Criterion Profiler impl to surround benchmarks with Points of Interest in Instruments

instruments_criterion.rs

struct InstrumentsPointsOfInterest;

impl InstrumentsPointsOfInterest {
    fn code(x: &std::path::Path) -> u32 {
        // NB: kdebug_signpost* only keeps the bottom 14 bits of this but that
        // seems fine.
        use std::collections::hash_map::DefaultHasher;
        let mut h = DefaultHasher::new();
        x.hash(&mut h);
        h.finish() as u32
    }
}

impl criterion::profiler::Profiler for InstrumentsPointsOfInterest {
    fn start_profiling(&mut self, _benchmark_id: &str, benchmark_dir: &std::path::Path) {
        // TODO: What happens if there's a collision and this gets called twice?
        let code = InstrumentsPointsOfInterest::code(benchmark_dir);
        unsafe {
            kdebug_signpost(code, 0, 0, 0, 0);
            kdebug_signpost_start(code, 0, 0, 0, 0);
        }
    }

    fn stop_profiling(&mut self, _benchmark_id: &str, benchmark_dir: &std::path::Path) {
        let code = InstrumentsPointsOfInterest::code(benchmark_dir);
        unsafe {
            kdebug_signpost_end(code, 0, 0, 0, 0);
        }
    }
}

extern "C" {
    fn kdebug_signpost(code: u32, arg1: usize, arg2: usize, arg3: usize, arg4: usize);
    fn kdebug_signpost_start(code: u32, arg1: usize, arg2: usize, arg3: usize, arg4: usize);
    fn kdebug_signpost_end(code: u32, arg1: usize, arg2: usize, arg3: usize, arg4: usize);
}