NDK编译X265库到ARM，遇到问题

之前两篇博客介绍了，如何用arm-none-linux-gnueabi-gcc编译器交叉编译x265的库，但用这个编译出的库必须要把动态库加上。我为了要在android项目上应用x265的静态库，还是要用NDK进行编译，这又出现了很多问题，我把我解决了的贴出来，供大家分享，我还在编译中。x265往android上编译，最主要的问题是，android基于linux内核开发，但却对一些库做了修改，有一些库android并不支持，所以我们要针对问题，再解决。

问题一：利用cmake在linux下编译，往cmakelist.txt下添加交叉编译器等信息后，设置如下：

set( CMAKE_SYSTEM_NAME Linux )
set( CMAKE_C_COMPILER "ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc ")
set( CMAKE_CXX_COMPILER "ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++")

但却出现问题：

-- cmake version 2.8.9
-- The C compiler identification is GNU 4.8.0
-- The CXX compiler identification is GNU 4.8.0
-- Check for working C compiler: /home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc
-- Check for working C compiler: /home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc -- broken
CMake Error at /usr/cmake-2.8.9-Linux-i386/share/cmake-2.8/Modules/CMakeTestCCompiler.cmake:52 (MESSAGE):
The C compiler
"/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc"
is not able to compile a simple test program.

It fails with the following output:

Change Dir: /home/heling/x265_1.6/source/CMakeFiles/CMakeTmp

Run Build Command:/usr/bin/make "cmTryCompileExec4150547758/fast"

/usr/bin/make -f CMakeFiles/cmTryCompileExec4150547758.dir/build.make
CMakeFiles/cmTryCompileExec4150547758.dir/build

make[1]: 正在进入目录
`/home/heling/x265_1.6/source/CMakeFiles/CMakeTmp'

/usr/cmake-2.8.9-Linux-i386/bin/cmake -E cmake_progress_report
/home/heling/x265_1.6/source/CMakeFiles/CMakeTmp/CMakeFiles 1

Building C object
CMakeFiles/cmTryCompileExec4150547758.dir/testCCompiler.c.o

/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc
-o CMakeFiles/cmTryCompileExec4150547758.dir/testCCompiler.c.o -c
/home/heling/x265_1.6/source/CMakeFiles/CMakeTmp/testCCompiler.c

Linking C executable cmTryCompileExec4150547758

/usr/cmake-2.8.9-Linux-i386/bin/cmake -E cmake_link_script
CMakeFiles/cmTryCompileExec4150547758.dir/link.txt --verbose=1

/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc
CMakeFiles/cmTryCompileExec4150547758.dir/testCCompiler.c.o -o
cmTryCompileExec4150547758 -rdynamic

/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/../lib/gcc/arm-linux-androideabi/4.8/../../../../arm-linux-androideabi/bin/ld:
error: cannot open crtbegin_dynamic.o: 没有那个文件或目录

/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/../lib/gcc/arm-linux-androideabi/4.8/../../../../arm-linux-androideabi/bin/ld:
error: cannot open crtend_android.o: 没有那个文件或目录

/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/../lib/gcc/arm-linux-androideabi/4.8/../../../../arm-linux-androideabi/bin/ld:
error: cannot find -lc

/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/../lib/gcc/arm-linux-androideabi/4.8/../../../../arm-linux-androideabi/bin/ld:
error: cannot find -ldl

collect2: error: ld returned 1 exit status

make[1]: *** [cmTryCompileExec4150547758] 错误 1

make[1]:正在离开目录
`/home/heling/x265_1.6/source/CMakeFiles/CMakeTmp'

make: *** [cmTryCompileExec4150547758/fast] 错误 2

在谷歌上搜索，发现很多人都出现这个问题，但没有一个解决方法，我利用NDK，做了一个交叉工具链，再把链接给cmake，如下进行设置：

cd  /ndk/build/tools  //进入ndk目录下的/build/tools
./make-standalone-toolchain.sh --platform=android-14 --ndk-dir=/home/heling/webrtc/WebRTC20140723_bak/trunk/third_party/android_tools/ndk/ --install-dir=/home/heling/android-14-toolchain/ --system=linux-x86_64  //对工具链进行设置    --install-dir工具链安装位置
//然后在cmakelist中做如下设置
set( CMAKE_SYSTEM_NAME Linux )
set( CMAKE_C_COMPILER "/home/heling/android-14-toolchain/arm-linux-androideabi/bin/gcc")
set( CMAKE_CXX_COMPILER "/home/heling/android-14-toolchain/arm-linux-androideabi/bin/g++")//工具链的绝对地址信息

然后执行 cmake ../source这个问题解决了，但还出现其他的问题。

问题二：

上面一个问题解决后，在make，出现了问题：

[ 30%] Building CXX object common/CMakeFiles/common.dir/picyuv.cpp.o
[ 32%] Building CXX object common/CMakeFiles/common.dir/common.cpp.o
/home/heling/桌面/x265_1.6/source/common/common.cpp: In function 'void* x265_malloc(size_t)':
/home/heling/桌面/x265_1.6/source/common/common.cpp:79:59: error: 'posix_memalign' was not declared in this scope
/home/heling/桌面/x265_1.6/source/common/common.cpp: In function 'double x265_qScale2qp(double)':
/home/heling/桌面/x265_1.6/source/common/common.cpp:151:33: error: 'log2' was not declared in this scope
make[2]: *** [common/CMakeFiles/common.dir/common.cpp.o] 错误 1
make[1]: *** [common/CMakeFiles/common.dir/all] 错误 2
make: *** [all] 错误 2

可以看到这些报错都是因为android不支持这些函数的原因，android不支持log2，所以用log来进行替换。

posix_memalign 这个函数android也不识别，换为memalign。

解决完这个问题后，接着make ，发现又出现了问题。

问题三：

[ 85%] Building CXX object encoder/CMakeFiles/encoder.dir/weightPrediction.cpp.o
[ 85%] Built target encoder
Scanning dependencies of target x265-shared
Linking CXX shared library libx265.so
/home/heling/android-14-toolchain/bin/../lib/gcc/arm-linux-androideabi/4.6/../../../../arm-linux-androideabi/bin/ld: error: cannot find -lpthread
collect2: ld returned 1 exit status
make[2]: *** [libx265.so.51] 错误 1
make[1]: *** [CMakeFiles/x265-shared.dir/all] 错误 2
make: *** [all] 错误 2

因为android的ndk虽然有pthread.h,但是没有libpthread.a,集成到libc.a里了，

所以在编译x265时，不需要去链接-lpthread，解决办法就是在source目录下的cmakelist.txt中将

list(APPEND PLATFORM_LIBS pthread)
更改为list(APPEND PLATFORM_LIBS)
list(REMOVE_ITEM PLIBLIST "-lc" "-lpthread")
更改为list(REMOVE_ITEM PLIBLIST "-lc")保存后，再cmake../source,最后make 就成功了！！！