Linux Kernel Module Cheat

33.10.3.1.4. gem5 ARM WFE

gem5 390a74f59934b85d91489f8a563450d8321b602d does not sleep on the first WFE on either syscall emulation or full system, because the code does:

Fault WfeInst::execute(
    ExecContext *xc, Trace::InstRecord *traceData) const
{
[...]
    if (SevMailbox == 1) {
        SevMailbox = 0;
        PseudoInst::quiesceSkip(tc);
    } else if (tc->getCpuPtr()->getInterruptController(
                tc->threadId())->checkInterrupts(tc)) {
        PseudoInst::quiesceSkip(tc);
    } else {
        fault = trapWFx(tc, cpsr, scr, true);
        if (fault == NoFault) {
            PseudoInst::quiesce(tc);
        } else {
            PseudoInst::quiesceSkip(tc);
        }
    }

where "quiesce" means "sleep" for laymen like Ciro, and quiesceSkip means don’t sleep.

SevMailbox is read from MISCREG_SEV_MAILBOX which is initialized to 1 at:

ISA::clear()
{
[...]
    miscRegs[MISCREG_SEV_MAILBOX] = 1;