diff --git a/ceno_emul/src/tracer.rs b/ceno_emul/src/tracer.rs
index 54dfafe78..8aa55cf79 100644
--- a/ceno_emul/src/tracer.rs
+++ b/ceno_emul/src/tracer.rs
@@ -286,6 +286,10 @@ impl StepRecord {
     pub fn is_busy_loop(&self) -> bool {
         self.pc.before == self.pc.after
     }
+
+    pub fn syscall(&self) -> Option<&SyscallWitness> {
+        self.syscall.as_ref()
+    }
 }
 
 #[derive(Debug)]
diff --git a/ceno_emul/tests/test_elf.rs b/ceno_emul/tests/test_elf.rs
index 7f5c328d6..afbd67a12 100644
--- a/ceno_emul/tests/test_elf.rs
+++ b/ceno_emul/tests/test_elf.rs
@@ -78,18 +78,43 @@ fn test_ceno_rt_io() -> Result<()> {
 fn test_ceno_rt_keccak() -> Result<()> {
     let program_elf = ceno_examples::ceno_rt_keccak;
     let mut state = VMState::new_from_elf(unsafe_platform(), program_elf)?;
-    let _steps = run(&mut state)?;
+    let steps = run(&mut state)?;
 
     // Expect the program to have written successive states between Keccak permutations.
     const ITERATIONS: usize = 3;
     let keccak_outs = sample_keccak_f(ITERATIONS);
 
     let all_messages = read_all_messages(&state);
-    for (got, expect) in izip!(&all_messages, keccak_outs) {
+    assert_eq!(all_messages.len(), ITERATIONS);
+    for (got, expect) in izip!(&all_messages, &keccak_outs) {
         let got = got
             .chunks_exact(8)
             .map(|chunk| u64::from_le_bytes(chunk.try_into().unwrap()))
             .collect_vec();
+        assert_eq!(&got, expect);
+    }
+
+    // Find the syscall records.
+    let syscalls = steps.iter().filter_map(|step| step.syscall()).collect_vec();
+    assert_eq!(syscalls.len(), ITERATIONS);
+
+    // Check the syscall effects.
+    for (witness, expect) in izip!(syscalls, keccak_outs) {
+        assert_eq!(witness.mem_writes.len(), expect.len() * 2);
+
+        let got = witness
+            .mem_writes
+            .chunks_exact(2)
+            .map(|write_ops| {
+                assert_eq!(
+                    write_ops[1].addr.baddr(),
+                    write_ops[0].addr.baddr() + WORD_SIZE as u32
+                );
+                let lo = write_ops[0].value.after as u64;
+                let hi = write_ops[1].value.after as u64;
+                lo | (hi << 32)
+            })
+            .collect_vec();
         assert_eq!(got, expect);
     }
 
@@ -103,8 +128,7 @@ fn unsafe_platform() -> Platform {
 }
 
 fn sample_keccak_f(count: usize) -> Vec<Vec<u64>> {
-    let input = [0_u64; 25];
-    let mut state = input.clone();
+    let mut state = [0_u64; 25];
 
     (0..count)
         .map(|_| {
diff --git a/examples/examples/ceno_rt_keccak.rs b/examples/examples/ceno_rt_keccak.rs
index 07fb7b9ca..cd68d17db 100644
--- a/examples/examples/ceno_rt_keccak.rs
+++ b/examples/examples/ceno_rt_keccak.rs
@@ -6,7 +6,7 @@
 #![no_std]
 extern crate ceno_rt;
 use ceno_rt::{info_out, syscall_keccak_permute};
-use core::{ptr::read_volatile, slice};
+use core::slice;
 
 const ITERATIONS: usize = 3;
 
@@ -22,7 +22,7 @@ fn main() {
 
 fn log_state(state: &[u64; 25]) {
     let out = unsafe {
-        slice::from_raw_parts_mut(state.as_ptr() as *mut u8, state.len() * size_of::<u64>())
+        slice::from_raw_parts(state.as_ptr() as *const u8, state.len() * size_of::<u64>())
     };
     info_out().write_frame(out);
 }