1.0.21.14: fix CHECK-FASL-HEADER buglet

[sbcl.git] / src / code / debug-int.lisp

;;;; the implementation of the programmer's interface to writing
;;;; debugging tools

;;;; 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.

(in-package "SB!DI")

;;; FIXME: There are an awful lot of package prefixes in this code.
;;; Couldn't we have SB-DI use the SB-C and SB-VM packages?
\f
;;;; conditions

;;;; The interface to building debugging tools signals conditions that
;;;; prevent it from adhering to its contract. These are
;;;; serious-conditions because the program using the interface must
;;;; handle them before it can correctly continue execution. These
;;;; debugging conditions are not errors since it is no fault of the
;;;; programmers that the conditions occur. The interface does not
;;;; provide for programs to detect these situations other than
;;;; calling a routine that detects them and signals a condition. For
;;;; example, programmers call A which may fail to return successfully
;;;; due to a lack of debug information, and there is no B the they
;;;; could have called to realize A would fail. It is not an error to
;;;; have called A, but it is an error for the program to then ignore
;;;; the signal generated by A since it cannot continue without A's
;;;; correctly returning a value or performing some operation.
;;;;
;;;; Use DEBUG-SIGNAL to signal these conditions.

(define-condition debug-condition (serious-condition)
  ()
  #!+sb-doc
  (:documentation
   "All DEBUG-CONDITIONs inherit from this type. These are serious conditions
    that must be handled, but they are not programmer errors."))

(define-condition no-debug-fun-returns (debug-condition)
  ((debug-fun :reader no-debug-fun-returns-debug-fun
              :initarg :debug-fun))
  #!+sb-doc
  (:documentation
   "The system could not return values from a frame with DEBUG-FUN since
    it lacked information about returning values.")
  (:report (lambda (condition stream)
             (let ((fun (debug-fun-fun
                         (no-debug-fun-returns-debug-fun condition))))
               (format stream
                       "~&Cannot return values from ~:[frame~;~:*~S~] since ~
                        the debug information lacks details about returning ~
                        values here."
                       fun)))))

(define-condition no-debug-blocks (debug-condition)
  ((debug-fun :reader no-debug-blocks-debug-fun
              :initarg :debug-fun))
  #!+sb-doc
  (:documentation "The debug-fun has no debug-block information.")
  (:report (lambda (condition stream)
             (format stream "~&~S has no debug-block information."
                     (no-debug-blocks-debug-fun condition)))))

(define-condition no-debug-vars (debug-condition)
  ((debug-fun :reader no-debug-vars-debug-fun
              :initarg :debug-fun))
  #!+sb-doc
  (:documentation "The DEBUG-FUN has no DEBUG-VAR information.")
  (:report (lambda (condition stream)
             (format stream "~&~S has no debug variable information."
                     (no-debug-vars-debug-fun condition)))))

(define-condition lambda-list-unavailable (debug-condition)
  ((debug-fun :reader lambda-list-unavailable-debug-fun
              :initarg :debug-fun))
  #!+sb-doc
  (:documentation
   "The DEBUG-FUN has no lambda list since argument DEBUG-VARs are
    unavailable.")
  (:report (lambda (condition stream)
             (format stream "~&~S has no lambda-list information available."
                     (lambda-list-unavailable-debug-fun condition)))))

(define-condition invalid-value (debug-condition)
  ((debug-var :reader invalid-value-debug-var :initarg :debug-var)
   (frame :reader invalid-value-frame :initarg :frame))
  (:report (lambda (condition stream)
             (format stream "~&~S has :invalid or :unknown value in ~S."
                     (invalid-value-debug-var condition)
                     (invalid-value-frame condition)))))

(define-condition ambiguous-var-name (debug-condition)
  ((name :reader ambiguous-var-name-name :initarg :name)
   (frame :reader ambiguous-var-name-frame :initarg :frame))
  (:report (lambda (condition stream)
             (format stream "~&~S names more than one valid variable in ~S."
                     (ambiguous-var-name-name condition)
                     (ambiguous-var-name-frame condition)))))
\f
;;;; errors and DEBUG-SIGNAL

;;; The debug-internals code tries to signal all programmer errors as
;;; subtypes of DEBUG-ERROR. There are calls to ERROR signalling
;;; SIMPLE-ERRORs, but these dummy checks in the code and shouldn't
;;; come up.
;;;
;;; While under development, this code also signals errors in code
;;; branches that remain unimplemented.

(define-condition debug-error (error) ()
  #!+sb-doc
  (:documentation
   "All programmer errors from using the interface for building debugging
    tools inherit from this type."))

(define-condition unhandled-debug-condition (debug-error)
  ((condition :reader unhandled-debug-condition-condition :initarg :condition))
  (:report (lambda (condition stream)
             (format stream "~&unhandled DEBUG-CONDITION:~%~A"
                     (unhandled-debug-condition-condition condition)))))

(define-condition unknown-code-location (debug-error)
  ((code-location :reader unknown-code-location-code-location
                  :initarg :code-location))
  (:report (lambda (condition stream)
             (format stream "~&invalid use of an unknown code-location: ~S"
                     (unknown-code-location-code-location condition)))))

(define-condition unknown-debug-var (debug-error)
  ((debug-var :reader unknown-debug-var-debug-var :initarg :debug-var)
   (debug-fun :reader unknown-debug-var-debug-fun
              :initarg :debug-fun))
  (:report (lambda (condition stream)
             (format stream "~&~S is not in ~S."
                     (unknown-debug-var-debug-var condition)
                     (unknown-debug-var-debug-fun condition)))))

(define-condition invalid-control-stack-pointer (debug-error)
  ()
  (:report (lambda (condition stream)
             (declare (ignore condition))
             (fresh-line stream)
             (write-string "invalid control stack pointer" stream))))

(define-condition frame-fun-mismatch (debug-error)
  ((code-location :reader frame-fun-mismatch-code-location
                  :initarg :code-location)
   (frame :reader frame-fun-mismatch-frame :initarg :frame)
   (form :reader frame-fun-mismatch-form :initarg :form))
  (:report (lambda (condition stream)
             (format
              stream
              "~&Form was preprocessed for ~S,~% but called on ~S:~%  ~S"
              (frame-fun-mismatch-code-location condition)
              (frame-fun-mismatch-frame condition)
              (frame-fun-mismatch-form condition)))))

;;; This signals debug-conditions. If they go unhandled, then signal
;;; an UNHANDLED-DEBUG-CONDITION error.
;;;
;;; ??? Get SIGNAL in the right package!
(defmacro debug-signal (datum &rest arguments)
  `(let ((condition (make-condition ,datum ,@arguments)))
     (signal condition)
     (error 'unhandled-debug-condition :condition condition)))
\f
;;;; structures
;;;;
;;;; Most of these structures model information stored in internal
;;;; data structures created by the compiler. Whenever comments
;;;; preface an object or type with "compiler", they refer to the
;;;; internal compiler thing, not to the object or type with the same
;;;; name in the "SB-DI" package.

;;;; DEBUG-VARs

;;; These exist for caching data stored in packed binary form in
;;; compiler DEBUG-FUNs.
(defstruct (debug-var (:constructor nil)
                      (:copier nil))
  ;; the name of the variable
  (symbol (missing-arg) :type symbol)
  ;; a unique integer identification relative to other variables with the same
  ;; symbol
  (id 0 :type index)
  ;; Does the variable always have a valid value?
  (alive-p nil :type boolean))
(def!method print-object ((debug-var debug-var) stream)
  (print-unreadable-object (debug-var stream :type t :identity t)
    (format stream
            "~S ~W"
            (debug-var-symbol debug-var)
            (debug-var-id debug-var))))

#!+sb-doc
(setf (fdocumentation 'debug-var-id 'function)
  "Return the integer that makes DEBUG-VAR's name and package unique
   with respect to other DEBUG-VARs in the same function.")

(defstruct (compiled-debug-var
            (:include debug-var)
            (:constructor make-compiled-debug-var
                          (symbol id alive-p sc-offset save-sc-offset))
            (:copier nil))
  ;; storage class and offset (unexported)
  (sc-offset nil :type sb!c:sc-offset)
  ;; storage class and offset when saved somewhere
  (save-sc-offset nil :type (or sb!c:sc-offset null)))

;;;; frames

;;; These represent call frames on the stack.
(defstruct (frame (:constructor nil)
                  (:copier nil))
  ;; the next frame up, or NIL when top frame
  (up nil :type (or frame null))
  ;; the previous frame down, or NIL when the bottom frame. Before
  ;; computing the next frame down, this slot holds the frame pointer
  ;; to the control stack for the given frame. This lets us get the
  ;; next frame down and the return-pc for that frame.
  (%down :unparsed :type (or frame (member nil :unparsed)))
  ;; the DEBUG-FUN for the function whose call this frame represents
  (debug-fun nil :type debug-fun)
  ;; the CODE-LOCATION where the frame's DEBUG-FUN will continue
  ;; running when program execution returns to this frame. If someone
  ;; interrupted this frame, the result could be an unknown
  ;; CODE-LOCATION.
  (code-location nil :type code-location)
  ;; an a-list of catch-tags to code-locations
  (%catches :unparsed :type (or list (member :unparsed)))
  ;; pointer to frame on control stack (unexported)
  pointer
  ;; This is the frame's number for prompt printing. Top is zero.
  (number 0 :type index))

(defstruct (compiled-frame
            (:include frame)
            (:constructor make-compiled-frame
                          (pointer up debug-fun code-location number
                                   &optional escaped))
            (:copier nil))
  ;; This indicates whether someone interrupted the frame.
  ;; (unexported). If escaped, this is a pointer to the state that was
  ;; saved when we were interrupted, an os_context_t, i.e. the third
  ;; argument to an SA_SIGACTION-style signal handler.
  escaped)
(def!method print-object ((obj compiled-frame) str)
  (print-unreadable-object (obj str :type t)
    (format str
            "~S~:[~;, interrupted~]"
            (debug-fun-name (frame-debug-fun obj))
            (compiled-frame-escaped obj))))
\f
;;;; DEBUG-FUNs

