nixpkgs/pkgs/build-support/setup-hooks/auto-patchelf.py

#!/usr/bin/env python3

from collections import defaultdict
from contextlib import contextmanager
from dataclasses import dataclass
from elftools.common.exceptions import ELFError # type: ignore
from elftools.elf.dynamic import DynamicSection # type: ignore
from elftools.elf.elffile import ELFFile # type: ignore
from elftools.elf.enums import ENUM_E_TYPE, ENUM_EI_OSABI # type: ignore
from itertools import chain
from pathlib import Path, PurePath

from typing import Tuple, Optional, Iterator, List, DefaultDict, Set

import argparse
import os
import pprint
import subprocess
import sys



@contextmanager
def open_elf(path: Path) -> Iterator[ELFFile]:
    with path.open('rb') as stream:
        yield ELFFile(stream)


def is_static_executable(elf: ELFFile) -> bool:
    # Statically linked executables have an ELF type of EXEC but no INTERP.
    return (elf.header["e_type"] == 'ET_EXEC'
            and not elf.get_section_by_name(".interp"))


def is_dynamic_executable(elf: ELFFile) -> bool:
    # We do not require an ELF type of EXEC. This also catches
    # position-independent executables, as they typically have an INTERP
    # section but their ELF type is DYN.
    return bool(elf.get_section_by_name(".interp"))


def get_dependencies(elf: ELFFile) -> List[str]:
    dependencies = []
    # This convoluted code is here on purpose. For some reason, using
    # elf.get_section_by_name(".dynamic") does not always return an
    # instance of DynamicSection, but that is required to call iter_tags
    for section in elf.iter_sections():
        if isinstance(section, DynamicSection):
            for tag in section.iter_tags('DT_NEEDED'):
                dependencies.append(tag.needed)
            break # There is only one dynamic section

    return dependencies


def get_rpath(elf: ELFFile) -> List[str]:
    # This convoluted code is here on purpose. For some reason, using
    # elf.get_section_by_name(".dynamic") does not always return an
    # instance of DynamicSection, but that is required to call iter_tags
    for section in elf.iter_sections():
        if isinstance(section, DynamicSection):
            for tag in section.iter_tags('DT_RUNPATH'):
                return tag.runpath.split(':')

            for tag in section.iter_tags('DT_RPATH'):
                return tag.rpath.split(':')

            break # There is only one dynamic section

    return []


def get_arch(elf: ELFFile) -> str:
    return elf.get_machine_arch()


def get_osabi(elf: ELFFile) -> str:
    return elf.header["e_ident"]["EI_OSABI"]


def osabi_are_compatible(wanted: str, got: str) -> bool:
    """
    Tests whether two OS ABIs are compatible, taking into account the
    generally accepted compatibility of SVR4 ABI with other ABIs.
    """
    if not wanted or not got:
        # One of the types couldn't be detected, so as a fallback we'll
        # assume they're compatible.
        return True

    # Generally speaking, the base ABI (0x00), which is represented by
    # readelf(1) as "UNIX - System V", indicates broad compatibility
    # with other ABIs.
    #
    # TODO: This isn't always true. For example, some OSes embed ABI
    # compatibility into SHT_NOTE sections like .note.tag and
    # .note.ABI-tag.  It would be prudent to add these to the detection
    # logic to produce better ABI information.
    if wanted == 'ELFOSABI_SYSV':
        return True

    # Similarly here, we should be able to link against a superset of
    # features, so even if the target has another ABI, this should be
    # fine.
    if got == 'ELFOSABI_SYSV':
        return True

    # Otherwise, we simply return whether the ABIs are identical.
    return wanted == got


def glob(path: Path, pattern: str, recursive: bool) -> Iterator[Path]:
    return path.rglob(pattern) if recursive else path.glob(pattern)


cached_paths: Set[Path] = set()
soname_cache: DefaultDict[Tuple[str, str], List[Tuple[Path, str]]] = defaultdict(list)


def populate_cache(initial: List[Path], recursive: bool =False) -> None:
    lib_dirs = list(initial)

    while lib_dirs:
        lib_dir = lib_dirs.pop(0)

        if lib_dir in cached_paths:
            continue

        cached_paths.add(lib_dir)

        for path in glob(lib_dir, "*.so*", recursive):
            if not path.is_file():
                continue

            resolved = path.resolve()
            try:
                with open_elf(path) as elf:
                    osabi = get_osabi(elf)
                    arch = get_arch(elf)
                    rpath = [Path(p) for p in get_rpath(elf)
                                     if p and '$ORIGIN' not in p]
                    lib_dirs += rpath
                    soname_cache[(path.name, arch)].append((resolved.parent, osabi))

            except ELFError:
                # Not an ELF file in the right format
                pass


def find_dependency(soname: str, soarch: str, soabi: str) -> Optional[Path]:
    for lib, libabi in soname_cache[(soname, soarch)]:
        if osabi_are_compatible(soabi, libabi):
            return lib
    return None


