trace_pc
cov_register_pc(&trace_pc);
cov_register_pc(cov_trace_pc_t trace_pc)
atomic_store_ptr(&cov_trace_pc, trace_pc);
cov_trace_pc_t trace_pc;
trace_pc = atomic_load_ptr(&cov_trace_pc);
if (trace_pc != NULL)
trace_pc((uint64_t)__builtin_return_address(0));