Share magic constants between genesis and editcore

[sbcl.git] / tools-for-build / editcore.lisp

;;;; Utilities for separating an SBCL core file into two pieces:
;;;; 1. An assembly language file containing the immobile code space
;;;; 2. A '.o' file wrapping a core file containing everything else
;;;; We operate as a "tool" that processes external files rather than
;;;; operating on the in-process data, but it is also possible to dump
;;;; the current image by creating a straight-through translation
;;;; of internal/external code addresses.

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(eval-when (:compile-toplevel :load-toplevel :execute)
  (require :sb-posix)) ; for mmap

(load (merge-pathnames "corefile.lisp" *load-pathname*))

(defpackage "SB-EDITCORE"
  (:use "CL" "SB-ALIEN" "SB-COREFILE" "SB-INT" "SB-EXT"
        "SB-KERNEL" "SB-SYS" "SB-VM")
  (:import-from "SB-ALIEN-INTERNALS"
                #:alien-type-bits #:parse-alien-type
                #:alien-value-sap #:alien-value-type)
  (:import-from "SB-C" #:+backend-page-bytes+)
  (:import-from "SB-VM" #:map-objects-in-range #:reconstitute-object
                #:%closure-callee)
  (:import-from "SB-DISASSEM" #:get-inst-space #:find-inst
                #:make-dstate #:%make-segment
                #:seg-virtual-location #:seg-length #:seg-sap-maker
                #:map-segment-instructions
                #:dstate-next-addr #:dstate-cur-offs)
  (:import-from "SB-X86-64-ASM" #:near-jump-displacement)
  (:import-from "SB-IMPL" #:package-hashtable #:package-%name
                #:package-hashtable-cells
                #:hash-table-table #:hash-table-number-entries))

(in-package "SB-EDITCORE")

(declaim (muffle-conditions compiler-note))

(eval-when (:execute)
  (setq *evaluator-mode* :compile))

(defconstant core-magic
  (logior (ash (char-code #\S) 24)
          (ash (char-code #\B) 16)
          (ash (char-code #\C) 8)
          (char-code #\L)))

(defglobal +noexec-stack-note+ ".section .note.GNU-stack, \"\", @progbits")

(defstruct (core-space ; "space" is a CL symbol
            (:conc-name space-)
            (:constructor make-space (id addr data-page page-adjust nwords)))
  id addr data-page page-adjust nwords)
(defun space-size (space) (* (space-nwords space) n-word-bytes))
(defun space-end (space) (+  (space-addr space) (space-size space)))
(defun space-nbytes-aligned (space)
  (logandc2 (+ (space-size space) (1- +backend-page-bytes+))
            (1- +backend-page-bytes+)))
(defun space-physaddr (space spaces)
  (sap+ (car spaces) (* (space-data-page space) +backend-page-bytes+)))

;;; Given ADDR which is an address in the target core, return the address at which
;;; ADDR is currently mapped while performing the split.
;;; SPACES is a cons of a SAP and an alist whose elements are (ADDR . CORE-SPACE)
(defun translate-ptr (addr spaces)
  (let ((space (find addr (cdr spaces) :key #'space-addr :test #'>=)))
    ;; FIXME: duplicates SPACE-PHYSADDR to avoid consing a SAP.
    ;; macroize or something.
    (+ (sap-int (car spaces)) (* (space-data-page space) +backend-page-bytes+)
       (- addr (space-addr space)))))

;;;
(defun get-space (id spaces)
  (find id (cdr spaces) :key #'space-id))
(defun compute-nil-object (spaces)
  (let ((space (get-space static-core-space-id spaces)))
    (%make-lisp-obj (logior (space-addr space) #x17))))

;;; Given OBJ which is tagged pointer into the target core, translate it into
;;; the range at which the core is now mapped during execution of this tool,
;;; so that host accessors can dereference its slots.
;;; Use extreme care: while it works to use host accessors on the target core,
;;; we must avoid type checks on instances because LAYOUTs need translation.
;;; Printing boxed objects from the target core will almost always crash.
(defun translate (obj spaces)
  (%make-lisp-obj (translate-ptr (get-lisp-obj-address obj) spaces)))

(defstruct (core-sym (:copier nil) (:predicate nil)
                     (:constructor make-core-sym (package name external)))
  (package nil)
  (name nil :read-only t)
  (external nil :read-only t))

(defun c-name (lispname pp-state)
  (when (and (symbolp lispname)
             (eq (symbol-package lispname) *cl-package*))
    (return-from c-name (concatenate 'string "cl:" (string-downcase lispname))))
  ;; Get rid of junk from LAMBDAs
  (setq lispname
        (named-let recurse ((x lispname))
                   (cond ((typep x '(cons (eql lambda)))
                          (let ((args (second x)))
                            `(lambda ,(if args sb-c::*debug-name-sharp* "()")
                               ,@(recurse (cddr x)))))
                         ((eq x :in) "in")
                         ((consp x)
                          (recons x (recurse (car x)) (recurse (cdr x))))
                         (t x))))

  ;; Shorten obnoxiously long printed representations of methods
  ;; by changing FAST-METHOD to METHOD (because who cares?)
  ;; and shorten
  ;;   (method my-long-package-name:my-method-name (my-long-package-name:type-name))
  ;; to
  ;;   (method my-method-name (type-name))
  ;; I suspect that can use DWARF info to provide even more description,
  ;; though I also suspect it's relatively unambiguous anyway
  ;; especially given that file information is available separately.
  (flet ((unpackageize (thing)
           (when (typep thing 'core-sym)
             (setf (core-sym-package thing) nil))
           thing))
    (when (typep lispname '(cons (eql sb-pcl::fast-method)))
      (setq lispname `(method ,@(cdr lispname)))
      (setf (second lispname) (unpackageize (second lispname)))
        (dolist (qual (car (last lispname)))
          (unpackageize qual))))

  ;; Perform backslash escaping on the exploded string
  ;; Strings were stringified without surrounding quotes,
  ;; but there might be quotes embedded anywhere, so escape them,
  ;; and also remove newlines and non-ASCII.
  (let ((characters
         (mapcan (lambda (char)
                   (cond ((not (base-char-p char)) (list #\?))
                         ((member char '(#\\ #\")) (list #\\ char))
                         ((eql char #\newline) (list #\_))
                         (t (list char))))
                 (coerce (if (and (stringp lispname)
                                     ;; L denotes a symbol which can not be global on macOS.
                                     (char= (char lispname 0) #\L))
                             (concatenate 'string "_" lispname)
                             (write-to-string lispname
                              :pretty t :pprint-dispatch (cdr pp-state)
                              ;; FIXME: should be :level 1, however see
                              ;; https://bugs.launchpad.net/sbcl/+bug/1733222
                              :escape t :level 2 :length 5
                              :case :downcase :gensym nil
                              :right-margin 10000))
                         'list))))
    (let* ((string (coerce characters 'string))
           (occurs (incf (gethash string (car pp-state) 0))))
      (if (> occurs 1)
          (concatenate 'string  string "_" (write-to-string occurs))
          string))))

(defmethod print-object ((sym core-sym) stream)
  (format stream "~(~:[~*~;~:*~A~:[:~;~]:~]~A~)"
          (core-sym-package sym)
          (core-sym-external sym)
          (core-sym-name sym)))

