fix: handle unfilled values in mul mod runner (#1976)

* fix: handle unfilled values in mul mod runner

* update changelog

* Move changelog entry

* Remove whiteline

* Add test

---------

Co-authored-by: Gabriel Bosio <[email protected]>
Co-authored-by: Julián González Calderón <[email protected]>

Author: 3 people

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 #### Upcoming Changes
 
+* fix: `mod_builtin_fill_memory` could be stuck in an infinite loop [#1975](https://github.com/lambdaclass/cairo-vm/issues/1975)
+
 * feat: replace `thiserror-no-std` with `thiserror 2` [#1919](https://github.com/lambdaclass/cairo-vm/pull/1919)
 
 #### [2.0.1] - 2025-03-17

Cargo.lock

@@ -0,0 +1,49 @@
+%builtins range_check add_mod mul_mod
+
+from cairo_programs.mod_builtin_feature.common.modulo import ModBuiltin, UInt384, run_mod_p_circuit
+from starkware.cairo.common.registers import get_label_location
+from starkware.cairo.common.alloc import alloc
+
+func main{range_check_ptr, add_mod_ptr: ModBuiltin*, mul_mod_ptr: ModBuiltin*}() {
+    alloc_locals;
+
+
+    // The circuit definition can be described as:
+    //
+    // x1 (input)
+    // x2 (input)
+    // a1 = x1 + x2
+    // a2 = ??
+    // a3 = a1 * a2
+    //
+    // As the first mul gate tries to compute a3 when a2 is unkown, it will fail.
+
+    let p = UInt384(d0=1, d1=1, d2=0, d3=0);
+    let x1 = UInt384(d0=1, d1=0, d2=0, d3=0);
+    let x2 = UInt384(d0=2, d1=1, d2=0, d3=0);
+
+    let (local values_arr: UInt384*) = alloc();
+    assert values_arr[0] = x1;
+    assert values_arr[1] = x2;
+
+    let (local add_mod_offsets_arr: felt*) = alloc();
+    assert add_mod_offsets_arr[0] = 0;  // x1
+    assert add_mod_offsets_arr[1] = 4;  // x2
+    assert add_mod_offsets_arr[2] = 8;  // a1 = x1 + x2
+
+    let (local mul_mod_offsets_arr: felt*) = alloc();
+    assert mul_mod_offsets_arr[0] = 8;  // a1
+    assert mul_mod_offsets_arr[1] = 12; // a2 (unknown)
+    assert mul_mod_offsets_arr[2] = 16; // a1 * a2 (impossible)
+
+    run_mod_p_circuit(
+        p=p,
+        values_ptr=values_arr,
+        add_mod_offsets_ptr=add_mod_offsets_arr,
+        add_mod_n=1,
+        mul_mod_offsets_ptr=mul_mod_offsets_arr,
+        mul_mod_n=1,
+    );
+
+    return ();
+}

cairo_programs/mod_builtin_feature/mod_builtin_no_solution.cairo

@@ -1153,6 +1153,14 @@ fn cairo_run_mod_builtin_failure() {
     run_program_with_custom_mod_builtin_params(program_data, false, 1, 3, Some(error_msg));
 }
 
+#[test]
+#[cfg(feature = "mod_builtin")]
+fn cairo_run_mod_builtin_no_solution() {
+    let program_data =
+        include_bytes!("../../../cairo_programs/mod_builtin_feature/mod_builtin_no_solution.json");
+    run_program_with_error(program_data, "Could not fill the values table");
+}
+
 #[test]
 #[cfg(feature = "mod_builtin")]
 fn cairo_run_mod_builtin_large_batch_size() {

vm/src/tests/cairo_run_test.rs

@@ -566,8 +566,13 @@ impl ModBuiltinRunner {
                 if let Some((_, mul_mod_runner, _)) = mul_mod {
                     if mul_mod_runner.fill_value(memory, &mul_mod_inputs, mul_mod_index)? {
                         mul_mod_index += 1;
+                        continue;
+                    } else {
+                        return Err(RunnerError::FillMemoryCoudNotFillTable(
+                            add_mod_index,
+                            mul_mod_index,
+                        ));
                     }
-                    continue;
                 }
             }