On 1/10/25 07:15, Alex Bennée wrote:
"Julian Ganz" <[email protected]> writes:
Hi Alex,
January 9, 2025 at 3:04 PM, "Alex Bennée" wrote:
Julian Ganz <[email protected]> writes:
We recently introduced new plugin API for registration of discontinuity
related callbacks. This change introduces a minimal plugin showcasing
the new API. It simply counts the occurances of interrupts, exceptions
and host calls per CPU and reports the counts when exitting.
---
contrib/plugins/meson.build | 3 +-
contrib/plugins/traps.c | 96 +++++++++++++++++++++++++++++++++++++
2 files changed, 98 insertions(+), 1 deletion(-)
create mode 100644 contrib/plugins/traps.c
diff --git a/contrib/plugins/meson.build b/contrib/plugins/meson.build
index 63a32c2b4f..9a3015e1c1 100644
--- a/contrib/plugins/meson.build
+++ b/contrib/plugins/meson.build
@@ -1,5 +1,6 @@
contrib_plugins = ['bbv', 'cache', 'cflow', 'drcov', 'execlog', 'hotblocks',
- 'hotpages', 'howvec', 'hwprofile', 'ips', 'stoptrigger']
+ 'hotpages', 'howvec', 'hwprofile', 'ips', 'stoptrigger',
+ 'traps']
I wonder if this is better in tests/tcg/plugins? We need to do something
to ensure it gets covered by CI although we might want to be smarter
about running it together with a test binary that will actually pick up
something.
The callback is intended as an example. The patch-series does contain a
dedicated testing plugin. And iirc the contrib plugins are now built
with the rest of qemu anyway?
They do - however we generate additional tests with tests/tcg/plugins
with the existing multiarch linux-user and softmmu check-tcg tests. Its
a fairly dumb expansion though:
# We need to ensure expand the run-plugin-TEST-with-PLUGIN
# pre-requistes manually here as we can't use stems to handle it. We
# only expand MULTIARCH_TESTS which are common on most of our targets
# to avoid an exponential explosion as new tests are added. We also
# add some special helpers the run-plugin- rules can use below.
# In more, extra tests can be added using ADDITIONAL_PLUGINS_TESTS variable.
ifneq ($(MULTIARCH_TESTS),)
$(foreach p,$(PLUGINS), \
$(foreach t,$(MULTIARCH_TESTS) $(ADDITIONAL_PLUGINS_TESTS),\
$(eval run-plugin-$(t)-with-$(p): $t $p) \
$(eval RUN_TESTS+=run-plugin-$(t)-with-$(p))))
endif # MULTIARCH_TESTS
endif # CONFIG_PLUGIN
We also have a hand-hacked test for validating memory instrumentation:
# Test plugin memory access instrumentation
run-plugin-test-plugin-mem-access-with-libmem.so: \
PLUGIN_ARGS=$(COMMA)print-accesses=true
run-plugin-test-plugin-mem-access-with-libmem.so: \
CHECK_PLUGIN_OUTPUT_COMMAND= \
$(SRC_PATH)/tests/tcg/multiarch/check-plugin-output.sh \
$(QEMU) $<
test-plugin-mem-access: CFLAGS+=-pthread -O0
test-plugin-mem-access: LDFLAGS+=-pthread -O0
That said as I mention in the reply to the cover letter the traps stuff
might be better exercised with the functional test so could utilise a
plugin built in contrib just as easily.
I agree, as it was discussed in previous versions, we should add a
functional test for this. I'm not sure if we should write a custom and
complicated test, or simply boot and shutdown an existing image, and
call it a day.
Do you have any opinion on this Alex?
+QEMU_PLUGIN_EXPORT
+int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
+ int argc, char **argv)
+{
+ if (!info->system_emulation) {
+ fputs("trap plugin can only be used in system emulation mode.\n",
+ stderr);
+ return -1;
+ }
+
+ max_vcpus = info->system.max_vcpus;
+ traps = qemu_plugin_scoreboard_new(sizeof(TrapCounters));
+ qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
+ qemu_plugin_vcpu_for_each(id, vcpu_init);
Hmm at first glances this seems redundant - however I guess this is
covering the use case you load the plugin after the system is up and
running.
Yep, but really that was just me being paranoid.
I wonder if you have unearthed a foot-gun in the API that is easy to
fall into? Maybe we should expand qemu_plugin_register_vcpu_init_cb to
call the call back immediately for existing vcpus?
Would probably not hurt.
Regards,
Julian
