Since JDK-8352251 (JEP 518: JFR Cooperative Sampling), jfrSampleRequest calls os::fetch_bcp_from_context(). On ARM32 port it is still Unimplemented(). It should read the corresponding field from uc_mcontext and return the BCP value.

 intptr_t* os::fetch_bcp_from_context(const void* ucVoid) {
  Unimplemented();
  return nullptr;
 }