getting the console output for s390 cdrom-test?

[Peter Maydell]

Hi; I've been looking at why the s390 cdrom test has an intermittent
failure on my aarch64 box. Looking at some TCG debug log output
I think what is happening is that sometimes execution diverges from
a successful run inside virtio_scsi_setup() and we end up failing
a vs_assert(), which triggers a "Guest crashed on cpu 0: disabled-wait"
which then makes the qtest hang until its timeout.

I think that vs_assert() ought to be printing some information
to the console about which assert fails when it happens, but
how do I need to tweak the qtest to get it to capture this
console log somewhere?

Specifically, the test in question is this one:
QTEST_QEMU_BINARY=qemu-system-s390x
./build/s390/tests/qtest/cdrom-test -p
/s390x/cdrom/boot/without-bootindex

PS: it would be nice if "guest BIOS asserts and puts the
system into a detected-guest-crash state" resulted in the
test failing rather than hanging :-)

(Annoyingly, most of my attempts to get more information about
where things go wrong seem to cause the bug to stop manifesting
itself: eg building the s390-ccw.img without -O2; enabling
TCG 'exec' logging; enabling 'trace:virtio*' tracepoints.
The failure itself started with commit 7a3d37a3f233 updating
the s390 bios blobs, but the changes that went into the new
blobs don't really look like they would be responsible.
I am starting to have gloomy thoughts about potential missing
memory barrier insns between the CPU thread and the iothread
doing the virtio device end of things...)

thanks
-- PMM