feat(specs): EIP-8037 diff-at-call-return state gas charging [DRAFT]

[spencer-tb]

Summary

Prototype implementation of diff-at-call-return state gas charging for EIP-8037, as proposed in the #eip-8037 discord channel by @chfast.

Instead of charging state gas at each opcode (CREATE, CALL, SSTORE, SELFDESTRUCT), compute a single state diff at each call return point and charge based on actual state growth. This eliminates most edge cases from Maria's state gas accounting review (points 1-6).

State gas charges at call return draw from the reservoir first, when exhausted, the remainder spills into regular gas, preserving the existing spillover semantics.

Open Spec Questions & Resolution

1. Who pays state gas for value transfer creating a new account?

Resolution: the callee's call frame pays.

A calls B (non-existent address) with value = 1 wei.
The value transfer creates B's account inside B's call frame.
At B's call return, the state diff shows +1 new account.
State gas is deducted from the reservoir at B's return.
If B's gas budget cannot cover GAS_NEW_ACCOUNT, the call fails.
A sees failure (0 on stack).

Consequence: the caller must forward enough gas to cover state creation costs at the callee's return.

2. How does code deposit failure work?

Resolution: CREATE is all-or-nothing at call return.

CREATE deploys a contract with 10KB of code.
At CREATE's call return, the state diff shows:
  +1 new account
  +10240 bytes of deployed code

If the reservoir covers the full cost: CREATE succeeds.
If not: the entire CREATE reverts. No account, no code.

Consequence: no partial state where an account exists without code. The call either fully succeeds or fully reverts.

3. Can the reservoir grow beyond its initial value?

Resolution: yes, capped at transaction level.

Contract clears a storage slot (nonzero to zero).
At call return, the state diff shows -1 storage slot.
The reservoir is credited by the slot's state gas cost.

At transaction end: tx_gas_used = max(0, tx.gas - gas_left - reservoir).
The floor at zero prevents the user from being paid to execute.

Test changes

These tests assumed per-opcode state gas charging. With diff-at-return, state gas is computed from the net state diff at call return, which changes gas amounts, failure modes, and who pays.

test_block_gas_refund_eip7778_no_block_reduction: Updated expected gas_used. The set-then-restore SSTORE pattern (0 to 1 to 0) now produces zero state gas because the net state diff is zero. Previously, state gas was charged on the first write and partially refunded via refund_counter.

test_call_value_transfer_existing_account_no_state_gas: Changed target from empty account (amount=0) to alive account (amount=1) and forwarded all gas via Op.GAS. With diff-at-return, the callee pays state gas at its call return, so the callee needs enough gas to cover GAS_NEW_ACCOUNT if the target is not alive.

test_caller_reservoir_preserved_after_callee_diff_reverts: Replaces test_code_deposit_oog_preserves_parent_reservoir. The caller CALLs a factory that does CREATE with large code. The factory's state diff (account + code) exceeds its budget, so the factory reverts. The caller's reservoir is preserved and used for a subsequent SSTORE.

test_parent_reverts_when_create_diff_exceeds_budget: Replaces test_nested_create_code_deposit_cannot_borrow_parent_gas. A wrapper CALLs a factory that does CREATE deploying 15000 bytes. The factory's diff cost (~17.7M) exceeds its gas budget (~16.4M), so the factory reverts. The wrapper verifies the CALL returned 0 (failure).

166/166 blockchain_test passing (excluding pre-existing fork transition failures).

Related

• Discord discussion: #eip-8037 channel, April 15 2026
• Maria's state gas accounting review
• EIP text clarifications: Update EIP-8037: more clarifcations for state gas accounting EIPs#11523

[spencer-tb]

Closing as no longer using this spec change!