# Source code for pex.glibc

    # This file was copied from the pip project master branch on 2016/12/05
    from __future__ import absolute_import

    import ctypes
    import platform
    import re
    import warnings

    def glibc_version_string():
      "Returns glibc version string, or None if not using glibc."

      # ctypes.CDLL(None) internally calls dlopen(NULL), and as the dlopen
      # manpage says, "If filename is NULL, then the returned handle is for the
      # main program". This way we can let the linker do the work to figure out
      # which libc our process is actually using.
      process_namespace = ctypes.CDLL(None)
      try:
        gnu_get_libc_version = process_namespace.gnu_get_libc_version
      except AttributeError:
        # Symbol doesn't exist -> therefore, we are not linked to
        # glibc.
        return None

      # Call gnu_get_libc_version, which returns a string like "2.5"
      gnu_get_libc_version.restype = ctypes.c_char_p
      version_str = gnu_get_libc_version()
      # py2 / py3 compatibility:
      if not isinstance(version_str, str):
        version_str = version_str.decode("ascii")

      return version_str

    # Separated out from have_compatible_glibc for easier unit testing
    def check_glibc_version(version_str, required_major, minimum_minor):
      # Parse string and check against requested version.
      #
      # We use a regexp instead of str.split because we want to discard any
      # random junk that might come after the minor version -- this might happen
      # in patched/forked versions of glibc (e.g. Linaro's version of glibc
      # uses version strings like "2.20-2014.11"). See gh-3588.
      m = re.match(r"(?P<major>[0-9]+)\.(?P<minor>[0-9]+)", version_str)
      if not m:
        warnings.warn("Expected glibc version with 2 components major.minor,"
                      " got: %s" % version_str, RuntimeWarning)
        return False
      return (int(m.group("major")) == required_major and
              int(m.group("minor")) >= minimum_minor)

    def have_compatible_glibc(required_major, minimum_minor):
      version_str = glibc_version_string()
      if version_str is None:
        return False
      return check_glibc_version(version_str, required_major, minimum_minor)

    # platform.libc_ver regularly returns completely nonsensical glibc
    # versions. E.g. on my computer, platform says:
    #
    #   ~$ python2.7 -c 'import platform; print(platform.libc_ver())'
    #   ('glibc', '2.7')
    #   ~$ python3.5 -c 'import platform; print(platform.libc_ver())'
    #   ('glibc', '2.9')
    #
    # But the truth is:
    #
    #   ~$ ldd --version
    #   ldd (Debian GLIBC 2.22-11) 2.22
    #
    # This is unfortunate, because it means that the linehaul data on libc
    # versions that was generated by pip 8.1.2 and earlier is useless and
    # misleading. Solution: instead of using platform, use our code that actually
    # works.
    def libc_ver():
      glibc_version = glibc_version_string()
      if glibc_version is None:
        # For non-glibc platforms, fall back on platform.libc_ver
        return platform.libc_ver()
      else:
        return ("glibc", glibc_version)