Gas Forwarding

MegaETH 98/100 gas forwarding rule — CALL, DELEGATECALL, STATICCALL, CALLCODE, and CREATE/CREATE2 forwarding semantics.

This page specifies how MegaETH forwards gas into child call frames and contract-creation call frames. It defines the stable 98/100 forwarding rule and its relation to value-transfer stipends.

Motivation

The standard 63/64 forwarding rule was introduced to mitigate call-depth attacks by ensuring that each nested call retains less gas than its parent. MegaETH is designed to support block gas limits up to 10 billion gas. At that scale, the inherited 63/64 rule again leaves enough gas available at deep call depth to reintroduce the attack it was meant to mitigate.

MegaETH therefore replaces the inherited forwarding fraction with a stricter rule.

Specification

Stable Forwarding Rule

A node MUST cap gas forwarded by CALL-like opcodes and contract-creation opcodes to 98/100 of the parent's remaining gas.

The stable forwarding rule applies to:

• CALL,
• CALLCODE,
• DELEGATECALL,
• STATICCALL,
• CREATE,
• CREATE2.

The forwarding cap is:

forwarded_gas_cap = parent_remaining_gas - parent_remaining_gas × 2 / 100

The child call frame gas limit MUST be the minimum of:

• the gas requested by the caller, and
• forwarded_gas_cap.

Value Transfer Stipend

For CALL and CALLCODE with non-zero value transfer, the standard EVM CALL_STIPEND MUST be preserved. The forwarding cap applies to the forwarded gas portion, not to the stipend itself.

The child call frame gas for value-transferring CALL and CALLCODE MUST be:

child_gas = min(requested_forwarded_gas, forwarded_gas_cap) + CALL_STIPEND

For DELEGATECALL, STATICCALL, CREATE, and CREATE2, no call stipend applies.

Storage Gas Stipend Interaction

For internal (call depth greater than zero) value-transferring CALL and CALLCODE, the callee frame receives a STORAGE_CALL_STIPEND allowance. This allowance MUST NOT inflate the callee's gas_limit: the child-frame gas limit is exactly min(requested_forwarded_gas, forwarded_gas_cap) + CALL_STIPEND, with no STORAGE_CALL_STIPEND term.

The allowance is a per-frame budget reserved exclusively for the storage-gas surcharges that MegaETH adds on top of standard EVM opcode costs. A node MUST apply the allowance only to the following storage-gas surcharge sites incurred within the callee frame:

• empty-account creation via value-transferring CALL / CALLCODE,
• contract creation via CREATE / CREATE2,
• the first-time zero-to-non-zero SSTORE write,
• LOG topic and data storage gas, and
• empty-beneficiary creation via SELFDESTRUCT.

At each such site, a node MUST draw up to STORAGE_CALL_STIPEND from the frame's remaining allowance and charge only the residual surcharge (the surcharge minus the amount drawn) against the frame's gas.

Because the allowance never enters the frame's gas limit, it MUST NOT be spendable on compute (standard EVM opcode) gas. The allowance does not apply to standard EVM opcode costs: a callee whose forwarded gas plus CALL_STIPEND does not cover the standard EVM cost of an opcode MUST run out of gas normally regardless of the remaining allowance. Any portion of the allowance not drawn by a surcharge site is not returned to the caller; the allowance never contributes to the gas a frame returns to its parent.

The allowance applies to internal value-transferring CALL and CALLCODE only. Top-level transactions, DELEGATECALL, STATICCALL, CREATE, CREATE2, and any value-zero call MUST NOT receive the allowance.

Constants

Constant	Value	Description
GAS_FORWARD_NUMERATOR	98	Numerator of the stable forwarding fraction
GAS_FORWARD_DENOMINATOR	100	Denominator of the stable forwarding fraction
CALL_STIPEND	2,300	Standard EVM stipend preserved for value-transferring CALL and CALLCODE
STORAGE_CALL_STIPEND	23,000	Per-frame storage-gas allowance for internal value-transferring CALL and CALLCODE

Rationale

Why 98/100 instead of 63/64? The inherited 63/64 rule was designed to mitigate call-depth attacks by ensuring that each nested call retains less gas than its parent. MegaETH is intended to support block gas limits up to 10 billion gas, which makes the inherited 63/64 reduction insufficient to suppress that attack pattern at deep call depth. Retaining 2% instead of approximately 1.56% reduces residual gas more aggressively and restores the protective intent of gas-based call-depth mitigation under MegaETH's higher gas regime.

Why make the storage gas stipend a per-frame allowance instead of inflating the child gas limit? The stipend exists so a value-transferring internal call can pay MegaETH's storage-gas surcharges even when the caller forwards little or no gas. Adding the stipend to the child's gas limit, Rex4 left it spendable on compute opcodes; the per-frame compute-gas cap that fenced it off was enforced only after each opcode completed, so a single expensive opcode could record its full compute cost into the parent's compute-gas counter before the cap triggered, and repeated value-transferring calls could amplify recorded compute gas beyond the transaction's compute-gas limit. Keeping the stipend as an allowance that never enters the child's gas limit makes it structurally unspendable on compute, removing the amplification path without changing the grant amount or which calls qualify.

Security Considerations

If more than 98/100 of gas is forwarded, MegaETH's high block gas limits (up to 10 billion) mean enough residual gas survives at deep call depth to sustain a call-depth denial-of-service attack. The 63/64 rule inherited from Ethereum was designed for much lower gas budgets; at 10B gas, 98/100 is needed to achieve the same protective effect.

Spec History

• MiniRex introduced the 98/100 rule for CALL, CREATE, and CREATE2 only.
• Rex extended the rule to all CALL-like opcodes.
• Rex4 — added storage-gas stipend for value-transferring CALL and CALLCODE.
• Rex5 — recast the storage-gas stipend as a per-frame allowance that no longer inflates the child's gas limit (so it cannot be spent on compute), and corrected the parent's compute-gas attribution to exclude the CALL_STIPEND for value-transferring CALL / CALLCODE; the 23,000 grant amount and admission conditions are unchanged.