How to cross compile OpenJDK for Arm32?

[Xerxes Rånby]

Den 2014-12-09 10:27, Severin Gehwolf skrev:
> Hi,
>
> On Mon, 2014-12-08 at 21:46 +1000, David Holmes wrote:
>> On 8/12/2014 7:10 PM, ChenLong wrote:
>>> Hi
>>>
>>> Apologize if this is not the right place to ask.
>>> I want to try OpenJDK8 on Armv7. Is there a guideline on how to cross compile OpenJDK8 for Armv7? And if not, could someone share some experiences? I went through the README-builds.html and did not find any clues for cross compiling.
>> The only OpenJDK build for ARM would be a ZERO build. But I don't know
>> how to do Zero builds - though I'm sure the Zero folk will chime in.
> CC'ing zero-dev.

when I cross-compile OpenJDK 9 for ARM32 I pass the following configure 
options

configure
# these options tell openjdk to do a cross compile build.
--build=x86_64-unknown-linux-gnu
--host=arm-buildroot-linux-gnueabi
--target=arm-buildroot-linux-gnueabi

# these two options enable zero
--with-jvm-interpreter=cpp
--with-jvm-variants=zero

# specific options to make the build find the X and freetype headers and 
librarys found on the ARM32 root filesystem.
--disable-freetype-bundling
--with-freetype-include=/home/xranby/rpi-buildroot/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/include/freetype2
--with-freetype-lib=/home/xranby/rpi-buildroot/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/lib
--with-freetype=/home/xranby/rpi-buildroot/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/
--with-x=/home/xranby/rpi-buildroot/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/include

# the sysroot shall point to the ARM32 root file system, the build will 
use librarys inside the sys root during linking native libraries.
--with-sys-root=/home/xranby/rpi-buildroot/output/host/usr/arm-buildroot-linux-gnueabi/sysroot
# The tools dir contains binarys to run on the host x86 system, you may 
point this to your system root dir /
# in my case the tools i use have been compiled by buildroot thus I use 
the buildroot tools dir.
--with-tools-dir=/home/xranby/rpi-buildroot/output/host
# OpenJDK 9 require OpenJDK 8, i point with boot jdk to an OpenJDK 8 
image that can be run on the host x86 system.
--with-boot-jdk=/home/xranby/images-jdk8/j2sdk-image/

# some parts of the openjdk build still expect that the cross compile 
tools are found in the system PATH
# on my system i have to explicitly tell where the tools are located 
because my cross compile toolchain is not found on the path.
# i use gcc to do the linking instead of ld because the openjdk build 
passes -Xlinker -z
OBJCOPY=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-objcopy
STRIP=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-strip
CPP=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-cpp
CXX=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-g++
CC=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-gcc
LD=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-gcc
CPP_FLAGS=-lstdc++
CXX_FLAGS=-lstdc++


when running make i pass the following options to make
# BUILD_CC and BUILD_LD shall point to host x86 executables.
BUILD_CC=gcc
BUILD_LD=gcc
OBJCOPY=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-objcopy
STRIP=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-strip
CPP=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-cpp
CXX=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-g++
CC=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-gcc
LD=/home/xranby/rpi-buildroot/output/host/usr/bin/arm-buildroot-linux-gnueabi-gcc
#and finally the target, this will build compact profiles, jre and jdk 
images.
all images profiles CONF=linux-arm-normal-zero-release


I have automated these configure and make options for openjdk 9 into 
buildroot build scripts
https://github.com/xranby/rpi-buildroot/tree/openjdk

>
> I've done Zero builds before but have never used OpenJDK's cross-compile
> feature to build it on ARMv7. There is an Arm32 bit JIT in IcedTea[1],
> but I don't know if that can be cross-compiled.

If you cross compile icedtea then you need to make sure that the 
bytecode generator tool is compiled by the host x86 toolchain.
openembedded meta-java contains buildscripts that can cross compile the 
Arm32 JIT found in IcedTea.
https://github.com/woglinde/meta-java

Cheers
Xerxes

>
> Cheers,
> Severin
>
> [1]
> http://blog.fuseyism.com/index.php/2014/03/28/icedtea-2-3-14-2-4-6-considered-armful-released/
>
>> David
>>
>>> Thanks
>>> Chen Long
>>>
>
>