linux下將Python3解釋器交叉編譯移植到android平臺

已知資料：

• http://www.srplab.com/cn/files/others/compile/cross_compiling_python_for_android.html Cross Compiling Python for Android

• https://m.2cto.com/kf/201511/448789.html 在arm上使用python-2.7.10

上述資料主要是在移植python2.7版本，具體移植python3的版本資料並很少。

 

起初打算移植python3.5.6版本，可是發現python3.5.6的移植性彷佛很差，在解決完python主程序和libpython3.5.so的編譯後，全部擴展均由於各類找不到c函數或者找不到python的對象或函數名之類的問題沒法編譯。後決定編譯python3.7.1版本。記錄以下。

編譯記錄：

• 源碼從python.org下載。

• 首先編譯Linux版本的Python3.7.1並安裝。我選擇安裝到~/opt目錄下，以加入環境變量的形式替代系統使用的python3.5。命令以下：

  ~/projects tar xvf ~/Download/Python-3.7.1.tar.xz -C .

  ~/projects cd Python-3.7.1

  ~/projects/Python-3.7.1 mkdir build.pc

  ~/projects/Python-3.7.1 cd build.pc

  ~/projects/Python-3.7.1/build.pc ../configure --prefix=/home/xys/opt/Python-3.7.1

  ~/projects/Python-3.7.1/build.pc make

  ~/projects/Python-3.7.1/build.pc make install

• 將python加入環境變量。因爲我同時使用bash和zsh，因而作了兩個動做：

首先創建公共的rc腳本~/rc.public，加入

#!/bin/sh                                                                                                                                      
# python
export PATH=/home/xys/opt/Python-3.7.1/bin:$PATH

 

而後在~/.zshrc中加入

 

# include ~/rc.public
if [ -f ~/rc.public ]; then
    . ~/rc.public
fi 

 

bashrc相似，我還沒加。

以後能夠在終端輸入python自動補全中發現python3.7程序。

• 編譯安卓版本。以32位爲例，

#!/bin/bash

# 使用android-ndk-r10e，其目錄設置環境變量ANDROID_NDK。

# 我將當前目錄定爲環境變量

 

WORKSPACE=`pwd`
if [[ -z "$ANDROID_NDK" ]]; then
   ANDROID_NDK=/opt/local/android-ndk-r10e

fi

 

ANDROID_SYSROOT=$ANDROID_NDK/platforms/android-21/arch-arm
ANDROID64_SYSROOT=$ANDROID_NDK/platforms/android-21/arch-arm64

cd $WORKSPACE
echo "building with $CMAKE_SYSTEM, processor=$CMAKE_SYSTEM_PROCESSOR, pwd=$WORKSPACE"

# generate Makefile
if [[ "$CMAKE_SYSTEM_PROCESSOR" =~ "x86" ]]; then
    # x86 or x86_64

    mkdir -p build.pc
    cd build.pc
    ../configure --enable-shared --enable-ipv6 --prefix=$WORKSPACE/out/x86

elif [[ "$CMAKE_SYSTEM_PROCESSOR" =~ "armv7" ]]; then

   # 64位時這裏要修改成$ANDROID_NDK/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/bin

   export PATH=$ANDROID_NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin:$ANDROID_NDK:$ANDROID_NDK/tools:/usr/local/bin:/usr/bin:/bin:$PATH

   # 64位時這裏要修改成"aarch64-linux-android-"

   CROSS_COMPILER_PREFIX="arm-linux-androideabi-"

   # 64位時要改爲aarch64

   export ARCH="armeabi"

   # android 4.4及以後版本有要求可執行程序爲PIE程序

   export CC="${CROSS_COMPILER_PREFIX}gcc --sysroot=$ANDROID_SYSROOT -pie -fPIE"
    export CXX="${CROSS_COMPILER_PREFIX}g++ --sysroot=$ANDROID_SYSROOT -pie -fPIE"
    export CPP="${CROSS_COMPILER_PREFIX}gcc -E --sysroot=$ANDROID_SYSROOT -pie -fPIE"
    export AS="${CROSS_COMPILER_PREFIX}as"
    export LD="${CROSS_COMPILER_PREFIX}ld --sysroot=$ANDROID_SYSROOT -pie -fPIE"
    export GDB="${CROSS_COMPILER_PREFIX}gdb"
    export STRIP="${CROSS_COMPILER_PREFIX}strip"
    export RANLIB="${CROSS_COMPILER_PREFIX}ranlib"
    export OBJCOPY="${CROSS_COMPILER_PREFIX}objcopy"
    export OBJDUMP="${CROSS_COMPILER_PREFIX}objdump"
    export AR="${CROSS_COMPILER_PREFIX}ar"
    export NM="${CROSS_COMPILER_PREFIX}nm"
    export READELF="${CROSS_COMPILER_PREFIX}readelf"
    export M4=m4
    export TARGET_PREFIX=$CROSS_COMPILER_PREFIX
    export CONFIG_SITE="config.site"

    # In python 3.7.1, we must define "__ANDROID_API__", we set the value=21
    export CFLAGS="-D__ANDROID_API__=21"
    export CXXFLAGS="-D__ANDROID_API__=21"
    export CPPFLAGS="-D__ANDROID_API__=21"
    # export STRIP="${CROSS_COMPILER_PREFIX}strip --strip-unneeded"
    
    mkdir -p build/android
    cd build/android

    echo -e "ac_cv_file__dev_ptmx=yes\nac_cv_file__dev_ptc=no" > config.site

 

