Fixing a broken snap build - part two

I wrote previously about debugging a broken x16emu snap. In short, something went wonky with ld. I started a thread on the snapcraft forum and Ken VanDine came to my assistance with an answer and a pull request.

I grabbed that pr, and it did indeed build successfully..

$ snapcraft --use-lxd
Launching instance...
Executed: pull alsa-pulseaudio
Executed: pull gnome/sdk
Executed: pull x16-roms
Executed: pull x16-emulator
Executed: build alsa-pulseaudio
Executed: build gnome/sdk
Executed: build x16-roms
Executed: skip pull x16-roms (already ran)
Executed: skip build x16-roms (already ran)
Executed: stage x16-roms (required to build 'x16-emulator')
Executed: skip pull alsa-pulseaudio (already ran)
Executed: skip build alsa-pulseaudio (already ran)
Executed: stage alsa-pulseaudio (required to build 'x16-emulator')
Executed: build x16-emulator
Executed: skip stage alsa-pulseaudio (already ran)
Executed: stage gnome/sdk
Executed: skip stage x16-roms (already ran)
Executed: stage x16-emulator
Executed: prime alsa-pulseaudio
Executed: prime gnome/sdk
Executed: prime x16-roms
Executed: prime x16-emulator
Executed parts lifecycle
Generated snap metadata
Created snap package x16emu_b16509b_amd64.snap

Even better, it’s smaller. The build I had in the store was 6MB in size:

$ snap info x16emu | grep stable
  latest/stable:    r44     2023-09-21 (1030) 6MB -

This new build is a paltry 1MB:

$ ls -lh x16emu_b16509b_amd64.snap 
-rw-r--r-- 1 alan alan 1.3M Oct  5 19:06 x16emu_b16509b_amd64.snap

Nice

Let’s take a quick look at the PR and break down what Ken did to fix this, in case it’s useful to someone else.

First up, we bump from core20 to core22 which means the snap will build on Ubuntu 22.04 LTS (Lunar) rather than Ubuntu 20.04 LTS (focal). There are a couple of knock-on effects of this. Any stage-packages will come from the newer archive, so will often be newer. That includes the build chain and other libraries. We need this, for the newer cc65 I mentioned in the previous blog post

  name: x16emu
- base: core20
+ base: core22
  adopt-info: x16-emulator
  summary: Commander X16 Emulator
  description: |

Here’s another effect of the core22 update. The snapcraft tool itself changes some behaviours and configuration options. Here we see a few such changes in the form of internal environment variables and commands. The change from $SNAPCRAFT_* to $CRAFT_* is a hint towards the universal nature of the new direction of snapcraft, not just building snaps anymore?

  layout:
-   /usr/lib/$SNAPCRAFT_ARCH_TRIPLET/alsa-lib:
-     bind: $SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/alsa-lib
+   /usr/lib/$CRAFT_ARCH_TRIPLET/alsa-lib:
+     bind: $SNAP/usr/lib/$CRAFT_ARCH_TRIPLET/alsa-lib

        - libsdl2-dev
        - git
      override-pull: |
-       snapcraftctl pull
+       craftctl default
        last_committed_tag="$(git describe --tags --abbrev=0)"
        echo $last_committed_tag
        last_released_tag="$(snap info $SNAPCRAFT_PROJECT_NAME | awk '$1 == "latest/beta:" { print $2 }')"

Here’s one of the main fixes to the snap. Adding the PATH will coerce the build to use make from the build system host, not from within the GNOME extension, which was the problem. This will prevent us from erroneously using the ld in the GNOME extension too.

-       make
-       cp x16emu $SNAPCRAFT_PART_INSTALL
+       PATH=/usr/bin:$PATH make
+       cp x16emu $CRAFT_PART_INSTALL

Here’s a super useful chunk of deletions! This is likely the big contributor to shrinking the size of the resulting snap. These libraries are all in the GNOME extension snap or just not needed, so there’s no point shipping them here too.

One thing I’ve been guilty of in the past is to ‘cargo-cult’ copy/paste a bunch of libraries I expect to be needed. What’s better - and what Ken did here - is start with nothing, and repeatedly iterate, adding only what’s needed.

The prime section explicitly spells out which files or groups of files will get ‘primed’ - that is, put forward to be packaged in the snap.

    stage-packages:
-       - libasound2
-       - libasound2-plugins
-       - libasyncns0
-       - libflac8
-       - libogg0
-       - libpulse0
+       - libdecor-0-0
-       - libsdl2-2.0-0
-       - libsndfile1
-       - libsndio7.0
-       - libvorbis0a
-       - libvorbisenc2
-       - libwayland-client0
-       - libwayland-cursor0
-       - libwayland-egl1
-       - libx11-6
-       - libxau6
-       - libxcb1
-       - libxcursor1
-       - libxdmcp6
-       - libxext6
-       - libxfixes3
-       - libxi6
-       - libxinerama1
-       - libxkbcommon0
-       - libxrandr2
-       - libxrender1
-       - libxss1
-       - libxxf86vm1
+ 
+     prime:
+       - usr/lib/*/libdecor*
+       - usr/lib/*/libSDL*
+       - usr/lib/*/libXss*
+       - x16emu

The final section bumps from the old core20-based gnome-3-38 extension to the core22-based gnome extension - which provides a ton of functionality. The snapcraft expand-extensions command can be used to show exactly what the extension provides. The output is quite large, so I have attached it here.

  apps:
    x16emu:
-     extensions: [ gnome-3-38 ]
+     extensions: [ gnome ]
      command: x16emu -rom $SNAP/rom.bin
      environment:
-       LD_LIBRARY_PATH: "$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/pulseaudio"
        ALSA_CONFIG_PATH: "$SNAP/etc/asound.conf"
      plugs:
        - joystick
-       - x11
-       - opengl
        - audio-playback
        - audio-record
        - alsa
        - network
        - network-bind
        - home
        - removable-media
-       - wayland

I merged Ken’s contribution, which triggered a new build, which was successful

This got automatically published to the edge channel.

When the upstream project release a stable version, we’ll get a build in the edge channel…

Thanks Ken!