gecko-dev/python/mozbuild/mozpack/executables.py

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

from __future__ import absolute_import

import os
import struct
import subprocess
from mozpack.errors import errors

MACHO_SIGNATURES = [
    0xfeedface,  # mach-o 32-bits big endian
    0xcefaedfe,  # mach-o 32-bits little endian
    0xfeedfacf,  # mach-o 64-bits big endian
    0xcffaedfe,  # mach-o 64-bits little endian
]

FAT_SIGNATURE = 0xcafebabe  # mach-o FAT binary

ELF_SIGNATURE = 0x7f454c46  # Elf binary

UNKNOWN = 0
MACHO = 1
ELF = 2

def get_type(path):
    '''
    Check the signature of the give file and returns what kind of executable
    matches.
    '''
    with open(path, 'rb') as f:
        signature = f.read(4)
        if len(signature) < 4:
            return UNKNOWN
        signature = struct.unpack('>L', signature)[0]
        if signature == ELF_SIGNATURE:
            return ELF
        if signature in MACHO_SIGNATURES:
            return MACHO
        if signature != FAT_SIGNATURE:
            return UNKNOWN
        # We have to sanity check the second four bytes, because Java class
        # files use the same magic number as Mach-O fat binaries.
        # This logic is adapted from file(1), which says that Mach-O uses
        # these bytes to count the number of architectures within, while
        # Java uses it for a version number. Conveniently, there are only
        # 18 labelled Mach-O architectures, and Java's first released
        # class format used the version 43.0.
        num = f.read(4)
        if len(num) < 4:
            return UNKNOWN
        num = struct.unpack('>L', num)[0]
        if num < 20:
            return MACHO
        return UNKNOWN


def is_executable(path):
    '''
    Return whether a given file path points to an executable or a library,
    where an executable or library is identified by:
        - the file extension on OS/2 and WINNT
        - the file signature on OS/X and ELF systems (GNU/Linux, Android, BSD,
          Solaris)

    As this function is intended for use to choose between the ExecutableFile
    and File classes in FileFinder, and choosing ExecutableFile only matters
    on OS/2, OS/X, ELF and WINNT (in GCC build) systems, we don't bother
    detecting other kind of executables.
    '''
    from buildconfig import substs
    if not os.path.exists(path):
        return False

    if substs['OS_ARCH'] == 'WINNT':
        return path.lower().endswith((substs['DLL_SUFFIX'],
                                      substs['BIN_SUFFIX']))

    return get_type(path) != UNKNOWN


def may_strip(path):
    '''
    Return whether strip() should be called
    '''
    from buildconfig import substs
    return not substs['PKG_SKIP_STRIP']


def strip(path):
    '''
    Execute the STRIP command with STRIP_FLAGS on the given path.
    '''
    from buildconfig import substs
    strip = substs['STRIP']
    flags = substs['STRIP_FLAGS'].split() if 'STRIP_FLAGS' in substs else []
    cmd = [strip] + flags + [path]
    if subprocess.call(cmd) != 0:
        errors.fatal('Error executing ' + ' '.join(cmd))


def may_elfhack(path):
    '''
    Return whether elfhack() should be called
    '''
    # elfhack only supports libraries. We should check the ELF header for
    # the right flag, but checking the file extension works too.
    from buildconfig import substs
    return ('USE_ELF_HACK' in substs and substs['USE_ELF_HACK'] and
        path.endswith(substs['DLL_SUFFIX']) and
        'COMPILE_ENVIRONMENT' in substs and substs['COMPILE_ENVIRONMENT'])


def elfhack(path):
    '''
    Execute the elfhack command on the given path.
    '''
    from buildconfig import topobjdir
    cmd = [os.path.join(topobjdir, 'build/unix/elfhack/elfhack'), path]
    if 'ELF_HACK_FLAGS' in os.environ:
        cmd[1:0] = os.environ['ELF_HACK_FLAGS'].split()
    if subprocess.call(cmd) != 0:
        errors.fatal('Error executing ' + ' '.join(cmd))


def xz_compress(path):
    '''
    Execute xz to compress the given path.
    '''
    if open(path, 'rb').read(5)[1:] == '7zXZ':
        print('%s is already compressed' % path)
        return
    
    from buildconfig import substs
    xz = substs.get('XZ')
    cmd = [xz, '-zkf', path]

    # For now, the mozglue XZStream ELF loader can only support xz files
    # with a single stream that contains a single block. In xz, there is no
    # explicit option to set the max block count. Instead, we force xz to use
    # single thread mode, which results in a single block.
    cmd.extend(['--threads=1'])

    bcj = None
    if substs.get('MOZ_THUMB2'):
        bcj = '--armthumb'
    elif substs.get('CPU_ARCH') == 'arm':
        bcj = '--arm'
    elif substs.get('CPU_ARCH') == 'x86':
        bcj = '--x86'

    if bcj:
        cmd.extend([bcj])

    # We need to explicitly specify the LZMA filter chain to ensure consistent builds
    # across platforms. Note that the dict size must be less then 16MiB per the hardcoded
    # value in mozglue/linker/XZStream.cpp. This is the default LZMA filter chain for for
    # xz-utils version 5.0. See:
    # https://github.com/xz-mirror/xz/blob/v5.0.0/src/liblzma/lzma/lzma_encoder_presets.c
    # https://github.com/xz-mirror/xz/blob/v5.0.0/src/liblzma/api/lzma/container.h#L31
    cmd.extend(['--lzma2=dict=8MiB,lc=3,lp=0,pb=2,mode=normal,nice=64,mf=bt4,depth=0'])
    print('xz-compressing %s with %s' % (path, ' '.join(cmd)))

    if subprocess.call(cmd) != 0:
        errors.fatal('Error executing ' + ' '.join(cmd))
        return

    os.rename(path + '.xz', path)