feat: precompile override via params.Extras hooks

core/vm/contracts.libevm_test.go

@@ -0,0 +1,113 @@
+package vm
+
+import (
+	"fmt"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/rawdb"
+	"github.com/ethereum/go-ethereum/core/state"
+	"github.com/ethereum/go-ethereum/libevm"
+	"github.com/ethereum/go-ethereum/params"
+	"github.com/holiman/uint256"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/exp/rand"
+)
+
+// precompileOverrides is a [params.RulesHooks] that overrides precompiles from
+// a map of predefined addresses.
+type precompileOverrides struct {
+	contracts        map[common.Address]PrecompiledContract
+	params.NOOPHooks // all other hooks
+}
+
+func (o precompileOverrides) PrecompileOverride(a common.Address) (libevm.PrecompiledContract, bool) {
+	c, ok := o.contracts[a]
+	return c, ok
+}
+
+// A precompileStub is a [PrecompiledContract] that always returns the same
+// values.
+type precompileStub struct {
+	requiredGas uint64
+	returnData  []byte
+}
+
+func (s *precompileStub) RequiredGas([]byte) uint64  { return s.requiredGas }
+func (s *precompileStub) Run([]byte) ([]byte, error) { return s.returnData, nil }
+
+func TestPrecompileOverride(t *testing.T) {
+	type test struct {
+		name        string
+		addr        common.Address
+		requiredGas uint64
+		stubData    []byte
+	}
+
+	const gasLimit = uint64(1e7)
+
+	tests := []test{
+		{
+			name:        "arbitrary values",
+			addr:        common.Address{'p', 'r', 'e', 'c', 'o', 'm', 'p', 'i', 'l', 'e'},
+			requiredGas: 314159,
+			stubData:    []byte("the return data"),
+		},
+	}
+
+	rng := rand.New(rand.NewSource(42))
+	for _, addr := range PrecompiledAddressesCancun {
+		tests = append(tests, test{
+			name:        fmt.Sprintf("existing precompile %v", addr),
+			addr:        addr,
+			requiredGas: rng.Uint64n(gasLimit),
+			stubData:    addr[:],
+		})
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			precompile := &precompileStub{
+				requiredGas: tt.requiredGas,
+				returnData:  tt.stubData,
+			}
+
+			params.TestOnlyClearRegisteredExtras()
+			params.RegisterExtras(params.Extras[params.NOOPHooks, precompileOverrides]{
+				NewRules: func(_ *params.ChainConfig, _ *params.Rules, _ *params.NOOPHooks, blockNum *big.Int, isMerge bool, timestamp uint64) *precompileOverrides {
+					return &precompileOverrides{
+						contracts: map[common.Address]PrecompiledContract{
+							tt.addr: precompile,
+						},
+					}
+				},
+			})
+
+			t.Run(fmt.Sprintf("%T.Call([overridden precompile address = %v])", &EVM{}, tt.addr), func(t *testing.T) {
+				gotData, gotGasLeft, err := newEVM(t).Call(AccountRef{}, tt.addr, nil, gasLimit, uint256.NewInt(0))
+				require.NoError(t, err)
+				assert.Equal(t, tt.stubData, gotData, "contract's return data")
+				assert.Equal(t, gasLimit-tt.requiredGas, gotGasLeft, "gas left")
+			})
+		})
+	}
+}
+
+func newEVM(t *testing.T) *EVM {
+	t.Helper()
+
+	sdb, err := state.New(common.Hash{}, state.NewDatabase(rawdb.NewMemoryDatabase()), nil)
+	require.NoError(t, err, "state.New()")
+
+	return NewEVM(
+		BlockContext{
+			Transfer: func(_ StateDB, _, _ common.Address, _ *uint256.Int) {},
+		},
+		TxContext{},
+		sdb,
+		&params.ChainConfig{},
+		Config{},
+	)
+}

core/vm/evm.go

@@ -38,6 +38,9 @@ type (
 )
 
 func (evm *EVM) precompile(addr common.Address) (PrecompiledContract, bool) {
+	if p, override := evm.chainRules.Hooks().PrecompileOverride(addr); override {
+		return p, p != nil
+	}
 	var precompiles map[common.Address]PrecompiledContract
 	switch {
 	case evm.chainRules.IsCancun:

libevm/interfaces_test.go

@@ -0,0 +1,16 @@
+package libevm_test
+
+import (
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/libevm"
+)
+
+// These two interfaces MUST be identical. If this breaks then the libevm copy
+// MUST be updated.
+var (
+	// Each assignment demonstrates that the methods of the LHS interface are a
+	// (non-strict) subset of the RHS interface's; both being possible
+	// proves that they are identical.
+	_ vm.PrecompiledContract     = (libevm.PrecompiledContract)(nil)
+	_ libevm.PrecompiledContract = (vm.PrecompiledContract)(nil)
+)

libevm/libevm.go

@@ -0,0 +1,9 @@
+package libevm
+
+// PrecompiledContract is an exact copy of vm.PrecompiledContract, mirrored here
+// for instances where importing that package would result in a circular
+// dependency.
+type PrecompiledContract interface {
+	RequiredGas(input []byte) uint64
+	Run(input []byte) ([]byte, error)
+}

params/config.libevm.go

@@ -5,13 +5,15 @@ import (
 	"fmt"
 	"math/big"
 	"reflect"
+	"runtime"
+	"strings"
 
