[TUHS] Is there a good, even definitive, list of reimplementations of the Unix kernel? What would good cut-off criteria be?

[John Cowan via TUHS]

On Sun, Apr 19, 2026 at 1:15 PM Dan Cross <crossd at gmail.com> wrote:

> I don't think there's a
> standard for doing something similar with ELF, though there was
> something called "FatELF" that made an attempt.  It appears to be
> defunct now.

It's ridiculously simple:

1) The FatELF magic number, version, and number of binaries (8 bytes)

2) A table of information about each binary: 24 bytes containing the
machine identifier, OSABI, OSABI version, word size, and byte order,
all drawn from the ELF header, plus the offset and length of the
binary within the FatELF file.

3) The concatenated ELF binaries,  padded so that they begin on a page
boundary, ,whatever that is for each architecture.

Since there are at most 255 binaries, you just need to read or mmap
the header (6136 bytes at most), and then mmap the appropriate binary.