;;; These exist for caching data stored in packed binary form in
;;; compiler DEBUG-FUNs. *COMPILED-DEBUG-FUNS* maps a SB!C::DEBUG-FUN
;;; to a DEBUG-FUN. There should only be one DEBUG-FUN in existence
;;; for any function; that is, all CODE-LOCATIONs and other objects
;;; that reference DEBUG-FUNs point to unique objects. This is
;;; due to the overhead in cached information.
(defstruct (debug-fun (:constructor nil)
                      (:copier nil))
  ;; some representation of the function arguments. See
  ;; DEBUG-FUN-LAMBDA-LIST.
  ;; NOTE: must parse vars before parsing arg list stuff.
  (%lambda-list :unparsed)
  ;; cached DEBUG-VARS information (unexported).
  ;; These are sorted by their name.
  (%debug-vars :unparsed :type (or simple-vector null (member :unparsed)))
  ;; cached debug-block information. This is NIL when we have tried to
  ;; parse the packed binary info, but none is available.
  (blocks :unparsed :type (or simple-vector null (member :unparsed)))
  ;; the actual function if available
  (%function :unparsed :type (or null function (member :unparsed))))
(def!method print-object ((obj debug-fun) stream)
  (print-unreadable-object (obj stream :type t)
    (prin1 (debug-fun-name obj) stream)))

(defstruct (compiled-debug-fun
            (:include debug-fun)
            (:constructor %make-compiled-debug-fun
                          (compiler-debug-fun component))
            (:copier nil))
  ;; compiler's dumped DEBUG-FUN information (unexported)
  (compiler-debug-fun nil :type sb!c::compiled-debug-fun)
  ;; code object (unexported).
  component
  ;; the :FUN-START breakpoint (if any) used to facilitate
  ;; function end breakpoints
  (end-starter nil :type (or null breakpoint)))

;;; This maps SB!C::COMPILED-DEBUG-FUNs to
;;; COMPILED-DEBUG-FUNs, so we can get at cached stuff and not
;;; duplicate COMPILED-DEBUG-FUN structures.
(defvar *compiled-debug-funs* (make-hash-table :test 'eq))

;;; Make a COMPILED-DEBUG-FUN for a SB!C::COMPILER-DEBUG-FUN and its
;;; component. This maps the latter to the former in
;;; *COMPILED-DEBUG-FUNS*. If there already is a COMPILED-DEBUG-FUN,
;;; then this returns it from *COMPILED-DEBUG-FUNS*.
;;;
;;; FIXME: It seems this table can potentially grow without bounds,
;;; and retains roots to functions that might otherwise be collected.
(defun make-compiled-debug-fun (compiler-debug-fun component)
  (let ((table *compiled-debug-funs*))
    (with-locked-hash-table (table)
      (or (gethash compiler-debug-fun table)
          (setf (gethash compiler-debug-fun table)
                (%make-compiled-debug-fun compiler-debug-fun component))))))

(defstruct (bogus-debug-fun
            (:include debug-fun)
            (:constructor make-bogus-debug-fun
                          (%name &aux
                                 (%lambda-list nil)
                                 (%debug-vars nil)
                                 (blocks nil)
                                 (%function nil)))
            (:copier nil))
  %name)
\f
;;;; DEBUG-BLOCKs

;;; These exist for caching data stored in packed binary form in compiler
;;; DEBUG-BLOCKs.
(defstruct (debug-block (:constructor nil)
                        (:copier nil))
  ;; Code-locations where execution continues after this block.
  (successors nil :type list)
  ;; This indicates whether the block is a special glob of code shared
  ;; by various functions and tucked away elsewhere in a component.
  ;; This kind of block has no start code-location. This slot is in
  ;; all debug-blocks since it is an exported interface.
  (elsewhere-p nil :type boolean))
(def!method print-object ((obj debug-block) str)
  (print-unreadable-object (obj str :type t)
    (prin1 (debug-block-fun-name obj) str)))

#!+sb-doc
(setf (fdocumentation 'debug-block-successors 'function)
  "Return the list of possible code-locations where execution may continue
   when the basic-block represented by debug-block completes its execution.")

#!+sb-doc
(setf (fdocumentation 'debug-block-elsewhere-p 'function)
  "Return whether debug-block represents elsewhere code.")

(defstruct (compiled-debug-block (:include debug-block)
                                 (:constructor
                                  make-compiled-debug-block
                                  (code-locations successors elsewhere-p))
                                 (:copier nil))
  ;; code-location information for the block
  (code-locations nil :type simple-vector))
\f
;;;; breakpoints

;;; This is an internal structure that manages information about a
;;; breakpoint locations. See *COMPONENT-BREAKPOINT-OFFSETS*.
(defstruct (breakpoint-data (:constructor make-breakpoint-data
                                          (component offset))
                            (:copier nil))
  ;; This is the component in which the breakpoint lies.
  component
  ;; This is the byte offset into the component.
  (offset nil :type index)
  ;; The original instruction replaced by the breakpoint.
  (instruction nil :type (or null sb!vm::word))
  ;; A list of user breakpoints at this location.
  (breakpoints nil :type list))
(def!method print-object ((obj breakpoint-data) str)
  (print-unreadable-object (obj str :type t)
    (format str "~S at ~S"
            (debug-fun-name
             (debug-fun-from-pc (breakpoint-data-component obj)
                                (breakpoint-data-offset obj)))
            (breakpoint-data-offset obj))))

(defstruct (breakpoint (:constructor %make-breakpoint
                                     (hook-fun what kind %info))
                       (:copier nil))
  ;; This is the function invoked when execution encounters the
  ;; breakpoint. It takes a frame, the breakpoint, and optionally a
  ;; list of values. Values are supplied for :FUN-END breakpoints as
  ;; values to return for the function containing the breakpoint.
  ;; :FUN-END breakpoint hook functions also take a cookie argument.
  ;; See the COOKIE-FUN slot.
  (hook-fun (required-arg) :type function)
  ;; CODE-LOCATION or DEBUG-FUN
  (what nil :type (or code-location debug-fun))
  ;; :CODE-LOCATION, :FUN-START, or :FUN-END for that kind
  ;; of breakpoint. :UNKNOWN-RETURN-PARTNER if this is the partner of
  ;; a :code-location breakpoint at an :UNKNOWN-RETURN code-location.
  (kind nil :type (member :code-location :fun-start :fun-end
                          :unknown-return-partner))
  ;; Status helps the user and the implementation.
  (status :inactive :type (member :active :inactive :deleted))
  ;; This is a backpointer to a breakpoint-data.
  (internal-data nil :type (or null breakpoint-data))
  ;; With code-locations whose type is :UNKNOWN-RETURN, there are
  ;; really two breakpoints: one at the multiple-value entry point,
  ;; and one at the single-value entry point. This slot holds the
  ;; breakpoint for the other one, or NIL if this isn't at an
  ;; :UNKNOWN-RETURN code location.
  (unknown-return-partner nil :type (or null breakpoint))
  ;; :FUN-END breakpoints use a breakpoint at the :FUN-START
  ;; to establish the end breakpoint upon function entry. We do this
  ;; by frobbing the LRA to jump to a special piece of code that
  ;; breaks and provides the return values for the returnee. This slot
  ;; points to the start breakpoint, so we can activate, deactivate,
  ;; and delete it.
  (start-helper nil :type (or null breakpoint))
  ;; This is a hook users supply to get a dynamically unique cookie
  ;; for identifying :FUN-END breakpoint executions. That is, if
  ;; there is one :FUN-END breakpoint, but there may be multiple
  ;; pending calls of its function on the stack. This function takes
  ;; the cookie, and the hook function takes the cookie too.
  (cookie-fun nil :type (or null function))
  ;; This slot users can set with whatever information they find useful.
  %info)
(def!method print-object ((obj breakpoint) str)
  (let ((what (breakpoint-what obj)))
    (print-unreadable-object (obj str :type t)
      (format str
              "~S~:[~;~:*~S~]"
              (etypecase what
                (code-location what)
                (debug-fun (debug-fun-name what)))
              (etypecase what
                (code-location nil)
                (debug-fun (breakpoint-kind obj)))))))
\f
;;;; CODE-LOCATIONs

(defstruct (code-location (:constructor nil)
                          (:copier nil))
  ;; the DEBUG-FUN containing this CODE-LOCATION
  (debug-fun nil :type debug-fun)
  ;; This is initially :UNSURE. Upon first trying to access an
  ;; :UNPARSED slot, if the data is unavailable, then this becomes T,
  ;; and the code-location is unknown. If the data is available, this
  ;; becomes NIL, a known location. We can't use a separate type
  ;; code-location for this since we must return code-locations before
  ;; we can tell whether they're known or unknown. For example, when
  ;; parsing the stack, we don't want to unpack all the variables and
  ;; blocks just to make frames.
  (%unknown-p :unsure :type (member t nil :unsure))
  ;; the DEBUG-BLOCK containing CODE-LOCATION. XXX Possibly toss this
  ;; out and just find it in the blocks cache in DEBUG-FUN.
  (%debug-block :unparsed :type (or debug-block (member :unparsed)))
  ;; This is the number of forms processed by the compiler or loader
  ;; before the top level form containing this code-location.
  (%tlf-offset :unparsed :type (or index (member :unparsed)))
  ;; This is the depth-first number of the node that begins
  ;; code-location within its top level form.
  (%form-number :unparsed :type (or index (member :unparsed))))
(def!method print-object ((obj code-location) str)
  (print-unreadable-object (obj str :type t)
    (prin1 (debug-fun-name (code-location-debug-fun obj))
           str)))

(defstruct (compiled-code-location
             (:include code-location)
             (:constructor make-known-code-location
                           (pc debug-fun %tlf-offset %form-number
                               %live-set kind step-info &aux (%unknown-p nil)))
             (:constructor make-compiled-code-location (pc debug-fun))
             (:copier nil))
  ;; an index into DEBUG-FUN's component slot
  (pc nil :type index)
  ;; a bit-vector indexed by a variable's position in
  ;; DEBUG-FUN-DEBUG-VARS indicating whether the variable has a
  ;; valid value at this code-location. (unexported).
  (%live-set :unparsed :type (or simple-bit-vector (member :unparsed)))
  ;; (unexported) To see SB!C::LOCATION-KIND, do
  ;; (SB!KERNEL:TYPE-EXPAND 'SB!C::LOCATION-KIND).
  (kind :unparsed :type (or (member :unparsed) sb!c::location-kind))
  (step-info :unparsed :type (or (member :unparsed :foo) simple-string)))
\f
;;;; DEBUG-SOURCEs

