Develop Reference

Cross compiling "Hello World" on Mac for Android

I'm trying to build a standard "Hello, World!" command-line executable for Android. The executable is to be run via adb shell.
0. The Go (Golang) Source
package main
import (
"fmt"
)
func main() {
fmt.Println("Hello, world!")
}
1A. The Build Command
$ CGO_ENABLED=0 GOOS=android GOARCH=arm GOARM=7 go build .
1B. The Output (Line Breaks Rearranged to Prevent Scrollbars)
# github.com/asukakenji/cross
warning: unable to find runtime/cgo.a
/usr/local/go/pkg/tool/darwin_amd64/link: running clang failed: exit status 1
ld: warning: ignoring file
/var/folders/dd/6k6vkzbd6d5803xj9zkjdhmh0000gn/T/go-link-150305609/go.o,
file was built for unsupported file format
( 0x7F 0x45 0x4C 0x46 0x01 0x01 0x01 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 )
which is not the architecture being linked (x86_64):
/var/folders/dd/6k6vkzbd6d5803xj9zkjdhmh0000gn/T/go-link-150305609/go.o
Undefined symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
1C. The Build Command, Again
The following command gives the same result:
$ env CGO_ENABLED=0 GOOS=android GOARCH=arm GOARM=7 go build .
2. The Build Command (Verbose)
I've tried using "-v" as mentioned like this:
$ CGO_ENABLED=0 GOOS=android GOARCH=arm GOARM=7 go build \
-x -ldflags "-extldflags -v" .
It gives me more than 100 lines of messages, so I don't post it here unless it's necessary. The go build command seems to try compiling the source with the clang bundled with Xcode.
3A. The Build Command (Successful, but...)
Given the hint that the wrong compiler is found, I tried to set $CC like this:
$ CGO_ENABLED=0 GOOS=android GOARCH=arm GOARM=7 \
CC=/path/to/arm-linux-androideabi/bin/clang go build .
arm-linux-androideabi is the output from make_standalone_toolchain.py (or make-standalone-toolchain.sh).
3B. The Output
The executable (named cross) is successfully built, with the following messages:
# github.com/asukakenji/cross
warning: unable to find runtime/cgo.a
I tried adb push it and run it with adb shell on Android, it worked fine.
My Questions
Why does it need a C compiler? Doesn't Go cross-compile out-of-the-box?
When building for Linux (instead of Android), the compilation works fine:
$ CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build .
Why?
The go build command keeps looking for runtime/cgo.a, even when I didn't use CGO in the source code, and even when I set CGO_ENABLED=0. How can I get rid of the warning? How is it harmful not having one?

if you run that code you find the android as an official target platform
listed as GOOS/GOARCH
$go tool dist list

Android isn't official target platform for cross-compilation. If all you need are command-line executables then you can set GOOS=linux because android is a linux under the hood, else take a look at https://github.com/golang/go/wiki/Mobile

The cgo requirement might be because go requires libc for DNS lookups on Android: https://github.com/golang/go/issues/8877

