core/vm: implement eip-8279: Block Access List Byte Floor

core/vm/floor.go

@@ -0,0 +1,76 @@
+// Copyright 2026 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package vm
+
+import "github.com/ethereum/go-ethereum/params"
+
+// FloorGasAccumulator implements the per-transaction floor accumulator defined
+// by EIP-8279 (Block Access List Byte Floor). It is an internal counter on the
+// execution environment, seeded with the EIP-8131 static floor and extended at
+// runtime by FloorGasPerByte for every byte an opcode adds to the EIP-7928
+// Block Access List.
+//
+// The accumulator is not part of the signed transaction, is not RLP-encoded,
+// gossiped, or persisted; no gas is reserved or deducted from the execution
+// budget. It is checked against the transaction's gas limit only to ensure the
+// sender can pay the floor if it ends up binding, and at transaction end the
+// receipt gas is settled as max(execution_gas_used, floor_gas_used).
+type FloorGasAccumulator struct {
+	floorGasUsed uint64 // accumulated floor gas (static seed + runtime extensions)
+	gasLimit     uint64 // tx.gas; the accumulator must never climb past this
+}
+
+// NewFloorGasAccumulator returns an accumulator seeded with the static floor
+// and bounded by the transaction gas limit.
+func NewFloorGasAccumulator(staticFloor, gasLimit uint64) *FloorGasAccumulator {
+	return &FloorGasAccumulator{floorGasUsed: staticFloor, gasLimit: gasLimit}
+}
+
+// FloorGasUsed returns the current value of the floor accumulator.
+func (f *FloorGasAccumulator) FloorGasUsed() uint64 {
+	if f == nil {
+		return 0
+	}
+	return f.floorGasUsed
+}
+
+// extendFloor extends the floor accumulator by numBytes BAL bytes, each priced
+// at params.FloorGasPerByte. It MUST be called BEFORE the matching BAL
+// insertion or state mutation: if the new floor would exceed the transaction
+// gas limit it returns ErrOutOfGas, which aborts the operation before any
+// unpaid BAL byte exists. A nil accumulator (pre-EIP-8279, or contexts without
+// BAL construction) is a no-op.
+func (f *FloorGasAccumulator) extendFloor(numBytes uint64) error {
+	if f == nil {
+		return nil
+	}
+	// numBytes is bounded by deployed-code length in the worst case; guard the
+	// multiplication against overflow before checking against the gas limit.
+	if numBytes > (^uint64(0))/params.FloorGasPerByte {
+		return ErrOutOfGas
+	}
+	extension := numBytes * params.FloorGasPerByte
+	if f.floorGasUsed > f.gasLimit-min(f.gasLimit, extension) {
+		return ErrOutOfGas
+	}
+	newFloor := f.floorGasUsed + extension
+	if newFloor > f.gasLimit {
+		return ErrOutOfGas
+	}
+	f.floorGasUsed = newFloor
+	return nil
+}