Fix instruction length setting in asm's step() (#181)

* Fix instruction length setting in asm's step()

* Make decoder mutable in test_asm_step()

src/machine/asm/mod.rs

@@ -448,9 +448,8 @@ impl<'a> AsmMachine<'a> {
         let pc = *self.machine.pc();
         let slot = calculate_slot(pc);
         let mut trace = Trace::default();
-        let mut instruction = decoder.decode(self.machine.memory_mut(), pc)?;
+        let instruction = decoder.decode(self.machine.memory_mut(), pc)?;
         let len = instruction_length(instruction) as u8;
-        instruction |= u64::from(len) << 24;
         trace.instructions[0] = instruction;
         trace.cycles += self
             .machine

tests/test_asm.rs

@@ -1,6 +1,7 @@
 #![cfg(has_asm)]
 
 use ckb_vm::{
+    decoder::build_decoder,
     machine::{
         asm::{AsmCoreMachine, AsmMachine},
         CoreMachine, VERSION0, VERSION1,
@@ -390,3 +391,25 @@ pub fn test_decoder_instructions_cache_pc_out_of_bound_timeout() {
     assert!(result.is_err());
     assert_eq!(result.unwrap_err(), Error::OutOfBound);
 }
+
+pub fn test_asm_step() {
+    let buffer = fs::read("tests/programs/simple64").unwrap().into();
+    let asm_core = AsmCoreMachine::new(ISA_IMC, VERSION0, u64::max_value());
+    let core = DefaultMachineBuilder::new(asm_core).build();
+    let mut machine = AsmMachine::new(core, None);
+    machine
+        .load_program(&buffer, &vec!["simple64".into()])
+        .unwrap();
+
+    let result = || -> Result<i8, Error> {
+        let mut decoder = build_decoder::<u64>(ISA_IMC);
+        machine.machine.set_running(true);
+        while machine.machine.running() {
+            machine.step(&mut decoder)?;
+        }
+        Ok(machine.machine.exit_code())
+    }();
+
+    assert!(result.is_ok());
+    assert_eq!(result.unwrap(), 0);
+}