make kernel addresses much more likely

src/single_instruction_test/callframe.rs

@@ -17,7 +17,14 @@ impl<'a> Arbitrary<'a> for Flags {
 
 impl<'a> Arbitrary<'a> for Callframe {
     fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
-        let address = u.arbitrary()?;
+        let mut address: H160 = u.arbitrary()?;
+
+        // Make kernel addresses much more likely
+        if address.to_low_u64_be() % 1117 < 200 {
+            for i in 0..18 {
+                address.0[i] = 0;
+            }
+        }
 
         // zk_evm requires a base page, which heap and aux heap are offset from
         let base_page = u.int_in_range(1..=u32::MAX - 10)?;