(defun fun-name-from-core (fun spaces core-nil packages
                               &aux (name (%simple-fun-name fun)))
  (named-let recurse ((depth 0) (x name))
    (unless (= (logand (get-lisp-obj-address x) 3) 3)
      (return-from recurse x)) ; immediate object
    (when (eq x core-nil)
      (return-from recurse nil))
    (setq x (translate x spaces))
    (ecase (lowtag-of x)
      (#.list-pointer-lowtag
       (cons (recurse (1+ depth) (car x))
             (recurse (1+ depth) (cdr x))))
      ((#.instance-pointer-lowtag #.fun-pointer-lowtag) "?")
      (#.other-pointer-lowtag
       (cond
        ((symbolp x)
         (let ((name (translate (symbol-name x) spaces)))
           (if (eq (symbol-package x) core-nil) ; uninterned
               (string-downcase name)
               (let* ((package (truly-the package
                                          (translate (symbol-package x) spaces)))
                      (package-name (translate (package-%name package) spaces))
                      (compute-externals
                       (not (or (string= package-name "KEYWORD")
                                (string= package-name "COMMON-LISP"))))
                      (externals (if compute-externals
                                     (gethash package-name packages)
                                     t)))
                 (unless externals
                   (dovector (x (translate
                                 (package-hashtable-cells
                                  (truly-the package-hashtable
                                   (translate (package-external-symbols package)
                                              spaces)))
                                 spaces))
                     (unless (fixnump x)
                       (push (if (eq x core-nil) ; random packages can export NIL. wow.
                                 "NIL"
                                 (translate (symbol-name (translate x spaces)) spaces))
                             externals)))
                   (setf externals (coerce externals 'vector)
                         (gethash package-name packages) externals))
                 ;; The name-cleaning code wants to compare against symbols
                 ;; in CL, PCL, and KEYWORD, so use real symbols for those.
                 ;; Other than that, we avoid finding host symbols
                 ;; because the externalness could be wrong and misleading.
                 ;; It's a very subtle point, but best to get it right.
                 (if (member package-name '("COMMON-LISP" "KEYWORD" "SB-PCL")
                             :test #'string=)
                     ; NIL can't occur, because it has list-pointer-lowtag
                     (find-symbol name package-name) ; if existing symbol, use it
                     (make-core-sym (if (string= package-name "KEYWORD") nil package-name)
                                    name
                                    (if compute-externals
                                        (find name externals :test 'string=)
                                        t)))))))
        ((stringp x) x)
        (t "?"))))))

(defstruct (core-state
            (:conc-name "CS-")
            (:predicate nil)
            (:copier nil)
            (:constructor make-core-state
                (code-space-start code-space-end
                 fixedobj-space-start fixedobj-space-end
                 &aux (inst-space (get-inst-space))
                      (call-inst (find-inst #b11101000 inst-space))
                      (jmp-inst (find-inst #b11101001 inst-space))
                      (pop-inst (find-inst #x5d inst-space)))))
  (code-space-start 0 :type fixnum :read-only t)
  (code-space-end 0 :type fixnum :read-only t)
  (fixedobj-space-start 0 :type fixnum :read-only t)
  (fixedobj-space-end 0 :type fixnum :read-only t)
  (dstate (make-dstate nil) :read-only t)
  (seg (%make-segment :sap-maker (lambda () (error "Bad sap maker"))
                      :virtual-location 0) :read-only t)
  (fixup-addrs nil)
  (call-inst nil :read-only t)
  (jmp-inst nil :read-only t)
  (pop-inst nil :read-only t))

;;; Emit .byte or .quad directives dumping memory from SAP for COUNT bytes
;;; to STREAM.  SIZE specifies which direcive to emit.
;;; EXCEPTIONS specify offsets at which a specific string should be
;;; written to the file in lieu of memory contents, useful for emitting
;;; expressions involving the assembler '.' symbol (the current PC).
(defun emit-asm-directives (size sap count stream &optional exceptions)
  (declare (optimize speed))
  (declare (stream stream))
  (let ((*print-base* 16)
        (string-buffer (make-array 18 :element-type 'base-char))
        (fmt #.(coerce "0x%lx" 'base-string))
        (per-line 0))
    (declare ((integer 0 32) per-line)
             (fixnum count))
    string-buffer fmt
    (ecase size
      (:qword
       (format stream " .quad")
       (dotimes (i count)
         (declare ((unsigned-byte 20) i))
         (declare (simple-vector exceptions))
         (write-char (if (> per-line 0) #\, #\space) stream)
         (acond ((and (< i (length exceptions)) (aref exceptions i))
                 (write-string it stream))
                (t
                 #+nil
                 (let ((len
                        ;; output-reasonable-integer-in-base is so slow comparated
                        ;; to printf() that the second-most amount of time spent
                        ;; writing the asm file occurs in that function.
                        ;; Unbelievable that we can't do better than that.
                        (with-pinned-objects (string-buffer fmt)
                          (alien-funcall
                           (extern-alien "snprintf"
                            (function int system-area-pointer unsigned system-area-pointer unsigned))
                           (vector-sap string-buffer)
                           (length string-buffer)
                           (vector-sap fmt)
                           (sap-ref-word sap (* i n-word-bytes))))))
                   (write-string string-buffer stream :end len))
                 (write-string "0x" stream)
                 (write (sap-ref-word sap (* i n-word-bytes)) :stream stream)))
         (when (and (= (incf per-line) 16) (< (1+ i) count))
           (format stream "~% .quad")
           (setq per-line 0))))
      (:byte
       (aver (not exceptions))
       (format stream " .byte")
       (dotimes (i count)
         (write-char (if (> per-line 0) #\, #\space) stream)
         (write-string "0x" stream)
         (write (sap-ref-8 sap i) :stream stream)
         (when (and (= (incf per-line) 32) (< (1+ i) count))
           (format stream "~% .byte")
           (setq per-line 0))))))
  (terpri stream))

(defun emit-lisp-asm-routines (spaces code-component output emit-sizes vector count)
  (emit-asm-directives :qword
                       (sap+ (code-instructions code-component)
                             (- (* sb-vm:code-constants-offset sb-vm:n-word-bytes)))
                       sb-vm:code-constants-offset
                       output #())
  (let ((list (loop for i from 2 by 2 repeat count
                    collect
                    (let* ((location (translate (svref vector (1+ i)) spaces))
                           (offset (car location))
                           (nbytes (- (1+ (cdr location)) offset))
                           (name (translate
                                  (symbol-name (translate (svref vector i) spaces))
                                  spaces)))
                      (list* offset name nbytes)))))
    (loop for (offset name . nbytes) in (sort list #'< :key #'car)
          do (format output " .set ~a, .~%~@[ .size ~:*~a, ~d~%~]"
                     (format nil "~(\"~a\"~)" name) (if emit-sizes nbytes))
             (emit-asm-directives
              :qword
              (sap+ (code-instructions code-component) offset)
              (ceiling nbytes sb-vm:n-word-bytes)
              output #()))))

(defun code-fixup-locs (code spaces)
  (let ((locs (sb-vm::%code-fixups code)))
    (unless (eql locs 0)
      (sb-c::unpack-code-fixup-locs
       (if (fixnump locs) locs (translate locs spaces))))))

;;; Disassemble the function pointed to by SAP for LENGTH bytes, returning
;;; all instructions that should be emitted using assembly language
;;; instead of assembler pseudo-ops. This includes two sets of instructions:
;;; - function prologue instructions that setup the call frame
;;; - jmp/call instructions that transfer control to the fixedoj space
;;;    delimited by bounds in STATE.
;;; At execution time the function will have virtual address LOAD-ADDR.
(defun list-annotated-instructions (sap length state load-addr emit-cfi)
  (let ((dstate (cs-dstate state))
        (seg (cs-seg state))
        (call-inst (cs-call-inst state))
        (jmp-inst (cs-jmp-inst state))
        (pop-inst (cs-pop-inst state))
        (next-fixup-addr
         (or (car (cs-fixup-addrs state)) most-positive-word))
        (list))
    (setf (seg-virtual-location seg) load-addr
          (seg-length seg) length
          (seg-sap-maker seg) (lambda () sap))
    ;; KLUDGE: "8f 45 08" is the standard prologue
    (when (and emit-cfi (= (logand (sap-ref-32 sap 0) #xFFFFFF) #x08458f))
      (push (list* 0 3 "pop" "8(%rbp)") list))
    (map-segment-instructions
     (lambda (dchunk inst)
       (cond
         ((< next-fixup-addr (dstate-next-addr dstate))
          (let ((operand (sap-ref-32 sap (- next-fixup-addr load-addr))))
            (when (<= (cs-code-space-start state) operand (cs-code-space-end state))
              (aver (eql (sap-ref-8 sap (- next-fixup-addr load-addr 1)) #xB8)) ; mov rax, imm32
              (push (list* (dstate-cur-offs dstate) 5 "mov" operand) list)))
          (pop (cs-fixup-addrs state))
          (setq next-fixup-addr (or (car (cs-fixup-addrs state)) most-positive-word)))
         ((or (eq inst jmp-inst) (eq inst call-inst))
          (let ((target-addr (+ (near-jump-displacement dchunk dstate)
                                (dstate-next-addr dstate))))
            (when (<= (cs-fixedobj-space-start state)
                      target-addr
                      (cs-fixedobj-space-end state))
              (push (list* (dstate-cur-offs dstate)
                           5 ; length
                           (if (eq inst call-inst) "call" "jmp")
                           target-addr)
                    list))))
         ((and (eq inst pop-inst) (eq (logand dchunk #xFF) #x5D))
          (push (list* (dstate-cur-offs dstate) 1 "pop" "%rbp") list))))
     seg
     dstate
     nil)
    (nreverse list)))

