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Re: qemu aarch64 info registers PC register not changing

From: Jiatong Shen
Subject: Re: qemu aarch64 info registers PC register not changing
Date: Thu, 13 Jul 2023 15:36:23 +0800

Thank you for your answer. 

I tried to build an qemu 6.2.0 binary and looks like PC register value is still unchanged.

virsh # version
Compiled against library: libvirt 7.8.0
Using library: libvirt 7.8.0
Using API: QEMU 7.8.0
Running hypervisor: QEMU 6.2.0

virsh # qemu-monitor-command --hmp 1 info registers
 PC=ffffa2bbf4a7c68c X00=ffff7ee4af45b6c0 X01=000000000006ab6c
X02=ffff7ee4af45b7e0 X03=000000000006ab6a X04=ffffdc28ba056000
X05=01ffffffffffffff X06=00000184d0f83120 X07=0000000000000000
X08=ffffa2bbf573d950 X09=ffffa2bbf4a88128 X10=0000000000000eb0
X11=0000000000000000 X12=0000000000000000 X13=0000000000000001
X14=0000000000000000 X15=0000000000000000 X16=ffffa2bbf43b6f20
X17=0000000000000000 X18=0000000000000000 X19=ffffa2bbf53ed000
X20=0000000000000000 X21=0000000000000000 X22=ffffa2bbf57326a8
X23=000022bbe3dc0000 X24=000000203baa33d0 X25=0000000000000000
X26=0000000000000004 X27=000000000000ffff X28=00000006fd896380
X29=ffffa2bbf5723ea0 X30=ffffa2bbf4a7c6f8  SP=ffffa2bbf5723ea0
PSTATE=60400085 -ZC- EL1h     FPCR=00000000 FPSR=00000000
Q00=0000000000000000:0000000000000000 Q01=37315b7374726170:2d6e75722033313a
Q02=0000000000000f51:000000203a5d3735 Q03=f00f000000000000:f00ff0000000f000
Q04=f00ff00ff00ff00f:f00ff00ff00ff00f Q05=ff000000fff000f0:ff000000fff000f0
Q06=ccccc000cccccc00:ccccc000cccccc00 Q07=0000000000000000:0000000000000000
Q08=0000000000000000:0000000000000000 Q09=0000000000000000:0000000000000000
Q10=0000000000000000:0000000000000000 Q11=0000000000000000:0000000000000000
Q12=0000000000000000:0000000000000000 Q13=0000000000000000:0000000000000000
Q14=0000000000000000:0000000000000000 Q15=0000000000000000:0000000000000000
Q16=0000000000000000:0000000000000000 Q17=0000000000000000:0000000000000000
Q18=0000000000000000:0000000000000000 Q19=0000000000000000:0000000000000000
Q20=0000000000000000:0000000000000000 Q21=0000000000000000:0000000000000000
Q22=0000000000000000:0000000000000000 Q23=0000000000000000:0000000000000000
Q24=0000000000000000:0000000000000000 Q25=0000000000000000:0000000000000000
Q26=0000000000000000:0000000000000000 Q27=0000000000000000:0000000000000000
Q28=0000000000000000:0000000000000000 Q29=0000000000000000:0000000000000000
Q30=0000000000000000:0000000000000000 Q31=0000000000000000:0000000000000000

Is it possible to get the instruction corresponding to the PC pointed address? 

Thank you very much for your generous help!

Jiatong Shen

On Mon, Jul 10, 2023 at 5:45 PM Peter Maydell <peter.maydell@linaro.org> wrote:
On Mon, 10 Jul 2023 at 09:12, Jiatong Shen <yshxxsjt715@gmail.com> wrote:
> Hello community experts,
>     I am trying to learn some arm64 basics using qemu. I would like to retrieve a register value
> through hmp command info register. The output is
> virsh # qemu-monitor-command --hmp eefcdf53-2fd5-40ee-91a8-858b3e621fc5 info registers -a

> every time I issue the command, PC register is always the value. My question is should PC value be changed every time an instruction completes? Thank you very much.
> The qemu version is 4.2.1. And the virtual machine is accelerated by KVM.

It's worth looking at what that PC is in the guest,
and what the guest is doing. If the guest is not particularly
doing much, then it's very likely that almost all of the time
when you look at it you'll find that the guest PC is pointing
to the WFI in the guest kernel's idle loop.

Other than that, QEMU 4.2.1 is pretty old, especially in
Arm terms (where KVM support has not been so mature for
as long as x86); so you could check whether a newer QEMU
also behaves the same way.

-- PMM


Best Regards,

Jiatong Shen

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