Java layer with 32bit binaries?

Product support balenaOS
1

I have built an image using the layer FROM balenalib/raspberrypi4-64-debian-openjdk:8-jdk-stretch-run . I’m running my app from the Dockerfile with a simple java -jar myapp.jar. It starts up and runs but I’m getting an error that appears to be an incompatibility with 64bit Java. I get the following:

java.lang.UnsatisfiedLinkError: /tmp/libNRJavaSerial_root_0/libNRJavaSerial.so: /tmp/libNRJavaSerial_root_0/libNRJavaSerial.so: wrong ELF class: ELFCLASS32 (Possible cause: architecture word width mismatch)

I’m able to run the app on raspbian running directly on my Pi’s using openjdk 8 without this error. What change do I need to make to resolve this? What other info might be useful?

2

Hey there! I did some quick Google research, and I think the error is telling you that libNRJavaSerial is compiled as 32-bit while the OpenJDK version on the base image is 64-bit.

How are you compiling the jar? Are you re-using any previously built library?

3

Unfortunately it’s a third party jar, our vendor provides the compiled app. I’m fairly sure they are using a prebuilt library for serial comms though, so it tracks.

Here’s the version output from the Pi running bare debian and openjdk:

openjdk version "1.8.0_212"
OpenJDK Runtime Environment (build 1.8.0_212-8u212-b01-1+rpi1-b01)
OpenJDK Client VM (build 25.212-b01, mixed mode)

And from the debian container on the Pi running balenaOS:

openjdk version "1.8.0_232"
OpenJDK Runtime Environment (build 1.8.0_232-8u232-b09-1~deb9u1-b09)
OpenJDK 64-Bit Server VM (build 25.232-b09, mixed mode)

So frankly I’m not smart enough to understand the difference between openjdk 64bit server and openjdk client vm. Is there just a package I need to install in the Dockerfile, combined with an update-alternatives?

4

The base image that you are using is Debian based and its installing the JDK from the official sources: https://github.com/balena-io-library/base-images/blob/master/balena-base-images/openjdk/raspberry-pi/debian/stretch/8-jdk/run/Dockerfile#L46.

How does that Dockerfile compare with the Debian Pi that you successfully ran this on? Could it be that you were using 32-bit Debian there?

5

So I’m not sure if this makes a big difference but the non-balena Pi is running Raspbian 10, whereas the container is Debian 9. I can’t imagine that makes a big difference, but maybe it does?

I noticed the Buster image for balena only has Java 11 available, but if that’s the lynch pin here then I could use the buster image and just install Java from my Dockerfile instead of relying on the image.

6

I noticed the Buster image for balena only has Java 11 available, but if that’s the lynch pin here then I could use the buster image and just install Java from my Dockerfile instead of relying on the image.

I’m not super familiar with Java, but that sounds worth trying

8

Ok so this is a bit hackey, but after trying several things the ultimate “fix” was to just use balenalib/raspberrypi3-debian-openjdk:8-jdk-stretch-run .

There may be some way to force 32bit Java 8 onto aarch64 but I think it’s easier to do it this way.

Oddly enough, Raspbian built for the Pi4 does use an arm7 build of Debian.

9

Good to see you got it working :). Update us if you need anything else.

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