Enable a rolling update of "Permit paying oneself"

[mvines]

#10337 will cause a hard fork if anybody sends a transfer to themselves with a collection of mixed validator nodes with/without this PR.

This affects both 1.2 and 1.1 and blocks an update of testnet and mainnet-beta

Options:

1. Back out Permit paying oneself #10337 entirely
2. Duplicate the system program, old and new version, and at a well-defined epoch swap in the new version

[garious]

What about rejecting payment to self below a particular epoch?

[mvines]

It's a plumbing problem, system program doesn't have epoch info

[garious]

Coincidentally, builtins have a different process_instruction signature than the ones loaders call. You can pass in whatever you'd like, so long as you pass it to all builtins. https://github.com/solana-labs/solana/blob/master/runtime/src/message_processor.rs#L295

[garious]

Also, keep in mind you can register the same process_instruction with multiple program IDs. The program ID is passed to process_instruction, which you can use to toggle operational semantics as-needed. This isn't a hack - it's actually what that program_id parameter was intended for.

[mvines]

Making everybody jump to System211111... doesn't sound nice though

[garious]

You don't need to. The trick is that you use System2 to represent the old behavior, not the new. Then, just add a special case such that before a certain epoch, System1 is swapped with System2.

[mvines]

The paths through bank to do this are very sneaky, unless you're seeing something I'm not.

[garious]

Thinking either here:
https://github.com/solana-labs/solana/blob/master/runtime/src/bank.rs#L1372

Or pass the epoch into process_message and do the swap in its for loop.

[mvines]

Here's the direction I'm thinking of, wdyt? #10375

[mvines]

Done.