[Python-Dev] Support of the Android platform

Steve Holden steve at holdenweb.com
Tue Jan 23 12:34:41 EST 2018 

For this to move forward more rapidly it would really help if there were a
utility VM appliance available with a ready-installed support an SDK. Or at
least that would lower impedance to joining the development effort. Does
any such beast by chance exist?

S

Steve Holden

On Tue, Jan 23, 2018 at 5:17 PM, Victor Stinner <victor.stinner at gmail.com>
wrote:

> Ok, I created https://bugs.python.org/issue32637
> "Android: set sys.platform and os.name to android"
>
> Victor
>
> 2018-01-23 18:01 GMT+01:00 Brett Cannon <brett at python.org>:
> >
> >
> > On Mon, 22 Jan 2018 at 09:29 Victor Stinner <victor.stinner at gmail.com>
> > wrote:
> >>
> >> Hi,
> >>
> >> I'm still talking with Paul Peny (pmpp on IRC) who is trying to build
> >> the master branch of Python on Android, using cross-compilation or
> >> directly on an Android device. I started to took notes since Android
> >> is a complex platforms and it's not easy for me to remember
> >> everything.
> >>
> >> http://vstinner.readthedocs.io/python_android.html
> >>
> >> Paul would like to support Android 4.4 Kitkat (API 19) just because
> >> it's possible to find cheap devices running Android, but usually only
> >> with old Android versions. Technically, it doesn't see difficult to
> >> support API 19+ (instead of 21+), a few tiny patches are needed. But I
> >> don't want to have a "full support" of API 19+, only basic support
> >> like "make sure that the compilation doesn't fail", not "all tests
> >> must pass".
> >>
> >> It seems like sys.platform == 'android' would be more appropriate
> >> since Android is not Linux: different libc, different filesystems,
> >> etc.
> >
> >
> > I've had a similar thought myself.
> >
> > -Brett
> >
> >>
> >>
> >> While Xavier promotes cross-compilation, Paul would like to build
> >> Python directly on Android to get pip and wheels.
> >>
> >> Honestly, I have no strong opinion, since I don't know well Android.
> >> I'm trying to help everybody working on the Android support. IMHO it's
> >> fine to support multiple ways to build Python for Android. It's not
> >> like there is very obvious option which has no drawback... Cross
> >> compilation is complex, getting a C compiler on Android also seems to
> >> be complex. From my point of view, compared to a common Fedora Linux,
> >> Android doesn't seem easy to use to develop on CPython...
> >>
> >> Victor
> >>
> >> 2017-12-10 15:19 GMT+01:00 Xavier de Gaye <xdegaye at gmail.com>:
> >> > The following note is a proposal to add the support of the Android
> >> > platform.
> >> >
> >> > The note is easier to read with clickable links at
> >> > https://github.com/xdegaye/cagibi/blob/master/doc/android_support.rst
> >> >
> >> > Motivations
> >> > ===========
> >> >
> >> > * Android is ubiquitous.
> >> > * This would be the first platform supported by Python that is
> >> > cross-compiled,
> >> >   thanks to many contributors.
> >> > * Although the Android operating system is linux, it is different from
> >> > most
> >> >   linux platforms, for example it does not use GNU libc and runs
> SELinux
> >> > in
> >> >   enforcing mode. Therefore supporting this platform would make Python
> >> > more
> >> >   robust and also would allow testing it on arm 64-bit processors.
> >> > * Python running on Android is also a handheld calculator, a successor
> >> > of
> >> > the
> >> >   slide rule and the `HP 41`_.
> >> >
> >> > Current status
> >> > ==============
> >> >
> >> > * The Python test suite succeeds when run on Android emulators using
> >> > buildbot
> >> >   strenuous settings with the following architectures on API 24: x86,
> >> > x86_64,
> >> >   armv7 and arm64.
> >> > * The `Android build system`_ is described in another section.
> >> > * The `buildmaster-config PR 26`_ proposes to update ``master.cfg`` to
> >> > enable
> >> >   buildbots to run a given Android API and architecture on the
> >> > emulators.
> >> > * The Android emulator is actually ``qemu``, so the test suites for
> x86
> >> > and
> >> >   x86_64 last about the same time as the test suite run natively when
> >> > the
> >> >   processor of the build system is of the x86 family. The test suites
> >> > for
> >> > the
> >> >   arm architectures last much longer: about 8 hours for arm64 and 10
> >> > hours
> >> > for
> >> >   armv7 on a four years old laptop.
> >> > * The changes that have been made to achieve this status are listed in
> >> >   `bpo-26865`_, the Android meta-issue.
> >> > * Given the cpu resources required to run the test suite on the arm
> >> > emulators,
> >> >   it may be difficult to find a contributed buildbot worker. So it
> >> > remains
> >> > to
> >> >   find the hardware to run these buildbots.
> >> >
> >> > Proposal
> >> > ========
> >> >
> >> > Support the Android platform on API 24 [1]_ for the x86_64, armv7 and
> >> > arm64
> >> > architectures built with NDK 14b.
> >> >
> >> > *API 24*
> >> >   * API 21 is the first version to provide usable support for wide
> >> > characters
> >> >     and where SELinux is run in enforcing mode.
> >> >
> >> >   * API 22 introduces an annoying bug on the linker that prints
> >> > something
> >> > like
> >> >     this when python is started::
> >> >
