Prefix exported symbols via UnmanagedCallersOnly attribute

[ivanpovazan]

This PR includes the following:

• All symbols exported via EntryPoint of UnmanagedCallersOnlyAttribute will be prefixed with a required _ on Apple platforms (as it is expected by the linker and dlsym)
• All symbols exported via undocumented (and legacy) ExportSymbol of MonoPInvokeCallbackAttribute will not be prefixed (in order to prevent breaking existing code)
• The change has been tested with the added functional test for iOS platforms

Fixes: #79491

/cc: @steveisok @mdh1418 @lateralusX

[ivanpovazan]

I have two questions regarding this change:

1. Should this PR also cover handling of: https://github.com/dotnet/runtime/blob/main/src/mono/mono/mini/aot-compiler.c#L5203-L5212
2. Should we add a functional test for apple devices which is testing this fix and the [mono] Export unmanagedcallersonly method symbols #79424

[steveisok]

2. Should we add a functional test for apple devices which is testing this fix and the [mono] Export unmanagedcallersonly method symbols #79424

Since iOS/tvOS doesn't run on PR's, it would be better to add a test for osx.

[ivanpovazan]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ivanpovazan]

2. Should we add a functional test for apple devices which is testing this fix and the [mono] Export unmanagedcallersonly method symbols #79424

Since iOS/tvOS doesn't run on PR's, it would be better to add a test for osx.

@steveisok, regarding your comment:

Afaik calling exported symbols is supposed to work only in full AOT mode, which makes the testing of this feature really specific.
I was thinking of adding it to the src/tests/Interop/UnmanagedCallersOnly runtime tests, but excluding its execution on other platforms or including it only in full AOT mode seems a bit impractical.
Instead I have added a functional test case for this purpose.

Does that make sense?

---

Additionally, with this change I also had to adapt: https://github.com/ivanpovazan/runtime/blob/unmanagedcallersonly-mangling/src/mono/msbuild/apple/build/AppleApp.targets#L143
to enable functional test to have a custom native main.
I can create a separate PR if you agree with this change.

[ivanpovazan]

Failures are unrelated

[steveisok]

Does that make sense?

Additionally, with this change I also had to adapt: https://github.com/ivanpovazan/runtime/blob/unmanagedcallersonly-mangling/src/mono/msbuild/apple/build/AppleApp.targets#L143 to enable functional test to have a custom native main. I can create a separate PR if you agree with this change.

Yeah, you're right in that we don't run many full aot legs. I'm fine with it.

It looks like the tvOS run timed out.

[ivanpovazan]

Created a separate PR to enable specifying custom native main for functional tests: #80546

[ivanpovazan]

Mentioning: xamarin/xamarin-macios#10470 for a reference

[lateralusX]

LGTM!