;;; Return the number of top level forms processed by the compiler
;;; before compiling this source. If this source is uncompiled, this
;;; is zero. This may be zero even if the source is compiled since the
;;; first form in the first file compiled in one compilation, for
;;; example, must have a root number of zero -- the compiler saw no
;;; other top level forms before it.
(defun debug-source-root-number (debug-source)
  (sb!c::debug-source-source-root debug-source))
\f
;;;; frames

;;; This is used in FIND-ESCAPED-FRAME and with the bogus components
;;; and LRAs used for :FUN-END breakpoints. When a component's
;;; debug-info slot is :BOGUS-LRA, then the REAL-LRA-SLOT contains the
;;; real component to continue executing, as opposed to the bogus
;;; component which appeared in some frame's LRA location.
(defconstant real-lra-slot sb!vm:code-constants-offset)

;;; These are magically converted by the compiler.
(defun current-sp () (current-sp))
(defun current-fp () (current-fp))
(defun stack-ref (s n) (stack-ref s n))
(defun %set-stack-ref (s n value) (%set-stack-ref s n value))
(defun fun-code-header (fun) (fun-code-header fun))
(defun lra-code-header (lra) (lra-code-header lra))
(defun %make-lisp-obj (value) (%make-lisp-obj value))
(defun get-lisp-obj-address (thing) (get-lisp-obj-address thing))
(defun fun-word-offset (fun) (fun-word-offset fun))

#!-sb-fluid (declaim (inline control-stack-pointer-valid-p))
(defun control-stack-pointer-valid-p (x)
  (declare (type system-area-pointer x))
  (let* (#!-stack-grows-downward-not-upward
         (control-stack-start
          (descriptor-sap *control-stack-start*))
         #!+stack-grows-downward-not-upward
         (control-stack-end
          (descriptor-sap *control-stack-end*)))
    #!-stack-grows-downward-not-upward
    (and (sap< x (current-sp))
         (sap<= control-stack-start x)
         (zerop (logand (sap-int x) sb!vm:fixnum-tag-mask)))
    #!+stack-grows-downward-not-upward
    (and (sap>= x (current-sp))
         (sap> control-stack-end x)
         (zerop (logand (sap-int x) sb!vm:fixnum-tag-mask)))))

(declaim (inline component-ptr-from-pc))
(sb!alien:define-alien-routine component-ptr-from-pc (system-area-pointer)
  (pc system-area-pointer))

#!+(or x86 x86-64)
(sb!alien:define-alien-routine valid-lisp-pointer-p sb!alien:int
  (pointer system-area-pointer))

(declaim (inline component-from-component-ptr))
(defun component-from-component-ptr (component-ptr)
  (declare (type system-area-pointer component-ptr))
  (make-lisp-obj (logior (sap-int component-ptr)
                         sb!vm:other-pointer-lowtag)))

;;;; (OR X86 X86-64) support

(defun compute-lra-data-from-pc (pc)
  (declare (type system-area-pointer pc))
  (let ((component-ptr (component-ptr-from-pc pc)))
    (unless (sap= component-ptr (int-sap #x0))
       (let* ((code (component-from-component-ptr component-ptr))
              (code-header-len (* (get-header-data code) sb!vm:n-word-bytes))
              (pc-offset (- (sap-int pc)
                            (- (get-lisp-obj-address code)
                               sb!vm:other-pointer-lowtag)
                            code-header-len)))
;        (format t "c-lra-fpc ~A ~A ~A~%" pc code pc-offset)
         (values pc-offset code)))))

#!+(or x86 x86-64)
(progn

(defconstant sb!vm::nargs-offset #.sb!vm::ecx-offset)

;;; Check for a valid return address - it could be any valid C/Lisp
;;; address.
;;;
;;; XXX Could be a little smarter.
#!-sb-fluid (declaim (inline ra-pointer-valid-p))
(defun ra-pointer-valid-p (ra)
  (declare (type system-area-pointer ra))
  (and
   ;; not the first page (which is unmapped)
   ;;
   ;; FIXME: Where is this documented? Is it really true of every CPU
   ;; architecture? Is it even necessarily true in current SBCL?
   (>= (sap-int ra) 4096)
   ;; not a Lisp stack pointer
   (not (control-stack-pointer-valid-p ra))))

;;; Try to find a valid previous stack. This is complex on the x86 as
;;; it can jump between C and Lisp frames. To help find a valid frame
;;; it searches backwards.
;;;
;;; XXX Should probably check whether it has reached the bottom of the
;;; stack.
;;;
;;; XXX Should handle interrupted frames, both Lisp and C. At present
;;; it manages to find a fp trail, see linux hack below.
(declaim (maybe-inline x86-call-context))
(defun x86-call-context (fp)
  (declare (type system-area-pointer fp))
  (labels ((fail ()
             (values nil
                     (int-sap 0)
                     (int-sap 0)))
           (handle (fp)
             (cond
               ((not (control-stack-pointer-valid-p fp))
                (fail))
               (t
                ;; Check the two possible frame pointers.
                (let ((lisp-ocfp (sap-ref-sap fp (- (* (1+ ocfp-save-offset)
                                                       sb!vm::n-word-bytes))))
                      (lisp-ra (sap-ref-sap fp (- (* (1+ return-pc-save-offset)
                                                     sb!vm::n-word-bytes))))
                      (c-ocfp (sap-ref-sap fp (* 0 sb!vm:n-word-bytes)))
                      (c-ra (sap-ref-sap fp (* 1 sb!vm:n-word-bytes))))
                  (cond ((and (sap> lisp-ocfp fp)
                              (control-stack-pointer-valid-p lisp-ocfp)
                              (ra-pointer-valid-p lisp-ra)
                              (sap> c-ocfp fp)
                              (control-stack-pointer-valid-p c-ocfp)
                              (ra-pointer-valid-p c-ra))
                         ;; Look forward another step to check their validity.
                         (let ((lisp-ok (handle lisp-ocfp))
                               (c-ok (handle c-ocfp)))
                           (cond ((and lisp-ok c-ok)
                                  ;; Both still seem valid - choose the lisp frame.
                                  #!+freebsd
                                  (if (sap> lisp-ocfp c-ocfp)
                                      (values t lisp-ra lisp-ocfp)
                                      (values t c-ra c-ocfp))
                                  #!-freebsd
                                  (values t lisp-ra lisp-ocfp))
                                 (lisp-ok
                                  ;; The lisp convention is looking good.
                                  (values t lisp-ra lisp-ocfp))
                                 (c-ok
                                  ;; The C convention is looking good.
                                  (values t c-ra c-ocfp))
                                 (t
                                  ;; Neither seems right?
                                  (fail)))))
                        ((and (sap> lisp-ocfp fp)
                              (control-stack-pointer-valid-p lisp-ocfp)
                              (ra-pointer-valid-p lisp-ra))
                         ;; The lisp convention is looking good.
                         (values t lisp-ra lisp-ocfp))
                        ((and (sap> c-ocfp fp)
                              (control-stack-pointer-valid-p c-ocfp)
                              #!-linux (ra-pointer-valid-p c-ra))
                         ;; The C convention is looking good.
                         (values t c-ra c-ocfp))
                        (t
                         (fail))))))))
    (handle fp)))

) ; #+x86 PROGN
\f
;;; Convert the descriptor into a SAP. The bits all stay the same, we just
;;; change our notion of what we think they are.
#!-sb-fluid (declaim (inline descriptor-sap))
(defun descriptor-sap (x)
  (int-sap (get-lisp-obj-address x)))

;;; Return the top frame of the control stack as it was before calling
;;; this function.
(defun top-frame ()
  (/noshow0 "entering TOP-FRAME")
  (multiple-value-bind (fp pc) (%caller-frame-and-pc)
    (compute-calling-frame (descriptor-sap fp) pc nil)))

;;; Flush all of the frames above FRAME, and renumber all the frames
;;; below FRAME.
(defun flush-frames-above (frame)
  (setf (frame-up frame) nil)
  (do ((number 0 (1+ number))
       (frame frame (frame-%down frame)))
      ((not (frame-p frame)))
    (setf (frame-number frame) number)))

;;; Return the frame immediately below FRAME on the stack; or when
;;; FRAME is the bottom of the stack, return NIL.
(defun frame-down (frame)
  (/noshow0 "entering FRAME-DOWN")
  ;; We have to access the old-fp and return-pc out of frame and pass
  ;; them to COMPUTE-CALLING-FRAME.
  (let ((down (frame-%down frame)))
    (if (eq down :unparsed)
        (let ((debug-fun (frame-debug-fun frame)))
          (/noshow0 "in DOWN :UNPARSED case")
          (setf (frame-%down frame)
                (etypecase debug-fun
                  (compiled-debug-fun
                   (let ((c-d-f (compiled-debug-fun-compiler-debug-fun
                                 debug-fun)))
                     (compute-calling-frame
                      (descriptor-sap
                       (get-context-value
                        frame ocfp-save-offset
                        (sb!c::compiled-debug-fun-old-fp c-d-f)))
                      (get-context-value
                       frame lra-save-offset
                       (sb!c::compiled-debug-fun-return-pc c-d-f))
                      frame)))
                  (bogus-debug-fun
                   (let ((fp (frame-pointer frame)))
                     (when (control-stack-pointer-valid-p fp)
                       #!+(or x86 x86-64)
                       (multiple-value-bind (ok ra ofp) (x86-call-context fp)
                         (and ok
                              (compute-calling-frame ofp ra frame)))
                       #!-(or x86 x86-64)
                       (compute-calling-frame
                        #!-alpha
                        (sap-ref-sap fp (* ocfp-save-offset
                                           sb!vm:n-word-bytes))
                        #!+alpha
                        (int-sap
                         (sap-ref-32 fp (* ocfp-save-offset
                                           sb!vm:n-word-bytes)))

