Im trying to reduce memory used by internal tables built into DYNAMIC_DEBUG the main savings available is in the per pr_debug* callsite data: modname, filename, funcname. I have segregated those fields to a new __dyndbg_sites section, described by struct _ddebug_site, and now refd by new ptr in struct _ddebug That new ptr enlarges the memory footprint, so I want to replace it with an integer index into the section / array. Existing padding could hold the index. To use the index, I need &dyndbg_sites[], and that only works for builtin-module's callsites. For loaded modules, I can/have added a pointer to the section into module load_info, giving me the base I will need for the ! builtin branch. I just need a not expensive is-it-builtin (modref)