SIMD-0129: Alt_BN128 Syscalls - Simplified Error Code

[0x0ece]

Summary

Simplify the return error code for the family of Alt_BN128 syscalls:
sol_alt_bn128_group_op, sol_alt_bn128_compression and sol_poseidon.

A single error code is sufficient, in line with all other syscalls.

Motivation

Syscalls in Solana can return:

• Success, e.g. represented in Rust as Ok(0) or Ok(SUCCESS)
• Error to the program, e.g. represented in Rust as Ok(1)
• Fatal error to the VM, aborting the transaction, e.g. represented in Rust
  as Err(<something>)

Most syscalls only have a single error code returned to the program, i.e. Ok(1).
The family of Alt_BN128 syscalls, viceversa, has a richer set of error codes.

This proposal aims to simplify the error value for these syscalls, in line with
all the other syscalls, and simply return Ok(1) (in addition to fatal errors,
that are left unchanged).

We stress that multiple error codes cause a maintenance burden for the validators.
Moreover, if two different implementation were to return different error codes,
an attacker could exploit the different behavior to cause consensus failure.

[samkim-crypto]

I think this proposal is straightforward, simple to implement, and a definite improvement for consensus/security.

[ripatel-fd]

I support this SIMD because it is straightforward and simplifies the runtime significantly. The proposal is well specified and unambiguous.

For the record, Light Protocol was concerned about any delays to the activation of alt_bn128 syscalls on mainnet. Discussions in Discord reached a rough agreement that the alt_bn128 syscalls will be activated with the complicated error logic first. Then, at a later point in time, this proposal will go into effect via a second feature gate.

https://discord.com/channels/428295358100013066/967028962746327060/1219725414960857232

[ripatel-fd]

@jacobcreech @t-nelson This SIMD is ready to move to 'finalized draft' stage. Please feel free to add more reviewers if you think more eyes are needed. Otherwise, I suggest we merge this PR.

[jacobcreech]

Going to do a last call for any comments on this SIMD. If there are no more issues, we'll merge this in on Friday.

[jacobcreech]

Looks like general consensus was made. Merging. Thank you @0x0ece for championing this!