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c – Want to compile native Android binary I can run in terminal on the phone

Posted by: admin April 23, 2020 Leave a comment

Questions:

I’ve been trying for a couple days to compile a native ARM Android binary that will execute on my phone using a terminal application. I want to generate the same type of binary as the standard Posix binaries installed on the phone like ls, mkdir etc. I’ve downloaded the Android NDK under Mac OS X and have been able to compile simple ELF binaries without errors. However, when I transfer them to the phone, they always segfault. That is, they segfault when compiled with -static in GCC. If I don’t use -static, they complain about not being linked, etc. Put simply, they don’t work.

My hypothesis is that they are not linking to the Android standard C library properly. Even though I am linking my binaries with the libc provided by the NDK, they still don’t work. I read that Android uses the Bionic C library, and tried to download source for it but I’m not sure how to build a library from it (it’s all ARM assembly, it seems).

Is it true that the Android C library on the phone is different from the one provided with the Android NDK? Will the one included with the NDK not allow me to compile native binaries I can execute through a terminal? Any guidance here is greatly appreciated!

Update:

I finally got this to work using GCC 4.7.0 on Mac OS X. I downloaded the Bionic headers and then compiled a dynamically linked binary using the C library that comes with the Android NDK. I was able to get a test app to work on the phone using the phone’s C lib (the binary was 33K). I also tried to statically link against the NDK’s C library, and that also worked.

In order to get this all working I had to pass -nostdlib to GCC and then manually add crtbegin_dynamic.o and crtend_android.o to GCC’s command line. It works something like this:

$CC \
$NDK_PATH/usr/lib/crtbegin_dynamic.o \
hello.c -o hello \
$CFLAGS \
$NDK_PATH/usr/lib/crtend_android.o

For static binaries, use “crtbegin_static.o.” This is explained in the crtbegin_dynamic.S/crtbegin_static.S source.

For this experiment, I only used plain ‘ol GCC 4.7.0 and Binutils 2.22. I also compiled GCC with newlib, but I am not actually linking my ARM binaries with newlib at all. I am forcing GCC/ld to link directly to the libc provided with the Android NDK, or in the case of dynamic binaries, to the libc on the phone.

How to&Answers:

Just use the android-ndk. And build a Android.mk like so.
include $(BUILD_EXECUTABLE) is what tells it build a executable instead of a JNI .lib

Android.mk

ifneq ($(TARGET_SIMULATOR),true)

LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_CFLAGS += -Wall


LOCAL_LDLIBS := -L$(LOCAL_PATH)/lib -llog -g

LOCAL_C_INCLUDES := bionic
LOCAL_C_INCLUDES += $(LOCAL_PATH)/include

LOCAL_SRC_FILES:= main.cpp

LOCAL_MODULE := mycmd

include $(BUILD_EXECUTABLE)

endif  # TARGET_SIMULATOR != true

Answer:

First, make sure you have the NDK:

http://developer.android.com/tools/sdk/ndk/index.html

Here is the easiest way to compile a C binary for your phone:

http://developer.android.com/tools/sdk/ndk/index.html

http://www.kandroid.org/ndk/docs/STANDALONE-TOOLCHAIN.html

Usually $NDK(may be different) =

Linux:

/home/<user>/android-ndk

Mac OS X:

/Users/<user>/android-ndk

In Terminal:

# create tool-chain - one line
# New method in ndk 12.
$NDK/build/tools/make_standalone_toolchain.py --arch arm --install-dir=/tmp/my-android-toolchain
# Old method.
#$NDK/build/tools/make-standalone-toolchain.sh --platform=android-3 --install-dir=/tmp/my-android-toolchain

# add to terminal PATH variable
export PATH=/tmp/my-android-toolchain/bin:$PATH

# make alias CC be the new gcc binary
export CC=arm-linux-androideabi-gcc

# compile your C code(I tried hello world)
$CC -o foo.o -c foo.c

# push binary to phone
adb push foo.o /data/local/tmp

# execute binary
adb /data/local/tmp/foo.o

Answer:

Using CMake with the Android NDK is a nice way to compile Android console applications.

Download CMake and android-cmake (set it up like this). If your program is called main.c, then write the following in file CMakeLists.txt:

project(test)
cmake_minimum_required(VERSION 2.8)
add_executable(test ./main.c)

and run cmake -DCMAKE_TOOLCHAIN_FILE=$ANDTOOLCHAIN .

You will then have a Makefile for your program, you can run make to have your test executable.

Answer:

Try if if the agcc wrapper can help you as referenced in the Android-tricks blog. According to the blog post you want to use the bionic library, but the one already installed on the phone, not some separately compiled version.