Yes true, but a given UNDEF symbol can resolve from *any* of the
libraries(DSOs) to which the binary is linked to, right? Or could we
predict that for sure?
If the SHN_UNDEF symbol has symbol version info, that constrains what
defining symbols can satisfy that reference. If not (0/1), then any
symbol(?) will match--or maybe it's any unversioned/base-version symbol?