Your copy of node appears to be compiled without sys/sdt.h markers. If they were compiled in, readelf -n
would show something like ...
stapsdt 0x00000040 NT_STAPSDT (SystemTap probe descriptors)
Provider: stap
Name: stap_system__spawn
Location: 0x000000000012e1b0, Base: 0x00000000001cb886, Semaphore: 0x0000000000000000
Arguments: -4@%ebx -4@%eax
Perhaps it was configured with --without-dtrace.