Re: what is qemu_system_guest_panicked() for?

[Fabiano Rosas <farosas@suse.de>]

Shivang Upadhyay <shivangu@linux.ibm.com> writes:

> On Tue, 2026-07-14 at 15:54 +0530, Aditya Gupta wrote:
>> > guest code.
>> > 
>> > PPC folks, please confirm, it's been years since I looked at this.
>> True. The way the spec mentions it seems the OS can get control back
>> after
>> execution of ibm,os-term.
>> 
>> This difference is noticeable with `panic=15`. On an LPAR, this would
>> print the
>> following line and do a reboot after a timeout of 15s (this happens
>> in linux
>> after it has done the os-term call):
>> 
>>      [  338.186072] Rebooting in 15 seconds..
>> 
>> But on QEMU, this isn't printed, and the machine powers down:
>> 
>>      qemu-system-ppc64: OS terminated:
>> 
>> Maybe worth taking a look. Didn't notice this earlier, thanks Fabiano
>> !
>> 
>
> Hi Aditya Fabiano,
>  As we register the rtas(os-term) as the panic handler for spapr in
> linux, I think we expect the machine to be shut-down properly and not
> handle any of the work. I am not sure how else would we implement this
> function in qemu without using `qemu_system_guest_panicked`. I mean,
> the name conveys, the guest has "paniced".
>
> But then again as per PAPR, we should expected limited number of rtas
> calls from the OS (the following list).
> - nvram-fetch
> - nvram-store
> - display-character
> - power-off
> - ibm,power-off-ups
> - system-reboot
> - check-exception
>
> PAPR reffers to host as "live-halt" after it has called os-term. Not
> very sure on the meaning of this.
>
> Maybe other platforms then linux will rely on this? As Fabiano
> suggested he found some case where he needed to comment it out, That
> would be interesting scenario to explore.
>

To be clear: I don't know of anything that currently depends on a more
rigorous behavior of os-term.

If Linux, and probably other major OSes, use os-term to relay a panic
state to the hypervisor, this is fine. For the purposes of Peter's
question I think we can leave it at that.

---

PS:
The use-case I had in the past was related to this test suite:
https://github.com/legoater/pnv-test. I was looking for a way to do
clean termination of a vm from the guest OS while conveying the test
output in the message.

E.g:

$ cat slof.s
li      3,0
ori     3,3,61440       # H_RTAS
li      4,argbuf
.long 0x44000022
b .

argbuf:
.long 0x201f    # ibm,os-term
.long 0x65786974 # "exit"
.long 0 
.long . -8

$ ./qemu-system-ppc64 -bios slof.bin -d guest_errors
qemu: OS terminated: exit
Guest crashed