The first six probes each proved a piece. merged.sh puts them together: the
program's @main is renamed out of the way, a C main takes the main thread and
runs it there, caml_startup happens on a thread beside it, and clang links the
lot -- the emitted program object, flan_rt.c, flan_dev.c, flan_agent.c and the
whole compiler as one -output-complete-obj. It runs, and the compiler inside it
compiles the very source the program was built from.
Nothing is wired up. The two halves share an address space and do not speak.
That is the point: the question was whether they can, not what they would say.
sig.sh and symbols.sh answer the two questions the first pass got wrong or
skipped. The SIGSEGV reading in harness5.c was taken at the wrong moment --
OCaml 5 starts domains after caml_startup returns, so the disposition had to be
read from inside the runtime, and against a plain ocamlopt executable as a
control. symbols.sh is the hazard nobody looks for until the link fails: four
.c files that are compiled into two different processes today, and the OCaml
runtime, all landing in one link.
Item 12 asks five questions and says to answer them with a spike rather than a
rewrite. spike/embed/ is that spike: one script, six binaries, each one built to
fail loudly at the thing it is asking about. It is deliberately not a dune
target -- the root dune only excludes old-ocaml/, so a dune file here would land
in @default and make the spike part of the build. It drives ocamlfind and clang
by hand against the flan.cmxa dune already produces.
The probes, in the order they would kill the idea: the smallest possible link, a
C main() reaching one OCaml function; the whole compiler linked in and doing
real work; the same again with lib/dynload_stubs.c from the unmerged dlopen
branch, because that is the only C the compiler itself is built from; the game
keeping the main thread while caml_startup happens on a pthread beside it; the
SIGSEGV disposition read on both sides of caml_startup; and an 8 MiB arena
checked byte for byte across a compaction.
No result is written down yet. This is the apparatus.