You need to use Android NDK to compile for android, you can download it from the link, or from Android Studio:
Then you can find the compilerlink in the route as below:
Last login: Fri Sep 4 09:25:16 on console
The default interactive shell is now zsh.
To update your account to use zsh, please run `chsh -s /bin/zsh`.
For more details, please visit https://support.apple.com/kb/HT208050.
Hasans-Air:~ hajsf$ pwd
/Users/hajsf
Hasans-Air:~ hajsf$ cd Library
Hasans-Air:Library hajsf$ cd android
Hasans-Air:android hajsf$ cd sdk
Hasans-Air:sdk hajsf$ cd ndk
Hasans-Air:ndk hajsf$ ls
21.3.6528147
Hasans-Air:ndk hajsf$ cd 21.3.6528147
Hasans-Air:21.3.6528147 hajsf$ cd toolchains
Hasans-Air:toolchains hajsf$ cd llvm
Hasans-Air:llvm hajsf$ cd prebuilt
Hasans-Air:prebuilt hajsf$ ls
darwin-x86_64
Hasans-Air:prebuilt hajsf$ cd darwin-x86_64
Hasans-Air:darwin-x86_64 hajsf$ cd bin
Hasans-Air:bin hajsf$ pwd
/Users/hajsf/Library/android/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/darwin-x86_64/bin
Then you can use the one reflectiong:
Archeticture you want to build your android app for, like aarch64
Android API you want to compile for, like Android 30
You can see full list of availbe options there, and you can seect the one you want like aarch64-linux-android30-clang
If you are at Windows 10 you'll find it at:
"C:\Users\${user}\AppData\Local\Android\Sdk\ndk\${NKD_version}\toolchains\llvm\prebuilt\windows-x86_64\bin\aarch64-linux-android30-clang"
There are 4 avaiailble linkers which are:
//CC_FOR_TARGET=/Users/hajsf/Library/android/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/darwin-x86_64/bin/aarch64-linux-android30-clang
//CC_FOR_TARGET=/Users/hajsf/Library/android/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/darwin-x86_64/bin/i686-linux-android30-clang
//CC_FOR_TARGET=/Users/hajsf/Library/android/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/darwin-x86_64/bin/x86_64-linux-android30-clang
//CC_FOR_TARGET=/Users/hajsf/Library/android/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/darwin-x86_64/bin/armv7a-linux-androideabi30-clang
After that only you can do cross copiling, as:
$ CGO_ENABLED=1
$ GOOS=android
$ GOARCH=arm64
$ CC_FOR_TARGET=/Users/hajsf/Library/android/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/darwin-x86_64/bin/aarch64-linux-android30-clang
$ go build -buildmode=c-shared -o lib-aarch64-android30.so lib.go
And a simple cgo file lib.go could be:
package main
import "C"
import "fmt"
//export HelloWorld
func HelloWorld() {
fmt.Printf("hello world from GO\n")
}
//export GetKey
func GetKey() *C.char {
theKey := "123-456-789"
return C.CString(theKey)
}
func main() {}
As shown copilation completed successfuly, and both lib-aarch64-android30.so and ib-aarch64-android30.h had been generated without any error.
Quick note, not to go far from the scope of the question, if you return a string, then the return value from this function must be explicitly freed in the C code if if you call it from C code, but as you call it from garbage collector environment, Java/Kotlin you do not want to worry about it.
If freeing the allocated buffer isn't convenient, its common to fill a buffer provided by the caller:
func GetKey(buff *C.char, n int) int
If you can allocate the memory but don't want to handle C strings, you can insert the buffer into a pointer and return the size.
func GetKey(buff **C.char) int

cross compiling using Android toolchains

I need to compile mpich for android , I used NDK arm-linux-andoirdeabi-4.8 toolchain to cross compile mpi , I did the following
export PATH="$NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/:$PATH"
export SYS_ROOT="$NDK_ROOT/platforms/android-8/arch-arm/"
export CC="arm-linux-androideabi-gcc --sysroot=$SYS_ROOT"
export LD="arm-linux-androideabi-ld"
export AR="arm-linux-androideabi-ar"
./configure --host=arm-linux-androideabi --prefix=/Crosscompile2/jni/mpich/ LIBS="-lc -lgcc " --disable-shared --disable-fortran --disable-cxx
but I got the following error:
checking for pthread_key_create in -lpthread... no
checking checkpointing library... configure: error: pthreads is required for checkpointing, but was not found
configure: error: src/pm/hydra configure failed
when I added -lpthread
LIBS="-lc -lgcc -lpthread"
it didn't compile
checking whether the C compiler works... no
configure: error: C compiler cannot create executables

Android is special in that it implements pthreads, but does not have a separate libpthread.a. The easy workaround is to add an empty library to your toolchain usr/lib
$AR q $SYS_ROOT/usr/lib/libpthread.a
before running ./configure

For the libpthread problems, you have 2 options.
sed out the requirement from the configure/makefiles since pthread is included in bionics libc
Or
Create a libpthead that's a symlink to libc
cd $SYSROOT/usr/lib
ln -s libc.a libpthread.a

Install valgrind for android, C compiler doesn't work

I'm trying to configure valgrind for android on Windows 7. I'm using guide from this site, but there is a problem with C compiler while configure. I'm using cygwin.
Error:
configure:3531: error: in /cygdrive/c/Tools/valgrind-3.9.0':
configure:3533: error: C compiler cannot create executables
Script:
#!/bin/bash
export NDKROOT=C:/Tools/AndroidNDK-r6
export HWKIND=generic # A generic Android device. eg, Pandaboard
export AR=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-ar.exe
export LD=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-ld.exe
export CC=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-gcc.exe
CPPFLAGS="--sysroot=$NDKROOT/platforms/android-3/arch-arm -DANDROID_HARDWARE_$HWKIND" \
CFLAGS="--sysroot=$NDKROOT/platforms/android-3/arch-arm" \
./configure --prefix=/data/local/Inst \
--host=armv7-unknown-linux --target=armv7-unknown-linux \
--with-tmpdir=/sdcard
make
make install
and config.log file

Obviously, there's a kind of a problem executing the compiler from within the NDK folder. The log file states:
configure:3422: checking for C compiler version
configure:3431: C:/Tools/AndroidNDK-r6
/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-gcc.exe
--version >&5
./configure: line 3433: C:/Tools/AndroidNDK-r6
/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-gcc.exe
: No such file or directory
So next you want to make sure that the path actually exists and the compiler executable is executable indeed. You can try yourself to type directly in cygwin shell:
C:/Tools/AndroidNDK-r6/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-gcc.exe -v
...and see what happens.

