Make crossgen trimmable

[agocke]

There are a couple of prerequisites here:

• Crossgen needs to be able to publish itself during the build:
  • The crossgen targets need to support running "publish"
  • The Publish targets need to use the locally-built runtime pack
  • The locally built runtime pack needs to use the live host (similar to Use live assets to construct the testhost #38034)
• Crossgen needs to use COMWrappers for all COM calls

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Issue Details

---

There are a couple of prerequisites here:

• Crossgen needs to be able to publish itself during the build:
  • The crossgen targets need to support running "publish"
  • The Publish targets need to use the locally-built runtime pack
  • The locally built runtime pack needs to use the live host (similar to Use live assets to construct the testhost #38034)
• Crossgen needs to use COMWrappers for all COM calls

Author:	agocke
Assignees:	-
Labels:	area-Infrastructure-coreclr
Milestone:	-

[agocke]

Work in progress here: https://github.com/agocke/runtime/tree/crossgen-trim

[MichalStrehovsky]

Crossgen needs to use COMWrappers for all COM calls

AFAIK crossgen is only using COM to read (non-portable) PDBs. It calls into .NET Framework APIs to do so. As a side effect, crossgen will ignore non-portable PDBs on any system that doesn't come with .NET Framework (be it Linux, mac, or even some Windows). That's a very subtle crosscompilation problem.

It might be worth looking into just replacing the COM in crossgen2 with a managed PDB reader - Cecil and CCI have code we might be able to just take.

[agocke]

Seems theoretically possible to re-implement in managed code, but I think there's more than just PDB reading, there's a writer too -- https://github.com/dotnet/runtime/blob/main/src/coreclr/tools/aot/ILCompiler.Diagnostics/ISymNGenWriter.cs