Dockerize building `sentry-native` for Linux

[bitsandfoxes]

Problem

Github no longer supports Ubuntu 20.04 runners, causing us to not be able to release without potentially breaking user's builds when running their game/server on older Ubuntu versions.

Context

We're currently building sentry-native as part of our CI (and package & release process).
For Linux, we've pinned the runner version to Ubuntu 20.04 which is no longer supported. We were building on the oldest available version to maintain compatibility.

sentry-unity/.github/workflows/ci.yml

Lines 34 to 37 in 3add276

	- target: Linux
	# Build using older Linux version to preserve sdk compatibility with old GLIBC
	# See discussion in https://github.com/getsentry/sentry-unity/issues/1730 for more details
	host: ubuntu-20.04

We're already fixing and installing additional Linux dependencies as part of the build pipeline.

The actual building happens from within a MSBuild target

sentry-unity/Directory.Build.targets

Lines 303 to 319 in 3add276

	<Target Name="BuildLinuxSDK" Condition="'$(MSBuildProjectName)' == 'Sentry.Unity'
	And $([MSBuild]::IsOsPlatform('Linux'))
	And !Exists('$(SentryLinuxArtifactsDestination)libsentry.so')" BeforeTargets="BeforeBuild">
	<Error Condition="!Exists('$(SentryNativeRoot)')" Text="Couldn't find the Native root at $(SentryNativeRoot)."></Error>
	<Message Importance="High" Text="Building artifacts of Sentry Native SDK for Linux." />
	<Exec WorkingDirectory="$(SentryNativeRoot)" Command="cmake -B build -D SENTRY_BACKEND=breakpad -D SENTRY_SDK_NAME=sentry.native.unity -D CMAKE_BUILD_TYPE=RelWithDebInfo -S ." />
	<Exec WorkingDirectory="$(SentryNativeRoot)" Command="cmake --build build --target sentry --parallel" />
	<MakeDir Directories="$(SentryLinuxArtifactsDestination)"/>
	<!-- strip all, including exported symbols except those starting with 'sentry_', except for 'sentry__' -->
	<Exec WorkingDirectory="$(SentryNativeRoot)" Command="strip -s build/libsentry.so -w -K sentry_[^_]* -o $(SentryLinuxArtifactsDestination)libsentry.so" />
	<Exec WorkingDirectory="$(SentryNativeRoot)" Command="cp build/libsentry.so $(SentryLinuxArtifactsDestination)libsentry.dbg.so" />
	<Exec WorkingDirectory="$(SentryLinuxArtifactsDestination)" Command="objcopy --add-gnu-debuglink=libsentry.dbg.so libsentry.so" />
	</Target>

Possible Solutions

Dockerize the build process for sentry-native on Linux.

[Dav1dde]

We had the same issue in Relay and ended up just building the binary in a container, the diff is here: getsentry/relay#4549

Using the container feature of github actions, this was quite pleasant:

    runs-on: ubuntu-latest // this used to be ubuntu-20.04
    container:
      image: ubuntu:20.04

Just note, that the container does not contain any of the pre-installed tools the github runner image has installed.

Hope that helps o/

[jpnurmi]

The ghcr.io/catthehacker/ubuntu:dotnet-20.04 container by nektosact.com would work almost out of the box (example jpnurmi@d74689f) but the vanilla ubuntu:20.04 container together with setup-dotnet (example jpnurmi@6c04eb6) might be nicer?

[jpnurmi]

Official ubuntu:20.04 + https://dot.net/v1/dotnet-install.sh could be a fine combo too.

[bitsandfoxes]

I'd be more happy with putting the actual build into a script for the action and call that from the target as well. So we don't need to install dotnet just to build a C library.