[Crash-utility] [PATCH] bug on get_be_long() and improvement of bt

[Hu Tao]

On Tue, Oct 19, 2010 at 09:06:33AM -0400, Dave Anderson wrote:
> 
> ----- "Hu Tao" <hutao at cn.fujitsu.com> 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