[fix] program counter could larger than code size

zkevm-circuits/src/evm_circuit/execution/stop.rs

@@ -1,14 +1,15 @@
 use crate::{
     evm_circuit::{
         execution::ExecutionGadget,
+        param::N_BYTES_PROGRAM_COUNTER,
         step::ExecutionState,
         util::{
             common_gadget::RestoreContextGadget,
             constraint_builder::{
                 ConstraintBuilder, StepStateTransition,
                 Transition::{Delta, Same},
             },
-            math_gadget::IsZeroGadget,
+            math_gadget::LtGadget,
             CachedRegion, Cell,
         },
         witness::{Block, Call, ExecStep, Transaction},
@@ -23,7 +24,7 @@ use halo2_proofs::{circuit::Value, plonk::Error};
 #[derive(Clone, Debug)]
 pub(crate) struct StopGadget<F> {
     code_length: Cell<F>,
-    is_out_of_range: IsZeroGadget<F>,
+    is_out_of_range: LtGadget<F, N_BYTES_PROGRAM_COUNTER>,
     opcode: Cell<F>,
     restore_context: RestoreContextGadget<F>,
 }
@@ -36,14 +37,12 @@ impl<F: Field> ExecutionGadget<F> for StopGadget<F> {
     fn configure(cb: &mut ConstraintBuilder<F>) -> Self {
         let code_length = cb.query_cell();
         cb.bytecode_length(cb.curr.state.code_hash.expr(), code_length.expr());
-        let is_out_of_range = IsZeroGadget::construct(
-            cb,
-            code_length.expr() - cb.curr.state.program_counter.expr(),
-        );
+        let is_out_of_range =
+            LtGadget::construct(cb, cb.curr.state.program_counter.expr(), code_length.expr());
         let opcode = cb.query_cell();
-        // cb.condition(1.expr() - is_out_of_range.expr(), |cb| {
-        // cb.opcode_lookup(opcode.expr(), 1.expr());
-        // });
+        cb.condition(1.expr() - is_out_of_range.expr(), |cb| {
+            cb.opcode_lookup(opcode.expr(), 1.expr());
+        });
 
         // We do the responsible opcode check explicitly here because we're not using
         // the `SameContextGadget` for `STOP`.
@@ -116,7 +115,8 @@ impl<F: Field> ExecutionGadget<F> for StopGadget<F> {
         self.is_out_of_range.assign(
             region,
             offset,
-            F::from(code.bytes.len() as u64) - F::from(step.program_counter),
+            F::from(step.program_counter),
+            F::from(code.bytes.len() as u64),
         )?;
 
         let opcode = step.opcode.unwrap();