Branch Monitor

Here is an example monitor that can be written in Whamm, it does not require an instrumentation library. Rather, it uses the DSL to express all of its monitoring logic.

// Matches _if and br_if events
wasm::*if:before {
  report unshared var taken: i32;
  report unshared var total: i32;

  // which branch was taken?
  var was_taken: bool = arg0 != 0;
  taken = taken + (was_taken as i32);
  total++;
}

wasm::br_table:before {
  report unshared var taken_branches: map<u32, u32>;

  // which branch was taken?
  // default branch is at 'num_targets' in the map
  var index: u32 = arg0 <= (num_targets - 1) ? arg0 : num_targets;

  // count stores an array of counters
  taken_branches[index]++;
}

wasm::select(arg0: i32):before {
  report unshared var selected_first: u32;
  report unshared var total: u32;

  // which branch was taken?
  var was_taken: bool = arg0 != 0;
  selected_first = selected_first + (was_taken as u32);
  total++;
}