Enforce_disable_trace_padding_used_only_in_proof_mode

Author: YairVaknin-starkware

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 #### Upcoming Changes
 
+* fix: Enforce `disable_trace_padding` used only in `proof_mode` [#1984](https://github.com/lambdaclass/cairo-vm/pull/1984)
+
 #### [2.0.0] - 2025-02-26
 
 * fix: Check overflow in cairo pie address calculation [#1945](https://github.com/lambdaclass/cairo-vm/pull/1945)

vm/src/tests/cairo_run_test.rs

@@ -8,8 +8,6 @@ use crate::{
     },
 };
 
-use num_traits::Zero;
-
 #[test]
 #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
 fn fibonacci() {
@@ -1029,14 +1027,17 @@ fn cairo_run_if_reloc_equal() {
 #[test]
 #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
 fn fibonacci_proof_mode_disable_trace_padding() {
-    let program_data = include_bytes!("../../../cairo_programs/fibonacci.json");
+    let program_data = include_bytes!("../../../cairo_programs/proof_programs/fibonacci.json");
     let config = CairoRunConfig {
+        proof_mode: true,
         disable_trace_padding: true,
         ..Default::default()
     };
     let mut hint_processor = BuiltinHintProcessor::new_empty();
     let runner = cairo_run(program_data, &config, &mut hint_processor).unwrap();
-    assert!(runner.get_memory_holes().unwrap().is_zero());
+    // The following check is to ensure that the trace is not padded. For this specific program,
+    // the number of steps doesn't end up as a power of 2 and we make sure it stays that way.
+    assert!(!runner.vm.current_step.is_power_of_two());
 }
 
 #[test]

vm/src/vm/errors/runner_errors.rs

@@ -136,6 +136,8 @@ pub enum RunnerError {
     MissingDynamicLayoutParams,
     #[error("dynamic layout {0} ratio should be 0 when disabled")]
     BadDynamicLayoutBuiltinRatio(BuiltinName),
+    #[error("Initialization failure: Cannot run with trace padding disabled without proof mode")]
+    DisableTracePaddingWithoutProofMode,
 }
 
 #[cfg(test)]

vm/src/vm/runners/cairo_runner.rs

@@ -229,6 +229,11 @@ impl CairoRunner {
         trace_enabled: bool,
         disable_trace_padding: bool,
     ) -> Result<CairoRunner, RunnerError> {
+        // `disable_trace_padding` can only be used in `proof_mode`, so we enforce this here to
+        // avoid unintended behavior.
+        if disable_trace_padding && !proof_mode {
+            return Err(RunnerError::DisableTracePaddingWithoutProofMode);
+        }
         if proof_mode {
             Self::new_v2(
                 program,
@@ -5399,4 +5404,15 @@ mod tests {
             })]
         );
     }
+
+    #[test]
+    fn test_disable_trace_padding_without_proof_mode() {
+        let program = program!();
+        // Attempt to create a runner in non-proof mode with trace padding disabled.
+        let result = CairoRunner::new(&program, LayoutName::plain, None, false, true, true);
+        match result {
+            Err(RunnerError::DisableTracePaddingWithoutProofMode) => { /* test passed */ }
+            _ => panic!("Expected DisableTracePaddingWithoutProofMode error"),
+        }
+    }
 }