tvx and conformance: use precondition state tree as the lookback tree.

conformance/driver.go

@@ -6,6 +6,7 @@ import (
 	"os"
 
 	"github.com/filecoin-project/go-state-types/network"
+	cbor "github.com/ipfs/go-ipld-cbor"
 
 	"github.com/filecoin-project/lotus/blockstore"
 	"github.com/filecoin-project/lotus/chain/consensus/filcns"
@@ -199,6 +200,9 @@ type ExecuteMessageParams struct {
 	// Rand is an optional vm.Rand implementation to use. If nil, the driver
 	// will use a vm.Rand that returns a fixed value for all calls.
 	Rand vm.Rand
+
+	// Lookback is the LookbackStateGetter; returns the state tree at a given epoch.
+	Lookback vm.LookbackStateGetter
 }
 
 // ExecuteMessage executes a conformance test vector message in a temporary VM.
@@ -213,6 +217,17 @@ func (d *Driver) ExecuteMessage(bs blockstore.Blockstore, params ExecuteMessageP
 		params.Rand = NewFixedRand()
 	}
 
+	// TODO: This lookback state returns the supplied precondition state tree, unconditionally.
+	//  This is obviously not correct, but the lookback state tree is only used to validate the
+	//  worker key when verifying a consensus fault. If the worker key hasn't changed in the
+	//  current finality window, this workaround is enough.
+	//  The correct solutions are documented in https://github.com/filecoin-project/ref-fvm/issues/381,
+	//  but they're much harder to implement, and the tradeoffs aren't clear.
+	var lookback vm.LookbackStateGetter = func(ctx context.Context, epoch abi.ChainEpoch) (*state.StateTree, error) {
+		cst := cbor.NewCborStore(bs)
+		return state.LoadStateTree(cst, params.Preroot)
+	}
+
 	vmOpts := &vm.VMOpts{
 		StateBase: params.Preroot,
 		Epoch:     params.Epoch,
@@ -224,6 +239,7 @@ func (d *Driver) ExecuteMessage(bs blockstore.Blockstore, params ExecuteMessageP
 		Rand:           params.Rand,
 		BaseFee:        params.BaseFee,
 		NetworkVersion: params.NetworkVersion,
+		LookbackState:  lookback,
 	}
 
 	lvm, err := vm.NewVM(context.TODO(), vmOpts)