使用CMake构建android原生库

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在android下进行原生C/C++应用程序开发，通常使用ndk-build脚本编译源代码，但是对于一些第三方库，采用ndk-build编译却是不太方便。我之前有些项目采用了CMake构建系统，现在希望把这些库拿到android下使用，因此想是否可以仍然采用CMake构建系统。本质上，ndk就是一套交叉编译工具链，加上一些方便使用的脚本，而CMake对交叉编译支持的很好，所以从理论上是可行的。上网查了一下，发现已经有老外做了这方面的工作，在此借用一下，以备今后参考。步骤如下：

1. 创建gcc-android文件，文件内容如下：

#!/bin/bash
# Android gcc/g++ wrapper
#
# As android uses completely hacked and gutted gcc, it also
# uses -nostdlib, so for the linking phase we must expilictly
# specify crtbegin, crtend and friends. => We can't just do
# with LDFLAGS. :-(
#
# set DRY_RUN=1 for dry run
# set V=1 for verbose run
V=1

if [ -z $CROSS_PREFIX ]; then
   echo "source android-build-env first!"
   exit 1
fi

REAL_CC="${CROSS_PREFIX}gcc"
REAL_CXX="${CROSS_PREFIX}g++"
# Inspired by ndk-wrappers:
COMMON_FLAGS="--sysroot=$SYSROOT -march=armv5te -mtune=xscale -msoft-float -mthumb-interwork -ffunction-sections -funwind-tables -fstack-protector -fno-short-enums -D__ARM_ARCH_5__ -D__ARM_ARCH_5T__ -D__ARM_ARCH_5E__ -D__ARM_ARCH_5TE__ -DANDROID"

CFLAGS="${COMMON_FLAGS}"

CXXFLAGS="${COMMON_FLAGS} -fno-exceptions -fno-rtti"

TARGET_LIBGCC=`${CROSS_PREFIX}gcc -mthumb-interwork -print-libgcc-file-name`

# Test if we're wrapping gcc or g++
THIS_SCRIPT=`basename "$0"`

if [[ "$THIS_SCRIPT" =~ 'gcc' ]]; then
   WRAPPED="$REAL_CC"
   COMPILE_FLAGS="$CFLAGS"
elif [[ "$THIS_SCRIPT" =~ 'g++' ]]; then
   WRAPPED="$REAL_CXX"
   COMPILE_FLAGS="$CXXFLAGS"
else
   echo "Wrong script name - matches neither '^gcc' nor '^g++'."
   exit 2
fi

