[Qemu-devel] Re: gdbstub: packet reply is too long

[Jan Kiszka]

Andreas Schultz wrote:
> Hi,
> 
> I'm trying to debug a 32bit (i386) kernel on a 64bit host under kvm, but
> gdb always refuses it with:
> Remote 'g' packet reply is too long:
> 0000000000000000000000000000000000000000000000002306000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f0ff0000000000000230020000f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000007f0300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
>  
> 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
> 
> I tried kvm-79 and kvm-git from today. gdb is v6.8 (ubuntu intrepid)
> 
> Any hints?

QEMU and also KVM's x86_64 version are currently broken /wrt debugging
targets < 64 bits. I've posted a fix a while ago, but there were
concerns that gdb should better be enhanced (which is basically true,
but unrealistic to achieve in the near future).

In the meantime, you may want to have a look at my kvm [1] or qemu patch
queue [2]. Note that unless you provide a binary to gdb that is 32 bit
already, you may have to switch the architecture manually ("set arch
i386" or "i8086") before attaching.

Jan

[1] git://git.kiszka.org/kvm-userspace.git gdb-queue
[2] git://git.kiszka.org/qemu.git gdb-queue

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