Implement side task

[kvinwang]

Steps:

• Support async IO in enclave
  Approches tried:

  • ❌ Port tokio to enclave. (Heavily using multi-threading things make it hard to port)
  • ❌ Implement a tiny http-client. (Not easy to implement a production quality async runtime)
  • ✅ Port async-std to enclave.
    The code is simpler than tokio. I have made much effort on letting the libstd support async stuffs. Finally failed due to that the futex syscall is impossible to be implemented in a C abi function in enclave. Tried a dirty hack on futex and got a working http client in SW mode, but I don't think it will work in HW mode.
    The next step is to modify the async-std to get rid of using futex.
    Update: httpclient works now after patched several of it's dependencies. 🎉

• Script to check unsupported syscalls.
  Difficulties:

  • The syscall number is a arg of the syscall function. So we need some sort of asm logic analysis.
  • Some calls are indrect calling into a GLOBAL_OFFSET_TABLE offset which is dynamically resolved by the runtime linker.

  Done, solved with the latest version of radare2.

• Implement a side task framework

Note:
surf uses getaddrinfo to resolve DNS which might block the exacutor.

Usage demos:

Low level way

Use AsyncSideTask