Add support for undefined_tramp and closure_tramp in read-only space.

* These are the two "tricky" trampolines, in that genesis needs
to know where they are in order to cold-load fasls, and where
undefined_tramp in particular is in order to even prepare to
cold-load fasls.

  * Add a concept of a "preload file" to genesis, to be loaded
after creating NIL but before creating any FDEFN objects.

  * Use a target feature to switch genesis to using an assembler
routine instead of a foreign symbol for the trampolines.

  * And use our new :NOT-GENESIS build flag to set up a file that
will contain the new trampolines, and arrange for it to be loaded
as the preload file, again under the same target feature.

  * As far as it goes, all this works, but it almost certainly has
some rough edges to it.  It probably isn't quite ready for
upstream yet.

build-order.lisp-expr

@@ -606,6 +606,8 @@
  ("src/assembly/target/array"      :assem :not-host)
  ("src/assembly/target/arith"      :assem :not-host)
  ("src/assembly/target/alloc"      :assem :not-host)
+ #!+read-only-tramps
+ ("src/assembly/target/tramps"     :assem :not-host :not-genesis)
 
  ("src/compiler/pseudo-vops")
 

make-genesis-2.lisp

@@ -11,7 +11,15 @@
                      :direction :input)
     (read s)))
 (host-cload-stem "src/compiler/generic/genesis" nil)
+
+(defparameter *preload-object-file*
+  (or #!+read-only-tramps
+      (stem-remap-target
+       "obj/from-xc/src/assembly/target/tramps.assem-obj")
+      nil))
+
 (sb!vm:genesis :object-file-names *target-object-file-names*
+               :preload-file *preload-object-file*
                :c-header-dir-name "output/genesis-2"
                :symbol-table-file-name "src/runtime/sbcl.nm"
                :core-file-name "output/cold-sbcl.core"

src/compiler/generic/genesis.lisp

@@ -1803,6 +1803,13 @@ core and return a descriptor to it."
             (write-wordindexed fdefn
                                sb!vm:fdefn-raw-addr-slot
                                (make-random-descriptor
+                                #!+read-only-tramps
+                                (or (lookup-assembler-reference 'sb!vm::undefined-tramp)
+                                    ;; Our preload for the tramps
+                                    ;; doesn't happen during host-1,
+                                    ;; so substitute a usable value.
+                                    0)
+                                #!-read-only-tramps
                                 (cold-foreign-symbol-address "undefined_tramp"))))
           fdefn))))
 
@@ -1846,6 +1853,9 @@ core and return a descriptor to it."
                           (bug "FSET got closure-header-widetag")
                           (/show0 "/static-fset (closure)")
                           (make-random-descriptor
+                           #!+read-only-tramps
+                           (lookup-assembler-reference 'sb!vm::closure-tramp)
+                           #!-read-only-tramps
                            (cold-foreign-symbol-address "closure_tramp")))))
     fdefn))
 
@@ -3684,6 +3694,7 @@ initially undefined function references:~2%")
 ;;; perhaps eventually in SB-LD or SB-BOOT.
 (defun sb!vm:genesis (&key
                       object-file-names
+                      preload-file
                       symbol-table-file-name
                       core-file-name
                       map-file-name
@@ -3784,6 +3795,14 @@ initially undefined function references:~2%")
            (*deferred-known-fun-refs* nil)
            #!+x86 (*load-time-code-fixups* (make-hash-table)))
 
+      ;; If we're given a preload file, it contains tramps and whatnot
+      ;; that must be loaded before we create any FDEFNs.  It can in
+      ;; theory be loaded any time between binding
+      ;; *COLD-ASSEMBLER-ROUTINES* above and calling
+      ;; INITIALIZE-STATIC-FNS below.
+      (when preload-file
+        (cold-load preload-file))
+
       ;; Prepare for cold load.
       (initialize-non-nil-symbols)
       (initialize-layouts)