프로그래밍과 경제

I have tested both the NDK (1.6) and SDK (2.1) on:

• Windows XP (32-bit) and Vista (64-bit)
  
• Mac OS X Snow Leopard
  
• Ubuntu Intrepid
  

Installing Android SDK


Important: You should add "$ANDROID_SDK_ROOT/tools" directory to the $PATH environment variable.
Under *nix:

export PATH=$ANDROID_SDK_ROOT/tools:$PATH

Under Cygwin: Open C:\Cygwin\Cygwin.bat and add:

set PATH=%ANDROID_SDK_TOOLS%;%PATH%

Installing Cygwin

If you are using Windows XP or Vista as host machine then you MUST install Cygwin Devel package with GNU Make (3.81 or later) before installing the NDK.
It should also work with MinGW.

Installing the Android NDK

cd $ANDROID_NDK_ROOT
build/host-setup.sh

If all is OK then the console will print Host setup complete.

cd $ANDROID_NDK_ROOT
make -APP=hello-jni

Creating an AVD

AVD stands for Android Virtual Device and can be seen as a device profile (keyboard, dialing pad, skin, screen dimensions, appearance ...) to load into your emulator. You can create as many AVDs as you need.
To create an AVD named "avdtest" targeting platform 2.1 (targetID=android-7):

android create avd -n avdtest -t android-7

If all is OK the console will print:

Created AVD 'avdtest' based on Android 2.1, with the following hardware config: hw.lcd.density=160

Create test.c

Here I will create a basic test.c file under C:\tmp with the following content:

#include <stdio.h>// printf

int main(int argc, char **argv)
{
int i = 1;
i+=2;

printf("Hello, world (i=%d)!\n", i);

return 0;
}

Create makefile

Just create an empty file named makefile (without any extension) under C:\tmp (which is the same directory as test.c).
Now We will fill the makefile step by step.

Add application name, $ROOT directory, install directory and the NDK platform version:

APP := test
ROOT:=/cygdrive/c
NDK_PLATFORM_VER := 1.5
INSTALL_DIR := /data/tm

Add useful environment vars:

ANDROID_NDK_ROOT:=$(ROOT)/android-ndk
ANDROID_NDK_HOST:=windows
ANDROID_SDK_ROOT:=$(ROOT)/android-sdk
PREBUILD:=$(ANDROID_NDK_ROOT)/build/prebuilt/$(ANDROID_NDK_HOST)/arm-eabi-4.2.1
BIN := $(PREBUILD)/bin

You MUST change ANDROID_NDK_HOST value from windows to linux-x86 if you are under *nix or darwin-x86 on MAC OS X.

Add GCC options:

CPP := $(BIN)/arm-eabi-g++
CC := $(BIN)/arm-eabi-gcc
CFLAGS :=
LDFLAGS := -Wl

Add targets

all: $(APP)

OBJS += $(APP).o

$(APP): $(OBJS)

$(CPP) $(LDFLAGS) -o $@ $^

%.o: %.c

$(CC) -c $(INCLUDE) $(CFLAGS) $< -o $@

install: $(APP)

$(ANDROID_SDK_ROOT)/tools/adb push $(APP) $(INSTALL_DIR)/$(APP)

$(ANDROID_SDK_ROOT)/tools/adb shell chmod 777 $(INSTALL_DIR)/$(APP)

shell:

$(ANDROID_SDK_ROOT)/tools/adb shell

run:

$(ANDROID_SDK_ROOT)/tools/adb shell $(INSTALL_DIR)/$(APP)

clean:

@rm -f $(APP).o $(APP)

Building the application

To build the application, switch to the directory where you have created both files and then:

make

At the output of the console you will get many errors saying that it's impossible to find stdlib.h, stdio.h etc etc.
To resolve this issue, add the Bionic header files to $CFLAGS variable like this:

CFLAGS := -I$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/include

If you retry (make) you will now get this link error:

rt0.o: No such file: No such file or directory

To avoid directly linking against the "C runtime" you must add "-nostdlib" flag to the link options like this:

