Android compiling environment (2)-manually compile the C Module

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In the previous article 《Android compiling environment (1)-compile the helloworld module of native C), We tried to pass the standardAndroid. mkFile to compile the C Module. Next we will try to use the GCC command line to compile it, so as to understand the details of the android compiling environment.

The android compilation environment provides the "showcommands" option to display the compilation command line. We can open this option to view some details during compilation. Of course, before that, we should clean the helloworld module in the previous article:

# Make clean-helloworld

The above "make clean-$ (local_module)" is the make clean method provided by the android compiling environment.

 

Next, use the showcommands option to re-compile helloworld:

# Make helloworld showcommands Build/CORE/product_config.mk: 229: Warning: adding test OTA key Target thumb C: helloworld <= Development/Hello. c Prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/ARM-Eabi-gcc-I system/CORE/include-I Hardware/libhardware/include-I Hardware/RIL/include-I Dalvik/ libnativehelper/include-I frameworks/base/include-I external/skia/include-I out/target/product/generic/obj/include-I bionic/libc/arch-arm/ include-I bionic/libc/include-I bionic/libstdc ++/include-I bionic/libc/kernel/common-I bionic/libc/kernel/arch-arm-I bionic /libm/include-I bionic/libm/include/ARCH/ARM-I bionic/libthread_db/include-I development/Hello-I out/target/product/generic/obj/executables /helloworld_intermediates-C-fno-exceptions-wno-multichar-March = armv5te-mtune = XScale-msoft-float-FPIC-mthumb-interwork-ffunction-sections-funwind-tables-fstack -protector-dctor arm_arch_5 _-d1_arm_arch_5t _-d1_arm_arch_5e _-d1_arm_arch_5te _-include system/CORE/include/ARCH/Linux-arm/androidconfig. h-dandroid-fmessage-length = 0-w-wall-wno-unused-dsk_release-dndebug-O2-g-wstrict-aliasing = 2-Finline-functions-fno-inline- functions-called-once-fgcse-after-reload-frerun-CSE-after-loop-frename-registers-dndebug-udebug-mthumb-OS-fomit-frame-pointer-fno- strict-aliasing-Finline-Limit = 64-MD-O out/target/product/generic/obj/executables/helloworld_intermediates/hello. o development/Hello/hello. c Target executable: helloworld (Out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld) Prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/ARM-Eabi-G ++-nostdlib-bdynamic-wl,-T, build/CORE/armelf. x-wl,-dynamic-linker,/system/bin/linker-wl, -- GC-sections-wl,-Z, nocopyreloc-O out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld-lout/target/product/generic/obj/lib-wl, -rpath-link = out/target/product/generic/obj/lib-LC-lstdc ++-lm out/target/product/generic/obj/lib/crtbegin_dynamic.o out/Target /product/generic/obj/executables/helloworld_intermediates/hello. o-wl, -- no-undefined prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin /.. /lib/GCC/ARM-Eabi/4.2.1/interwork/libgcc. A out/target/product/generic/obj/lib/crtend_android.o Target non-prelinked: helloworld (Out/target/product/generic/symbols/system/bin/helloworld) Out/host/linux-x86/bin/ACP-FPT out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld out/target/product/generic/symbols/system/ bin/helloworld Target Strip: helloworld (Out/target/product/generic/obj/executables/helloworld_intermediates/helloworld) Out/host/linux-x86/bin/soslim -- strip -- shady -- Quiet out/target/product/generic/symbols/system/bin/helloworld -- OUTFILE out/target/product/generic/ OBJ/executables/helloworld_intermediates/helloworld Install: Out/target/product/generic/system/bin/helloworld Out/host/linux-x86/bin/ACP-FPT out/target/product/generic/obj/executables/helloworld_intermediates/helloworld out/target/product/generic/system/bin/helloworld

 

From the command line above, we can see that the cross-compilation tool chain used by the android compiling environment is prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/ARM-Eabi-GCC, the-I and-l Parameters specify the C-library header files and the dynamic library file paths respectively: bionic/libc/include and out/target/product/generic/obj/lib, others also include many compilation options and pre-compiled macros defined by-D.

 

We can use the above compilation command to make it easier to manually compile the helloworld program. Manually delete the last compiled helloworld program:

# Rm out/target/product/generic/obj/executables/helloworld_intermediates/Hello. o # Rm out/target/product/generic/system/bin/helloworld

Compile with GCC to generate the target file:

# Prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/ARM-Eabi-gcc-I bionic/libc/arch-arm/include-I bionic/libc/ kernel/common-I bionic/libc/kernel/arch-arm-C-fno-tions-wno-multichar-March = armv5te-mtune = XScale-msoft-float-FPIC-mthumb -interwork-ffunction-sections-funwind-tables-fstack-protector-d1_arm_arch_5 _-d1_arm_arch_5t _-character _-d1_arm_arch_5te _-include system/CORE/include/ARCH/ linux-arm/androidconfig. h-dandroid-fmessage-length = 0-w-wall-wno-unused-dsk_release-dndebug-O2-g-wstrict-aliasing = 2-Finline-functions-fno-inline- functions-called-once-fgcse-after-reload-frerun-CSE-after-loop-frename-registers-dndebug-udebug-mthumb-OS-fomit-frame-pointer-fno- strict-aliasing-Finline-Limit = 64-MD-O out/target/product/generic/obj/executables/helloworld_intermediates/hello. o development/Hello/hello. c

Compared with Android. mk compilation parameters, the above mainly reduces unnecessary-I parameters.

Next, generate the executable file:

# Pre built/linux-x86/toolchain/arm-eabi-4.2.1/bin/ARM-Eabi-gcc-nostdlib-bdynamic-wl,-T, build/CORE/armelf. x-wl,-dynamic-linker,/system/bin/linker-wl, -- GC-sections-wl,-Z, nocopyreloc-O out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld-lout/target/product/generic/obj/lib-wl, -rpath-link = out/target/product/generic/obj/lib-LC-lm out/target/product/generic/obj/executables/helloworld_intermediates/hello. O out/target/product/generic/obj/lib/crtbegin_dynamic.o-wl, -- no-undefined. /prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin /.. /lib/GCC/ARM-Eabi/4.2.1/interwork/libgcc. A out/target/product/generic/obj/lib/crtend_android.o

It is worth noting that the parameter "-wl,-dynamic-linker,/system/bin/linker" specifies the Android-specific dynamic linker/system/bin/linker, instead of the commonly used lD. so.

 

The generated executable program can be viewed using the file and readelf commands:

# File out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld Out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld: Elf 32-bit LSB executable, arm, Version 1 (sysv ), dynamically linked (uses SHARED libs), not stripped # Readelf-d out/target/product/generic/obj/executables/helloworld_intermediates/linked/helloworld | grep needed 0x00000001 (needed) Shared Library: [libc. So] 0x00000001 (needed) Shared Library: [libm. So]

This is a dynamic link executable file in arm format. libc. So and libm. So are required for running. "Not stripped" indicates that it has not been strip. In an embedded system, the compiled executable files or dynamic libraries are strip to save space. That is, redundant symbol table information is removed. At the end of the "make helloworld showcommands" command, we can also see that the out/host/linux-x86/bin/soslim tool is used in the android compiling environment for strip.

For more information about Android toolchain, see:Android toolchain and bionic libc