   # 64位時--host要改爲aarch64-linux，prefix和上面的builddir隨便

   ../../configure LDFLAGS="-Wl,--allow-shlib-undefined" --host=arm-linux --build=x86_64-linux-gnu --enable-shared --prefix=$WORKSPACE/out/android --enable-ipv6

• 編譯過程當中幾乎只有一處c代碼報錯：

../Modules/posixmodule.c:6903:9: error: implicit declaration of function 'wait3' [-Werror=implicit-function-declaration]
        pid = wait3(&status, options, &ru);
        ^
進入代碼，補充wait3的定義。（由於ndk提供的接口中沒有公開wait3函數調用，可是安卓的bionic libc中有包含這個調用）

#if defined(HAVE_SYS_RESOURCE_H)

#include /resource.h>

#endif

+#ifdef __ANDROID_API__

+

+# ifndef wait3

+ extern pid_t wait3(WAIT_TYPE *status, int option, struct rusage *usage);

+# endif

+#endif+

• 繼續編譯python，編譯完成時會給出已經編譯的模塊（extension）和未編譯的模塊。

INFO: Could not locate ffi libs and/or headers

Python build finished successfully!
The necessary bits to build these optional modules were not found:
_bz2                 _curses              _curses_panel     
_dbm                 _gdbm                _hashlib          
_lzma                _sqlite3             _ssl              
_tkinter             _uuid                nis               
readline             spwd                                    
To find the necessary bits, look in setup.py in detect_modules() for the module's name.


The following modules found by detect_modules() in setup.py, have been
built by the Makefile instead, as configured by the Setup files:
_abc                 atexit               pwd               
time                                                          


Failed to build these modules:
_crypt               _ctypes                                 


Could not build the ssl module!
Python requires an OpenSSL 1.0.2 or 1.1 compatible libssl with X509_VERIFY_PARAM_set1_host().
LibreSSL 2.6.4 and earlier do not provide the necessary APIs, https://github.com/libressl-portable/portable/issues/381

• make install，將生成的bin目錄合併至安卓設備的/system/bin下，將lib目錄合併至設備的/system/lib下。執行效果：

130|(略):/ # pyth python3 python3.7 python3.7m python3-config python3.7-config python3.7m-config 130|(略):/ # python3 Python 3.7.1 (default, Nov 6 2018, 20:11:05) [GCC 4.9 20140827 (prerelease)] on linux Type "help", "copyright", "credits" or "license" for more information. >>> import base64 >>> base64.b64encode(b'abcd') b'YWJjZA==' >>> base64.b64decode(b'YWJjZA==') b'abcd' >>> (略):/ #

注意：

根據編譯python3.5.6的經驗：

 

Ubuntu 16.04安裝的版本爲python3.5.2，相比於3.5.6版本，其主程序在weakref.py/_weakref.c中少了_remove_dead_weakref()函數等。所以python在交叉編譯，使用系統自帶python3.5執行下列命令的過程當中，會出現找不到函數的異常：

 

$ _PYTHON_PROJECT_BASE=/home/xys/projects/Python-3.5.6/build.android _PYTHON_HOST_PLATFORM=linux-arm PYTHONPATH=../Lib:../Lib/plat-linux python3.5 -S -m sysconfig --generate-posix-vars
Could not import runpy module
Traceback (most recent call last):
  File "../Lib/runpy.py", line 14, in
    import importlib.machinery # importlib first so we can test #15386 via -m
  File "../Lib/importlib/__init__.py", line 57, in
    import types
  File "../Lib/types.py", line 166, in
    import functools as _functools
  File "../Lib/functools.py", line 23, in
    from weakref import WeakKeyDictionary
  File "../Lib/weakref.py", line 12, in
    from _weakref import (
ImportError: cannot import name '_remove_dead_weakref'

 

所以，交叉編譯Python的時候最好保證電腦上的Python版本和要編譯的Python版本一致，即先編譯安裝Linux版本，再編譯arm版本。

已查閱得知的其餘方案

• Android 平臺的Python——JNI方案（二） - 血色@殘陽的專欄 - CSDN博客

這種方案採用crystax ndk (1)（ BSD 2-clause license協議），編譯時在安卓app項目中嵌入libpython3.5m.so，從而實現Android Java ↔ JNI ↔ Python的相互調用。

• Android 平臺的Python——CLE方案實現（三） - 血色@殘陽的專欄 - CSDN博客

這種方案採用 CLE（Common Language Extension）提供的解決方案，一樣在安卓app項目中嵌入libpython3.5m.so，從而實現Android Java ↔ JNI ↔ Python的相互調用。

資料

1. https://www.crystax.net/android/ndk CrystaX NDK，聽說在Android NDK的基礎上作了不少改進
2. https://github.com/joaoventura/pybridge joaoventura/pybridge: Reuse Python code in native Android applications
3. http://www.srplab.com/cn/index.html CLE方案 用中間件的方式在不一樣平臺執行腳本
4. https://kivy.org/#home Kivy: Cross-platform Python Framework for NUI Development，用kv這個東西管理界面，用Python代碼完成邏輯，從而讓Python在各個平臺上運行。

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