Hello,

I am seeing a weird crash in my system and I am trying to figure out if it is a software bug or a qemu emulation bug.  From the software perspective I am getting a GP fault at a time where it looks like everything should be running normally.  After digging into the Qemu source code I found out where the GPF was coming from.  It looks like intno = -1 when it was being passed into do_interrupt64, which was triggering one of the GPF checks.  From what I can tell, intno was being set to -1 by an interrupt_request in cpu-exec.c, which was going down the following if statement around line 409 of that file:

else if ((interrupt_request & CPU_INTERRUPT_HARD) &&
                                   (((env->hflags2 & HF2_VINTR_MASK) &&
                                     (env->hflags2 & HF2_HIF_MASK)) ||
                                    (!(env->hflags2 & HF2_VINTR_MASK) &&
                                     (env->eflags & IF_MASK &&
                                      !(env->hflags & HF_INHIBIT_IRQ_MASK)))))

and from within that else if statement, env has the following state:

hflags2 = 0x00000001
eflags = 0x00003202
hflags = 0x0040c0b7
interrupt request = 0x00000002

But intno is being set equal to -1 by the call to cpu_get_pic_interrupt, from the call to apic_accept_pic_intr returning 0.  If I change the cpu_get_pic_interrupt code to this:

int cpu_get_pic_interrupt(CPUState *env)
{
    int intno;

    intno = apic_get_interrupt(env);
    if (intno >= 0) {
        /* set irq request if a PIC irq is still pending */
        /* XXX: improve that */
        pic_update_irq(isa_pic);
        return intno;
    }
    /* read the irq from the PIC */
    if (!apic_accept_pic_intr(env)) {
        //return -1;
    }

    intno = pic_read_irq(isa_pic);

    return intno;
}

Then the issue manifests as a spurious interrupt and the software ignores it, avoiding the GPF.  Does anyone have any ideas as to what is going wrong here?  Should I look more closely at the Qemu emulation code or my software? Any help is appreciated.

Thanks!

--Sam