Build script for Android NDK in linux

How can I build my source for android with NDK.
Already I download ndk and I don't know how can I set arch compiler path.
This is my "build-for-android.sh" code:
#!/bin/sh
cairo=system
curl=system
pal=android
alsa=no
pulse=no
sles=yes
ffmpeg=yes
gallium=no
egl=yes
glx=no
PKG_CONFIG_PATH=$MOONLIGHT_PREFIX/lib/pkgconfig
if [ -d /usr/X11/share/aclocal ]; then
export ACLOCAL_FLAGS="-I /usr/X11/share/aclocal"
fi
./autogen.sh --host=arm-linux-androideabi --prefix=$MOONLIGHT_PREFIX --with-manual-mono=yes --with-testing=no --enable-browser-support --disable-desktop-support --with-unwind=no --with-ffmpeg=$ffmpeg --with-alsa=$alsa --with-pulseaudio=$pulse --with-opensles=$sles --with-pal=$pal --with-curl=$curl --with-cairo=$cairo --with-gallium-path=$gallium --enable-sdk=no --with-egl=$egl --with-glx=$glx CFLAGS="-DPLATFORM_ANDROID -I$MOONLIGHT_PREFIX/include $CFLAGS" LDFLAGS="-L$MOONLIGHT_PREFIX/lib $LDFLAGS" CXXFLAGS="-fno-rtti -DPLATFORM_ANDROID -I$MOONLIGHT_PREFIX/include $CFLAGS"
make $#
when I run it I get error below:
checking for arm-linu-androideabi-g++... no
checking for arm-linu-androideabi-c++... no
checking for arm-linu-androideabi-gpp... no
checking for arm-linu-androideabi-aCC... no
checking for arm-linu-androideabi-cc... no
.
.
.
.
I can see them in ~/Android/android-ndk-r8b/toolchains/arm-linux-androideabi-4.4.3/prebuild/linux-x86/bin/* directory.

OK. I found it.:
First, a standalone toolchain is created to make the configure script easier to use
~$ android-ndk-r5b/build/tools/make-standalone-toolchain.sh --platform=android-8 --install-dir=android-8-toolchain
Next, the toolchain's bin directory is added to the PATH.
~$ export PATH=$PATH:~/android-8-toolchain/bin/

