On Tue, Oct 19, 2010 at 09:06:33AM -0400, Dave Anderson wrote:
>
> ----- "Hu Tao" <hutao@xxxxxxxxxxxxxx> wrote:
>
> > Hi Dave,
> >
> > These are updated patches tested with SMP system and panic task.
> >
> > When testing a x86 guest, I found another bug about reading cpu
> > registers from dumpfile. Qemu simulated system is x86_64
> > (qemu-system-x86_64), guest OS is x86. When crash reads cpu registers
> > from dumpfile, it uses cpu_load_32(), this will read gp registers by
> > get_be_long(fp, 32), that is, treate them as 32bits. But in fact,
> > qemu-system-x86_64 saves 64bits for each of them(although guest OS
> > uses only lower 32 bits). As a result, crash gets wrong cpu gp
> > register values.
>
> As I understand it, you're running a 32-bit guest on a 64-bit host.
Yes.
> If you were to read 64-bit register values instead of 32-bit register
> values, wouldn't that cause the file offsets of the subsequent get_xxx()
> calls in cpu_load() to read from the wrong file offsets? And then
> that would leave the ending file offset incorrect, such that the
> qemu_load() loop would fail to find the next device?
>
> In other words, the cpu_load() function, which is used for both
> 32-bit and 64-bit guests, must be reading the correct amount of
> data from the "cpu" device, or else qemu_load() would fail to
> find the next device in the next location in the dumpfile.
True. In fact, in my case if read 32-bit registers, following devices
are found:
block, ram, kvm-tpr-opt, kvmclock, timer, cpu_common, cpu.
If read 64-bit registers, following devices are found:
block, ram, kvm-tpr-opt, kvmclock, timer, cpu_common, cpu, apic, fw_cfg
>
> > Is there any way we can know from dumpfile that these gp
> > registers(and those similar registers) are 32bits or 64bits?
>
> I don't know. If what you say is true, when would those registers
> ever be 32-bit values?
I did tests on a 64-bit machine. Result is:
machine OS guest machine guest OS saved gp regs
------------------------------------------------------------------------
64-bit x86 qemu-kvm(kvm enabled) x86 64 bits
64-bit x86 qemu(kvm disabled) x86 32 bits
I guess on a 32-bit machine saved gp regs shoule be 32bits, but I have no
32-bit machine to test.
--
Thanks,
Hu Tao
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