LDFLAGS := -Wl -nostdlib

If you retry (make) you will now get these link errors:

test.c:(.text+0x34): undefined reference to `printf'
test.c:(.text+0x3c): undefined reference to `exit'

You get these errors because Bionic libc is missing. To add libc you MUST change $LDFLAGS like this:

LDFLAGS := -Wl -L$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib
LDFLAGS += -nostdlib -lc

If you retry (make) you will now get this link error:

/cygdrive/c/android-ndk/build/platforms/android-1.5/arch-arm/usr/lib/libc.so: undefined reference to `dl_unwind_find_exidx'

To resolve this issue you MUST specify the first set of directories into which to search the system shared libraries (*.so) . This is done by adding the "-rpath-link" option to the link options like this:

LDFLAGS := -Wl,-rpath-link=$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib -L$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib

If you retry (make) you will now get this warning:

/cygdrive/c/android-ndk/build/prebuilt/windows/arm-eabi-4.2.1/bin/../lib/gcc/arm
-eabi/4.2.1/../../../../arm-eabi/bin/ld: warning: cannot find entry symbol _start; defaulting to 000082c8

This is an Android known issue. You have this warning because the linker search "_start" as entry point. You can resolve this issue by renaming your main function. But the elegant way to resolve this issue is to specify the entry point in the link options like this:

LDFLAGS := -Wl,--entry=main,-rpath-link=$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib -L$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib
LDFLAGS += -nostdlib -lc

Now When you retry (make) your application will successfully build without any errors or warnings.

Testing your application

Before testing your application you MUST run the emulator like this:

emulator -avd avdtest

where "avdtest" is the name of the previously created avd (see "creating an avd" section).
To install the application on the emulator, open a new console and go to to directory where you have created test.c andmakefile. Install your application on the emulator like this:

make install

If all is OK the console will print:

/cygdrive/c/android-sdk/tools/adb push test /data/tmp/test
304 KB/s (2493 bytes in 0.008s)
/cygdrive/c/android-sdk/tools/adb shell chmod 777 /data/tmp/test

To run the application type:

make run

You will probably get an error message saying:

/cygdrive/c/android-sdk/tools/adb shell /data/tmp/test
/data/tmp/test: not found

This error message is a bit confusing because if you browse the /data/tmp directory you will notice that the executable is here. The question is why?
I spent hours searching and I found that this error happens because the loader fails to load the application because it cannot found a proper linker.
To specify a search directory for the dynamic linker (at run time) you MUST change the link options like this:

LDFLAGS := -Wl,--entry=main,-rpath-link=$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib,-dynamic-linker=/system/bin/linker -L$(ANDROID_NDK_ROOT)/build/platforms/android-$(NDK_PLATFORM_VER)/arch-arm/usr/lib
LDFLAGS += -nostdlib -lc

Now rebuild and install your application (make clean && make && make install) then run it again (make run).
The console will print the expected result ("hello, world (i=3)!") but just after we have an segmentation fault error("[1] Segmentation fault /data/tmp/test").
To resolve this issue you can exit the program (exit(0);) just before the main function returns (return 0;). You should also include <stdlib.h>.
If you retry the build&&run process (make clean && make && make install && make run) then you should have:

/cygdrive/c/android-sdk/tools/adb shell /data/tmp/test
Hello, world (i=3)!

which is the expected result.

Debugging your application
Before doing anything you MUST copy the gdbserver file to the emultor.
This file is under $BIN ($ANDROID_NDK_ROOT/build/prebuilt/$ANDROID_NDK_HOST/arm-eabi-4.2.1/bin).
Copy gdbserver to the emulator like this:

adb push gdbserver $INSTALL_DIR/gdbserver
adb shell chmod 777 $INSTALL_DIR/gdbserver

where $INSTALL_DIR is the directory where you have installed your application (it's not mandatory to copy it in this directory).