Compiling ICU using arm-linux-androideabi-4.4.3

I would like to cross-compile ICU static libs for Android using Cygwin. So far, I have been able to configure and make the Cygwin/MSVC and Cygwin versions. I have installed the android-ndk-r7 and can see a version of gcc in the toolchains directory. Several examples suggest using host:arm-eabi - but this is not present on my machine.
I have copied mh-linux to mh-unknown in /icu/source/config and run the following:
export HOST_ICU=/cygdrive/d/__/External/SQLite/icu
export ICU_CROSS_BUILD=/cygdrive/d/__/External/SQLite/icu-cygwin
export NDK_ROOT=/cygdrive/d/__/android-ndk-r7
export CPPFLAGS="-I$NDK_ROOT/platforms/android-8/arch-arm/usr/include/ -O3 -fno-short-wchar -DU_USING_ICU_NAMESPACE=0 -DU_GNUC_UTF16_STRING=0 -fno-short-enums -nostdlib"
export CXXFLAGS="-I$NDK_ROOT/platforms/android-8/arch-arm/usr/include/ -O3 -fno-short-wchar -DU_USING_ICU_NAMESPACE=0 -DU_GNUC_UTF16_STRING=0 -fno-short-enums -nostdlib"
export CFLAGS="-I$NDK_ROOT/platforms/android-8/arch-arm/usr/include/ -O3 -fno-short-wchar -DU_USING_ICU_NAMESPACE=0 -DU_GNUC_UTF16_STRING=0 -fno-short-enums -nostdlib"
export LDFLAGS="-lc -Wl,-rpath-link=$NDK_ROOT/platforms/android-8/arch-arm/usr/lib/ -L $NDK_ROOT/platforms/android-8/arch-arm/usr/lib/"
$HOST_ICU/source/configure --with-cross-build=$ICU_CROSS_BUILD --enable-extras=no --enable-strict=no --enable-static --enable-shared=no --enable-tests=no --enable-samples=no --enable-dyload=no --enable-tools=no --host=arm-eabi --with-data-packaging=archive
I get the following error:
checking for ICU version numbers... release 4.8.1.1, library 48.1.1, unicode version 6.0
checking build system type... i686-pc-cygwin
checking host system type... arm-unknown-eabi
checking target system type... arm-unknown-eabi
checking whether to build debug libraries... no
checking whether to build release libraries... yes
checking for arm-eabi-gcc... no
checking for gcc... gcc
checking whether the C compiler works... no
configure: error: in `/cygdrive/d/Projects/__/External/SQLite/icu-android':
configure: error: C compiler cannot create executables
See `config.log' for more details
I'm sure this is a "stupid" question, but how do I get the ICU configure script to point to the gcc under $NDK_ROOT\toolchains\arm-linux-androideabi-4.4.3\prebuilt\windows\arm-linux-androideabi\bin? Am I missing some setup or install? Should I be setting my PATH so that the first gcc found is the one in arm-linux-androiedeabi?
Update 1. I just noticed that while windows\arm-linux=androideabi\bin contains gcc, windows\bin contains arm-linux-androideabi-gcc. How do I get ICU to call this?
Update 2. On the suggestion of Steven R. Loomis, I picked up updates for config.sub and config.guess from
http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD
http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD
placed android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin into my path, and re-ran configure with --host=arm-linux-androideabi... this time:
checking for arm-linux-androideabi-gcc... arm-linux-androideabi-gcc
checking whether the C compiler works... no
Definitely closer. Detailed error from config.log
gcc version 4.4.3 (GCC)
configure:3125: $? = 0
configure:3114: arm-linux-androideabi-gcc -V >&5
arm-linux-androideabi-gcc.exe: '-V' option must have argument
configure:3125: $? = 1
configure:3114: arm-linux-androideabi-gcc -qversion >&5
arm-linux-androideabi-gcc.exe: unrecognized option '-qversion'
arm-linux-androideabi-gcc.exe: no input files
configure:3125: $? = 1
configure:3145: checking whether the C compiler works
configure:3167: arm-linux-androideabi-gcc -I/cygdrive/d/Projects/android-ndk-r7/platforms/android-8/arch-arm/usr/include
/ -O3 -fno-short-wchar -DU_USING_ICU_NAMESPACE=0 -DU_GNUC_UTF16_STRING=0 -fno-short-enums -nostdlib -I/cygdrive/d/Projec
ts/android-ndk-r7/platforms/android-8/arch-arm/usr/include/ -O3 -fno-short-wchar -DU_USING_ICU_NAMESPACE=0 -DU_GNUC_UTF1
6_STRING=0 -fno-short-enums -nostdlib -lc -Wl,-rpath-link=/cygdrive/d/Projects/android-ndk-r7/platforms/android-8/arch-a
rm/usr/lib/ -L /cygdrive/d/Projects/android-ndk-r7/platforms/android-8/arch-arm/usr/lib/ conftest.c >&5
D:/Projects/android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/../lib/gcc/arm-linux-androideabi/
4.4.3/../../../../arm-linux-androideabi/bin/ld.exe: cannot find -lc
collect2: ld returned 1 exit status
configure:3171: $? = 1
configure:3209: result: no
configure: failed program was:
| /* confdefs.h */
| #define PACKAGE_NAME ""
| #define PACKAGE_TARNAME ""
| #define PACKAGE_VERSION ""
| #define PACKAGE_STRING ""
| #define PACKAGE_BUGREPORT ""
| #define PACKAGE_URL ""
| /* end confdefs.h. */
|
| int
| main ()
| {
|
| ;
| return 0;
| }
configure:3214: error: in `/cygdrive/d/Projects/__/External/SQLITE/icu-android':
configure:3216: error: C compiler cannot create executables
See `config.log' for more details
Update 3. The changes to config.sub and config.guess worked in that we are now using the right gcc compiler. The -lc failure comes from not being able to find libc.so (which is in android-ndk-r7/platforms/android-8/arch-arm/usr/lib" even though this is in the LDFLAGS. I did have an extra space after -L in the original LDFLAGS, but removing this did not help.
Update 4. According to an older post in http://groups.google.com/group/android-ndk/browse_thread/thread/46295616a889bc12
"The windows ndk toolchain is (thankfully) native to windows, so it
doesnt go through the cygwin translation layer which would translate
/cygdrive paths."
Update 5. Swapped all instances of /cygdrive/d/ with D:/. Now C compiler works though it still doesn't make. Suspect that ICU_CROSS_BUILD has to be in the icu/source directory.
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... yes
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether arm-linux-androideabi-gcc accepts -g... yes
checking for arm-linux-androideabi-gcc option to accept ISO C89... none needed
checking for arm-linux-androideabi-g++... arm-linux-androideabi-g++
checking whether we are using the GNU C++ compiler... yes
checking whether arm-linux-androideabi-g++ accepts -g... yes
checking how to run the C preprocessor... arm-linux-androideabi-gcc -E
checking for a BSD-compatible install... /usr/bin/install -c
checking for gmake... /usr/bin/gmake
configure: error: D:/Projects/__/External/SQLite/icu-cygwin/config/icucross.mk not found. Please build ICU in
D:/Projects/__/External/SQLite/icu-cygwin first.
Update 6. I re-configured and rbuilt my Cygwin folder in icu-cygwin. Go figure, this time icucross.mk was there. Successful configuration! But...
Update 7 Make did not end up so well.
$ make
D:/Projects/__/External/SQLite/icu/source/config/mh-linux:41: *** target pattern contains no `%'. Stop.
What?!?! It seems that now we want Cygwin paths again.. :(
Update 8. Changed my paths so that HOST_ICU and ICU_CROSS_BUILD use Cygwin paths, but NDK_ROOT is Windows path (since Android NDK ld can't handle cygwin paths).
THis time further but
arm-linux-androideabi-gcc.exe: /cygdrive/d/Projects/__/External/SQLit e/icu/source/stubdata/stubdata.c: No such file or directory
arm-linux-androideabi-gcc.exe: no input files
Seems that what has to happen is that arm-linux-androideabi-gcc needs to be made for cygwin, or the cross-build will not work.
Update 9. It seems that arm-linux-androideabi-gcc does not support cygwin paths - though ndk_build does. However, ICU is set to call arm-linux-androideabi-gcc while "make" requires cygwin paths. Maybe time to switch to OSX or Linux to do this.
Update 10 - Still no success.
Cygwin - Apparently the arm-linux-androideabi Crystax build also doesn't support cygwin paths in -L. Attempting to cross-compile under Cygwin will give the -lc error, since it cannot parse the -L/cygdrive/d/... path to the library. Changing to D:/ helps, but later causes make to fail since it is Cygwin make.
Linux - Using the normal NDK r7 build, configuration will fail with a wchar_t = 0 error. The Crystax NDK build will fix this, and make will fail complaining about uint64_t in Android's sys/type.h. See ICU library in Android NDK. You can force it to be defined and it will lead to yet another error about size mismatch.
OSX - Probably the most successful, compiling using the official build or the Crystax build, it leads directly to the uint64_t bug. If you hack around it, it will lead you to
icu/source/common/ustrenum.cpp:118: error: must #include <typeinfo> before using typeid
Help!