> >> >       ``WARNING: linker: libpython3.6m.so.1.0: unused DT entry: type
> >> > 0x6ffffffe arg 0x14554``.
> >> >
> >> >     The `termux`_ Android terminal emulator describes this problem at
> >> > the
> >> > end
> >> >     of its `termux-packages`_ gitlab page and has implemented a
> >> >     ``termux-elf-cleaner`` tool to strip the useless entries from the
> >> > ELF
> >> >     header of executables.
> >> >
> >> >   * API 24 is the first version where the `adb`_ shell is run on the
> >> > emulator
> >> >     as a ``shell`` user instead of the ``root`` user previously, and
> the
> >> > first
> >> >     version that supports arm64.
> >> >
> >> > *x86_64*
> >> >   It seems that no handheld device exists using that architecture. It
> is
> >> >   supported because the x86_64 Android emulator runs fast and
> therefore
> >> > is a
> >> >   good candidate as a buildbot worker.
> >> >
> >> > *NDK 14b*
> >> >   This release of the NDK is the first one to use `Unified headers`_
> >> > fixing
> >> >   numerous problems that had been fixed by updating the Python
> configure
> >> > script
> >> >   until now (those changes have been reverted by now).
> >> >
> >> > Android idiosyncrasies
> >> > ======================
> >> >
> >> > * The default shell is ``/system/bin/sh``.
> >> > * The file system layout is not a traditional unix layout, there is no
> >> >   ``/tmp`` for example. Most directories have user restricted access,
> >> >   ``/sdcard`` is mounted as ``noexec`` for example.
> >> > * The (java) applications are allocated a unix user id and a
> >> > subdirectory on
> >> >   ``/data/data``.
> >> > * SELinux is run in enforcing mode.
> >> > * Shared memory and semaphores are not supported.
> >> > * The default encoding is UTF-8.
> >> >
> >> > Android build system
> >> > ====================
> >> >
> >> > The Android build system is implemented at `bpo-30386`_ with `PR
> 1629`_
> >> > and
> >> > is documented by its `README`_. It provides the following features:
> >> >
> >> > * To build a distribution for a device or an emulator with a given API
> >> > level
> >> >   and a given architecture.
> >> > * To start the emulator and
> >> >     + install the distribution
> >> >     + start a remote interactive shell
> >> >     + or run remotely a python command
> >> >     + or run remotely the buildbottest
> >> > * Run gdb on the python process that is running on the emulator with
> >> > python
> >> >   pretty-printing.
> >> >
> >> > The build system adds the ``Android/`` directory and the
> >> > ``configure-android``
> >> > script to the root of the Python source directory on the master branch
> >> > without
> >> > modifying any other file. The build system can be installed, upgraded
> >> > (i.e.
> >> > the
> >> > SDK and NDK) and run remotely, through ssh for example.
> >> >
> >> > The following external libraries, when they are configured in the
> build
> >> > system,
> >> > are downloaded from the internet and cross-compiled (only once, on the
> >> > first
> >> > run of the build system) before the cross-compilation of the extension
> >> > modules:
> >> >
> >> > * ``ncurses``
> >> > * ``readline``
> >> > * ``sqlite``
> >> > * ``libffi``
> >> > * ``openssl``, the cross-compilation of openssl fails on x86_64 and
> >> > arm64
> >> > and
> >> >   this step is skipped on those architectures.
> >> >
> >> > The following extension modules are disabled by adding them to the
> >> > ``*disabled*`` section of ``Modules/Setup``:
> >> >
> >> > * ``_uuid``, Android has no uuid/uuid.h header.
> >> > * ``grp`` some grp.h functions are not declared.
> >> > * ``_crypt``, Android does not have crypt.h.
> >> > * ``_ctypes`` on x86_64 where all long double tests fail
> (`bpo-32202`_)
> >> > and
> >> > on
> >> >   arm64 (see `bpo-32203`_).
> >> >
> >> > .. [1] On Wikipedia `Android version history`_ lists the
> correspondence
> >> > between
> >> >    API level, commercial name and version for each release. It also
> >> > provides
> >> >    information on the global Android version distribution, see the two
> >> > charts
> >> >    on top.
> >> >
> >> > .. _`README`:
> >> > https://github.com/xdegaye/cpython/blob/bpo-30386/Android/README.rst
> >> > .. _`bpo-26865`: https://bugs.python.org/issue26865
> >> > .. _`bpo-30386`: https://bugs.python.org/issue30386
> >> > .. _`bpo-32202`: https://bugs.python.org/issue32202
> >> > .. _`bpo-32203`: https://bugs.python.org/issue32203
> >> > .. _`PR 1629`: https://github.com/python/cpython/pull/1629
> >> > .. _`buildmaster-config PR 26`:
> >> > https://github.com/python/buildmaster-config/pull/26
> >> > .. _`Android version history`:
> >> > https://en.wikipedia.org/wiki/Android_version_history
> >> > .. _`termux`: https://termux.com/
> >> > .. _`termux-packages`: https://gitlab.com/jbwhips883/termux-packages
> >> > .. _`adb`: https://developer.android.com/studio/command-line/adb.html
> >> > .. _`Unified headers`:
> >> >
> >> > https://android.googlesource.com/platform/ndk.git/+/ndk-
> r14-release/docs/UnifiedHeaders.md
> >> > .. _`HP 41`: https://en.wikipedia.org/wiki/HP-41C
> >> > .. vim:filetype=rst:tw=78:ts=8:sts=2:sw=2:et:
> >> > _______________________________________________
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> victor.stinner%40gmail.com
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