Disassembly on request, and it is a debugging aid rather than evidence

SPIKE_DISASM=1 objdumps the exact buffers that ran. Kept behind a flag and
kept out of the pass/fail path: a disassembly that reads correctly beside a
function answering the wrong number is the normal outcome of hand-encoding.

spike/backend/driver.ml

@@ -96,12 +96,19 @@ let run src =
   Hashtbl.iter (fun n c -> Printf.printf "  %-20s %4d bytes at %nx\n"
                    n (String.length c) (Hashtbl.find addrs n)) bytes;
 
-  (* Dumped so oracle.sh can disassemble exactly the bytes that ran. *)
-  (try
-     let oc = open_out_bin (Filename.concat (Filename.dirname Sys.argv.(0)) "spike-add.bin") in
-     output_string oc (Hashtbl.find bytes "spike-add");
-     close_out oc
-   with Not_found -> ());
+  (* The bytes that actually ran, dumped where run.sh can objdump them.
+     A debugging aid and not the evidence: a disassembly that reads correctly
+     next to a function that answers 656 when it should answer 650 is the
+     normal outcome of hand-encoding, which is why the checks below compare
+     numbers. *)
+  (match Sys.getenv_opt "SPIKE_DUMP" with
+   | None -> ()
+   | Some dir ->
+     Hashtbl.iter
+       (fun n c ->
+          let oc = open_out_bin (Filename.concat dir (n ^ ".bin")) in
+          output_string oc c; close_out oc)
+       bytes);
 
   (* ── The SysV boundary ──────────────────────────────────────────────
      Three synthetic functions, built as Tast by hand rather than written in

spike/backend/run.sh

@@ -32,7 +32,17 @@ ocamlfind ocamlopt -thread -package unix,threads.posix -linkpkg \
 
 test -x "$out/spike" || { echo "build failed"; exit 1; }
 
-"$out/spike" "$here/probe.flan"
+SPIKE_DUMP=$out "$out/spike" "$here/probe.flan"
 rc=$?
+
+# Disassembly on request. objdump over the raw buffer, which is what to reach
+# for when a function answers the wrong number -- not what proves it answers
+# the right one.
+if [ "${SPIKE_DISASM:-}" = 1 ]; then
+  for f in "$out"/*.bin; do
+    echo; echo "== $(basename "$f" .bin)"
+    objdump -D -b binary -m i386:x86-64 -M intel "$f" | tail -n +7
+  done
+fi
 echo "exit: $rc"
 exit $rc