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.