insert(0, "-DUSE_DNLOAD_LOADER")
if args.fuse_interp: args.asflags.insert(0, "-DUSE_INTERP")
if args.falign_stack: args.asflags.insert(0, "-DALIGN_STACK")
for x in ['nasm','cc','scanelf','readelf']:
val = args.__dict__[x]
if val is None or not os.path.isfile(val):
error("'" + x + "' binary" + (" " if val is None
else " ('" + val + "')") + " not found")
arch = args.target.tolower() if len(args.target) != 0 else decide_arch(args.input)
if arch not in archmagic:
error("Unknown/unsupported architecture '" + str(arch) + "'")
if args.verbose: eprintf("arch: %s" % arch)
objinput = None
objinputistemp = False
tmp_asm_file = tempfile.mkstemp(prefix='smoltab',suffix='.asm',text=True)
tmp_asm_fd = tmp_asm_file[0]
tmp_asm_file = tmp_asm_file[1]
tmp_elf_file = tempfile.mkstemp(prefix='smolout',suffix='.o')
tmp_elf_file = tmp_elf_file[1]
# if >1 input OR input is LTO object:
if len(args.input) > 1 or has_lto_object(args.readelf, args.input):
fd, objinput = tempfile.mkstemp(prefix='smolin',suffix='.o')
cc_relink_objs(args.verbose, args.cc, arch, args.input, objinput, args.cflags)
else: objinput = args.input[0]
# generate smol hashtab
cc_paths = get_cc_paths(args.cc)
syms = get_needed_syms(args.readelf, objinput)
spaths = args.libdir + cc_paths['libraries']
libraries = cc_paths['libraries']
libs = list(find_libs(spaths, args.library))
if args.verbose: eprintf("libs = " + str(libs))
symbols = {}
for symbol, reloc in syms:
library = find_symbol(args.scanelf, libs, args.library, symbol)
if not library:
error("could not find symbol: {}".format(symbol))
symbols.setdefault(library, [])
symbols[library].append((symbol, reloc))
with os.fdopen(tmp_asm_fd, mode='w') as taf:
output(arch, symbols, args.nx, args.hash16, taf, args.det)
if args.verbose:
eprintf("wrote symtab to %s" % tmp_asm_file)
# assemble hash table/ELF header
nasm_assemble_elfhdr(args.verbose, args.nasm, arch, args.smolrt,
tmp_asm_file, tmp_elf_file, args.asflags)
# link with LD into the final executable, w/ special linker script
ld_link_final(args.verbose, args.cc, arch, args.smolld, [objinput, tmp_elf_file],
args.output, args.ldflags)
if not args.keeptmp:
if objinputistemp: os.remove(objinput)
if __name__ == '__main__':
rv = main()
if rv is None: pass
try: sys.exit(int(rv))
except: sys.exit(1)