# Determine what mode (link, compile, nothing) we're in
LINK=1
COMPILE=0
SHARED=0
for ARG in "$@"; do
   case "$ARG" in
   # Preprocess-only (-E) and don't assemble (-S) mean the same as -c for us - the same CFLAGS are needed
   -c|-S|-E)
   LINK=0
   ;;
   *.c|*.cpp|*.c++|*.cxx)
   COMPILE=1
   ;;
# This is broken: gcc -c src.c -o object.o
# *.o)
# LINK=1
# ;;
   -shared)
   SHARED=1
   ;;
   -static)
   echo "$0: Static executables not supported by this wrapper."
   exit 5
   ;;
   -v)
   LINK=0
   COMPILE=0
   break
   ;;
   esac
done
if [ $# -eq 0 ]; then
   COMPILE=0
   LINK=0
fi
function verbose_command
{
   if [ "$V" = "1" -o "$DRY_RUN" = "1" ]; then
   echo "$@"
   fi
   if [ "$DRY_RUN" != "1" ]; then
   "$@"
   fi
}
# Compile source
function compile
{
   # That's easy
   verbose_command "$WRAPPED" $COMPILE_FLAGS "$@"
}
# Link a binary
function link
{
   # TODO: Separate libraries, sources and other arguments
   # Idea: read args till hitting sources -> that's USER_LIBS
   # rest is USER_OBJECTS, ignore USER_ARGS
   USER_LIBS=""
   USER_OBJECTS=""
   USER_ARGS=""
   OBJECTS_HIT=0
   for ARG in "$@"; do
   if [ $OBJECTS_HIT -eq 0 ]; then
   # Test if ARG is a lib
   if [[ "$ARG" == *.o ]]; then
   # is an object
   OBJECTS_HIT=1
   USER_OBJECTS="$USER_OBJECTS $ARG"
   else
   # a lib or an early param
   USER_LIBS="$USER_LIBS $ARG"
   fi
   else
   # We already reached objects, stuff all into USER_OBJECTS
   USER_OBJECTS="$USER_OBJECTS $ARG"
   fi
   done
   # Mess starts here
   if [ $SHARED -eq 1 ]; then
   # TODO: Remove -shared from args
   # Building a shared library
   LD_PREFIX="--sysroot=$SYSROOT -nostdlib -Wl,-shared,-Bsymbolic"
   LD_BEGIN="$SYSROOT/usr/lib/libc.so $SYSROOT/usr/lib/libm.so"
   # user objects
   # user dyn. libs
   LD_END="-Wl,--no-undefined -Wl,-rpath-link=$SYSROOT/usr/lib $TARGET_LIBGCC"
   verbose_command "$WRAPPED" $LD_PREFIX $USER_OBJECTS $USER_LIBS $LD_BEGIN $LD_END $USER_ARGS
   else
   # Building dynamic executable
   LD_PREFIX="--sysroot=$SYSROOT -nostdlib -Bdynamic -Wl,-dynamic-linker,/system/bin/linker -Wl,--gc-sections -Wl,-z,nocopyreloc"
   # STLport static lib explodes here, needs to come after objects (??)
   LD_BEGIN="$SYSROOT/usr/lib/libc.so $SYSROOT/usr/lib/libm.so $SYSROOT/usr/lib/crtbegin_dynamic.o"
   # user objects
   # user dyn. libs
   LD_END="-Wl,--no-undefined -Wl,-rpath-link=$SYSROOT/usr/lib $TARGET_LIBGCC $SYSROOT/usr/lib/crtend_android.o"
   verbose_command "$WRAPPED" $LD_PREFIX $LD_BEGIN $USER_OBJECTS $USER_LIBS $LD_END $USER_ARGS
   fi
}
if [ $COMPILE -eq 0 -a $LINK -eq 0 ]; then
   # No special handling needed, call $WRAPPED
   verbose_command "$WRAPPED" "$@"
fi
# TODO: support link+compile
if [ $COMPILE -eq 1 -a $LINK -eq 1 ]; then
   echo "$0: Link and compile in one step is not supported by this wrapper."
   exit 4
fi
if [ $COMPILE -eq 1 ]; then
   compile "$@"
elif [ $LINK -eq 1 ]; then
   link "$@"
else
   echo "$0: Internal error: Uknown compiler mode."
   exit 3
fi

2. 为gcc-android创建一个软链接g++-android

3. 创建android-build-env文件，文件内容如下：

export ANDROID_NDK_ROOT="$HOME/android/android-ndk-r4"
export ANDROID_GCC_WRAPPERS="$HOME/android/ex/androidcodes/cmaketest/script"
export PATH="$ANDROID_GCC_WRAPPERS:$ANDROID_NDK_ROOT/build/prebuilt/linux-x86/arm-eabi-4.2.1/bin/:$PATH"
export CROSS_PREFIX="arm-eabi-"
export SYSROOT="$ANDROID_NDK_ROOT/build/platforms/android-4/arch-arm"
# The config is specified in $ANDROID_NDK_ROOT/build/toolchains/arm-eabi-4.2.1/setup.mk
# and $ANDROID_NDK_ROOT/build/core/build-*.mk
export MAKE="make"
# Use android wrappers
export CC="gcc-android"
export CXX="g++-android"
export LD="deliberatey-undefined-do-not-use-directly"
export CPP="${CROSS_PREFIX}gcc -E"
export AS="${CROSS_PREFIX}as"
export OBJCOPY="${CROSS_PREFIX}objcopy"
export OBJDUMP="${CROSS_PREFIX}objdump"
export STRIP="${CROSS_PREFIX}strip"
export RANLIB="${CROSS_PREFIX}ranlib"
export CCLD="${CROSS_PREFIX}gcc"
export AR="${CROSS_PREFIX}ar"

（请根据实际的路径修改脚本）

3. 在运行cmake之前，执行source android-build-env，设置相关环境变量。

为此，我写了一个完整的demo，供参考: http://androidcodes.googlecode.com/svn/trunk/cmaketest

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