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

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