From 3b9d30edc0ba9f9871b1bcea37bd869367a06a16 Mon Sep 17 00:00:00 2001
From: Martin Holst Swende <martin@swende.se>
Date: Tue, 27 Apr 2021 13:21:41 +0200
Subject: [PATCH] core/vm: make gas cost reporting to tracers correct (#22702)

Previously, the makeCallVariantGasCallEIP2929 charged the cold account access cost directly, leading to an incorrect gas cost passed to the tracer from the main execution loop.
This change still temporarily charges the cost (to allow for an accurate calculation of the available gas for the call), but then afterwards refunds it and instead returns the correct total gas cost to be then properly charged in the main loop.
---
 core/vm/operations_acl.go       | 22 +++++++--
 core/vm/runtime/runtime_test.go | 80 +++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+), 4 deletions(-)

diff --git a/core/vm/operations_acl.go b/core/vm/operations_acl.go
index ba811cdaa865e..c0d8ba67876ed 100644
--- a/core/vm/operations_acl.go
+++ b/core/vm/operations_acl.go
@@ -177,10 +177,15 @@ func makeCallVariantGasCallEIP2929(oldCalculator gasFunc) gasFunc {
 	return func(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
 		addr := common.Address(stack.Back(1).Bytes20())
 		// Check slot presence in the access list
-		if !evm.StateDB.AddressInAccessList(addr) {
+		warmAccess := evm.StateDB.AddressInAccessList(addr)
+		// The WarmStorageReadCostEIP2929 (100) is already deducted in the form of a constant cost, so
+		// the cost to charge for cold access, if any, is Cold - Warm
+		coldCost := ColdAccountAccessCostEIP2929 - WarmStorageReadCostEIP2929
+		if !warmAccess {
 			evm.StateDB.AddAddressToAccessList(addr)
-			// The WarmStorageReadCostEIP2929 (100) is already deducted in the form of a constant cost
-			if !contract.UseGas(ColdAccountAccessCostEIP2929 - WarmStorageReadCostEIP2929) {
+			// Charge the remaining difference here already, to correctly calculate available
+			// gas for call
+			if !contract.UseGas(coldCost) {
 				return 0, ErrOutOfGas
 			}
 		}
@@ -189,7 +194,16 @@ func makeCallVariantGasCallEIP2929(oldCalculator gasFunc) gasFunc {
 		// - transfer value
 		// - memory expansion
 		// - 63/64ths rule
-		return oldCalculator(evm, contract, stack, mem, memorySize)
+		gas, err := oldCalculator(evm, contract, stack, mem, memorySize)
+		if warmAccess || err != nil {
+			return gas, err
+		}
+		// In case of a cold access, we temporarily add the cold charge back, and also
+		// add it to the returned gas. By adding it to the return, it will be charged
+		// outside of this function, as part of the dynamic gas, and that will make it
+		// also become correctly reported to tracers.
+		contract.Gas += coldCost
+		return gas + coldCost, nil
 	}
 }
 
diff --git a/core/vm/runtime/runtime_test.go b/core/vm/runtime/runtime_test.go
index fc986c3a76287..48c707f006e98 100644
--- a/core/vm/runtime/runtime_test.go
+++ b/core/vm/runtime/runtime_test.go
@@ -597,3 +597,83 @@ func TestEip2929Cases(t *testing.T) {
 			"account (cheap)", code)
 	}
 }
+
+// TestColdAccountAccessCost test that the cold account access cost is reported
+// correctly
+// see: https://github.com/ethereum/go-ethereum/issues/22649
+func TestColdAccountAccessCost(t *testing.T) {
+	for i, tc := range []struct {
+		code []byte
+		step int
+		want uint64
+	}{
+		{ // EXTCODEHASH(0xff)
+			code: []byte{byte(vm.PUSH1), 0xFF, byte(vm.EXTCODEHASH), byte(vm.POP)},
+			step: 1,
+			want: 2600,
+		},
+		{ // BALANCE(0xff)
+			code: []byte{byte(vm.PUSH1), 0xFF, byte(vm.BALANCE), byte(vm.POP)},
+			step: 1,
+			want: 2600,
+		},
+		{ // CALL(0xff)
+			code: []byte{
+				byte(vm.PUSH1), 0x0,
+				byte(vm.DUP1), byte(vm.DUP1), byte(vm.DUP1), byte(vm.DUP1),
+				byte(vm.PUSH1), 0xff, byte(vm.DUP1), byte(vm.CALL), byte(vm.POP),
+			},
+			step: 7,
+			want: 2855,
+		},
+		{ // CALLCODE(0xff)
+			code: []byte{
+				byte(vm.PUSH1), 0x0,
+				byte(vm.DUP1), byte(vm.DUP1), byte(vm.DUP1), byte(vm.DUP1),
+				byte(vm.PUSH1), 0xff, byte(vm.DUP1), byte(vm.CALLCODE), byte(vm.POP),
+			},
+			step: 7,
+			want: 2855,
+		},
+		{ // DELEGATECALL(0xff)
+			code: []byte{
+				byte(vm.PUSH1), 0x0,
+				byte(vm.DUP1), byte(vm.DUP1), byte(vm.DUP1),
+				byte(vm.PUSH1), 0xff, byte(vm.DUP1), byte(vm.DELEGATECALL), byte(vm.POP),
+			},
+			step: 6,
+			want: 2855,
+		},
+		{ // STATICCALL(0xff)
+			code: []byte{
+				byte(vm.PUSH1), 0x0,
+				byte(vm.DUP1), byte(vm.DUP1), byte(vm.DUP1),
+				byte(vm.PUSH1), 0xff, byte(vm.DUP1), byte(vm.STATICCALL), byte(vm.POP),
+			},
+			step: 6,
+			want: 2855,
+		},
+		{ // SELFDESTRUCT(0xff)
+			code: []byte{
+				byte(vm.PUSH1), 0xff, byte(vm.SELFDESTRUCT),
+			},
+			step: 1,
+			want: 7600,
+		},
+	} {
+		tracer := vm.NewStructLogger(nil)
+		Execute(tc.code, nil, &Config{
+			EVMConfig: vm.Config{
+				Debug:  true,
+				Tracer: tracer,
+			},
+		})
+		have := tracer.StructLogs()[tc.step].GasCost
+		if want := tc.want; have != want {
+			for ii, op := range tracer.StructLogs() {
+				t.Logf("%d: %v %d", ii, op.OpName(), op.GasCost)
+			}
+			t.Fatalf("tescase %d, gas report wrong, step %d, have %d want %d", i, tc.step, have, want)
+		}
+	}
+}