                        (stack-ref fp lra-save-offset)

                        frame)))))))
        down)))

;;; Get the old FP or return PC out of FRAME. STACK-SLOT is the
;;; standard save location offset on the stack. LOC is the saved
;;; SC-OFFSET describing the main location.
(defun get-context-value (frame stack-slot loc)
  (declare (type compiled-frame frame) (type unsigned-byte stack-slot)
           (type sb!c:sc-offset loc))
  (let ((pointer (frame-pointer frame))
        (escaped (compiled-frame-escaped frame)))
    (if escaped
        (sub-access-debug-var-slot pointer loc escaped)
        #!-(or x86 x86-64)
        (stack-ref pointer stack-slot)
        #!+(or x86 x86-64)
        (ecase stack-slot
          (#.ocfp-save-offset
           (stack-ref pointer stack-slot))
          (#.lra-save-offset
           (sap-ref-sap pointer (- (* (1+ stack-slot)
                                      sb!vm::n-word-bytes))))))))

(defun (setf get-context-value) (value frame stack-slot loc)
  (declare (type compiled-frame frame) (type unsigned-byte stack-slot)
           (type sb!c:sc-offset loc))
  (let ((pointer (frame-pointer frame))
        (escaped (compiled-frame-escaped frame)))
    (if escaped
        (sub-set-debug-var-slot pointer loc value escaped)
        #!-(or x86 x86-64)
        (setf (stack-ref pointer stack-slot) value)
        #!+(or x86 x86-64)
        (ecase stack-slot
          (#.ocfp-save-offset
           (setf (stack-ref pointer stack-slot) value))
          (#.lra-save-offset
           (setf (sap-ref-sap pointer (- (* (1+ stack-slot)
                                            sb!vm::n-word-bytes))) value))))))

(defun foreign-function-backtrace-name (sap)
  (let ((name (sap-foreign-symbol sap)))
    (if name
        (format nil "foreign function: ~A" name)
        (format nil "foreign function: #x~X" (sap-int sap)))))

;;; This returns a frame for the one existing in time immediately
;;; prior to the frame referenced by current-fp. This is current-fp's
;;; caller or the next frame down the control stack. If there is no
;;; down frame, this returns NIL for the bottom of the stack. UP-FRAME
;;; is the up link for the resulting frame object, and it is null when
;;; we call this to get the top of the stack.
;;;
;;; The current frame contains the pointer to the temporally previous
;;; frame we want, and the current frame contains the pc at which we
;;; will continue executing upon returning to that previous frame.
;;;
;;; Note: Sometimes LRA is actually a fixnum. This happens when lisp
;;; calls into C. In this case, the code object is stored on the stack
;;; after the LRA, and the LRA is the word offset.
#!-(or x86 x86-64)
(defun compute-calling-frame (caller lra up-frame)
  (declare (type system-area-pointer caller))
  (/noshow0 "entering COMPUTE-CALLING-FRAME")
  (when (control-stack-pointer-valid-p caller)
    (/noshow0 "in WHEN")
    (multiple-value-bind (code pc-offset escaped)
        (if lra
            (multiple-value-bind (word-offset code)
                (if (fixnump lra)
                    (let ((fp (frame-pointer up-frame)))
                      (values lra
                              (stack-ref fp (1+ lra-save-offset))))
                    (values (get-header-data lra)
                            (lra-code-header lra)))
              (if code
                  (values code
                          (* (1+ (- word-offset (get-header-data code)))
                             sb!vm:n-word-bytes)
                          nil)
                  (values :foreign-function
                          0
                          nil)))
            (find-escaped-frame caller))
      (if (and (code-component-p code)
               (eq (%code-debug-info code) :bogus-lra))
          (let ((real-lra (code-header-ref code real-lra-slot)))
            (compute-calling-frame caller real-lra up-frame))
          (let ((d-fun (case code
                         (:undefined-function
                          (make-bogus-debug-fun
                           "undefined function"))
                         (:foreign-function
                          (make-bogus-debug-fun
                           (foreign-function-backtrace-name
                            (int-sap (get-lisp-obj-address lra)))))
                         ((nil)
                          (make-bogus-debug-fun
                           "bogus stack frame"))
                         (t
                          (debug-fun-from-pc code pc-offset)))))
            (/noshow0 "returning MAKE-COMPILED-FRAME from COMPUTE-CALLING-FRAME")
            (make-compiled-frame caller up-frame d-fun
                                 (code-location-from-pc d-fun pc-offset
                                                        escaped)
                                 (if up-frame (1+ (frame-number up-frame)) 0)
                                 escaped))))))

#!+(or x86 x86-64)
(defun compute-calling-frame (caller ra up-frame)
  (declare (type system-area-pointer caller ra))
  (/noshow0 "entering COMPUTE-CALLING-FRAME")
  (when (control-stack-pointer-valid-p caller)
    (/noshow0 "in WHEN")
    ;; First check for an escaped frame.
    (multiple-value-bind (code pc-offset escaped) (find-escaped-frame caller)
      (/noshow0 "at COND")
      (cond (code
             ;; If it's escaped it may be a function end breakpoint trap.
             (when (and (code-component-p code)
                        (eq (%code-debug-info code) :bogus-lra))
               ;; If :bogus-lra grab the real lra.
               (setq pc-offset (code-header-ref
                                code (1+ real-lra-slot)))
               (setq code (code-header-ref code real-lra-slot))
               (aver code)))
            ((not escaped)
             (multiple-value-setq (pc-offset code)
               (compute-lra-data-from-pc ra))
             (unless code
               (setf code :foreign-function
                     pc-offset 0))))
      (let ((d-fun (case code
                     (:undefined-function
                      (make-bogus-debug-fun
                       "undefined function"))
                     (:foreign-function
                      (make-bogus-debug-fun
                       (foreign-function-backtrace-name ra)))
                     ((nil)
                      (make-bogus-debug-fun
                       "bogus stack frame"))
                     (t
                      (debug-fun-from-pc code pc-offset)))))
        (/noshow0 "returning MAKE-COMPILED-FRAME from COMPUTE-CALLING-FRAME")
        (make-compiled-frame caller up-frame d-fun
                             (code-location-from-pc d-fun pc-offset
                                                    escaped)
                             (if up-frame (1+ (frame-number up-frame)) 0)
                             escaped)))))

(defun nth-interrupt-context (n)
  (declare (type (unsigned-byte 32) n)
           (optimize (speed 3) (safety 0)))
  (sb!alien:sap-alien (sb!vm::current-thread-offset-sap
                       (+ sb!vm::thread-interrupt-contexts-offset n))
                      (* os-context-t)))

#!+(or x86 x86-64)
(defun find-escaped-frame (frame-pointer)
  (declare (type system-area-pointer frame-pointer))
  (/noshow0 "entering FIND-ESCAPED-FRAME")
  (dotimes (index *free-interrupt-context-index* (values nil 0 nil))
      (/noshow0 "at head of WITH-ALIEN")
    (let ((context (nth-interrupt-context index)))
        (/noshow0 "got CONTEXT")
        (when (= (sap-int frame-pointer)
                 (sb!vm:context-register context sb!vm::cfp-offset))
          (without-gcing
           (/noshow0 "in WITHOUT-GCING")
           (let* ((component-ptr (component-ptr-from-pc
                                  (sb!vm:context-pc context)))
                  (code (unless (sap= component-ptr (int-sap #x0))
                          (component-from-component-ptr component-ptr))))
             (/noshow0 "got CODE")
             (when (null code)
               (return (values code 0 context)))
             (let* ((code-header-len (* (get-header-data code)
                                        sb!vm:n-word-bytes))
                    (pc-offset
                     (- (sap-int (sb!vm:context-pc context))
                        (- (get-lisp-obj-address code)
                           sb!vm:other-pointer-lowtag)
                        code-header-len)))
               (/noshow "got PC-OFFSET")
               (unless (<= 0 pc-offset
                           (* (code-header-ref code sb!vm:code-code-size-slot)
                              sb!vm:n-word-bytes))
                 ;; We were in an assembly routine. Therefore, use the
                 ;; LRA as the pc.
                 ;;
                 ;; FIXME: Should this be WARN or ERROR or what?
                 (format t "** pc-offset ~S not in code obj ~S?~%"
                         pc-offset code))
               (/noshow0 "returning from FIND-ESCAPED-FRAME")
               (return
               (values code pc-offset context)))))))))

#!-(or x86 x86-64)
(defun find-escaped-frame (frame-pointer)
  (declare (type system-area-pointer frame-pointer))
  (/noshow0 "entering FIND-ESCAPED-FRAME")
  (dotimes (index *free-interrupt-context-index* (values nil 0 nil))
      (/noshow0 "at head of WITH-ALIEN")
    (let ((scp (nth-interrupt-context index)))
        (/noshow0 "got SCP")
      (when (= (sap-int frame-pointer)
               (sb!vm:context-register scp sb!vm::cfp-offset))
        (without-gcing
         (/noshow0 "in WITHOUT-GCING")
         (let ((code (code-object-from-bits
                      (sb!vm:context-register scp sb!vm::code-offset))))
           (/noshow0 "got CODE")
           (when (symbolp code)
             (return (values code 0 scp)))
           (let* ((code-header-len (* (get-header-data code)
                                      sb!vm:n-word-bytes))
                  (pc-offset
                   (- (sap-int (sb!vm:context-pc scp))
                      (- (get-lisp-obj-address code)
                         sb!vm:other-pointer-lowtag)
                      code-header-len)))
             (let ((code-size (* (code-header-ref code
                                                  sb!vm:code-code-size-slot)
                                 sb!vm:n-word-bytes)))
               (unless (<= 0 pc-offset code-size)
                 ;; We were in an assembly routine.
                 (multiple-value-bind (new-pc-offset computed-return)
                     (find-pc-from-assembly-fun code scp)
                   (setf pc-offset new-pc-offset)
                   (unless (<= 0 pc-offset code-size)
                     (cerror
                      "Set PC-OFFSET to zero and continue backtrace."
                      'bug
                      :format-control
                      "~@<PC-OFFSET (~D) not in code object. Frame details:~
                       ~2I~:@_PC: #X~X~:@_CODE: ~S~:@_CODE FUN: ~S~:@_LRA: ~
                       #X~X~:@_COMPUTED RETURN: #X~X.~:>"
                      :format-arguments
                      (list pc-offset
                            (sap-int (sb!vm:context-pc scp))
                            code
                            (%code-entry-points code)
                            (sb!vm:context-register scp sb!vm::lra-offset)
                            computed-return))
                     ;; We failed to pinpoint where PC is, but set
                     ;; pc-offset to 0 to keep the backtrace from
                     ;; exploding.
                     (setf pc-offset 0)))))
             (/noshow0 "returning from FIND-ESCAPED-FRAME")
             (return
               (if (eq (%code-debug-info code) :bogus-lra)
                   (let ((real-lra (code-header-ref code
                                                    real-lra-slot)))
                     (values (lra-code-header real-lra)
                             (get-header-data real-lra)
                             nil))
                   (values code pc-offset scp))))))))))

