diff --git a/src/bootfiles/21c/boot-21c-cross-x86.lisp b/src/bootfiles/21c/boot-21c-cross-x86.lisp
new file mode 100644
index 0000000000000000000000000000000000000000..7ac6cc7fddc8c28ec184fba10c2ac885f26c0403
--- /dev/null
+++ b/src/bootfiles/21c/boot-21c-cross-x86.lisp
@@ -0,0 +1,225 @@
+;; Basic cross-compile script for cross-compiling from x86 to x86.
+;; May require tweaking for more difficult cross-compiles.
+
+(in-package :cl-user)
+
+;;; Rename the X86 package and backend so that new-backend does the
+;;; right thing.
+(rename-package "X86" "OLD-X86" '("OLD-VM"))
+(setf (c:backend-name c:*native-backend*) "OLD-X86")
+
+(c::new-backend "X86"
+   ;; Features to add here.  These are just examples.  You may not
+   ;; need to list anything here.  We list them here anyway as a
+   ;; record of typical features for all x86 ports.
+   '(:x86 :i486 :pentium
+     :stack-checking			; Catches stack overflow
+     :heap-overflow-check		; Catches heap overflows
+     :relative-package-names		; relative package names
+     :mp				; multiprocessing
+     :gencgc				; Generational GC
+     :conservative-float-type
+     :hash-new
+     :random-xoroshiro
+     :cmu :cmu20 :cmu20a		; Version features
+     :double-double			; double-double float support
+     )
+   ;; Features to remove from current *features* here.  Normally don't
+   ;; need to list anything here unless you are trying to remove a
+   ;; feature.
+   '(:x86-bootstrap
+     ;; :alpha :osf1 :mips
+     :propagate-fun-type :propagate-float-type :constrain-float-type
+     ;; :openbsd :freebsd :glibc2 :linux
+     :long-float :new-random :small
+     :random-mt19937))
+
+;;; Compile the new backend.
+(pushnew :bootstrap *features*)
+(pushnew :building-cross-compiler *features*)
+
+;; Make fixup-code-object and sanctify-for-execution in the VM package
+;; be the same as the original.  Needed to get rid of a compiler error
+;; in generic/core.lisp.  (This halts cross-compilations if the
+;; compiling lisp uses the -batch flag.
+(import 'old-vm::fixup-code-object "VM")
+(import 'old-vm::sanctify-for-execution "VM")
+(export 'vm::fixup-code-object "VM")
+(export 'vm::sanctify-for-execution "VM")
+
+(do-external-symbols (sym "OLD-VM")
+  (export (intern (symbol-name sym) "VM") "VM"))
+
+(load "target:tools/comcom")
+
+;;; Load the new backend.
+(setf (search-list "c:")
+      '("target:compiler/"))
+(setf (search-list "vm:")
+      '("c:x86/" "c:generic/"))
+(setf (search-list "assem:")
+      '("target:assembly/" "target:assembly/x86/"))
+
+;; Load the backend of the compiler.
+
+(in-package "C")
+
+(load "vm:vm-macs")
+(load "vm:parms")
+(load "vm:objdef")
+(load "vm:interr")
+(load "assem:support")
+
+(load "target:compiler/srctran")
+(load "vm:vm-typetran")
+(load "target:compiler/float-tran")
+(load "target:compiler/saptran")
+
+(load "vm:macros")
+(load "vm:utils")
+
+(load "vm:vm")
+(load "vm:insts")
+(load "vm:primtype")
+(load "vm:move")
+(load "vm:sap")
+(when (target-featurep :sse2)
+  (load "vm:sse2-sap"))
+(load "vm:system")
+(load "vm:char")
+(if (target-featurep :sse2)
+    (load "vm:float-sse2")
+    (load "vm:float"))
+
+(load "vm:memory")
+(load "vm:static-fn")
+(load "vm:arith")
+(load "vm:cell")
+(load "vm:subprim")
+(load "vm:debug")
+(load "vm:c-call")
+(if (target-featurep :sse2)
+    (load "vm:sse2-c-call")
+    (load "vm:x87-c-call"))
+
+(load "vm:print")
+(load "vm:alloc")
+(load "vm:call")
+(load "vm:nlx")
+(load "vm:values")
+;; These need to be loaded before array because array wants to use
+;; some vops as templates.
+(load (if (target-featurep :sse2)
+	  "vm:sse2-array"
+	  "vm:x87-array"))
+(load "vm:array")
+(load "vm:pred")
+(load "vm:type-vops")
+
+(load "assem:assem-rtns")
+
+(load "assem:array")
+(load "assem:arith")
+(load "assem:alloc")
+
+(load "c:pseudo-vops")
+
+(check-move-function-consistency)
+
+(load "vm:new-genesis")
+
+;;; OK, the cross compiler backend is loaded.
+
+(setf *features* (remove :building-cross-compiler *features*))
+
+;;; Info environment hacks.
