On 4/8/22 17:36, Mathieu Desnoyers wrote:
LTTng is an out of tree kernel module, which currently relies on the export.
Indeed, arch/x86/kvm/x86.c exports a set of tracepoints to kernel modules, e.g.:
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry)
But any probe implementation hooking on that tracepoint would need kvm_x86_ops
to translate the struct kvm_vcpu * into meaningful tracing data.
I could work-around this on my side in ugly ways, but I would like to discuss
how kernel module tracers are expected to implement kvm events probes without
the kvm_x86_ops symbol ?
The conversion is done in the TP_fast_assign snippets, which are part of
kvm.ko and therefore do not need the export. As I understand it, the
issue is that LTTng cannot use the TP_fast_assign snippets, because they
are embedded in the trace_event_raw_event_* symbols?
We cannot do the extraction before calling trace_kvm_exit, because it's
expensive.
Paolo
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