Cross-Compiling Snaps for Core24: Building on AMD64 for ARM64

snapcraft
1

What is the current state of cross-compiling snaps for Core24? Specifically, is it possible to build snaps for ARM64 on an AMD64 machine?

On Core20, I was able to use the --target-arch and --enable-experimental-target-arch flags to achieve this. Outside of Snapcraft, I can cross-compile most software using CMake and appropriate toolchains. I cannot use Launchpad build farms, as the software is proprietary, and I don’t currently have access to a decent ARM64 build server.

For Core24, is there a way to emulate ARM64 for snap builds, or is building directly on an ARM64 machine still required?

2

We’ve recently improved cross-compiling for core24. See this how-to for more information. It’s currently only available on the latest/edge channel, but will be included in the Snapcraft 8.8 release later this month.

3 Likes
3

We do not use autotools, but I get the gist of it.

In principle, this means that I should be able to cross compile our software by normal means, then use dump plugin to dump the resulting ARM64 executables into a snap. Then I can use stage-dependencies to source ARM64 run-time dependencies from ubuntu-ports as long as I remember to suffix the packages with :$CRAFT_ARCH_BUILD_FOR (except for those dependencies with architecture all).

Is this correctly understood?

4

I tried it out, but I have some trouble pulling dependencies outside of ubuntu and ubuntu-ports. Consider this minimal example - I create part foo with dependency libc6 and ros-jazzy-ros-base, the latter of which is available in the ROS2 repo. The following snapcraft.yaml builds fine on Ubuntu 24.04.2 LTS (AMD64) with snapcraft 8.7.4.post91:

name: foo
version: '0.0.0'
summary: foo
description: foo

grade: devel
confinement: devmode
base: core24

lint:
  ignore:
    - library
    - classic

package-repositories:
  - type: apt
    architectures: [$CRAFT_ARCH_BUILD_FOR]
    formats: [deb, deb-src]
    components: [main]
    suites: [noble]
    key-id: C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
    url: http://repo.ros2.org/ubuntu/main

parts:
  foo:
    plugin: nil
    source: .
    stage-packages:
      - libc6:$CRAFT_ARCH_BUILD_FOR
      - ros-jazzy-ros-base:$CRAFT_ARCH_BUILD_FOR

Then I change the schema to cross compile for ARM64, by adding platforms property and ubuntu-ports repository for libc6:arm64.

name: foo
version: '0.0.0'
summary: foo
description: foo

grade: devel
confinement: devmode
base: core24

lint:
  ignore:
    - library
    - classic

platforms:
  arm64:
    build-on: [amd64]
    build-for: [arm64]

package-repositories:
  - type: apt
    architectures: [$CRAFT_ARCH_BUILD_FOR]
    formats: [deb, deb-src]
    components: [main, universe]
    suites: [noble, noble-updates, noble-backports]
    key-id: F6ECB3762474EDA9D21B7022871920D1991BC93C
    url: http://ports.ubuntu.com/ubuntu-ports
  - type: apt
    architectures: [$CRAFT_ARCH_BUILD_FOR]
    formats: [deb, deb-src]
    components: [main]
    suites: [noble]
    key-id: C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
    url: http://repo.ros2.org/ubuntu/main

parts:
  foo:
    plugin: nil
    source: .
    stage-packages:
      - libc6:$CRAFT_ARCH_BUILD_FOR
      - ros-jazzy-ros-base:$CRAFT_ARCH_BUILD_FOR

When building this file, I get the error:

Stage package not found in part 'foo': ros-jazzy-ros-base:arm64.

I think it is odd that libc6:arm64 is successfully marked and installed while ros-jazzy-ros-base:arm64 is not. I wanted to file a bug, but I am not sure if this is intentional or I am missing something.

5

Thanks for trying it out! This smells like a bug to me.

I suspect it’s related to craft-parts passing the host architecture when downloading the package here. It appears this causes craft-parts to see if the package is available for the host arch and then download it for the foreign arch. In your scenario, it fails because ros-jazzy-ros-base isn’t available for AMD64. (edit: I don’t think this is the root cause anymore)

Would you mind making a bug report in snapcraft?

6

Right. I filed a bug here.

Thank you! :smile:

1 Like