+(macrolet ((frob (&rest syms)
+	     `(progn ,@(mapcar #'(lambda (sym)
+				   `(defconstant ,sym
+				      (symbol-value
+				       (find-symbol ,(symbol-name sym)
+						    :vm))))
+			       syms))))
+  (frob OLD-VM:BYTE-BITS OLD-VM:WORD-BITS
+	OLD-VM:CHAR-BITS
+	OLD-VM:CHAR-BYTES
+	#+long-float OLD-VM:SIMPLE-ARRAY-LONG-FLOAT-TYPE 
+	OLD-VM:SIMPLE-ARRAY-DOUBLE-FLOAT-TYPE 
+	OLD-VM:SIMPLE-ARRAY-SINGLE-FLOAT-TYPE
+	#+long-float OLD-VM:SIMPLE-ARRAY-COMPLEX-LONG-FLOAT-TYPE 
+	OLD-VM:SIMPLE-ARRAY-COMPLEX-DOUBLE-FLOAT-TYPE 
+	OLD-VM:SIMPLE-ARRAY-COMPLEX-SINGLE-FLOAT-TYPE
+	OLD-VM:SIMPLE-ARRAY-UNSIGNED-BYTE-2-TYPE 
+	OLD-VM:SIMPLE-ARRAY-UNSIGNED-BYTE-4-TYPE
+	OLD-VM:SIMPLE-ARRAY-UNSIGNED-BYTE-8-TYPE 
+	OLD-VM:SIMPLE-ARRAY-UNSIGNED-BYTE-16-TYPE 
+	OLD-VM:SIMPLE-ARRAY-UNSIGNED-BYTE-32-TYPE 
+	OLD-VM:SIMPLE-ARRAY-SIGNED-BYTE-8-TYPE 
+	OLD-VM:SIMPLE-ARRAY-SIGNED-BYTE-16-TYPE
+	OLD-VM:SIMPLE-ARRAY-SIGNED-BYTE-30-TYPE 
+	OLD-VM:SIMPLE-ARRAY-SIGNED-BYTE-32-TYPE
+	OLD-VM:SIMPLE-BIT-VECTOR-TYPE
+	OLD-VM:SIMPLE-STRING-TYPE OLD-VM:SIMPLE-VECTOR-TYPE 
+	OLD-VM:SIMPLE-ARRAY-TYPE OLD-VM:VECTOR-DATA-OFFSET
+	OLD-VM:DOUBLE-FLOAT-EXPONENT-BYTE
+	OLD-VM:DOUBLE-FLOAT-NORMAL-EXPONENT-MAX 
+	OLD-VM:DOUBLE-FLOAT-SIGNIFICAND-BYTE
+	OLD-VM:SINGLE-FLOAT-EXPONENT-BYTE
+	OLD-VM:SINGLE-FLOAT-NORMAL-EXPONENT-MAX
+	OLD-VM:SINGLE-FLOAT-SIGNIFICAND-BYTE
+	)
+  #+double-double
+  (frob OLD-VM:SIMPLE-ARRAY-COMPLEX-DOUBLE-DOUBLE-FLOAT-TYPE
+	OLD-VM:SIMPLE-ARRAY-DOUBLE-DOUBLE-FLOAT-TYPE))
+
+;; Modular arith hacks
+(setf (fdefinition 'vm::ash-left-mod32) #'old-vm::ash-left-mod32)
+(setf (fdefinition 'vm::lognot-mod32) #'old-vm::lognot-mod32)
+;; End arith hacks
+
+(let ((function (symbol-function 'kernel:error-number-or-lose)))
+  (let ((*info-environment* (c:backend-info-environment c:*target-backend*)))
+    (setf (symbol-function 'kernel:error-number-or-lose) function)
+    (setf (info function kind 'kernel:error-number-or-lose) :function)
+    (setf (info function where-from 'kernel:error-number-or-lose) :defined)))
+
+(defun fix-class (name)
+  (let* ((new-value (find-class name))
+	 (new-layout (kernel::%class-layout new-value))
+	 (new-cell (kernel::find-class-cell name))
+	 (*info-environment* (c:backend-info-environment c:*target-backend*)))
+    (remhash name kernel::*forward-referenced-layouts*)
+    (kernel::%note-type-defined name)
+    (setf (info type kind name) :instance)
+    (setf (info type class name) new-cell)
+    (setf (info type compiler-layout name) new-layout)
+    new-value))
+(fix-class 'c::vop-parse)
+(fix-class 'c::operand-parse)
+
+#+random-mt19937
+(declaim (notinline kernel:random-chunk))
+
+(setf c:*backend* c:*target-backend*)
+
+;;; Extern-alien-name for the new backend.
+(in-package :vm)
+(defun extern-alien-name (name)
+  (declare (type simple-string name))
+  #-elf
+  (concatenate 'simple-string "_" name)
+  #+elf
+  name)
+(export 'extern-alien-name)
+(in-package :cl-user)
+
+;;; Don't load compiler parts from the target compilation
+
+(defparameter *load-stuff* nil)
+
+;; hack, hack, hack: Make old-vm::any-reg the same as
+;; x86::any-reg as an SC.  Do this by adding old-vm::any-reg
+;; to the hash table with the same value as x86::any-reg.
+(let ((ht (c::backend-sc-names c::*target-backend*)))
+  (setf (gethash 'old-vm::any-reg ht)
+	(gethash 'vm::any-reg ht)))
diff --git a/src/bootfiles/21c/boot-21c-cross.lisp b/src/bootfiles/21c/boot-21c-cross.lisp
new file mode 100644
index 0000000000000000000000000000000000000000..08c21e260108d369792f7faa837dce0c9c2e4d6c
--- /dev/null
+++ b/src/bootfiles/21c/boot-21c-cross.lisp
@@ -0,0 +1,13 @@
+;; Cross-compile script to change the default random number generator
+;; from MT19937 to xoroshiro128+.
+
+;; The cross-script is basically the default platform script, but we
+;; remove :random-mt19937 and add :random-xoroshiro to the backend
+;; features.
+
+#+x86
+(load "src/bootfiles/21c/boot-21c-cross-x86.lisp")
+
+#+sparc
+(load "src/bootfiles/21c/boot-21c-cross-sparc.lisp")
+