;;; Using assembler directives and/or real mnemonics, dump COUNT bytes
;;; of memory at PADDR (physical addr) to STREAM.
;;; The function's address as per the core file is VADDR.
;;; (Its eventual address is indeterminate)
;;; If EMIT-CFI is true, then also emit cfi directives.
;;;
;;; Notice that we can use one fewer cfi directive than usual because
;;; Lisp always carries a frame pointer as set up by the caller.
;;;
;;; C convention
;;; ============
;;; pushq %rbp
;;; .cfi_def_cfa_offset 16   # CFA offset from default register (rsp) is +16
;;; .cfi_offset 6, -16       # old rbp was saved in -16(CFA)
;;; movq %rsp, %rbp
;;; .cfi_def_cfa_register 6  # use rbp as CFA register
;;;
;;; Lisp convention
;;; ===============
;;; popq 8(%rbp) # place saved %rip in its ABI-compatible stack slot
;;;              # making RSP = RBP after the pop, and RBP = CFA - 16
;;; .cfi_def_cfa 6, 16
;;; .cfi_offset 6, -16
;;;
;;; Of course there is a flip-side to this: unwinders think that the new frame
;;; is already begun in the caller. Interruption between these two instructions:
;;;   MOV RBP, RSP / CALL #xzzzzz
;;; will show the backtrace as if two invocations of the caller are on stack.
;;; This is tricky to fix because while we can relativize the CFA to the
;;; known frame size, we can't do that based only on a disassembly.

(defun emit-lisp-function (paddr vaddr count stream emit-cfi core-state)
  (when emit-cfi
    (format stream " .cfi_startproc~%"))
  ;; Any byte offset that appears as a key in the INSTRUCTIONS causes the indicated
  ;; bytes to be written as an assembly language instruction rather than opaquely,
  ;; thereby affecting the ELF data (cfi or relocs) produced.
  (let ((instructions
         (list-annotated-instructions (int-sap paddr) count core-state vaddr emit-cfi))
        (ptr paddr))
    (symbol-macrolet ((cur-offset (- ptr paddr)))
      (loop
        (let ((until (if instructions (caar instructions) count)))
          ;; if we're not aligned, then write some number of bytes
          ;; to cause alignment. But do not write past the next offset
          ;; that needs to be written as an instruction.
          (when (logtest ptr #x7) ; unaligned
            (let ((n (min (- (nth-value 1 (ceiling ptr 8)))
                          (- until cur-offset))))
              (aver (<= 0 n 7))
              (emit-asm-directives :byte (int-sap ptr) n stream)
              (incf ptr n)))
          ;; Now we're either aligned to a multiple of 8, or the current
          ;; offset needs to be written as a textual instruction.
          (let ((n (- until cur-offset)))
            (aver (>= n 0))
            (multiple-value-bind (qwords remainder) (floor n 8)
              (when (plusp qwords)
                (emit-asm-directives :qword (int-sap ptr) qwords stream #())
                (incf ptr (* qwords 8)))
              (when (plusp remainder)
                (emit-asm-directives :byte (int-sap ptr) remainder stream)
                (incf ptr remainder))))
          ;; If the current offset is COUNT, we're done.
          (when (= cur-offset count) (return))
          (aver (= cur-offset until))
          (destructuring-bind (length opcode . operand) (cdr (pop instructions))
            (when (cond ((member opcode '("jmp" "call") :test #'string=)
                         (format stream " ~A 0x~X~%" opcode operand))
                        ((string= opcode "pop")
                         (format stream " ~A ~A~%" opcode operand)
                         (cond ((string= operand "8(%rbp)")
                                (format stream " .cfi_def_cfa 6, 16~% .cfi_offset 6, -16~%"))
                               ((string= operand "%rbp")
                                ;(format stream " .cfi_def_cfa 7, 8~%")
                                nil)
                               (t)))
                        ((string= opcode "mov")
                         (format stream " mov $(__lisp_code_start+0x~x),%eax~%"
                                 (- operand (cs-code-space-start core-state))))
                        (t))
              (bug "Random annotated opcode ~S" opcode))
            (incf ptr length))
          (when (= cur-offset count) (return))))))
  (when emit-cfi
    (format stream " .cfi_endproc~%")))

;;; Convert immobile CODE-SPACE to an assembly file in OUTPUT.
;;; TODO: relocate fdefns and instances of standard-generic-function
;;; into the space that is dumped into an ELF section.
(defun write-assembler-text
    (spaces fixedobj-range output
     &optional emit-sizes (emit-cfi t)
     &aux (code-space (get-space immobile-varyobj-core-space-id spaces))
          (code-space-start (space-addr code-space)) ; target virtual address
          (code-space-end (+ code-space-start (space-size code-space)))
          (code-addr code-space-start)
          (core-state
           (make-core-state code-space-start code-space-end
                            (car fixedobj-range)
                            (+ (car fixedobj-range) (cdr fixedobj-range))))
          (total-code-size 0)
          (pp-state (cons (make-hash-table :test 'equal)
                          ;; copy no entries for macros/special-operators (flet, etc)
                          (sb-pretty::make-pprint-dispatch-table)))
          (packages (make-hash-table :test 'equal))
          (core-nil (compute-nil-object spaces))
          (prev-namestring "")
          (n-linker-relocs 0)
          end-loc)
  (set-pprint-dispatch 'string
                       ;; Write strings without string quotes
                       (lambda (stream string) (write-string string stream))
                       0
                       (cdr pp-state))
  (labels ((ldsym-quote (name)
             (concatenate 'string '(#\") name '(#\")))
           (dumpwords (addr count stream &optional (exceptions #()) logical-addr)
             (let ((sap (int-sap addr)))
               (aver (sap>= sap (car spaces)))
               ;; Make intra-code-space pointers computed at link time
               (dotimes (i (if logical-addr count 0))
                 (unless (and (< i (length exceptions)) (svref exceptions i))
                   (let ((word (sap-ref-word sap (* i n-word-bytes))))
                     (when (and (= (logand word 3) 3) ; is a pointer
                                (<= code-space-start word (1- code-space-end))) ; to code space
                       #+nil
                       (format t "~&~(~x: ~x~)~%" (+ logical-addr  (* i n-word-bytes))
                               word)
                       (incf n-linker-relocs)
                       (setf exceptions (adjust-array exceptions (max (length exceptions) (1+ i))
                                                      :initial-element nil)
                             (svref exceptions i)
                             (format nil "__lisp_code_start+0x~x"
                                     (- word code-space-start)))))))
               (emit-asm-directives :qword sap count stream exceptions)))
           (make-code-obj (addr)
             (let ((translation (translate-ptr addr spaces)))
               (aver (= (%widetag-of (sap-ref-word (int-sap translation) 0))
                        code-header-widetag))
               (%make-lisp-obj (logior translation other-pointer-lowtag))))
           (calc-obj-size (code)
             ;; No need to pin - it's not managed by GC
             (nth-value 2
              (reconstitute-object
               (ash (logandc2 (get-lisp-obj-address code) lowtag-mask)
                    (- n-fixnum-tag-bits)))))
           (%widetag-of (word)
             (logand word widetag-mask)))
    (format output " .text~% .file \"sbcl.core\"
 .globl __lisp_code_start, __lisp_code_end~% .balign 4096~%__lisp_code_start:~%")

    ;; Scan the assembly routines.
    (let* ((code-component (make-code-obj code-addr))
           (size (calc-obj-size code-component))
           (hashtable
            (truly-the hash-table
                       (translate (car (translate (%code-debug-info code-component)
                                                  spaces))
                                  spaces)))
           (cells (translate (hash-table-table hashtable) spaces))
           (count (hash-table-number-entries hashtable)))
      (incf code-addr size)
      (setf total-code-size size)
      (emit-lisp-asm-routines spaces code-component output emit-sizes cells count))