#!-(or x86 x86-64)
(defun find-pc-from-assembly-fun (code scp)
  "Finds the PC for the return from an assembly routine properly.
For some architectures (such as PPC) this will not be the $LRA
register."
  (let ((return-machine-address (sb!vm::return-machine-address scp))
        (code-header-len (* (get-header-data code) sb!vm:n-word-bytes)))
    (values (- return-machine-address
               (- (get-lisp-obj-address code)
                  sb!vm:other-pointer-lowtag)
               code-header-len)
            return-machine-address)))

;;; Find the code object corresponding to the object represented by
;;; bits and return it. We assume bogus functions correspond to the
;;; undefined-function.
#!-(or x86 x86-64)
(defun code-object-from-bits (bits)
  (declare (type (unsigned-byte 32) bits))
  (let ((object (make-lisp-obj bits nil)))
    (if (functionp object)
        (or (fun-code-header object)
            :undefined-function)
        (let ((lowtag (lowtag-of object)))
          (when (= lowtag sb!vm:other-pointer-lowtag)
            (let ((widetag (widetag-of object)))
              (cond ((= widetag sb!vm:code-header-widetag)
                     object)
                    ((= widetag sb!vm:return-pc-header-widetag)
                     (lra-code-header object))
                    (t
                     nil))))))))
\f
;;;; frame utilities

;;; This returns a COMPILED-DEBUG-FUN for COMPONENT and PC. We fetch the
;;; SB!C::DEBUG-INFO and run down its FUN-MAP to get a
;;; SB!C::COMPILED-DEBUG-FUN from the PC. The result only needs to
;;; reference the COMPONENT, for function constants, and the
;;; SB!C::COMPILED-DEBUG-FUN.
(defun debug-fun-from-pc (component pc)
  (let ((info (%code-debug-info component)))
    (cond
      ((not info)
       ;; FIXME: It seems that most of these (at least on x86) are
       ;; actually assembler routines, and could be named by looking
       ;; at the sb-fasl:*assembler-routines*.
       (make-bogus-debug-fun "no debug information for frame"))
     ((eq info :bogus-lra)
      (make-bogus-debug-fun "function end breakpoint"))
     (t
      (let* ((fun-map (sb!c::compiled-debug-info-fun-map info))
             (len (length fun-map)))
        (declare (type simple-vector fun-map))
        (if (= len 1)
            (make-compiled-debug-fun (svref fun-map 0) component)
            (let ((i 1)
                  (elsewhere-p
                   (>= pc (sb!c::compiled-debug-fun-elsewhere-pc
                           (svref fun-map 0)))))
              (declare (type sb!int:index i))
              (loop
                (when (or (= i len)
                          (< pc (if elsewhere-p
                                    (sb!c::compiled-debug-fun-elsewhere-pc
                                     (svref fun-map (1+ i)))
                                    (svref fun-map i))))
                  (return (make-compiled-debug-fun
                           (svref fun-map (1- i))
                           component)))
                (incf i 2)))))))))

;;; This returns a code-location for the COMPILED-DEBUG-FUN,
;;; DEBUG-FUN, and the pc into its code vector. If we stopped at a
;;; breakpoint, find the CODE-LOCATION for that breakpoint. Otherwise,
;;; make an :UNSURE code location, so it can be filled in when we
;;; figure out what is going on.
(defun code-location-from-pc (debug-fun pc escaped)
  (or (and (compiled-debug-fun-p debug-fun)
           escaped
           (let ((data (breakpoint-data
                        (compiled-debug-fun-component debug-fun)
                        pc nil)))
             (when (and data (breakpoint-data-breakpoints data))
               (let ((what (breakpoint-what
                            (first (breakpoint-data-breakpoints data)))))
                 (when (compiled-code-location-p what)
                   what)))))
      (make-compiled-code-location pc debug-fun)))

;;; Return an alist mapping catch tags to CODE-LOCATIONs. These are
;;; CODE-LOCATIONs at which execution would continue with frame as the
;;; top frame if someone threw to the corresponding tag.
(defun frame-catches (frame)
  (let ((catch (descriptor-sap sb!vm:*current-catch-block*))
        (reversed-result nil)
        (fp (frame-pointer frame)))
    (loop until (zerop (sap-int catch))
          finally (return (nreverse reversed-result))
          do
          (when (sap= fp
                      #!-alpha
                      (sap-ref-sap catch
                                   (* sb!vm:catch-block-current-cont-slot
                                      sb!vm:n-word-bytes))
                      #!+alpha
                      (int-sap
                       (sap-ref-32 catch
                                   (* sb!vm:catch-block-current-cont-slot
                                      sb!vm:n-word-bytes))))
            (let* (#!-(or x86 x86-64)
                   (lra (stack-ref catch sb!vm:catch-block-entry-pc-slot))
                   #!+(or x86 x86-64)
                   (ra (sap-ref-sap
                        catch (* sb!vm:catch-block-entry-pc-slot
                                 sb!vm:n-word-bytes)))
                   #!-(or x86 x86-64)
                   (component
                    (stack-ref catch sb!vm:catch-block-current-code-slot))
                   #!+(or x86 x86-64)
                   (component (component-from-component-ptr
                               (component-ptr-from-pc ra)))
                   (offset
                    #!-(or x86 x86-64)
                    (* (- (1+ (get-header-data lra))
                          (get-header-data component))
                       sb!vm:n-word-bytes)
                    #!+(or x86 x86-64)
                    (- (sap-int ra)
                       (- (get-lisp-obj-address component)
                          sb!vm:other-pointer-lowtag)
                       (* (get-header-data component) sb!vm:n-word-bytes))))
              (push (cons #!-(or x86 x86-64)
                          (stack-ref catch sb!vm:catch-block-tag-slot)
                          #!+(or x86 x86-64)
                          (make-lisp-obj
                           (sap-ref-word catch (* sb!vm:catch-block-tag-slot
                                                  sb!vm:n-word-bytes)))
                          (make-compiled-code-location
                           offset (frame-debug-fun frame)))
                    reversed-result)))
          (setf catch
                #!-alpha
                (sap-ref-sap catch
                             (* sb!vm:catch-block-previous-catch-slot
                                sb!vm:n-word-bytes))
                #!+alpha
                (int-sap
                 (sap-ref-32 catch
                             (* sb!vm:catch-block-previous-catch-slot
                                sb!vm:n-word-bytes)))))))

;;; Modify the value of the OLD-TAG catches in FRAME to NEW-TAG
(defun replace-frame-catch-tag (frame old-tag new-tag)
  (let ((catch (descriptor-sap sb!vm:*current-catch-block*))
        (fp (frame-pointer frame)))
    (loop until (zerop (sap-int catch))
          do (when (sap= fp
                         #!-alpha
                         (sap-ref-sap catch
                                      (* sb!vm:catch-block-current-cont-slot
                                         sb!vm:n-word-bytes))
                         #!+alpha
                         (int-sap
                          (sap-ref-32 catch
                                      (* sb!vm:catch-block-current-cont-slot
                                         sb!vm:n-word-bytes))))
               (let ((current-tag
                      #!-(or x86 x86-64)
                      (stack-ref catch sb!vm:catch-block-tag-slot)
                      #!+(or x86 x86-64)
                      (make-lisp-obj
                       (sap-ref-word catch (* sb!vm:catch-block-tag-slot
                                              sb!vm:n-word-bytes)))))
                 (when (eq current-tag old-tag)
                   #!-(or x86 x86-64)
                   (setf (stack-ref catch sb!vm:catch-block-tag-slot) new-tag)
                   #!+(or x86 x86-64)
                   (setf (sap-ref-word catch (* sb!vm:catch-block-tag-slot
                                                sb!vm:n-word-bytes))
                         (get-lisp-obj-address new-tag)))))
          do (setf catch
                   #!-alpha
                   (sap-ref-sap catch
                                (* sb!vm:catch-block-previous-catch-slot
                                   sb!vm:n-word-bytes))
                   #!+alpha
                   (int-sap
                    (sap-ref-32 catch
                                (* sb!vm:catch-block-previous-catch-slot
                                   sb!vm:n-word-bytes)))))))


\f
;;;; operations on DEBUG-FUNs

;;; Execute the forms in a context with BLOCK-VAR bound to each
;;; DEBUG-BLOCK in DEBUG-FUN successively. Result is an optional
;;; form to execute for return values, and DO-DEBUG-FUN-BLOCKS
;;; returns nil if there is no result form. This signals a
;;; NO-DEBUG-BLOCKS condition when the DEBUG-FUN lacks
;;; DEBUG-BLOCK information.
(defmacro do-debug-fun-blocks ((block-var debug-fun &optional result)
                               &body body)
  (let ((blocks (gensym))
        (i (gensym)))
    `(let ((,blocks (debug-fun-debug-blocks ,debug-fun)))
       (declare (simple-vector ,blocks))
       (dotimes (,i (length ,blocks) ,result)
         (let ((,block-var (svref ,blocks ,i)))
           ,@body)))))

