Method readCounter

src/perfEvents_linux.cpp:711–750

}

u64 PerfEvents::readCounter(siginfo_t* siginfo, void* ucontext) {
    switch (_event_type->counter_arg) {
        case 1: return StackFrame(ucontext).arg0();
        case 2: return StackFrame(ucontext).arg1();
        case 3: return StackFrame(ucontext).arg2();
        case 4: return StackFrame(ucontext).arg3();
        default: {
            // Read counter with multiplexing metadata for accurate scaling
            struct PerfCounter counter;
            if (read(siginfo->si_fd, &counter, sizeof(counter)) == sizeof(counter)) {
                u64 current_val = counter.value;
                if (counter.time_enabled > counter.time_running) {
                    int fd = siginfo->si_fd;
                    if (fd < MAX_MULTIPLEXED_FD) {
                        u64 delta_enabled = counter.time_enabled - multiplex_state[fd].time_enabled;
                        u64 delta_running = counter.time_running - multiplex_state[fd].time_running;

                        multiplex_state[fd].time_enabled = counter.time_enabled;
                        multiplex_state[fd].time_running = counter.time_running;

                        if (!multiplex_state_dirty) {
                            multiplex_state_dirty = true;
                        }

                        if (delta_running > 0 && delta_enabled > delta_running) {
                            // scaled counter = (counter) * (delta_enabled / delta_running)
                            double ratio = (double)delta_enabled / delta_running;
                            return (u64)(current_val * ratio);
                        }
                    } else if (counter.time_running > 0) {
                        double ratio = (double)counter.time_enabled / counter.time_running;
                        return (u64)(current_val * ratio);
                    }
                }
                return current_val;
            }
            return 1;
        }
    }
}

void PerfEvents::signalHandler(int signo, siginfo_t* siginfo, void* ucontext) {
    if (siginfo->si_code <= 0) {