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From: | Sam King |
Subject: | [Qemu-devel] debugging apic |
Date: | Tue, 28 Sep 2010 10:15:41 -0500 |
User-agent: | Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.9) Gecko/20100915 Thunderbird/3.1.4 |
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 |
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