On Mon, 22 Jan 2018 at 09:29 Victor Stinner <victor.stin...@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 <xdeg...@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: > > _______________________________________________ > > Python-Dev mailing list > > Python-Dev@python.org > > https://mail.python.org/mailman/listinfo/python-dev > > Unsubscribe: > > > https://mail.python.org/mailman/options/python-dev/victor.stinner%40gmail.com > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/brett%40python.org >
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