fix(libevm/legacy): PrecompiledStatefulContract gas and remaining gas handling

libevm/legacy/legacy.go

@@ -1,4 +1,4 @@
-// Copyright 2024 the libevm authors.
+// Copyright 2024-2025 the libevm authors.
 //
 // The libevm additions to go-ethereum are free software: you can redistribute
 // them and/or modify them under the terms of the GNU Lesser General Public License
@@ -18,7 +18,11 @@
 // equivalents.
 package legacy
 
-import "github.com/ava-labs/libevm/core/vm"
+import (
+	"fmt"
+
+	"github.com/ava-labs/libevm/core/vm"
+)
 
 // PrecompiledStatefulContract is the legacy signature of
 // [vm.PrecompiledStatefulContract], which explicitly accepts and returns gas
@@ -31,7 +35,10 @@ func (c PrecompiledStatefulContract) Upgrade() vm.PrecompiledStatefulContract {
 	return func(env vm.PrecompileEnvironment, input []byte) ([]byte, error) {
 		gas := env.Gas()
 		ret, remainingGas, err := c(env, input, gas)
-		if used := gas - remainingGas; used < gas {
+		if remainingGas > gas {
+			return nil, fmt.Errorf("remaining gas %d exceeds supplied gas %d", remainingGas, gas)
+		}
+		if used := gas - remainingGas; used <= gas {
 			env.UseGas(used)
 		}
 		return ret, err

libevm/legacy/legacy_test.go

@@ -0,0 +1,100 @@
+// Copyright 2025 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them 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 libevm additions are distributed in the hope that they 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 legacy
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/ava-labs/libevm/core/vm"
+)
+
+func TestPrecompiledStatefulContract_Upgrade(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		envGas        uint64
+		input         []byte
+		cRet          []byte
+		cRemainingGas uint64
+		cErr          error
+		wantRet       []byte
+		wantErr       string
+		wantGasUsed   uint64
+	}{
+		"call_error": {
+			envGas:        10,
+			input:         []byte{1},
+			cRet:          []byte{2},
+			cRemainingGas: 6,
+			cErr:          errors.New("test error"),
+			wantRet:       []byte{2},
+			wantErr:       "test error",
+			wantGasUsed:   4,
+		},
+		"remaining_gas_exceeds_supplied_gas": {
+			envGas:        10,
+			input:         []byte{1},
+			cRet:          []byte{2},
+			cRemainingGas: 11,
+			wantErr:       "remaining gas 11 exceeds supplied gas 10",
+		},
+		"zero_remaining_gas": {
+			envGas:      10,
+			input:       []byte{1},
+			cRet:        []byte{2},
+			wantRet:     []byte{2},
+			wantGasUsed: 10,
+		},
+		"used_one_gas": {
+			envGas:        10,
+			input:         []byte{1},
+			cRet:          []byte{2},
+			cRemainingGas: 9,
+			wantRet:       []byte{2},
+			wantGasUsed:   1,
+		},
+	}
+
+	for name, testCase := range testCases {
+		testCase := testCase
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			env := &stubPrecompileEnvironment{
+				gasToReturn: testCase.envGas,
+			}
+			c := PrecompiledStatefulContract(func(env vm.PrecompileEnvironment, input []byte, suppliedGas uint64) (ret []byte, remainingGas uint64, err error) {
+				return testCase.cRet, testCase.cRemainingGas, testCase.cErr
+			})
+
+			upgraded := c.Upgrade()
+
+			ret, err := upgraded(env, testCase.input)
+			if testCase.wantErr == "" {
+				require.NoError(t, err)
+			} else {
+				require.EqualError(t, err, testCase.wantErr)
+			}
+			assert.Equal(t, testCase.wantRet, ret)
+			assert.Equal(t, testCase.wantGasUsed, env.gasUsed)
+		})
+	}
+}

libevm/legacy/stubs_test.go

@@ -0,0 +1,67 @@
+// Copyright 2025 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them 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 libevm additions are distributed in the hope that they 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 legacy provides converters between legacy types and their refactored
+// equivalents.
+
+package legacy
+
+import (
+	"math/big"
+
+	"github.com/holiman/uint256"
+
+	"github.com/ava-labs/libevm/common"
+	"github.com/ava-labs/libevm/core/types"
+	"github.com/ava-labs/libevm/core/vm"
+	"github.com/ava-labs/libevm/libevm"
+	"github.com/ava-labs/libevm/params"
+)
+
+var _ vm.PrecompileEnvironment = (*stubPrecompileEnvironment)(nil)
+
+// stubPrecompileEnvironment implements [vm.PrecompileEnvironment] for testing.
+type stubPrecompileEnvironment struct {
+	gasToReturn uint64
+	gasUsed     uint64
+}
+
+// Gas returns the gas supplied to the precompile.
+func (s *stubPrecompileEnvironment) Gas() uint64 {
+	return s.gasToReturn
+}
+
+// UseGas records the gas used by the precompile.
+func (s *stubPrecompileEnvironment) UseGas(gas uint64) bool {
+	s.gasUsed += gas
+	return true
+}
+
+func (s *stubPrecompileEnvironment) Call(addr common.Address, input []byte, gas uint64, value *uint256.Int, _ ...vm.CallOption) (ret []byte, _ error) {
+	return nil, nil
+}
+
+func (s *stubPrecompileEnvironment) ChainConfig() *params.ChainConfig         { return nil }
+func (s *stubPrecompileEnvironment) Rules() params.Rules                      { return params.Rules{} }
+func (s *stubPrecompileEnvironment) StateDB() vm.StateDB                      { return nil }
+func (s *stubPrecompileEnvironment) ReadOnlyState() libevm.StateReader        { return nil }
+func (s *stubPrecompileEnvironment) IncomingCallType() vm.CallType            { return vm.Call }
+func (s *stubPrecompileEnvironment) Addresses() *libevm.AddressContext        { return nil }
+func (s *stubPrecompileEnvironment) ReadOnly() bool                           { return false }
+func (s *stubPrecompileEnvironment) Value() *uint256.Int                      { return nil }
+func (s *stubPrecompileEnvironment) BlockHeader() (h types.Header, err error) { return h, nil }
+func (s *stubPrecompileEnvironment) BlockNumber() *big.Int                    { return nil }
+func (s *stubPrecompileEnvironment) BlockTime() uint64                        { return 0 }