    (loop
      (when (>= code-addr code-space-end) (return))
      ;(format t "~&vaddr ~x paddr ~x~%" code-addr (get-lisp-obj-address (make-code-obj code-addr)))
      (let* ((code (make-code-obj code-addr))
             (objsize (calc-obj-size code)))
        (setq end-loc (+ code-addr objsize))
        (incf total-code-size objsize)
        (cond
          ((< (code-header-words code) 4) ; filler object
           ;; Shouldn't occur unless defrag was not performed
           (format output "#x~x:~% .quad 0x~X, 0x~X~% .fill ~D~%"
                   code-addr
                   simple-array-unsigned-byte-8-widetag
                   (ash (- objsize (* 2 n-word-bytes))
                        n-fixnum-tag-bits)
                   (- objsize (* 2 n-word-bytes))))
          ((%instancep (%code-debug-info code)) ; assume it's a COMPILED-DEBUG-INFO
           (aver (plusp (code-n-entries code)))
           (let* ((source
                   (sb-c::compiled-debug-info-source
                    (truly-the sb-c::compiled-debug-info
                               (translate (%code-debug-info code) spaces))))
                  (namestring
                   (sb-c::debug-source-namestring
                    (truly-the sb-c::debug-source (translate source spaces)))))
             (setq namestring (if (eq namestring core-nil)
                                  "sbcl.core"
                                  (translate namestring spaces)))
             (unless (string= namestring prev-namestring)
               (format output " .file \"~a\"~%" namestring)
               (setq prev-namestring namestring)))
           (let* ((code-physaddr (logandc2 (get-lisp-obj-address code) lowtag-mask))
                  (boxed-end (+ code-physaddr
                                (ash (code-header-words code) word-shift)))
                  (first-fun (logandc2 (get-lisp-obj-address (%code-entry-point code 0))
                                       lowtag-mask)))
             (format output "#x~x:~%" code-addr)
             (dumpwords code-physaddr (code-header-words code) output #() code-addr)
             ;; Any words after 'boxed' preceding 'first-fun' are unboxed
             (when (> first-fun boxed-end)
               (dumpwords boxed-end (floor (- first-fun boxed-end) n-word-bytes)
                          output)))
           (setf (cs-fixup-addrs core-state)
                 (mapcar (lambda (x)
                           (+ code-addr (ash (code-header-words code) word-shift) x))
                         (code-fixup-locs code spaces)))
           ;; Loop over all embedded functions.
           ;; Because simple-fun offsets are relative to the code start
           ;; (and not in a linked list as they were in the past),
           ;; iteratation in a "foreign" code object works just fine,
           ;; subject to the caution about reading boxed words.
           (dotimes (j (code-n-entries code))
             (let* ((fun (%code-entry-point code j))
                    (fun-addr (logandc2 (get-lisp-obj-address fun) lowtag-mask))
                    (end (if (< (1+ j) (code-n-entries code))
                             (logandc2 (get-lisp-obj-address (%code-entry-point code (1+ j)))
                                       lowtag-mask)
                             (+ (translate-ptr code-addr spaces) objsize)))
                    (entrypoint
                     (+ fun-addr (* simple-fun-code-offset n-word-bytes)))
                    (size (- end entrypoint))
                    (lispname (fun-name-from-core fun spaces core-nil packages))
                    (quotname (ldsym-quote (c-name lispname pp-state))))
               ;; Globalize the C symbol only if the name is a legal function designator
               ;; per the standard definition.
               ;; This is a technique to try to avoid appending a uniquifying suffix
               ;; on all the junky internal things like "(lambda # in srcfile.lisp)"
               (format output "~:[~*~; .globl ~a~%~]~@[ .type ~:*~a, @function~%~]"
                       (typep lispname '(or symbol core-sym (cons (eql setf))))
                       quotname emit-sizes)
               (dumpwords fun-addr
                          simple-fun-code-offset output
                          (load-time-value
                           `#(nil ,(format nil ".+~D"
                                           (* (1- simple-fun-code-offset)
                                              n-word-bytes)))
                           t)
                          nil)
               (format output " .set ~a, .~%~@[ .size ~:*~a, ~d~%~]"
                       quotname (if emit-sizes size))
               ;; entrypoint is the current physical address.
               ;; Also pass in the virtual address in the core
               ;; (which will differ from the actual load-time address)
               (emit-lisp-function entrypoint
                                   (+ code-addr (- entrypoint
                                                   (logandc2 (get-lisp-obj-address code)
                                                             lowtag-mask)))
                                   size output emit-cfi core-state)))
           (terpri output)
           ;; All fixups should have been consumed by writing the code out
           (aver (null (cs-fixup-addrs core-state))))
          (t
           (error "Strange code component: ~S" code)))
        (incf code-addr objsize))))

  ;; coreparse uses unpadded __lisp_code_end to set varyobj_free_pointer
  (format output "__lisp_code_end:~%")

  ;; Pad so that non-lisp code can't be colocated on a GC page.
  ;; (Lack of Lisp object headers in C code is the issue)
  (let ((aligned-end (logandc2 (+ end-loc 4095) 4095)))
    (when (> aligned-end end-loc)
      (multiple-value-bind (nwords remainder)
          (floor (- aligned-end end-loc) n-word-bytes)
        (aver (>= nwords 2))
        (aver (zerop remainder))
        (decf nwords 2)
        (format output " .quad ~d, ~d # (simple-array fixnum (~d))~%"
                simple-array-fixnum-widetag
                (ash nwords n-fixnum-tag-bits)
                nwords)
        (when (plusp nwords)
          (format output " .fill ~d~%" (* nwords n-word-bytes))))))
  ; (format t "~&linker-relocs=~D~%" n-linker-relocs)
  (values total-code-size n-linker-relocs))

;;; Return either the physical or logical address of the specified symbol.
(defun find-target-symbol (package-name symbol-name spaces
                           &optional (address-mode :physical))
  (let* ((space (find immobile-fixedobj-core-space-id (cdr spaces) :key #'space-id))
         (start (translate-ptr (space-addr space) spaces))
         (end (+ start (space-size space)))
         (physaddr start))
    (loop
      (when (>= physaddr end) (bug "Can't find symbol"))
      (multiple-value-bind (obj tag size)
          (reconstitute-object (ash physaddr (- n-fixnum-tag-bits)))
        (when (and (= tag symbol-widetag)
                   (string= symbol-name (translate (symbol-name obj) spaces))
                   (%instancep (symbol-package obj))
                   (string= package-name
                            (translate
                             (package-%name
                              (truly-the package (translate (symbol-package obj) spaces)))
                             spaces)))
          (return (%make-lisp-obj
                   (logior (ecase address-mode
                             (:physical physaddr)
                             (:logical (+ (space-addr space) (- physaddr start))))
                           other-pointer-lowtag))))
        (incf physaddr size)))))

