tvOS: Mono runtime for device is missing bitcode

[rolfbjarne]

Trying to link with libmonosgen-2.0.dylib from the tvOS runtime pack yields:

ld: '/Users/rolf/work/maccore/coreclr/xamarin-macios/builds/downloads/microsoft.netcore.app.runtime.tvos-arm64/6.0.0-preview.1.21102.12/runtimes/tvos-arm64/native/libmonosgen-2.0.dylib' does not contain bitcode. You must rebuild it with bitcode enabled (Xcode setting ENABLE_BITCODE), obtain an updated library from the vendor, or disable bitcode for this target. file '/Users/rolf/work/maccore/coreclr/xamarin-macios/builds/downloads/microsoft.netcore.app.runtime.tvos-arm64/6.0.0-preview.1.21102.12/runtimes/tvos-arm64/native/libmonosgen-2.0.dylib'

This is also evident in the size difference between the runtime pack and the old mono archive:

$ ls -la builds/downloads/microsoft.netcore.app.runtime.*/6.0.0-preview.1.21102.12/runtimes/tvos-arm64/native/libmonosgen-2.0.dylib
-rwxr--r--  1 rolf  staff  4307416 Feb  3 03:54 builds/downloads/microsoft.netcore.app.runtime.tvos-arm64/6.0.0-preview.1.21102.12/runtimes/tvos-arm64/native/libmonosgen-2.0.dylib

$ ls -la builds/downloads/ios-release-Darwin-5e9cb6d1c1de430965312927d5aed7fcb27bfa73/ios-libs/tvos/libmonosgen-2.0.dylib     
-rwxr-xr-x  1 rolf  staff  29800456 Feb 19 11:43 builds/downloads/ios-release-Darwin-5e9cb6d1c1de430965312927d5aed7fcb27bfa73/ios-libs/tvos/libmonosgen-2.0.dylib

[rolfbjarne]

CC @akoeplinger @steveisok

[akoeplinger]

@rolfbjarne is this a tvOS specific requirement? from what I can see we're doing pretty much the same on iOS/tvOS.

[rolfbjarne]

@akoeplinger yes, this is specific to tvOS, we don't need bitcode on any other platform (except for watchOS, but that's not on the roadmap right now).

[spouliot]

This is blocking us from enabling globalization (ICU) on tvOS.

see #50912

[filipnavara]

This should do for the bitcode in the libs+mono (doesn't enable the --with-bitcode option as in Mono's configure, just the ios.mk build flags): bf95449

Unfortunately the ICU build itself is not built with bitcode and that has to be done first:

  ld: warning: object file (/Users/filipnavara/.nuget/packages/microsoft.netcore.runtime.icu.transport/6.0.0-preview.4.21205.1/runtimes/tvOS-arm64/native/lib/libicuuc.a(uinvchar.ao)) was built for newer tvOS version (10.0) than being linked (9.0)
  ld: '/Users/filipnavara/.nuget/packages/microsoft.netcore.runtime.icu.transport/6.0.0-preview.4.21205.1/runtimes/tvOS-arm64/native/lib/libicuuc.a(uinvchar.ao)' does not contain bitcode. You must rebuild it with bitcode enabled (Xcode setting ENABLE_BITCODE), obtain an updated library from the vendor, or disable bitcode for this target.

https://github.com/dotnet/icu/blob/maint/maint-67/eng/icu.tvos.mk looks like a good start.

[filipnavara]

Now that ICU build is fixed and consumed I submitted #51220 to generate bitcode for the Mono runtime and native libraries. Once/if that gets accepted and the packages are bumped on Xamarin side this needs to be removed:

https://github.com/xamarin/xamarin-macios/blob/312ab983a134cca50091873b5f936b099757d209/runtime/Makefile#L670-L672
https://github.com/xamarin/xamarin-macios/blob/312ab983a134cca50091873b5f936b099757d209/runtime/monovm-bridge.m#L205-L210
https://github.com/xamarin/xamarin-macios/blob/312ab983a134cca50091873b5f936b099757d209/runtime/monovm-bridge.m#L215

[akoeplinger]

@filipnavara do you think there's anything left for us to do here, or just follow-up on the XI side?

[filipnavara]

@akoeplinger I am honestly not sure. The MonoVM build may not work exactly like the --with-bitcode configure option did in classic Mono. I tried to test the end-to-end scenario to ensure that all the necessary bits are present but I stopped short of actually running the code on a device. On the reverse side the runtime may contain unnecessary bits which are never used in llvmonly mode.

[akoeplinger]

@filipnavara I looked at the mono/mono code and it seems like the --with-bitcode was essentially only used to add -no-undefined to the linker flags so we should be good here though I'll open a PR to add that flag back.

[akoeplinger]

Opened #51241, I think we can close this here and open new issues if needed.

[spouliot]

The current package points to 3ffaab9 which does not include "Add additional compiler flags for tvOS (#51241)"

l builds//downloads/microsoft.netcore.app.runtime.mono.tvos-arm64/6.0.0-preview.4.21213.3/runtimes/tvos-arm64/native/libmonosgen-2.0.dylib
-rwxr--r--  1 poupou  staff  7108720 13 Apr 09:02 builds//downloads/microsoft.netcore.app.runtime.mono.tvos-arm64/6.0.0-preview.4.21213.3/runtimes/tvos-arm64/native/libmonosgen-2.0.dylib

^ current lib is without bitcode (confirmed by size and tried to build it locally)

I'll check back next week to see if we can re-enable this. Thanks!

[filipnavara]

I will double check the output but I think it should be linking against libmonosgen-2.0.a (static library), shouldn't it?

[filipnavara]

Version 6.0.0-preview.4.21215.1 does contain it for both .a and .dylib. The PR xamarin/xamarin-macios#11175 should bump way beyond that.

[spouliot]

We need both .a and .dylib

The latter is important to build a framework (still todo for dotnet) so we can share the runtime between the app and the extensions (which also exists, even if less common, in tvOS).

[spouliot]

The PR xamarin/xamarin-macios#11175 should bump way beyond that.

afaict the dotnet/runtime specific changes (quick script generated) for PR #11175 are

0f64b26...5d0817a

and this does not have the tvOS changes (so I'm not too worried about my current results)

[spouliot]

The current dotnet/installer has the missing commits

5d0817a...3ffaab9

Maestro has not (yet) updated the PR but doing a local build with the following diff worked (or at least it build)
https://gist.github.com/spouliot/78aabb8c09a6127da2e5b8ee0a7a0123