;;; Execute body in a context with VAR bound to each DEBUG-VAR in
;;; DEBUG-FUN. This returns the value of executing result (defaults to
;;; nil). This may iterate over only some of DEBUG-FUN's variables or
;;; none depending on debug policy; for example, possibly the
;;; compilation only preserved argument information.
(defmacro do-debug-fun-vars ((var debug-fun &optional result) &body body)
  (let ((vars (gensym))
        (i (gensym)))
    `(let ((,vars (debug-fun-debug-vars ,debug-fun)))
       (declare (type (or null simple-vector) ,vars))
       (if ,vars
           (dotimes (,i (length ,vars) ,result)
             (let ((,var (svref ,vars ,i)))
               ,@body))
           ,result))))

;;; Return the object of type FUNCTION associated with the DEBUG-FUN,
;;; or NIL if the function is unavailable or is non-existent as a user
;;; callable function object.
(defun debug-fun-fun (debug-fun)
  (let ((cached-value (debug-fun-%function debug-fun)))
    (if (eq cached-value :unparsed)
        (setf (debug-fun-%function debug-fun)
              (etypecase debug-fun
                (compiled-debug-fun
                 (let ((component
                        (compiled-debug-fun-component debug-fun))
                       (start-pc
                        (sb!c::compiled-debug-fun-start-pc
                         (compiled-debug-fun-compiler-debug-fun debug-fun))))
                   (do ((entry (%code-entry-points component)
                               (%simple-fun-next entry)))
                       ((null entry) nil)
                     (when (= start-pc
                              (sb!c::compiled-debug-fun-start-pc
                               (compiled-debug-fun-compiler-debug-fun
                                (fun-debug-fun entry))))
                       (return entry)))))
                (bogus-debug-fun nil)))
        cached-value)))

;;; Return the name of the function represented by DEBUG-FUN. This may
;;; be a string or a cons; do not assume it is a symbol.
(defun debug-fun-name (debug-fun)
  (declare (type debug-fun debug-fun))
  (etypecase debug-fun
    (compiled-debug-fun
     (sb!c::compiled-debug-fun-name
      (compiled-debug-fun-compiler-debug-fun debug-fun)))
    (bogus-debug-fun
     (bogus-debug-fun-%name debug-fun))))

;;; Return a DEBUG-FUN that represents debug information for FUN.
(defun fun-debug-fun (fun)
  (declare (type function fun))
  (ecase (widetag-of fun)
    (#.sb!vm:closure-header-widetag
     (fun-debug-fun (%closure-fun fun)))
    (#.sb!vm:funcallable-instance-header-widetag
     (fun-debug-fun (funcallable-instance-fun fun)))
    (#.sb!vm:simple-fun-header-widetag
      (let* ((name (%simple-fun-name fun))
             (component (fun-code-header fun))
             (res (find-if
                   (lambda (x)
                     (and (sb!c::compiled-debug-fun-p x)
                          (eq (sb!c::compiled-debug-fun-name x) name)
                          (eq (sb!c::compiled-debug-fun-kind x) nil)))
                   (sb!c::compiled-debug-info-fun-map
                    (%code-debug-info component)))))
        (if res
            (make-compiled-debug-fun res component)
            ;; KLUDGE: comment from CMU CL:
            ;;   This used to be the non-interpreted branch, but
            ;;   William wrote it to return the debug-fun of fun's XEP
            ;;   instead of fun's debug-fun. The above code does this
            ;;   more correctly, but it doesn't get or eliminate all
            ;;   appropriate cases. It mostly works, and probably
            ;;   works for all named functions anyway.
            ;; -- WHN 20000120
            (debug-fun-from-pc component
                               (* (- (fun-word-offset fun)
                                     (get-header-data component))
                                  sb!vm:n-word-bytes)))))))

;;; Return the kind of the function, which is one of :OPTIONAL,
;;; :EXTERNAL, :TOPLEVEL, :CLEANUP, or NIL.
(defun debug-fun-kind (debug-fun)
  ;; FIXME: This "is one of" information should become part of the function
  ;; declamation, not just a doc string
  (etypecase debug-fun
    (compiled-debug-fun
     (sb!c::compiled-debug-fun-kind
      (compiled-debug-fun-compiler-debug-fun debug-fun)))
    (bogus-debug-fun
     nil)))

;;; Is there any variable information for DEBUG-FUN?
(defun debug-var-info-available (debug-fun)
  (not (not (debug-fun-debug-vars debug-fun))))

;;; Return a list of DEBUG-VARs in DEBUG-FUN having the same name
;;; and package as SYMBOL. If SYMBOL is uninterned, then this returns
;;; a list of DEBUG-VARs without package names and with the same name
;;; as symbol. The result of this function is limited to the
;;; availability of variable information in DEBUG-FUN; for
;;; example, possibly DEBUG-FUN only knows about its arguments.
(defun debug-fun-symbol-vars (debug-fun symbol)
  (let ((vars (ambiguous-debug-vars debug-fun (symbol-name symbol)))
        (package (and (symbol-package symbol)
                      (package-name (symbol-package symbol)))))
    (delete-if (if (stringp package)
                   (lambda (var)
                     (let ((p (debug-var-package-name var)))
                       (or (not (stringp p))
                           (string/= p package))))
                   (lambda (var)
                     (stringp (debug-var-package-name var))))
               vars)))

;;; Return a list of DEBUG-VARs in DEBUG-FUN whose names contain
;;; NAME-PREFIX-STRING as an initial substring. The result of this
;;; function is limited to the availability of variable information in
;;; debug-fun; for example, possibly debug-fun only knows
;;; about its arguments.
(defun ambiguous-debug-vars (debug-fun name-prefix-string)
  (declare (simple-string name-prefix-string))
  (let ((variables (debug-fun-debug-vars debug-fun)))
    (declare (type (or null simple-vector) variables))
    (if variables
        (let* ((len (length variables))
               (prefix-len (length name-prefix-string))
               (pos (find-var name-prefix-string variables len))
               (res nil))
          (when pos
            ;; Find names from pos to variable's len that contain prefix.
            (do ((i pos (1+ i)))
                ((= i len))
              (let* ((var (svref variables i))
                     (name (debug-var-symbol-name var))
                     (name-len (length name)))
                (declare (simple-string name))
                (when (/= (or (string/= name-prefix-string name
                                        :end1 prefix-len :end2 name-len)
                              prefix-len)
                          prefix-len)
                  (return))
                (push var res)))
            (setq res (nreverse res)))
          res))))

;;; This returns a position in VARIABLES for one containing NAME as an
;;; initial substring. END is the length of VARIABLES if supplied.
(defun find-var (name variables &optional end)
  (declare (simple-vector variables)
           (simple-string name))
  (let ((name-len (length name)))
    (position name variables
              :test (lambda (x y)
                      (let* ((y (debug-var-symbol-name y))
                             (y-len (length y)))
                        (declare (simple-string y))
                        (and (>= y-len name-len)
                             (string= x y :end1 name-len :end2 name-len))))
              :end (or end (length variables)))))

;;; Return a list representing the lambda-list for DEBUG-FUN. The
;;; list has the following structure:
;;;   (required-var1 required-var2
;;;    ...
;;;    (:optional var3 suppliedp-var4)
;;;    (:optional var5)
;;;    ...
;;;    (:rest var6) (:rest var7)
;;;    ...
;;;    (:keyword keyword-symbol var8 suppliedp-var9)
;;;    (:keyword keyword-symbol var10)
;;;    ...
;;;   )
;;; Each VARi is a DEBUG-VAR; however it may be the symbol :DELETED if
;;; it is unreferenced in DEBUG-FUN. This signals a
;;; LAMBDA-LIST-UNAVAILABLE condition when there is no argument list
;;; information.
(defun debug-fun-lambda-list (debug-fun)
  (etypecase debug-fun
    (compiled-debug-fun (compiled-debug-fun-lambda-list debug-fun))
    (bogus-debug-fun nil)))

;;; Note: If this has to compute the lambda list, it caches it in DEBUG-FUN.
(defun compiled-debug-fun-lambda-list (debug-fun)
  (let ((lambda-list (debug-fun-%lambda-list debug-fun)))
    (cond ((eq lambda-list :unparsed)
           (multiple-value-bind (args argsp)
               (parse-compiled-debug-fun-lambda-list debug-fun)
             (setf (debug-fun-%lambda-list debug-fun) args)
             (if argsp
                 args
                 (debug-signal 'lambda-list-unavailable
                               :debug-fun debug-fun))))
          (lambda-list)
          ((bogus-debug-fun-p debug-fun)
           nil)
          ((sb!c::compiled-debug-fun-arguments
            (compiled-debug-fun-compiler-debug-fun debug-fun))
           ;; If the packed information is there (whether empty or not) as
           ;; opposed to being nil, then returned our cached value (nil).
           nil)
          (t
           ;; Our cached value is nil, and the packed lambda-list information
           ;; is nil, so we don't have anything available.
           (debug-signal 'lambda-list-unavailable
                         :debug-fun debug-fun)))))