00. Download android ndk http://developer.android.com/tools/sdk/ndk/index.html
example install d:\android-r9b
01. Download install example d:\msys MSys http://www.mingw.org/wiki/MSYS 1.01
02. Download gcc 3.8.1 w64 http://mingw-w64.sourceforge.net/ example install d:\mingw32_64
03. Download icu versin 52.1 http://site.icu-project.org/download/52#TOC-ICU4C-Download
04. Extract icu source code to d:\icu
05. Enter msys use export PATH=/d/msys/1.0/bin:/d/ming32_64/mingw32/bin:$PATH
06. cd /d/icu;mkdir mingw;mkdir android;cd mingw
this is follow icu readme.html cross compile steps
07. cd /d/icu/ming ;../source/runConfigureICU MinGW ;make
no problem,all is working and under /d/icu/mingw/bin generate tools for cross compile later.
08. cd /d/icu/android
09. /d/android-ndk-r9b/build/tools/make-standalone-toolchain.sh --platform=android-9 --install-dir=/d/androidgcc/ -- toolchain=arm-linux-androideabi-4.8
if use window 7/8 64bit add additional options: --system=windowx86_64
10. export PATH again; export PATH=/d/msys/1.0/bin/:/d/androidgcc/bin/:/d/androidgcc/arm-linux-androideabi/bin/
the path must include the ar.exe execute for create library.
11. create shared library.
sh ../source/configure --host=armv6-google-linux --enable-shared=yes --disable-static -with-cross-build=/d/icu/mingw CC=arm-linux-androideabi-gcc CXX=arm-linux-androideabi-g++ AR=arm-linux-androideabi-ar --with-data-packaging=archive
12. make
all is successful