为 Android 构建谷歌 protobug 库时出错

Question

I want to use protobuf in native c++ code in Android. I have done the steps descriped in https://developers.google.com/cardboard/develop/c/protobuf . But it stucks on cross compiling the protobuflib with:

/tmp/protobuf/../arm-21-toolchain-clang-32/sysroot/usr/lib/../lib/crtbegin_dynamic.o:crtbegin.c:function _start: error: undefined reference to 'main'
clang50++: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [protoc] Error 1

and

  CXXLD    protoc
./.libs/libprotobuf.a: error adding symbols: Archive has no index; run ranlib to add one
clang50++: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [protoc] Error 1

I am using this script for building:

cd /tmp


### Cross-compile Protocol Buffers library ###
#git clone https://github.com/protocolbuffers/protobuf.git
cd /tmp/protobuf
git checkout v3.10.1
git submodule update --init --recursive
./autogen.sh
mkdir -p `pwd`/../libprotobuf/android

## buildscript32
export build_dir=`pwd`/../libprotobuf/android
export sysroot=`pwd`/../arm-21-toolchain-clang-32/sysroot
export PATH=`pwd`/../arm-21-toolchain-clang-32/bin:$PATH
export CC="arm-linux-androideabi-clang --sysroot $sysroot"
export CXX="arm-linux-androideabi-clang++ --sysroot $sysroot"

./configure \
--host=arm-linux-androideabi \
--with-protoc=protoc \
--with-sysroot="$sysroot" \
--disable-shared \
--prefix="$build_dir/armeabi-v7a" \
--enable-cross-compile \
CFLAGS="-march=armv7-a -D__ANDROID_API__=21" \
CXXFLAGS="-frtti -fexceptions -march=armv7-a -D__ANDROID_API__=21" \
LIBS="-llog -lz -lc++_static"

make -j8
make install


## clean 
make distclean


## buildscript64
export build_dir=`pwd`/../libprotobuf/android
export sysroot=`pwd`/../arm-21-toolchain-clang-64/sysroot
export PATH=`pwd`/../arm-21-toolchain-clang-64/bin:$PATH
export CC="aarch64-linux-android-clang --sysroot $sysroot"
export CXX="aarch64-linux-android-clang++ --sysroot $sysroot"

./configure \
--host=arm-linux-androideabi \
--with-protoc=protoc \
--with-sysroot="$sysroot" \
--disable-shared \
--prefix="$build_dir/arm64-v8a" \
--enable-cross-compile \
CFLAGS="-march=armv8-a -D__ANDROID_API__=21" \
CXXFLAGS="-frtti -fexceptions -march=armv8-a -D__ANDROID_API__=21" \
LIBS="-llog -lz -lc++_static"

make -j8
make install

## generate file structure
mkdir -p ../libprotobuf/android/lib/armeabi-v7a
mkdir -p ../libprotobuf/android/lib/arm64-v8a
cp ../libprotobuf/android/armeabi-v7a/lib/libprotobuf-lite.a ../libprotobuf/android/lib/armeabi-v7a
cp ../libprotobuf/android/arm64-v8a/lib/libprotobuf-lite.a ../libprotobuf/android/lib/arm64-v8a
cp -r ../libprotobuf/android/armeabi-v7a/include ../libprotobuf/android/include
rm -rf ../libprotobuf/android/armeabi-v7a
rm -rf ../libprotobuf/android/arm64-v8a
### End: Cross-compile Protocol Buffers library ###

How do I build libprotobuf for Android?? Host is linux-x86_64 Thank you

Answer 1

I had the same issue building doing a cross compile for Android using the clang based NDK. I simply did a post step of 'ranlib libprotobuf.a' and it worked.

I'm using v3.11.4

My script is as follows: (I'm using ubuntu 16.04 with NDK 21 for android27 with an arm64v8a target) (in the path, ndk-bundle is likely "/ndk/21.0.6113669/" or something like that)

create a directory called 'android_build' and run the following from there:

export PREFIX=$HOME/protobuf_android/
export PATH=$HOME/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/:$PATH
export SYSROOT=$HOME/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/
export CC="aarch64-linux-android27-clang --sysroot $SYSROOT"
export CXX="aarch64-linux-android27-clang++ --sysroot $SYSROOT"

../configure \
    --prefix=$PREFIX \
    --host=arm-linux-androideabi \
    --with-sysroot="${SYSROOT}" \
    --enable-shared \
    --enable-cross-compile \
    --with-protoc=protoc \
    CFLAGS="-march=arm64v8-a -D__ANDROID_API__=27" \
    CXXFLAGS="-frtti -fexceptions -march=arm64v8-a -D__ANDROID_API__=27" \
    LIBS="-llog -lz -lc++_static"

make -j4

make install

/usr/bin/ranlib ${PREFIX}/lib/libprotobuf.a