 	"github.com/ethereum/go-ethereum/libevm/pseudo"
 )
 
 // Extras are arbitrary payloads to be added as extra fields in [ChainConfig]
 // and [Rules] structs. See [RegisterExtras].
-type Extras[C any, R any] struct {
+type Extras[C ChainConfigHooks, R RulesHooks] struct {
 	// NewRules, if non-nil is called at the end of [ChainConfig.Rules] with the
 	// newly created [Rules] and other context from the method call. Its
 	// returned value will be the extra payload of the [Rules]. If NewRules is
@@ -37,19 +39,38 @@ type Extras[C any, R any] struct {
 //
 // The payloads can be accessed via the [ExtraPayloadGetter.FromChainConfig] and
 // [ExtraPayloadGetter.FromRules] methods of the getter returned by
-// RegisterExtras.
-func RegisterExtras[C any, R any](e Extras[C, R]) ExtraPayloadGetter[C, R] {
+// RegisterExtras. Where stated in the interface definitions, they will also be
+// used as hooks to alter Ethereum behaviour; if this isn't desired then they
+// can embed [NOOPHooks] to satisfy either interface.
+func RegisterExtras[C ChainConfigHooks, R RulesHooks](e Extras[C, R]) ExtraPayloadGetter[C, R] {
 	if registeredExtras != nil {
 		panic("re-registration of Extras")
 	}
 	mustBeStruct[C]()
 	mustBeStruct[R]()
+
+	getter := e.getter()
 	registeredExtras = &extraConstructors{
 		chainConfig: pseudo.NewConstructor[C](),
 		rules:       pseudo.NewConstructor[R](),
 		newForRules: e.newForRules,
+		getter:      getter,
 	}
-	return e.getter()
+	return getter
+}
+
+// TestOnlyClearRegisteredExtras clears the [Extras] previously passed to
+// [RegisterExtras]. It panics if called from a non-test file.
+//
+// In tests it SHOULD be called before every call to [RegisterExtras] and then
+// defer-called afterwards. This is a workaround for the single-call limitation
+// on [RegisterExtras].
+func TestOnlyClearRegisteredExtras() {
+	_, file, _, ok := runtime.Caller(1 /* 0 would be here, not our caller */)
+	if !ok || !strings.HasSuffix(file, "_test.go") {
+		panic("call from non-test file")
+	}
+	registeredExtras = nil
 }
 
 // registeredExtras holds non-generic constructors for the [Extras] types
@@ -59,6 +80,12 @@ var registeredExtras *extraConstructors
 type extraConstructors struct {
 	chainConfig, rules pseudo.Constructor
 	newForRules        func(_ *ChainConfig, _ *Rules, blockNum *big.Int, isMerge bool, timestamp uint64) *pseudo.Type
+	// use top-level hooksFrom<X>() functions instead of these as they handle
+	// instances where no [Extras] were registered.
+	getter interface {
+		hooksFromChainConfig(*ChainConfig) ChainConfigHooks
+		hooksFromRules(*Rules) RulesHooks
+	}
 }
 
 func (e *Extras[C, R]) newForRules(c *ChainConfig, r *Rules, blockNum *big.Int, isMerge bool, timestamp uint64) *pseudo.Type {
@@ -88,7 +115,7 @@ func notStructMessage[T any]() string {
 // An ExtraPayloadGettter provides strongly typed access to the extra payloads
 // carried by [ChainConfig] and [Rules] structs. The only valid way to construct
 // a getter is by a call to [RegisterExtras].
-type ExtraPayloadGetter[C any, R any] struct {
+type ExtraPayloadGetter[C ChainConfigHooks, R RulesHooks] struct {
 	_ struct{} // make godoc show unexported fields so nobody tries to make their own getter ;)
 }
 
@@ -97,20 +124,42 @@ func (ExtraPayloadGetter[C, R]) FromChainConfig(c *ChainConfig) *C {
 	return pseudo.MustNewValue[*C](c.extraPayload()).Get()
 }
 
+// hooksFromChainConfig is equivalent to FromChainConfig(), but returns an
+// interface instead of the concrete type implementing it; this allows it to be
+// used in non-generic code. If the concrete-type value is nil (typically
+// because no [Extras] were registered) a [noopHooks] is returned so it can be
+// used without nil checks.
+func (e ExtraPayloadGetter[C, R]) hooksFromChainConfig(c *ChainConfig) ChainConfigHooks {
+	if h := e.FromChainConfig(c); h != nil {
+		return *h
+	}
+	return NOOPHooks{}
+}
+
 // FromRules returns the Rules' extra payload.
 func (ExtraPayloadGetter[C, R]) FromRules(r *Rules) *R {
 	return pseudo.MustNewValue[*R](r.extraPayload()).Get()
 }
 