(defun extract-required-c-symbols (spaces asm-file &optional (verbose nil))
  (flet ((symbol-fdefn-fun (symbol)
           (let ((vector (translate (symbol-info-vector symbol) spaces)))
             ;; TODO: allow for (plist . info-vector) in the info slot
             (aver (simple-vector-p vector))
             (translate (fdefn-fun (translate (info-vector-fdefn vector) spaces))
                        spaces))))
    (let ((linkage-info
           (translate (symbol-global-value
                       (find-target-symbol "SB-SYS" "*LINKAGE-INFO*" spaces))
                      spaces))
          (dyn-syminfo
           (symbol-fdefn-fun
            (find-target-symbol "SB-SYS"
                                "ENSURE-DYNAMIC-FOREIGN-SYMBOL-ADDRESS"
                                spaces))))
      (aver (= (get-closure-length dyn-syminfo) 3))
      (let* ((ht1 (translate (%closure-index-ref dyn-syminfo 1) spaces))
             (ht2 (translate (%closure-index-ref dyn-syminfo 0) spaces))
             (table0 (translate (hash-table-table (truly-the hash-table linkage-info))
                                spaces))
             (table1 (translate (hash-table-table (truly-the hash-table ht1)) spaces))
             (table2 (translate (hash-table-table (truly-the hash-table ht2)) spaces))
             (linkage)
             (foreign))
        (declare (simple-vector table0 table1 table2))
        (flet ((show (x)
                 (push x foreign)
                 (when verbose
                   (format t "~A~%" x)))
               (scan-table (table name fun &aux (n 0) (end (length table)))
                 (when verbose
                   (format t "~&~A:~%~A~%"
                           name (make-string (1+ (length name)) :initial-element #\-)))
                 (do ((i 2 (+ i 2)))
                     ((= i end))
                   (let ((val (svref table i)))
                     (unless (unbound-marker-p val)
                       (funcall fun (translate val spaces))
                       (incf n))))
                 (when verbose
                   (format t "TOTAL: ~D entries~2%" n))))
          (scan-table table0 "linkage info"
                      (lambda (x &aux (type #\T))
                        (when (consp x)
                          (setq x (translate (car x) spaces) type #\D))
                        (format asm-file " .long ~A~%" x)
                        (when verbose
                          (format t "~A ~A~%" type x))
                        (push x linkage)))
          (scan-table table1 "defined" #'show)
          (scan-table table2 "undefined" #'show)
          (let ((diff1 ; linkage not in foreign
                 (remove-if (lambda (x) (member x foreign :test #'string=)) linkage))
                (diff2 ; foreign not in linkage
                 (remove-if (lambda (x) (member x linkage :test #'string=)) foreign)))
            (when verbose
              (format t "~&Linkage not in foreign:~%~S~%" diff1)
              (format t "~&Foreign not in linkage:~%~S~%" diff2))
            )))))
  (terpri asm-file))

;;;; ELF file I/O

(defconstant +sht-null+     0)
(defconstant +sht-progbits+ 1)
(defconstant +sht-symtab+   2)
(defconstant +sht-strtab+   3)
(defconstant +sht-rela+     4)
(defconstant +sht-rel+      9)

(define-alien-type elf64-ehdr
  (struct elf64-edhr
    (ident     (array unsigned-char 16)) ; 7F 45 4C 46 2 1 1 0 0 0 0 0 0 0 0 0
    (type      (unsigned 16))   ; 1 0
    (machine   (unsigned 16))   ; 3E 0
    (version   (unsigned 32))   ; 1 0 0 0
    (entry     unsigned)        ; 0 0 0 0 0 0 0 0
    (phoff     unsigned)        ; 0 0 0 0 0 0 0 0
    (shoff     unsigned)        ;
    (flags     (unsigned 32))   ; 0 0 0 0
    (ehsize    (unsigned 16))   ; 40 0
    (phentsize (unsigned 16))   ;  0 0
    (phnum     (unsigned 16))   ;  0 0
    (shentsize (unsigned 16))   ; 40 0
    (shnum     (unsigned 16))   ;  n 0
    (shstrndx  (unsigned 16)))) ;  n 0
(define-alien-type elf64-shdr
  (struct elf64-shdr
    (name      (unsigned 32))
    (type      (unsigned 32))
    (flags     (unsigned 64))
    (addr      (unsigned 64))
    (off       (unsigned 64))
    (size      (unsigned 64))
    (link      (unsigned 32))
    (info      (unsigned 32))
    (addralign (unsigned 64))
    (entsize   (unsigned 64))))
(define-alien-type elf64-sym
  (struct elf64-sym
    (name  (unsigned 32))
    (info  (unsigned 8))
    (other (unsigned 8))
    (shndx (unsigned 16))
    (value unsigned)
    (size  unsigned)))
(define-alien-type elf64-rela
  (struct elf64-rela
    (offset (unsigned 64))
    (info   (unsigned 64))
    (addend (signed 64))))

(defun make-elf64-sym (name info)
  (let ((a (make-array 24 :element-type '(unsigned-byte 8))))
    (with-pinned-objects (a)
      (setf (sap-ref-32 (vector-sap a) 0) name
            (sap-ref-8 (vector-sap a) 4) info))
    a))

;;; Return two values: an octet vector comprising a string table
;;; and an alist which maps string to offset in the table.
(defun string-table (strings)
  (let* ((length (+ (1+ (length strings)) ; one more null than there are strings
                    (reduce #'+ strings :key #'length))) ; data length
         (bytes (make-array length :element-type '(unsigned-byte 8)
                            :initial-element 0))
         (index 1)
         (alist))
    (dolist (string strings)
      (push (cons string index) alist)
      (replace bytes (map 'vector #'char-code string) :start1 index)
      (incf index (1+ (length string))))
    (cons (nreverse alist) bytes)))

(defun write-alien (alien size stream)
  (dotimes (i size)
    (write-byte (sap-ref-8 (alien-value-sap alien) i) stream)))

(defun copy-bytes (in-stream out-stream nbytes
                             &optional (buffer
                                        (make-array 1024 :element-type '(unsigned-byte 8))))
  (loop (let ((chunksize (min (length buffer) nbytes)))
          (aver (eql (read-sequence buffer in-stream :end chunksize) chunksize))
          (write-sequence buffer out-stream :end chunksize)
          (when (zerop (decf nbytes chunksize)) (return)))))

;;; core header should be an array of words in '.rodata', not a 32K page
(defconstant core-header-size +backend-page-bytes+) ; stupidly large (FIXME)

;;; Write everything except for the core file itself into OUTPUT-STREAM
;;; and leave the stream padded to a 4K boundary ready to receive data.
(defun prepare-elf (core-size relocs output)
  (let* ((sym-entry-size   24)
         (reloc-entry-size 24)
         (core-align 4096)
         (sections
          `#((:core "lisp.core"       ,+sht-progbits+ 0 0 0 ,core-align 0)
             (:sym  ".symtab"         ,+sht-symtab+   0 3 1 8 ,sym-entry-size)
                          ; section with the strings -- ^ ^ -- 1+ highest local symbol
             (:str  ".strtab"         ,+sht-strtab+   0 0 0 1  0)
             (:rel  ".relalisp.core"  ,+sht-rela+     0 2 1 8 ,reloc-entry-size)
                                      ; symbol table -- ^ ^ -- for which section
             (:note ".note.GNU-stack" ,+sht-null+     0 0 0 1  0)))
         (string-table
          (string-table (append '("__lisp_code_start") (map 'list #'second sections))))
         (strings (cdr string-table))
         (padded-strings-size (logandc2 (+ (length strings) 7) 7))
         (ehdr-size #.(ceiling (alien-type-bits (parse-alien-type 'elf64-ehdr nil)) 8))
         (shdr-size #.(ceiling (alien-type-bits (parse-alien-type 'elf64-shdr nil)) 8))
         (symbols-size (* 2 sym-entry-size))
         (shdrs-start (+ ehdr-size symbols-size padded-strings-size))
         (shdrs-end (+ shdrs-start (* (1+ (length sections)) shdr-size)))
         (relocs-size (* (length relocs) reloc-entry-size))
         (relocs-end (+ shdrs-end relocs-size))
         (core-start (logandc2 (+ relocs-end (1- core-align)) (1- core-align)))
         (ident #.(coerce '(#x7F #x45 #x4C #x46 2 1 1 0 0 0 0 0 0 0 0 0)
                          '(array (unsigned-byte 8) 1))))

    (with-alien ((ehdr elf64-ehdr))
      (dotimes (i (ceiling ehdr-size n-word-bytes))
        (setf (sap-ref-word (alien-value-sap ehdr) (* i n-word-bytes)) 0))
      (with-pinned-objects (ident)
        (%byte-blt (vector-sap ident) 0 (alien-value-sap ehdr) 0 16))
      (setf (slot ehdr 'type)      1
            (slot ehdr 'machine)   #x3E
            (slot ehdr 'version)   1
            (slot ehdr 'shoff)     shdrs-start
            (slot ehdr 'ehsize)    ehdr-size
            (slot ehdr 'shentsize) shdr-size
            (slot ehdr 'shnum)     (1+ (length sections)) ; section 0 is implied
            (slot ehdr 'shstrndx)  (1+ (position :str sections :key #'car)))
      (write-alien ehdr ehdr-size output))

