How to determine cpu_target of a sysimage

General Usage
1

tl;dr

I’m using julia 1.5.4, and I have a few custom sysimages. Is there a way to tell what cpu_target these sysimages were compiled for?

Background

  1. I create a docker image with julia,
  2. A few of the build stages involve creating julia sysimages (using PackageCompiler v1.2.5, the cpu_target parameter is unset.).
  3. The docker image is created successfully and contains the custom sysimage.
  4. When I start a container, it contains the same version of julia and the sysimage
  5. If I try to start julia inside this container using the sysimage, I get
    ERROR: Unable to find compatible target in system image.
  6. If I rebuild the sysimage in the running container, it now has a different file size, and works.

Hypotheses

  1. One guess is that the host that runs the docker build has a different CPU architecture than the host where containers are run, and this is causing an issue, but the default julia sysimage clearly works in both.
  2. There’s something special with docker / virtualization systems that I’m not clear on

How to debug?

My first step in debugging this is to try and determine what cpu_target is being used during build vs runtime, however I don’t know how to tell what julia sees as the cpu_target.

Thanks in advance.