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
