Joseph Ferano
d272a5b1e5
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.
27 lines
1.2 KiB
OCaml
27 lines
1.2 KiB
OCaml
(* Step 3: the project's own C stubs, in the same link as the compiler.
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lib/dynload_stubs.c is taken verbatim from 9e0ae3a (the unmerged dlopen
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branch) -- it is the only C the compiler itself is built from, and it is the
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case that -output-complete-obj has to carry through. *)
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external dl_open : string -> nativeint = "flan_dl_open"
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external dl_sym : nativeint -> string -> nativeint = "flan_dl_sym"
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external mem_alloc : int -> nativeint = "flan_mem_alloc"
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external mem_free : nativeint -> unit = "flan_mem_free"
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external poke_i64 : nativeint -> int -> int64 -> unit = "flan_poke_i64"
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external peek_i64 : nativeint -> int -> int64 = "flan_peek_i64"
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let () =
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Callback.register "spike_stubs" (fun () ->
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(* peek/poke: the raw memory the marshaller lays a Form image out in. *)
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let p = mem_alloc 64 in
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poke_i64 p 8 0xfeedfacedeadbeefL;
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let got = peek_i64 p 8 in
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mem_free p;
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(* dlopen from inside the embedded runtime, on the process's own image. *)
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let h = dl_open "libm.so.6" in
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let s = dl_sym h "sqrt" in
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Printf.sprintf "peek/poke %s; dlopen+dlsym %s"
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(if got = 0xfeedfacedeadbeefL then "ok" else "WRONG")
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(if s <> 0n then "ok" else "WRONG"));
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ignore dl_open
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