I don't think undump is a hack except to the extent the whole thing is a hack. Linux shoves a lot of stuff to userspace that other operating systems put in kernel space; this is just another one of them.

The program loader is not magic - it just reads a list of things to mmap and then mmaps them. If you write a thing that writes a list of what's mmapped and call it the unloader... fine?

I really wish that would be possible. I sometimes suspend things, but I would really be able to store them to disk. Sure sometimes you can suspend the whole OS to disk, but that's worse and also doesn't scale. You can't suspend to disk, boot normally, suspend a second time, boot into the first, etc.

Pascal TeX to the best of my knowledge never did it but the web2c version does.

The description is a bit confusing because it can both dump only the warmed up interpreter image or the whole process, I think.

"With the program undump, you can use `core' to reconstitute a preloaded executable, which does not need to read a `.fmt' file to get started. Although preloaded executables save startup time, they have a big disadvantage: neither the disk space to store them nor their code segments (at runtime) can be shared. Therefore, if both tex and latex are running, twice as much memory will be consumed, to the general detriment of performance."

https://mirror.gutenberg-asso.fr/tex.loria.fr/texlive-htmldo...

> Don’t think TeX ever did that, that was a “simple” Pascal program.

Not exactly the entire process image, no, but essentially all of its data in a single chunk. It’s a peculiar Pascal program because it bypasses basically all of Pascal’s typing, records, etc., and instead builds its own from a set of (WEB) macros on top of a giant untyped array. Quoth Knuth in TeX: The Program §115:

> The dynamic storage requirements of TeX are handled by providing a large array mem in which consecutive blocks of words are used as nodes by the TeX routines. Pointer variables are indices into this array [...].

There are a few more areas designated for specific purposes, but at the end of the day (§1302) it works out about the way you’d expect:

  procedure store_fmt_file;
  [...] begin ⟨ If dumping is not allowed, abort 1304 ⟩
  ⟨ Create the format ident, open the format file, and inform the user that dumping has begun 1328 ⟩;
  ⟨ Dump constants for consistency check 1307 ⟩;
  ⟨ Dump the string pool 1309 ⟩;
  ⟨ Dump the dynamic memory 1311 ⟩;
  ⟨ Dump the table of equivalents 1313 ⟩;
  ⟨ Dump the font information 1320 ⟩;
  ⟨ Dump the hyphenation tables 1324 ⟩;
  ⟨ Dump a couple more things and the closing check word 1326 ⟩;
  ⟨ Close the format file 1329 ⟩;
  end;

And didn't stop doing this until 2020! (Specifically Emacs 27.1, which replaced "unexec", which dumped the process image, with the "portable dumper", which despite the name does not.)