+// hooksFromRules is the [RulesHooks] equivalent of hooksFromChainConfig().
+func (e ExtraPayloadGetter[C, R]) hooksFromRules(r *Rules) RulesHooks {
+	if h := e.FromRules(r); h != nil {
+		return *h
+	}
+	return NOOPHooks{}
+}
+
 // UnmarshalJSON implements the [json.Unmarshaler] interface.
 func (c *ChainConfig) UnmarshalJSON(data []byte) error {
 	type raw ChainConfig // doesn't inherit methods so avoids recursing back here (infinitely)
 	cc := &struct {
 		*raw
 		Extra *pseudo.Type `json:"extra"`
 	}{
-		raw:   (*raw)(c),                                 // embedded to achieve regular JSON unmarshalling
-		Extra: registeredExtras.chainConfig.NilPointer(), // `c.extra` is otherwise unexported
+		raw: (*raw)(c), // embedded to achieve regular JSON unmarshalling
+	}
+	if e := registeredExtras; e != nil {
+		cc.Extra = e.chainConfig.NilPointer() // `c.extra` is otherwise unexported
 	}
 
 	if err := json.Unmarshal(data, cc); err != nil {

params/config.libevm_test.go

@@ -10,15 +10,9 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-// testOnlyClearRegisteredExtras SHOULD be called before every call to
-// [RegisterExtras] and then defer-called afterwards. This is a workaround for
-// the single-call limitation on [RegisterExtras].
-func testOnlyClearRegisteredExtras() {
-	registeredExtras = nil
-}
-
 type rawJSON struct {
 	json.RawMessage
+	NOOPHooks
 }
 
 var _ interface {
@@ -30,15 +24,19 @@ func TestRegisterExtras(t *testing.T) {
 	type (
 		ccExtraA struct {
 			A string `json:"a"`
+			ChainConfigHooks
 		}
 		rulesExtraA struct {
 			A string
+			RulesHooks
 		}
 		ccExtraB struct {
 			B string `json:"b"`
+			ChainConfigHooks
 		}
 		rulesExtraB struct {
 			B string
+			RulesHooks
 		}
 	)
 
@@ -79,20 +77,20 @@ func TestRegisterExtras(t *testing.T) {
 		{
 			name: "custom JSON handling honoured",
 			register: func() {
-				RegisterExtras(Extras[rawJSON, struct{}]{})
+				RegisterExtras(Extras[rawJSON, struct{ RulesHooks }]{})
 			},
 			ccExtra: pseudo.From(&rawJSON{
 				RawMessage: []byte(`"hello, world"`),
 			}).Type,
-			wantRulesExtra: (*struct{})(nil),
+			wantRulesExtra: (*struct{ RulesHooks })(nil),
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			testOnlyClearRegisteredExtras()
+			TestOnlyClearRegisteredExtras()
 			tt.register()
-			defer testOnlyClearRegisteredExtras()
+			defer TestOnlyClearRegisteredExtras()
 
 			in := &ChainConfig{
 				ChainID: big.NewInt(142857),
@@ -116,42 +114,35 @@ func TestRegisterExtras(t *testing.T) {
 }
 
 func TestExtrasPanic(t *testing.T) {
-	testOnlyClearRegisteredExtras()
-	defer testOnlyClearRegisteredExtras()
-
-	assertPanics(
-		t, func() {
-			RegisterExtras(Extras[int, struct{}]{})
-		},
-		notStructMessage[int](),
-	)
+	TestOnlyClearRegisteredExtras()
+	defer TestOnlyClearRegisteredExtras()
 
 	assertPanics(
 		t, func() {
-			RegisterExtras(Extras[struct{}, bool]{})
+			new(ChainConfig).extraPayload()
 		},
-		notStructMessage[bool](),
+		"before RegisterExtras",
 	)
 
 	assertPanics(
 		t, func() {
-			new(ChainConfig).extraPayload()
+			new(Rules).extraPayload()
 		},
 		"before RegisterExtras",
 	)
 
 	assertPanics(
 		t, func() {
-			new(Rules).extraPayload()
+			mustBeStruct[int]()
 		},
-		"before RegisterExtras",
+		notStructMessage[int](),
 	)
 
-	RegisterExtras(Extras[struct{}, struct{}]{})
+	RegisterExtras(Extras[struct{ ChainConfigHooks }, struct{ RulesHooks }]{})
 
 	assertPanics(
 		t, func() {
-			RegisterExtras(Extras[struct{}, struct{}]{})
+			RegisterExtras(Extras[struct{ ChainConfigHooks }, struct{ RulesHooks }]{})
 		},
 		"re-registration",
 	)