    ;; Write symbol table
    (aver (eql (file-position output) ehdr-size))
    (write-sequence (make-elf64-sym 0 0) output)
    ;; The symbol name index is always 1 by construction. The type is #x10
    ;; given: #define STB_GLOBAL 1
    ;;   and: #define ELF32_ST_BIND(val) ((unsigned char) (val)) >> 4)
    ;; which places the binding in the high 4 bits of the low byte.
    (write-sequence (make-elf64-sym 1 #x10) output)

    ;; Write string table
    (aver (eql (file-position output) (+ ehdr-size symbols-size)))
    (write-sequence strings output) ; an octet vector at this point
    (dotimes (i (- padded-strings-size (length strings)))
      (write-byte 0 output))

    ;; Write section headers
    (aver (eql (file-position output) shdrs-start))
    (with-alien ((shdr elf64-shdr))
      (dotimes (i (ceiling shdr-size n-word-bytes)) ; Zero-fill
        (setf (sap-ref-word (alien-value-sap shdr) (* i n-word-bytes)) 0))
      (dotimes (i (1+ (length sections)))
        (when (plusp i) ; Write the zero-filled header as section 0
          (destructuring-bind (key name type flags link info alignment entsize)
              (aref sections (1- i))
            (multiple-value-bind (offset size)
                (ecase key
                  (:sym  (values ehdr-size symbols-size))
                  (:str  (values (+ ehdr-size symbols-size) (length strings)))
                  (:rel  (values shdrs-end relocs-size))
                  (:core (values core-start core-size))
                  (:note (values 0 0)))
              (let ((name (cdr (assoc name (car string-table) :test #'string=))))
                (setf (slot shdr 'name)  name
                      (slot shdr 'type)  type
                      (slot shdr 'flags) flags
                      (slot shdr 'off)   offset
                      (slot shdr 'size)  size
                      (slot shdr 'link)  link
                      (slot shdr 'info)  info
                      (slot shdr 'addralign) alignment
                      (slot shdr 'entsize) entsize)))))
        (write-alien shdr shdr-size output)))

    ;; Write relocations
    (aver (eql (file-position output) shdrs-end))
    (let ((buf (make-array relocs-size :element-type '(unsigned-byte 8)))
          (ptr 0))
      (with-alien ((rela elf64-rela))
        (dovector (reloc relocs)
          (destructuring-bind (place addend . kind) reloc
            (setf (slot rela 'offset) place
                  (slot rela 'info)   (logior (ash 1 32) kind) ; 1 = symbol index
                  (slot rela 'addend) addend))
          (setf (%vector-raw-bits buf (+ ptr 0)) (sap-ref-word (alien-value-sap rela) 0)
                (%vector-raw-bits buf (+ ptr 1)) (sap-ref-word (alien-value-sap rela) 8)
                (%vector-raw-bits buf (+ ptr 2)) (sap-ref-word (alien-value-sap rela) 16))
          (incf ptr 3)))
      (write-sequence buf output))

    ;; Write padding
    (dotimes (i (- core-start (file-position output)))
      (write-byte 0 output))
    (aver (eq (file-position output) core-start))))

;;; Return a list of fixups (FIXUP-WHERE KIND ADDEND) to peform in a foreign core
;;; whose code space is subject to link-time relocation.
(defconstant R_X86_64_64    1) ; /* Direct 64 bit  */
(defconstant R_X86_64_PC32  2) ; /* PC relative 32 bit signed */
(defconstant R_X86_64_32   10) ; /* Direct 32 bit zero extended */
;;;
(defun collect-relocations (spaces fixups &aux (print nil))
  (binding* (((static-start static-end)
              (let ((space (get-space static-core-space-id spaces)))
                (values (space-addr space) (space-end space))))
             ((code-start code-end)
              (let ((space (get-space immobile-varyobj-core-space-id spaces)))
                (values (space-addr space) (space-end space))))
             ;; the distance between fixedobj space address (i.e following the pages of
             ;; dynamic space) in the ELF section which has a presumptive address of 0
             ;; due to being non-loaded, to where it will be later mapped by coreparse
             (fixedobj-space-displacement
              (let ((space (get-space immobile-fixedobj-core-space-id spaces)))
                (- (* (1+ (space-data-page space)) +backend-page-bytes+) ; 1+ = core header
                   (space-addr space))))
             (n-abs 0)
             (n-rel 0))
    (labels
        ((abs-fixup (core-offs referent)
           (incf n-abs)
           (when print
              (format t "~x = 0x~(~x~): (a)~%" core-offs (core-to-logical core-offs) #+nil referent))
           (setf (sap-ref-word (car spaces) core-offs) 0)
           (vector-push-extend `(,(+ core-header-size core-offs)
                                 ,(- referent code-start) . ,R_X86_64_64)
                               fixups))
         (abs32-fixup (core-offs referent)
           (incf n-abs)
           (when print
              (format t "~x = 0x~(~x~): (a)~%" core-offs (core-to-logical core-offs) #+nil referent))
           (setf (sap-ref-32 (car spaces) core-offs) 0)
           (vector-push-extend `(,(+ core-header-size core-offs)
                                 ,(- referent code-start) . ,R_X86_64_32)
                               fixups))
         (rel-fixup (core-offs referent)
           (incf n-rel)
           (when print
             (format t "~x = 0x~(~x~): (r)~%" core-offs (core-to-logical core-offs) #+nil referent))
           (setf (sap-ref-32 (car spaces) core-offs) 0)
           (vector-push-extend `(,(+ core-header-size core-offs)
                                 ,(- referent code-start) . ,R_X86_64_PC32)
                               fixups))
         (in-code-space-p (ptr)
           (and (<= code-start ptr) (< ptr code-end)))
         ;; Given a address which is an offset into the data pages of the target core,
         ;; compute the logical address which that offset would be mapped to.
         ;; For example core address 0 is the virtual address of static space.
         (core-to-logical (core-offs &aux (page (floor core-offs +backend-page-bytes+)))
           (dolist (space (cdr spaces)
                          (bug "Can't translate core offset ~x using ~x"
                               core-offs spaces))
             (let* ((page0 (space-data-page space))
                    (nwords (space-nwords space))
                    (id (space-id space))
                    (npages (ceiling nwords (/ +backend-page-bytes+ n-word-bytes))))
               (when (and (<= page0 page (+ page0 (1- npages)))
                          (/= id immobile-varyobj-core-space-id))
                 (return (+ (space-addr space)
                            (* (- page page0) +backend-page-bytes+)
                            (logand core-offs (1- +backend-page-bytes+))))))))
         (scanptrs (obj wordindex-min wordindex-max &aux (n-fixups 0))
           (do* ((base-addr (logandc2 (get-lisp-obj-address obj) lowtag-mask))
                 (sap (int-sap base-addr))
                 ;; core-offs is the offset in the lisp.core ELF section.
                 (core-offs (- base-addr (sap-int (car spaces))))
                 (i wordindex-min (1+ i)))
                ((> i wordindex-max) n-fixups)
             (let ((ptr (sap-ref-word sap (ash i word-shift))))
               (when (and (= (logand ptr 3) 3) (in-code-space-p ptr))
                 (abs-fixup (+ core-offs (ash i word-shift)) ptr)
                 (incf n-fixups)))))
         (scanptr (obj wordindex)
           (plusp (scanptrs obj wordindex wordindex))) ; trivial wrapper
         (scan-obj (obj widetag size vaddr
                    &aux (core-offs (- (logandc2 (get-lisp-obj-address obj) lowtag-mask)
                                       (sap-int (car spaces))))
                         (nwords (ceiling size n-word-bytes)))
           (when (listp obj)
             (scanptrs obj 0 1)
             (return-from scan-obj))
           (case widetag
             (#.instance-widetag
              (let ((layout (truly-the layout
                             (translate (%instance-layout obj) spaces))))
                ;; FIXME: even though the layout is supplied, it's not good enough,
                ;; because the macro references the layout-bitmap which might
                ;; be a bignum which is a pointer into the logical core address.
                (unless (fixnump (layout-bitmap layout))
                  (error "Can't process bignum bitmap"))
                (do-instance-tagged-slot (i obj :layout layout)
                  (scanptr obj (1+ i))))
              (return-from scan-obj))
             (#.simple-vector-widetag
              (let ((len (length (the simple-vector obj))))
                (when (eql (logand (get-header-data obj) #xFF) vector-valid-hashing-subtype)
                  (do ((i 2 (+ i 2)) (needs-rehash))
                      ((= i len)
                       (when needs-rehash
                         (setf (svref obj 1) 1)))
                    (when (scanptr obj (+ vector-data-offset i))
                      (format t "~&SET REHASH: vector=~X~%" (get-lisp-obj-address obj))
                      (setq needs-rehash t))
                    (scanptr obj (+ vector-data-offset i 1)))
                  (return-from scan-obj))
                (setq nwords (+ len 2))))
             (#.fdefn-widetag
              (scanptrs obj 1 2)
              (let* ((fdefn-pc-sap ; where to read to access the rel32 operand
                      (int-sap (+ (- (get-lisp-obj-address obj) other-pointer-lowtag)
                                  (ash fdefn-raw-addr-slot word-shift))))
                     ;; what the fdefn's logical PC will be
                     (fdefn-logical-pc (+ vaddr (ash fdefn-raw-addr-slot word-shift)))
                     (rel32off (signed-sap-ref-32 fdefn-pc-sap 1))
                     (target (+ fdefn-logical-pc 1 rel32off))
                     (space-displacement
                      (if (<= static-start vaddr static-end)
                          (+ (- sb-vm:static-space-start) +backend-page-bytes+)
                          fixedobj-space-displacement)))
                (when (in-code-space-p target)
                  ;; This addend needs to account for the fact that the location
                  ;; where fixup occurs is not where the fdefn will actually exist.
                  (rel-fixup (+ core-offs (ash 3 word-shift) 1)
                             (+ target space-displacement))))
              (return-from scan-obj))
             ((#.closure-widetag #.funcallable-instance-widetag)
              (let ((word (sap-ref-word (int-sap (get-lisp-obj-address obj))
                                        (- n-word-bytes fun-pointer-lowtag))))
                (when (in-code-space-p word)
                  (abs-fixup (+ core-offs (ash 1 word-shift)) word)))
              (when (eq widetag funcallable-instance-widetag)
                (let ((layout (truly-the layout
                               (translate (%funcallable-instance-layout obj) spaces))))
                  (unless (fixnump (layout-bitmap layout))
                    (error "Can't process bignum bitmap"))
                  (let ((bitmap (layout-bitmap layout)))
                    (unless (eql bitmap -1)
                      ;; tagged slots precede untagged slots,
                      ;; so integer-length is the count of tagged slots.
                      (setq nwords (1+ (integer-length bitmap))))))))
             ;; mixed boxed/unboxed objects
             (#.code-header-widetag
              (dolist (loc (code-fixup-locs obj spaces))
                (let ((val (sap-ref-32 (code-instructions obj) loc)))
                  (when (in-code-space-p val)
                    (abs32-fixup (sap- (sap+ (code-instructions obj) loc) (car spaces))
                                 val))))
              (dotimes (i (code-n-entries obj))
                (scanptrs (%code-entry-point obj i) 2 5))
              (setq nwords (code-header-words obj)))
             ;; boxed objects that can reference code/simple-funs
             ((#.value-cell-widetag #.symbol-widetag #.weak-pointer-widetag))
             (t
              (return-from scan-obj)))
           (scanptrs obj 1 (1- nwords))))
      (dolist (space (reverse (cdr spaces)))
        (let* ((logical-addr (space-addr space))
               (size (space-size space))
               (physical-addr (space-physaddr space spaces))
               (physical-end (sap+ physical-addr size))
               (vaddr-translation (+ (- (sap-int physical-addr)) logical-addr)))
          (unless (= (space-id space) immobile-varyobj-core-space-id)
            (dx-flet ((visit (obj widetag size)
                        ;; Compute the object's intended virtual address
                        (let ((vaddr (+ (logandc2 (get-lisp-obj-address obj) lowtag-mask)
                                        vaddr-translation)))
                          (scan-obj obj widetag size vaddr))))
              (map-objects-in-range
               #'visit
               (ash (sap-int physical-addr) (- n-fixnum-tag-bits))
               (ash (sap-int physical-end) (- n-fixnum-tag-bits))))
            (when (and (plusp (logior n-abs n-rel)) print)
              (format t "space @ ~x: ~d absolute + ~d relative fixups~%"
                      logical-addr n-abs n-rel))
            (setq n-abs 0 n-rel 0))))))
  (when print
    (format t "total of ~D linker fixups~%" (length fixups)))
  fixups)

