Error when trying to build an image for ruby 2.5.9 with an arm64 arch

Hello,

I've got a problem when trying to build an image for ruby 2.5.9 with an arm64 arch with the focal version of Ubuntu.

I need a docker image for ruby 2.5.9 with a arm64 architecture working on a M1 processor from Apple (on macOS 12.1), but I've got this error:

rake --trace docker:build arch=arm64 ruby_version=2.5.9 ubuntu_version=focal
** Invoke docker:build (first_time)
** Execute docker:build
docker run --rm --privileged multiarch/qemu-user-static:register --reset
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
standard_init_linux.go:228: exec user process caused: exec format error
rake aborted!
Command failed with status (1): [docker run --rm --privileged multiarch/qem...]
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/file_utils.rb:67:in `block in create_shell_runner'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/file_utils.rb:57:in `sh'
/Users/alex/git/ruby-docker-images/Rakefile:133:in `block (2 levels) in <top (required)>'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/task.rb:281:in `block in execute'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/task.rb:281:in `each'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/task.rb:281:in `execute'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/task.rb:219:in `block in invoke_with_call_chain'
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/monitor.rb:235:in `mon_synchronize'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/task.rb:199:in `invoke_with_call_chain'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/task.rb:188:in `invoke'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:160:in `invoke_task'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `block (2 levels) in top_level'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `each'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `block in top_level'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:125:in `run_with_threads'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:110:in `top_level'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:83:in `block in run'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:186:in `standard_exception_handling'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/lib/rake/application.rb:80:in `run'
/Users/alex/.gem/ruby/2.6.0/gems/rake-13.0.6/exe/rake:27:in `<top (required)>'
/usr/bin/rake:23:in `load'
/usr/bin/rake:23:in `<main>'
Tasks: TOP => docker:build

Am I missing something ?

Thank you

Start with Rakefile:133 and the reported docker:build command, especially the multiarch/qemu-user-static registration step. Reproduce the arm64 Ruby 2.5.9 build with Ubuntu focal and trace the exec format error; done means the requested image builds successfully without that failure.