@dataclass
class Dependency:
    file: Path              # The file that contains the dependency
    name: Path              # The name of the dependency
    found: bool = False     # Whether it was found somewhere


def auto_patchelf_file(path: Path, runtime_deps: list[Path]) -> list[Dependency]:
    try:
        with open_elf(path) as elf:

            if is_static_executable(elf):
                # No point patching these
                print(f"skipping {path} because it is statically linked")
                return []

            if elf.num_segments() == 0:
                # no segment (e.g. object file)
                print(f"skipping {path} because it contains no segment")
                return []

            file_arch = get_arch(elf)
            if interpreter_arch != file_arch:
                # Our target architecture is different than this file's
                # architecture, so skip it.
                print(f"skipping {path} because its architecture ({file_arch})"
                      f" differs from target ({interpreter_arch})")
                return []

            file_osabi = get_osabi(elf)
            if not osabi_are_compatible(interpreter_osabi, file_osabi):
                print(f"skipping {path} because its OS ABI ({file_osabi}) is"
                      f" not compatible with target ({interpreter_osabi})")
                return []

            file_is_dynamic_executable = is_dynamic_executable(elf)

            file_dependencies = map(Path, get_dependencies(elf))

    except ELFError:
        return []

    rpath = []
    if file_is_dynamic_executable:
        print("setting interpreter of", path)
        subprocess.run(
                ["patchelf", "--set-interpreter", interpreter_path.as_posix(), path.as_posix()],
                check=True)
        rpath += runtime_deps

    print("searching for dependencies of", path)
    dependencies = []
    # Be sure to get the output of all missing dependencies instead of
    # failing at the first one, because it's more useful when working
    # on a new package where you don't yet know the dependencies.
    for dep in file_dependencies:
        if dep.is_absolute() and dep.is_file():
            # This is an absolute path. If it exists, just use it.
            # Otherwise, we probably want this to produce an error when
            # checked (because just updating the rpath won't satisfy
            # it).
            continue
        elif (libc_lib / dep).is_file():
            # This library exists in libc, and will be correctly
            # resolved by the linker.
            continue

        if found_dependency := find_dependency(dep.name, file_arch, file_osabi):
            rpath.append(found_dependency)
            dependencies.append(Dependency(path, dep, True))
            print(f"    {dep} -> found: {found_dependency}")
        else:
            dependencies.append(Dependency(path, dep, False))
            print(f"    {dep} -> not found!")

    # Dedup the rpath
    rpath_str = ":".join(dict.fromkeys(map(Path.as_posix, rpath)))

    if rpath:
        print("setting RPATH to:", rpath_str)
        subprocess.run(
                ["patchelf", "--set-rpath", rpath_str, path.as_posix()],
                check=True)

    return dependencies


def auto_patchelf(
        paths_to_patch: List[Path],
        lib_dirs: List[Path],
        runtime_deps: List[Path],
        recursive: bool =True,
        ignore_missing: bool =False) -> None:

    if not paths_to_patch:
        sys.exit("No paths to patch, stopping.")

    # Add all shared objects of the current output path to the cache,
    # before lib_dirs, so that they are chosen first in find_dependency.
    populate_cache(paths_to_patch, recursive)
    populate_cache(lib_dirs)

    dependencies = []
    for path in chain.from_iterable(glob(p, '*', recursive) for p in paths_to_patch):
        if not path.is_symlink() and path.is_file():
            dependencies += auto_patchelf_file(path, runtime_deps)

    missing = [dep for dep in dependencies if not dep.found]

    # Print a summary of the missing dependencies at the end
    for dep in missing:
        print(f"auto-patchelf could not satisfy dependency {dep.name} wanted by {dep.file}")

    if missing and not ignore_missing:
        sys.exit('auto-patchelf failed to find all the required dependencies.\n'
                 'Add the missing dependencies to --libs or use --ignore-missing.')


def main() -> None:
    parser = argparse.ArgumentParser(
        prog="auto-patchelf",
        description='auto-patchelf tries as hard as possible to patch the'
                    ' provided binary files by looking for compatible'
                    'libraries in the provided paths.')
    parser.add_argument(
        "--ignore-missing",
        action="store_true",
        help="Do not fail when some dependencies are not found.")
    parser.add_argument(
        "--no-recurse",
        dest="recursive",
        action="store_false",
        help="Patch only the provided paths, and ignore their children")
    parser.add_argument(
        "--paths", nargs="*", type=Path,
        help="Paths whose content needs to be patched.")
    parser.add_argument(
        "--libs", nargs="*", type=Path,
        help="Paths where libraries are searched for.")
    parser.add_argument(
        "--runtime-dependencies", nargs="*", type=Path,
        help="Paths to prepend to the runtime path of executable binaries.")

    print("automatically fixing dependencies for ELF files")
    args = parser.parse_args()
    pprint.pprint(vars(args))

    auto_patchelf(
        args.paths,
        args.libs,
        args.runtime_dependencies,
        args.recursive,
        args.ignore_missing)


interpreter_path: Path  = None # type: ignore
interpreter_osabi: str  = None # type: ignore
interpreter_arch: str   = None # type: ignore
libc_lib: Path          = None # type: ignore

if __name__ == "__main__":
    nix_support = Path(os.environ['NIX_BINTOOLS']) / 'nix-support'
    interpreter_path = Path((nix_support / 'dynamic-linker').read_text().strip())
    libc_lib = Path((nix_support / 'orig-libc').read_text().strip()) / 'lib'

    with open_elf(interpreter_path) as interpreter:
        interpreter_osabi = get_osabi(interpreter)
        interpreter_arch = get_arch(interpreter)

    if interpreter_arch and interpreter_osabi and interpreter_path and libc_lib:
        main()
    else:
        sys.exit("Failed to parse dynamic linker (ld) properties.")