OpenHarmony的2种快速编译方法

简介

通过./build.sh脚本进行编译，是OpenHarmony官方推荐的编译程序的方法。但是这样的方法牵扯方便广，速度慢，接下来我们来熟悉下OpenHarmony的另外两种编译方法。

GCC编译方法

1. 工具链位置：

   [源码路径]/prebuilts/gcc/linux-x86/arm/gcc-linaro-7.5.0-arm-linux-gnueabi/bin/

2. 编译命令：

   arm-linux-gnueabi-gcc -static helloworld.c -o gcchelloworld

3. 方法解析： **使用gcc工具链的编译方法是嵌入式开发的通用方法。但是这里有个特殊的地方-static。 gcc 加上 -**static,会在链接阶段, 查找对应模块的静态库, 而非动态库, 并把需要的东西,都带进目标文件),编译好后,文件会非常大,但是,运行时就不需要依赖。这个原因则是在OpenHarmony的镜像文件里放的是musl的lib库，没有glibc的lib库，所以如果不用-static标志则有可能在运行时找其他运行库，找不到则运行不成功。

CLang编译方法

1. 工具链位置：[源码路径]/prebuilts/clang/ohos/linux-x86_64/llvm/bin

2. 编译命令：

   • clang --sysroot=[ohos代码路径]/out/rk3568/obj/third_party/musl/ --target=arm-linux-ohosmusl -D**clang** -march=armv7-a -mfloat-abi=softfp -mfpu=neon-vfpv4 -w -o helloworld.c.o -c helloworld.c
   • clang --sysroot=[ohos代码路径]/out/rk3568/obj/third_party/musl/ --target=arm-linux-ohosmusl -D**clang** -march=armv7-a -mfloat-abi=softfp -mfpu=neon-vfpv4 -w -Wl,--dynamic-linker,/lib/ld-musl-arm.so.1 -rdynamic helloworld.c.o -o muslhelloworld

3. 方法解析： clang编译器是APPLE公司的编译器大牛Chris Lattner主导下编写的,其目标是替换大名鼎鼎的GCC编译器。一般编译器的流程如下：

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   通过上面的命令分析分了两部，第一步编译生成中间文件：helloworld.c.o，也就是从预处理一直到后端的过程；第二步链接helloworld.c.o和/lib/ld-musl-arm.so.1生成目标文件muslhelloworld也就是链接和生成文件。这部分和上部分的区别就是手动引用musl库。那么musl库和glibc的库的区别是什么呢？

   1. 开源版本：glibc（LGPLv2.1），musl(MIT)
   2. 运行速度：glibc优于musl，同时稳定性也是glibc更好
   3. 代码可读性：musl由于glibc

总结

OpenHarmony的官方编译方法就是使用./build.sh脚本文件，调用顺序大致如下：

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所以如果要缩减编译时间还有一些特殊方法：

• ./build.sh --product-name 【产品名称如：rk3568】--ccache --build-target 【编译对象模块，如：moduleb_lib】 此方法也是官方的一种编译方法，虽说只编译一个模块，但是流程是完整的，即：
  • 用BUILD.gn生成ninja文件，然后通过上面的流程编译最总的模块二进制文件
• ninja -C /out/rk3568(根据编译的productname来填) moduleb_lib(编译对象模块，如：moduleb_lib) 此方法的前提是首先用./build.sh编译过一遍，然后因为out目录里提前生成了build.ninja，所以可以直接用ninja命令直接编译对应模块