[Mono] Split QCall table declarations from their implementations

[lambdageek]

For icalls, Mono can optionally be compiled wihout the big icall table in icall-def-netcore.h. Instead, the icall table is defined by a special IL Linker step based on the icalls that are actually reachable from managed code.

This allows the native linker to tree-shake the native code and remove unused icalls. (Otherwise every icall looks like it is referenced from the big native function pointer array that is defined based on the contents of icall-def-netcore).

As we migrate to using QCalls more, we should enhance that infrastructure to also allow the qcall tables to be created based on use, too.

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Issue Details

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For icalls, Mono can optionally be compiled wihout the big icall table in icall-def-netcore.h. Instead, the icall table is defined by a special IL Linker step based on the icalls that are actually reachable from managed code.

This allows the native linker to tree-shake the native code and remove unused icalls. (Otherwise every icall looks like it is referenced from the big native function pointer array that is defined based on the contents of icall-def-netcore).

As we migrate to using QCalls more, we should enhance that infrastructure to also allow the qcall tables to be created based on use, too.

Author:	lambdageek
Assignees:	-
Labels:	area-Infrastructure-mono
Milestone:	7.0.0

[lambdageek]

An example of adding a new qcall to mono is #57610

[steveisok]

@lambdageek Do you think this can be completed in the 7 timeframe?

[lambdageek]

I don't think so. We also didn't migrate very many icalls to qcalls in 7, so there's not much impact from doing this in the next release