;;; COMPILED-DEBUG-FUN-LAMBDA-LIST calls this when a
;;; COMPILED-DEBUG-FUN has no lambda list information cached. It
;;; returns the lambda list as the first value and whether there was
;;; any argument information as the second value. Therefore,
;;; (VALUES NIL T) means there were no arguments, but (VALUES NIL NIL)
;;; means there was no argument information.
(defun parse-compiled-debug-fun-lambda-list (debug-fun)
  (let ((args (sb!c::compiled-debug-fun-arguments
               (compiled-debug-fun-compiler-debug-fun debug-fun))))
    (cond
     ((not args)
      (values nil nil))
     ((eq args :minimal)
      (values (coerce (debug-fun-debug-vars debug-fun) 'list)
              t))
     (t
      (let ((vars (debug-fun-debug-vars debug-fun))
            (i 0)
            (len (length args))
            (res nil)
            (optionalp nil))
        (declare (type (or null simple-vector) vars))
        (loop
          (when (>= i len) (return))
          (let ((ele (aref args i)))
            (cond
             ((symbolp ele)
              (case ele
                (sb!c::deleted
                 ;; Deleted required arg at beginning of args array.
                 (push :deleted res))
                (sb!c::optional-args
                 (setf optionalp t))
                (sb!c::supplied-p
                 ;; SUPPLIED-P var immediately following keyword or
                 ;; optional. Stick the extra var in the result
                 ;; element representing the keyword or optional,
                 ;; which is the previous one.
                 ;;
                 ;; FIXME: NCONC used for side-effect: the effect is defined,
                 ;; but this is bad style no matter what.
                 (nconc (car res)
                        (list (compiled-debug-fun-lambda-list-var
                               args (incf i) vars))))
                (sb!c::rest-arg
                 (push (list :rest
                             (compiled-debug-fun-lambda-list-var
                              args (incf i) vars))
                       res))
                (sb!c::more-arg
                 ;; Just ignore the fact that the next two args are
                 ;; the &MORE arg context and count, and act like they
                 ;; are regular arguments.
                 nil)
                (t
                 ;; &KEY arg
                 (push (list :keyword
                             ele
                             (compiled-debug-fun-lambda-list-var
                              args (incf i) vars))
                       res))))
             (optionalp
              ;; We saw an optional marker, so the following
              ;; non-symbols are indexes indicating optional
              ;; variables.
              (push (list :optional (svref vars ele)) res))
             (t
              ;; Required arg at beginning of args array.
              (push (svref vars ele) res))))
          (incf i))
        (values (nreverse res) t))))))

;;; This is used in COMPILED-DEBUG-FUN-LAMBDA-LIST.
(defun compiled-debug-fun-lambda-list-var (args i vars)
  (declare (type (simple-array * (*)) args)
           (simple-vector vars))
  (let ((ele (aref args i)))
    (cond ((not (symbolp ele)) (svref vars ele))
          ((eq ele 'sb!c::deleted) :deleted)
          (t (error "malformed arguments description")))))

(defun compiled-debug-fun-debug-info (debug-fun)
  (%code-debug-info (compiled-debug-fun-component debug-fun)))
\f
;;;; unpacking variable and basic block data

(defvar *parsing-buffer*
  (make-array 20 :adjustable t :fill-pointer t))
(defvar *other-parsing-buffer*
  (make-array 20 :adjustable t :fill-pointer t))
;;; PARSE-DEBUG-BLOCKS and PARSE-DEBUG-VARS
;;; use this to unpack binary encoded information. It returns the
;;; values returned by the last form in body.
;;;
;;; This binds buffer-var to *parsing-buffer*, makes sure it starts at
;;; element zero, and makes sure if we unwind, we nil out any set
;;; elements for GC purposes.
;;;
;;; This also binds other-var to *other-parsing-buffer* when it is
;;; supplied, making sure it starts at element zero and that we nil
;;; out any elements if we unwind.
;;;
;;; This defines the local macro RESULT that takes a buffer, copies
;;; its elements to a resulting simple-vector, nil's out elements, and
;;; restarts the buffer at element zero. RESULT returns the
;;; simple-vector.
(eval-when (:compile-toplevel :execute)
(sb!xc:defmacro with-parsing-buffer ((buffer-var &optional other-var)
                                     &body body)
  (let ((len (gensym))
        (res (gensym)))
    `(unwind-protect
         (let ((,buffer-var *parsing-buffer*)
               ,@(if other-var `((,other-var *other-parsing-buffer*))))
           (setf (fill-pointer ,buffer-var) 0)
           ,@(if other-var `((setf (fill-pointer ,other-var) 0)))
           (macrolet ((result (buf)
                        `(let* ((,',len (length ,buf))
                                (,',res (make-array ,',len)))
                           (replace ,',res ,buf :end1 ,',len :end2 ,',len)
                           (fill ,buf nil :end ,',len)
                           (setf (fill-pointer ,buf) 0)
                           ,',res)))
             ,@body))
     (fill *parsing-buffer* nil)
     ,@(if other-var `((fill *other-parsing-buffer* nil))))))
) ; EVAL-WHEN

;;; The argument is a debug internals structure. This returns the
;;; DEBUG-BLOCKs for DEBUG-FUN, regardless of whether we have unpacked
;;; them yet. It signals a NO-DEBUG-BLOCKS condition if it can't
;;; return the blocks.
(defun debug-fun-debug-blocks (debug-fun)
  (let ((blocks (debug-fun-blocks debug-fun)))
    (cond ((eq blocks :unparsed)
           (setf (debug-fun-blocks debug-fun)
                 (parse-debug-blocks debug-fun))
           (unless (debug-fun-blocks debug-fun)
             (debug-signal 'no-debug-blocks
                           :debug-fun debug-fun))
           (debug-fun-blocks debug-fun))
          (blocks)
          (t
           (debug-signal 'no-debug-blocks
                         :debug-fun debug-fun)))))

;;; Return a SIMPLE-VECTOR of DEBUG-BLOCKs or NIL. NIL indicates there
;;; was no basic block information.
(defun parse-debug-blocks (debug-fun)
  (etypecase debug-fun
    (compiled-debug-fun
     (parse-compiled-debug-blocks debug-fun))
    (bogus-debug-fun
     (debug-signal 'no-debug-blocks :debug-fun debug-fun))))

;;; This does some of the work of PARSE-DEBUG-BLOCKS.
(defun parse-compiled-debug-blocks (debug-fun)
  (let* ((var-count (length (debug-fun-debug-vars debug-fun)))
         (compiler-debug-fun (compiled-debug-fun-compiler-debug-fun
                              debug-fun))
         (blocks (sb!c::compiled-debug-fun-blocks compiler-debug-fun))
         ;; KLUDGE: 8 is a hard-wired constant in the compiler for the
         ;; element size of the packed binary representation of the
         ;; blocks data.
         (live-set-len (ceiling var-count 8))
         (tlf-number (sb!c::compiled-debug-fun-tlf-number compiler-debug-fun)))
    (unless blocks
      (return-from parse-compiled-debug-blocks nil))
    (macrolet ((aref+ (a i) `(prog1 (aref ,a ,i) (incf ,i))))
      (with-parsing-buffer (blocks-buffer locations-buffer)
        (let ((i 0)
              (len (length blocks))
              (last-pc 0))
          (loop
            (when (>= i len) (return))
            (let ((succ-and-flags (aref+ blocks i))
                  (successors nil))
              (declare (type (unsigned-byte 8) succ-and-flags)
                       (list successors))
              (dotimes (k (ldb sb!c::compiled-debug-block-nsucc-byte
                               succ-and-flags))
                (push (sb!c:read-var-integer blocks i) successors))
              (let* ((locations
                      (dotimes (k (sb!c:read-var-integer blocks i)
                                  (result locations-buffer))
                        (let ((kind (svref sb!c::*compiled-code-location-kinds*
                                           (aref+ blocks i)))
                              (pc (+ last-pc
                                     (sb!c:read-var-integer blocks i)))
                              (tlf-offset (or tlf-number
                                              (sb!c:read-var-integer blocks i)))
                              (form-number (sb!c:read-var-integer blocks i))
                              (live-set (sb!c:read-packed-bit-vector
                                         live-set-len blocks i))
                              (step-info (sb!c:read-var-string blocks i)))
                          (vector-push-extend (make-known-code-location
                                               pc debug-fun tlf-offset
                                               form-number live-set kind
                                               step-info)
                                              locations-buffer)
                          (setf last-pc pc))))
                     (block (make-compiled-debug-block
                             locations successors
                             (not (zerop (logand
                                          sb!c::compiled-debug-block-elsewhere-p
                                          succ-and-flags))))))
                (vector-push-extend block blocks-buffer)
                (dotimes (k (length locations))
                  (setf (code-location-%debug-block (svref locations k))
                        block))))))
        (let ((res (result blocks-buffer)))
          (declare (simple-vector res))
          (dotimes (i (length res))
            (let* ((block (svref res i))
                   (succs nil))
              (dolist (ele (debug-block-successors block))
                (push (svref res ele) succs))
              (setf (debug-block-successors block) succs)))
          res)))))

;;; The argument is a debug internals structure. This returns NIL if
;;; there is no variable information. It returns an empty
;;; simple-vector if there were no locals in the function. Otherwise
;;; it returns a SIMPLE-VECTOR of DEBUG-VARs.
(defun debug-fun-debug-vars (debug-fun)
  (let ((vars (debug-fun-%debug-vars debug-fun)))
    (if (eq vars :unparsed)
        (setf (debug-fun-%debug-vars debug-fun)
              (etypecase debug-fun
                (compiled-debug-fun
                 (parse-compiled-debug-vars debug-fun))
                (bogus-debug-fun nil)))
        vars)))

;;; VARS is the parsed variables for a minimal debug function. We need
;;; to assign names of the form ARG-NNN. We must pad with leading
;;; zeros, since the arguments must be in alphabetical order.
(defun assign-minimal-var-names (vars)
  (declare (simple-vector vars))
  (let* ((len (length vars))
         (width (length (format nil "~W" (1- len)))))
    (dotimes (i len)
      (without-package-locks
        (setf (compiled-debug-var-symbol (svref vars i))
              (intern (format nil "ARG-~V,'0D" width i)
                      ;; KLUDGE: It's somewhat nasty to have a bare
                      ;; package name string here. It would be
                      ;; nicer to have #.(FIND-PACKAGE "SB!DEBUG")
                      ;; instead, since then at least it would transform
                      ;; correctly under package renaming and stuff.
                      ;; However, genesis can't handle dumped packages..
                      ;; -- WHN 20000129
                      ;;
                      ;; FIXME: Maybe this could be fixed by moving the
                      ;; whole debug-int.lisp file to warm init? (after
                      ;; which dumping a #.(FIND-PACKAGE ..) expression
                      ;; would work fine) If this is possible, it would
                      ;; probably be a good thing, since minimizing the
                      ;; amount of stuff in cold init is basically good.
                      (or (find-package "SB-DEBUG")
                          (find-package "SB!DEBUG"))))))))

