Version 28.1+
By experimentation I've found the following issues are all that prevent dumping with large numbers of pre-loaded native compiled units. The improvement in start-up performance versus requiring the same libraries in a .emacs file is ridiculous, even with all libraries pre-compiled. The same fixes would provide support for user's construction of personal dump files.
+ Add additional build stage so a compile phase that only loads loadup is produced first, with a following stage to compile all the libraries loaded by site-load. Originally suggested by Stefan Monnier, it appears absolutely necessary. Most libraries not 8n loadup implicitly assume those libraries are in the compile-time environment.
+. Add a flag variable to turn off the docstring hack in lead.c once loadup has been processed (or eliminate the hack entirely).
+ Also turn off the prohibition on implicit loading while in dump mode based on that flag variable. The file dependencies of site-load can be determined using load-history once the baseline (loadup only) dump has been constructed.
+ Turn off purification flag before loading site-load, or fix bugs in purecopy/pure_alloc (elimination of pure space counts as a bug fix). Note that when I've selectively turned off the purify flag in site-load to avoid purecopy bugs, the process would reach the stage of calling pdump, but that call would hang indefinitely (I let it go for a couple of hours the first time, and it just burned cpu cycles without any change in memory use).
+ Enable the standard load path before loading site-load.
+ Make all_loaded_comp_units_h visible as a lisp variable, so loadup can explicitly fix up all loaded comp units, whether there is a symbol bound to a subr in that unit or not.
+ Make it possible to cleanly turn off further asynchronous compilation. I currently set native-comp-deferred-compilation-deny-list to '("/.*/"), but I've still seen an occasional job running the compiler on some subr.
+ Ensure the compiler is run using the pdmp file constructed just from loadup. It will be impossible to support or debug compiling with arbitrary compile-time environments. I've already encountered an issue from having call-interactive somehow advise itself when compiling with only additional core emacs libraries in the dump.
I think that covers all the issues I dealt with. If my employer allows I can donate code to fix the purecopy issues in versions prior to 29.
Lynn