;;;;

(macrolet ((do-core-header-entry (((id-var len-var ptr-var) buffer) &body body)
             `(let ((,ptr-var 1))
                (loop
                  (let ((,id-var (%vector-raw-bits ,buffer ,ptr-var))
                        (,len-var (%vector-raw-bits ,buffer (1+ ,ptr-var))))
                    (incf ,ptr-var 2)
                    (decf ,len-var 2)
                    (when (= ,id-var end-core-entry-type-code) (return))
                    ,@body
                    (incf ,ptr-var ,len-var)))))
           (do-directory-entry (((index-var start-index input-nbytes) buffer) &body body)
             `(let ((words-per-dirent 5))
                (multiple-value-bind (n-entries remainder)
                    (floor ,input-nbytes words-per-dirent)
                  (aver (zerop remainder))
                  (symbol-macrolet ((id        (%vector-raw-bits ,buffer index))
                                    (nwords    (%vector-raw-bits ,buffer (+ index 1)))
                                    (data-page (%vector-raw-bits ,buffer (+ index 2)))
                                    (addr      (%vector-raw-bits ,buffer (+ index 3)))
                                    (npages    (%vector-raw-bits ,buffer (+ index 4))))
                    (do ((,index-var ,start-index (+ ,index-var words-per-dirent)))
                        ((= ,index-var (+ ,start-index (* n-entries words-per-dirent))))
                      ,@body)))))
           (with-mapped-core ((sap-var start npages stream) &body body)
             `(let (,sap-var)
                (unwind-protect
                     (progn
                       (setq ,sap-var
                             (sb-posix:mmap nil
                                            (* ,npages +backend-page-bytes+)
                                            (logior sb-posix:prot-read sb-posix:prot-write)
                                            sb-posix:map-private
                                            (sb-sys:fd-stream-fd ,stream)
                                            ;; Skip the core header
                                            (+ ,start +backend-page-bytes+)))
                       ,@body)
                  (when ,sap-var
                    (sb-posix:munmap ,sap-var (* ,npages +backend-page-bytes+)))))))

;;; Given a native SBCL '.core' file, or one attached to the end of an executable,
;;; separate it into pieces.
;;; ASM-PATHNAME is the name of the assembler file that will hold all the Lisp code.
;;; The other two output pathnames are implicit: "x.s" -> "x.core" and "x-core.o"
;;; The ".core" file is a native core file used for starting a binary that
;;; contains the asm code using the "--core" argument.  The "-core.o" file
;;; is for linking in to a binary that needs no "--core" argument.
(defun split-core
    (input-pathname asm-pathname
     &key emit-sizes (verbose nil)
     &aux (split-core-pathname
           (merge-pathnames (make-pathname :type "core") asm-pathname))
          (elf-core-pathname
           (merge-pathnames
            (make-pathname :name (concatenate 'string (pathname-name asm-pathname) "-core")
                           :type "o")
            asm-pathname))
          (core-header (make-array +backend-page-bytes+ :element-type '(unsigned-byte 8)))
          (original-total-npages 0)
          (core-offset 0)
          (page-adjust 0)
          (code-start-fixup-ofs 0) ; where to fixup the core header
          (spaces)
          (copy-actions)
          (fixedobj-range) ; = (START . SIZE-IN-BYTES)
          (relocs (make-array 100000 :adjustable t :fill-pointer 0)))

