Screen share causes segmentation fault in Wayland

[Nathan Teodosio]

latest/candidate: 127.0.6533.72 2024-07-26 (2919) 176MB -

Trying to share screen in Wayland causes segmentation fault. Not happening in latest/stable: 126.0.6478.182 2024-07-19 (2910).

--->
[W][06188.305863] default | [ thread.c: 137 pw_thread_utils_set()] pw_thread_utils_set is deprecated and does nothing anymore
[0729/101708.956104:ERROR:ptracer.cc(605)] ptrace: Input/output error (5)
[0729/101709.056429:ERROR:elf_dynamic_array_reader.h(64)] tag not found
[0729/101709.082714:ERROR:elf_dynamic_array_reader.h(64)] tag not found
[0729/101709.096608:WARNING:thread_snapshot_linux.cc(112)] Unknown scheduling policy 1073741824
[0729/101709.099478:WARNING:thread_snapshot_linux.cc(112)] Unknown scheduling policy 1073741824
Segmentation fault (core dumped)
<---

[Nathan Teodosio (nteodosio)]

We're using 24.04's Pipewire to build Chromium (as it will fail to build with 22.04's).

Chromium's snapcraft.yaml furthermore specifies

  PIPEWIRE_MODULE_DIR: $SNAP/usr/lib/$CRAFT_ARCH_TRIPLET/pipewire-0.3

It is however not being respected as, inside the snap,

  PIPEWIRE_MODULE_DIR=/snap/chromium/2916/gnome-platform/usr/lib/x86_64-linux-gnu/pipewire-0.3

That's 22.04's Pipewire as Chromium candidate and stable are still on core22.

[Nathan Teodosio (nteodosio)]

Problem located:

--->
% cat /snap/chromium/current/snap/command-chain/desktop-launch
#!/bin/bash

set -- "${SNAP}/gnome-platform/command-chain/desktop-launch" "$@"
# shellcheck source=/dev/null
source "${SNAP}/snap/command-chain/run"
<---

And ${SNAP}/gnome-platform/command-chain/desktop-launch forces

--->
# Tell Pipewire where to find its configuration and plugins
export PIPEWIRE_CONFIG_DIR="$SNAP_DESKTOP_RUNTIME/usr/share/pipewire"
export PIPEWIRE_MODULE_DIR="$SNAP_DESKTOP_RUNTIME/usr/lib/$ARCH/pipewire-0.3"
export SPA_PLUGIN_DIR="$SNAP_DESKTOP_RUNTIME/usr/lib/$ARCH/spa-0.2"
<---

This is 8 months old[1] so that is why we didn't get it last year, which was the last time we used this work-around.

There is already a merge request[2] addressing this.

[1] https://github.com/snapcore/snapcraft-desktop-integration/blame/main/common/desktop-exports#L131
[2] https://github.com/snapcore/snapcraft-desktop-integration/pull/24

[Nathan Teodosio (nteodosio)]

James provided an alternative that I verified to solve the issue.

jamesh: I know we had trouble with some Rust apps due to pipewire-rs being incompatible with the old Pipewire[1]. But for some of those cases, the resulting binaries actually worked with the core22 pipewire since they weren't using any of the newer features the binding covered. I wonder if Chromium is similar?
nteodosio: No, it does cause a segmentation fault when attempting a screen share, <LP#2074358>. jamesh: You'll get a segfault if you mix one version of libpipewire/libspa with a different version of the plugins. One test would be to unpack the snap with unsquashfs, remove all pipewire libraries and plugins, and repack it with snap pack. See if it still crashes.

[1] https://gitlab.freedesktop.org/pipewire/pipewire-rs/-/issues/75