[移动开发]【安卓实践】apex导致的安卓编译失败原因调查

背景

在实现功能的时候，我把我的功能逻辑实现在libmeminfo.so库当中。
由于我的功能需要调用libmemtrack.so库中的一些函数，我就在libmeminfo的Androidbp中将libmemtrack.so动态连接过来了。如下：

cc_library {
    name: "libmeminfo",
    defaults: ["libmeminfo_defaults"],
    export_include_dirs: ["include"],
    export_shared_lib_headers: ["libbase"],
    srcs: [
        "pageacct.cpp",
        "procmeminfo.cpp",
        "sysmeminfo.cpp",
    ],
    //ADD START: {
    shared_libs: [
        "libmemtrack",
    ],
    //END}
}

这样增加之后无论是在 其他so库中调用我提供的方法，还是单独编译libmeminfo都可以编译通过，并且功能验证不会有问题。
但是当我带patch编译整个rom包的时候，却报了以下错误：

[ 99% 111787/112588] //art/build/apex:art-check-debug-apex-gen generate art-check-debug-apex-gen.dummy
FAILED: out/soong/.intermediates/art/build/apex/art-check-debug-apex-gen/gen/art-check-debug-apex-gen.dummy
rm -rf out/soong/.intermediates/art/build/apex/art-check-debug-apex-gen/gen && out/soong/host/linux-x86/bin/sbox --sandbox-path out/soong/.temp --output-root out/soong/.intermediates/art/build/apex/art-check-debug-apex-gen/gen -c 'out/soong/host/linux-x86/bin/art-apex-tester --debugfs out/soong/host/linux-x86/bin/debugfs --tmpdir __SBOX_OUT_DIR__ --debug out/soong/.intermediates/art/build/apex/com.android.runtime.debug/android_common_com.android.runtime.debug/com.android.runtime.debug.apex && touch __SBOX_OUT_FILES__'  __SBOX_OUT_DIR__/art-check-debug-apex-gen.dummy
--bitness=auto, trying to autodetect. This may be incorrect!
  Detected multilib
Unexpected file 'lib64/libcutils.so'
Unexpected file 'lib64/libutils.so'
Unexpected file 'lib64/libhwbinder.so'
Unexpected file 'lib64/libhidlbase.so'
Unexpected file 'lib64/libbinderthreadstate.so'
Unexpected file 'lib64/libhidltransport.so'
Unexpected file 'lib64/libprocessgroup.so'
Unexpected file 'lib64/libhardware.so'
Unexpected file 'lib64/libmemtrack.so'
Unexpected file 'lib64/android.hardware.memtrack@1.0.so'
No superfluous libraries checker FAILED

拿到这个错误的时候，由于这个错误最多是“Unexpected file ‘lib64/libmemtrack.so’”这一行与我的修改有关系，
所以我一度觉得不是我的问题。后来调查了两个小时我才发现编译错误的原因。

原因

确实我的修改不会导致问题，但是在安卓编译的过程中编译com.android.runtime.debug时，编译脚本会检查/apex/com.android.runtime.debug/目录下多个目录lib/lib64/bin/以及lib/bionic等路径下是否包含非法的so库。
如果包含非法的so库，就会在编译脚本中报错，导致rom包的编译失败。

art/build/apex/art_apex_test.py
  def check_no_superfluous_files(self, dir_path):
    paths = []
    for name in sorted(self._provider.read_dir(dir_path).keys()):
      if name not in ('.', '..'):
        paths.append(os.path.join(dir_path, name))
    expected_paths = set()
    dir_prefix = dir_path + '/'
    for path_glob in self._expected_file_globs:
      expected_paths |= set(fnmatch.filter(paths, path_glob))
      # If there are globs in subdirectories of dir_path we want to match their
      # path segments at this directory level.
      if path_glob.startswith(dir_prefix):
        subpath = path_glob[len(dir_prefix):]
        subpath_first_segment, _, _ = subpath.partition('/')
        expected_paths |= set(fnmatch.filter(paths, dir_prefix + subpath_first_segment))
    for unexpected_path in set(paths) - expected_paths:
      self.fail('Unexpected file \'%s\'', unexpected_path)

修改编译脚本，执行“make art-check-debug-apex-gen -j16”打印expected_paths如下：

expected_paths '{'lib64/libziparchive.so', 'lib64/libz.so', 'lib64/libmeminfo.so', 'lib64/libprofile.so', 'lib64/libnpt.so', 'lib64/libart-compiler.so', 'lib64/libvixl.so', 'lib64/libc_malloc_debug.so', 'lib64/libopenjdkjvmd.so', 'lib64/libprofiled.so', 'lib64/libcrypto.so', 'lib64/libjavacore.so', 'lib64/libartd.so', 'lib64/libartbase.so', 'lib64/libartd-dexlayout.so', 'lib64/libprocinfo.so', 'lib64/libart-dexlayout.so', 'lib64/libc_malloc_hooks.so', 'lib64/libnativeloader.so', 'lib64/bionic', 'lib64/libc++.so', 'lib64/libexpat.so', 'lib64/libbase.so', 'lib64/liblzma.so', 'lib64/libunwindstack.so', 'lib64/libpac.so', 'lib64/libdt_fd_forward.so', 'lib64/libopenjdkd.so', 'lib64/libopenjdkjvmtid.so', 'lib64/libnativehelper.so', 'lib64/libicui18n.so', 'lib64/libadbconnection.so', 'lib64/libsigchain.so', 'lib64/libdexfile_support.so', 'lib64/libopenjdkjvmti.so', 'lib64/libopenjdkjvm.so', 'lib64/libartpalette.so', 'lib64/libvixld.so', 'lib64/libdexfile.so', 'lib64/libdexfile_external.so', 'lib64/libdt_socket.so', 'lib64/libopenjdk.so', 'lib64/libartd-disassembler.so', 'lib64/libandroidicu.so', 'lib64/libjdwp.so', 'lib64/libbacktrace.so', 'lib64/libart-disassembler.so', 'lib64/libartd-compiler.so', 'lib64/libnativebridge.so', 'lib64/libicuuc.so', 'lib64/libadbconnectiond.so', 'lib64/libdexfiled.so', 'lib64/libartbased.so', 'lib64/libart.so', 'lib64/libandroidio.so'}'

可以看到libmeminfo.so包含在这些库当中。
这意味着，如果我在libmeminfo.so中想要动态连接其他非expected_paths中的so库，如libmemtrack，就会在编译的时候把libmemtrack放在apex/com.anroid.runtime.debug/lib64/路径下。
而编译脚本会检查此路径下的库是否都是expected_paths中所包含的库，如果不是，就会报错。
而这次报错中之所以会有其他库如libhwbinder.so，原因是libmemtrack动态连接了这些库。
至此，问题原因调查完毕。
那只能换一种方式实现我的功能了，至少不能放在libmeminfo.so中去实现。