  ;; Remove old files
  (ignore-errors (delete-file asm-pathname))
  (ignore-errors (delete-file split-core-pathname))
  (ignore-errors (delete-file elf-core-pathname))
  ;; Ensure that all files can be opened
  (with-open-file (input input-pathname :element-type '(unsigned-byte 8))
    (with-open-file (asm-file asm-pathname :direction :output :if-exists :supersede)
      (with-open-file (split-core split-core-pathname :direction :output
                                 :element-type '(unsigned-byte 8) :if-exists :supersede)
        (read-sequence core-header input)
        (cond ((= (%vector-raw-bits core-header 0) core-magic))
              (t ; possible embedded core
               (file-position input (- (file-length input)
                                       (* 2 n-word-bytes)))
               (aver (eql (read-sequence core-header input) (* 2 n-word-bytes)))
               (aver (= (%vector-raw-bits core-header 1) core-magic))
               (setq core-offset (%vector-raw-bits core-header 0))
               (when verbose
                 (format t "~&embedded core starts at #x~x into input~%" core-offset))
               (file-position input core-offset)
               (read-sequence core-header input)
               (aver (= (%vector-raw-bits core-header 0) core-magic))))
        (do-core-header-entry ((id len ptr) core-header)
          (case id
            (#.build-id-core-entry-type-code
             (when verbose
               (let ((string (make-string (%vector-raw-bits core-header ptr)
                                          :element-type 'base-char)))
                 (%byte-blt core-header (* (1+ ptr) n-word-bytes) string 0 (length string))
                 (format t "Build ID [~a]~%" string))))
            (#.directory-core-entry-type-code
             (do-directory-entry ((index ptr len) core-header)
               (incf original-total-npages npages)
               (push (make-space id addr data-page page-adjust nwords) spaces)
               (when verbose
                 (format t "id=~d page=~5x + ~5x addr=~10x words=~8x~:[~; (drop)~]~%"
                         id data-page npages addr nwords
                         (= id immobile-varyobj-core-space-id)))
               (cond ((= id immobile-varyobj-core-space-id)
                      (setq code-start-fixup-ofs (+ index 3))
                      ;; Keep this entry but delete the page count. We need to know
                      ;; where the space was supposed to be mapped and at what size.
                      ;; Subsequent core entries will need to adjust their start page
                      ;; downward (just the PTEs's start page now).
                      (setq page-adjust npages data-page 0 npages 0))
                     (t
                      ;; Keep track of where the fixedobj space wants to be.
                      (when (= id immobile-fixedobj-core-space-id)
                        (setq fixedobj-range (cons addr (ash nwords word-shift))))
                      (when (plusp npages) ; enqueue
                        (push (cons data-page (* npages +backend-page-bytes+))
                              copy-actions))
                      ;; adjust this entry's start page in the new core
                      (decf data-page page-adjust)))))
            (#.page-table-core-entry-type-code
             (aver (= len 3))
             (symbol-macrolet ((nbytes (%vector-raw-bits core-header (1+ ptr)))
                               (data-page (%vector-raw-bits core-header (+ ptr 2))))
               (aver (= data-page original-total-npages))
               (aver (= (ceiling (space-nwords
                                  (find dynamic-core-space-id spaces :key #'space-id))
                                 (/ +backend-page-bytes+ n-word-bytes))
                        (%vector-raw-bits core-header ptr))) ; number of PTEs
               (when verbose
                 (format t "PTE: page=~5x~40tbytes=~8x~%" data-page nbytes))
               (push (cons data-page nbytes) copy-actions)
               (decf data-page page-adjust)))))
        (let ((buffer (make-array +backend-page-bytes+
                                  :element-type '(unsigned-byte 8)))
              (filepos))
          ;; Write the new core file
          (write-sequence core-header split-core)
          (dolist (action (reverse copy-actions)) ; nondestructive
            ;; page index convention assumes absence of core header.
            ;; i.e. data page 0 is the file page immediately following the core header
            (let ((offset (* (1+ (car action)) +backend-page-bytes+))
                  (nbytes (cdr action)))
              (when verbose
                (format t "File offset ~10x: ~10x bytes~%" offset nbytes))
              (setq filepos (+ core-offset offset))
              (file-position input filepos)
              (copy-bytes input split-core nbytes buffer)))
          ;; Trailer (runtime options and magic number)
          (let ((nbytes (read-sequence buffer input)))
            ;; expect trailing magic number
            (let ((ptr (floor (- nbytes n-word-bytes) n-word-bytes)))
              (aver (= (%vector-raw-bits buffer ptr) core-magic)))
            ;; File position of the core header needs to be set to 0
            ;; regardless of what it was
            (setf (%vector-raw-bits buffer 4) 0)
            (when verbose
              (format t "Trailer words:(~{~X~^ ~})~%"
                      (loop for i below (floor nbytes n-word-bytes)
                            collect (%vector-raw-bits buffer i))))
            (write-sequence buffer split-core :end nbytes)
            (finish-output split-core))
          ;; Sanity test
          (aver (= (+ core-offset
                      (* page-adjust +backend-page-bytes+)
                      (file-length split-core))
                   (file-length input)))
          ;; Seek back to the PTE pages so they can be copied to the '.o' file
          (file-position input filepos)))

      ;; Map the original core file to memory
      (with-mapped-core (sap core-offset original-total-npages input)
        (let* ((data-spaces
                (delete immobile-varyobj-core-space-id (reverse spaces)
                        :key #'space-id))
               (map (cons sap (sort (copy-list spaces) #'> :key #'space-addr)))
               (pte-nbytes (cdar copy-actions)))
          (collect-relocations map relocs)
          (with-open-file (output elf-core-pathname
                                  :direction :output :if-exists :supersede
                                  :element-type '(unsigned-byte 8))
            (vector-push-extend
             `(,(ash code-start-fixup-ofs word-shift) 0 . ,R_X86_64_64) relocs)
            (prepare-elf (+ (apply #'+ (mapcar #'space-nbytes-aligned data-spaces))
                            +backend-page-bytes+ ; core header
                            pte-nbytes)
                         relocs output)
            (setf (%vector-raw-bits core-header code-start-fixup-ofs) 0)
            (write-sequence core-header output) ; Copy prepared header
            (force-output output)
            ;; Change SB-C::*COMPILE[-FILE]-TO-MEMORY-SPACE* to :DYNAMIC
            ;; in case the resulting executable needs to compile anything.
            ;; (Call frame info will be missing, but at least it's something.)
            (dolist (name '("*COMPILE-FILE-TO-MEMORY-SPACE*"
                            "*COMPILE-TO-MEMORY-SPACE*"))
              (%set-symbol-global-value
               (find-target-symbol "SB-C" name map)
               (find-target-symbol "KEYWORD" "DYNAMIC" map :logical)))
            ;;
            (dolist (space data-spaces) ; Copy pages from memory
              (let ((start (space-physaddr space map))
                    (size (space-nbytes-aligned space)))
                (aver (eql (sb-unix:unix-write (sb-sys:fd-stream-fd output)
                                               start 0 size)
                           size))))
            (when verbose
              (format t "Copying ~d bytes (#x~x) from ptes = ~d PTEs~%"
                      pte-nbytes pte-nbytes (floor pte-nbytes 10)))
            (copy-bytes input output pte-nbytes)) ; Copy PTEs from input

          ;; There's no relation between emit-sizes and which section to put
          ;; C symbol references in, however it's a safe bet that if sizes
          ;; are supported then so is the .rodata directive.
          (format asm-file (if emit-sizes " .rodata~%" " .data~%"))
          (extract-required-c-symbols map asm-file)
          (write-assembler-text map fixedobj-range asm-file emit-sizes)))

      (format asm-file "~% ~A~%" +noexec-stack-note+))))

) ; end MACROLET

;;;;

(defun cl-user::elfinate (&optional (args (cdr sb-ext:*posix-argv*)))
  (cond ((string= (car args) "split")
         (pop args)
         (let ((sizes (string= (car args) "--sizes")))
           (when sizes
             (pop args))
           (destructuring-bind (input asm) args
             (split-core input asm :emit-sizes sizes))))
        #+nil
        ((string= (car args) "relocate")
         (destructuring-bind (input output binary start-sym) (cdr args)
           (relocate-core
            input output binary (parse-integer start-sym :radix 16))))
        (t
         (error "Unknown command: ~S" args))))

;; If loaded as a script, do this
(eval-when (:execute)
  (let ((args (cdr sb-ext:*posix-argv*)))
    (when args
      (let ((*print-pretty* nil))
        (format t "Args: ~S~%" args)
        (cl-user::elfinate args)))))