;;; Parse the packed representation of DEBUG-VARs from
;;; DEBUG-FUN's SB!C::COMPILED-DEBUG-FUN, returning a vector
;;; of DEBUG-VARs, or NIL if there was no information to parse.
(defun parse-compiled-debug-vars (debug-fun)
  (let* ((cdebug-fun (compiled-debug-fun-compiler-debug-fun
                      debug-fun))
         (packed-vars (sb!c::compiled-debug-fun-vars cdebug-fun))
         (args-minimal (eq (sb!c::compiled-debug-fun-arguments cdebug-fun)
                           :minimal)))
    (when packed-vars
      (do ((i 0)
           (buffer (make-array 0 :fill-pointer 0 :adjustable t)))
          ((>= i (length packed-vars))
           (let ((result (coerce buffer 'simple-vector)))
             (when args-minimal
               (assign-minimal-var-names result))
             result))
        (flet ((geti () (prog1 (aref packed-vars i) (incf i))))
          (let* ((flags (geti))
                 (minimal (logtest sb!c::compiled-debug-var-minimal-p flags))
                 (deleted (logtest sb!c::compiled-debug-var-deleted-p flags))
                 (live (logtest sb!c::compiled-debug-var-environment-live
                                flags))
                 (save (logtest sb!c::compiled-debug-var-save-loc-p flags))
                 (symbol (if minimal nil (geti)))
                 (id (if (logtest sb!c::compiled-debug-var-id-p flags)
                         (geti)
                         0))
                 (sc-offset (if deleted 0 (geti)))
                 (save-sc-offset (if save (geti) nil)))
            (aver (not (and args-minimal (not minimal))))
            (vector-push-extend (make-compiled-debug-var symbol
                                                         id
                                                         live
                                                         sc-offset
                                                         save-sc-offset)
                                buffer)))))))
\f
;;;; CODE-LOCATIONs

;;; If we're sure of whether code-location is known, return T or NIL.
;;; If we're :UNSURE, then try to fill in the code-location's slots.
;;; This determines whether there is any debug-block information, and
;;; if code-location is known.
;;;
;;; ??? IF this conses closures every time it's called, then break off the
;;; :UNSURE part to get the HANDLER-CASE into another function.
(defun code-location-unknown-p (basic-code-location)
  (ecase (code-location-%unknown-p basic-code-location)
    ((t) t)
    ((nil) nil)
    (:unsure
     (setf (code-location-%unknown-p basic-code-location)
           (handler-case (not (fill-in-code-location basic-code-location))
             (no-debug-blocks () t))))))

;;; Return the DEBUG-BLOCK containing code-location if it is available.
;;; Some debug policies inhibit debug-block information, and if none
;;; is available, then this signals a NO-DEBUG-BLOCKS condition.
(defun code-location-debug-block (basic-code-location)
  (let ((block (code-location-%debug-block basic-code-location)))
    (if (eq block :unparsed)
        (etypecase basic-code-location
          (compiled-code-location
           (compute-compiled-code-location-debug-block basic-code-location))
          ;; (There used to be more cases back before sbcl-0.7.0, when
          ;; we did special tricks to debug the IR1 interpreter.)
          )
        block)))

;;; Store and return BASIC-CODE-LOCATION's debug-block. We determines
;;; the correct one using the code-location's pc. We use
;;; DEBUG-FUN-DEBUG-BLOCKS to return the cached block information
;;; or signal a NO-DEBUG-BLOCKS condition. The blocks are sorted by
;;; their first code-location's pc, in ascending order. Therefore, as
;;; soon as we find a block that starts with a pc greater than
;;; basic-code-location's pc, we know the previous block contains the
;;; pc. If we get to the last block, then the code-location is either
;;; in the second to last block or the last block, and we have to be
;;; careful in determining this since the last block could be code at
;;; the end of the function. We have to check for the last block being
;;; code first in order to see how to compare the code-location's pc.
(defun compute-compiled-code-location-debug-block (basic-code-location)
  (let* ((pc (compiled-code-location-pc basic-code-location))
         (debug-fun (code-location-debug-fun
                          basic-code-location))
         (blocks (debug-fun-debug-blocks debug-fun))
         (len (length blocks)))
    (declare (simple-vector blocks))
    (setf (code-location-%debug-block basic-code-location)
          (if (= len 1)
              (svref blocks 0)
              (do ((i 1 (1+ i))
                   (end (1- len)))
                  ((= i end)
                   (let ((last (svref blocks end)))
                     (cond
                      ((debug-block-elsewhere-p last)
                       (if (< pc
                              (sb!c::compiled-debug-fun-elsewhere-pc
                               (compiled-debug-fun-compiler-debug-fun
                                debug-fun)))
                           (svref blocks (1- end))
                           last))
                      ((< pc
                          (compiled-code-location-pc
                           (svref (compiled-debug-block-code-locations last)
                                  0)))
                       (svref blocks (1- end)))
                      (t last))))
                (declare (type index i end))
                (when (< pc
                         (compiled-code-location-pc
                          (svref (compiled-debug-block-code-locations
                                  (svref blocks i))
                                 0)))
                  (return (svref blocks (1- i)))))))))

;;; Return the CODE-LOCATION's DEBUG-SOURCE.
(defun code-location-debug-source (code-location)
  (let ((info (compiled-debug-fun-debug-info
               (code-location-debug-fun code-location))))
    (or (sb!c::debug-info-source info)
        (debug-signal 'no-debug-blocks :debug-fun
                      (code-location-debug-fun code-location)))))

;;; Returns the number of top level forms before the one containing
;;; CODE-LOCATION as seen by the compiler in some compilation unit. (A
;;; compilation unit is not necessarily a single file, see the section
;;; on debug-sources.)
(defun code-location-toplevel-form-offset (code-location)
  (when (code-location-unknown-p code-location)
    (error 'unknown-code-location :code-location code-location))
  (let ((tlf-offset (code-location-%tlf-offset code-location)))
    (cond ((eq tlf-offset :unparsed)
           (etypecase code-location
             (compiled-code-location
              (unless (fill-in-code-location code-location)
                ;; This check should be unnecessary. We're missing
                ;; debug info the compiler should have dumped.
                (bug "unknown code location"))
              (code-location-%tlf-offset code-location))
             ;; (There used to be more cases back before sbcl-0.7.0,,
             ;; when we did special tricks to debug the IR1
             ;; interpreter.)
             ))
          (t tlf-offset))))

;;; Return the number of the form corresponding to CODE-LOCATION. The
;;; form number is derived by a walking the subforms of a top level
;;; form in depth-first order.
(defun code-location-form-number (code-location)
  (when (code-location-unknown-p code-location)
    (error 'unknown-code-location :code-location code-location))
  (let ((form-num (code-location-%form-number code-location)))
    (cond ((eq form-num :unparsed)
           (etypecase code-location
             (compiled-code-location
              (unless (fill-in-code-location code-location)
                ;; This check should be unnecessary. We're missing
                ;; debug info the compiler should have dumped.
                (bug "unknown code location"))
              (code-location-%form-number code-location))
             ;; (There used to be more cases back before sbcl-0.7.0,,
             ;; when we did special tricks to debug the IR1
             ;; interpreter.)
             ))
          (t form-num))))

;;; Return the kind of CODE-LOCATION, one of:
;;;  :INTERPRETED, :UNKNOWN-RETURN, :KNOWN-RETURN, :INTERNAL-ERROR,
;;;  :NON-LOCAL-EXIT, :BLOCK-START, :CALL-SITE, :SINGLE-VALUE-RETURN,
;;;  :NON-LOCAL-ENTRY
(defun code-location-kind (code-location)
  (when (code-location-unknown-p code-location)
    (error 'unknown-code-location :code-location code-location))
  (etypecase code-location
    (compiled-code-location
     (let ((kind (compiled-code-location-kind code-location)))
       (cond ((not (eq kind :unparsed)) kind)
             ((not (fill-in-code-location code-location))
              ;; This check should be unnecessary. We're missing
              ;; debug info the compiler should have dumped.
              (bug "unknown code location"))
             (t
              (compiled-code-location-kind code-location)))))
    ;; (There used to be more cases back before sbcl-0.7.0,,
    ;; when we did special tricks to debug the IR1
    ;; interpreter.)
    ))

;;; This returns CODE-LOCATION's live-set if it is available. If
;;; there is no debug-block information, this returns NIL.
(defun compiled-code-location-live-set (code-location)
  (if (code-location-unknown-p code-location)
      nil
      (let ((live-set (compiled-code-location-%live-set code-location)))
        (cond ((eq live-set :unparsed)
               (unless (fill-in-code-location code-location)
                 ;; This check should be unnecessary. We're missing
                 ;; debug info the compiler should have dumped.
                 ;;
                 ;; FIXME: This error and comment happen over and over again.
                 ;; Make them a shared function.
                 (bug "unknown code location"))
               (compiled-code-location-%live-set code-location))
              (t live-set)))))

;;; true if OBJ1 and OBJ2 are the same place in the code
(defun code-location= (obj1 obj2)
  (etypecase obj1
    (compiled-code-location
     (etypecase obj2
       (compiled-code-location
        (and (eq (code-location-debug-fun obj1)
                 (code-location-debug-fun obj2))
             (sub-compiled-code-location= obj1 obj2)))
       ;; (There used to be more cases back before sbcl-0.7.0,,
       ;; when we did special tricks to debug the IR1
       ;; interpreter.)
       ))
    ;; (There used to be more cases back before sbcl-0.7.0,,
    ;; when we did special tricks to debug IR1-interpreted code.)
    ))
(defun sub-compiled-code-location= (obj1 obj2)
  (= (compiled-code-location-pc obj1)
     (compiled-code-location-pc obj2)))

;;; Fill in CODE-LOCATION's :UNPARSED slots, returning T or NIL
;;; depending on whether the code-location was known in its
;;; DEBUG-FUN's debug-block information. This may signal a
;;; NO-DEBUG-BLOCKS condition due to DEBUG-FUN-DEBUG-BLOCKS, and
;;; it assumes the %UNKNOWN-P slot is already set or going to be set.
(defun fill-in-code-location (code-location)
  (declare (type compiled-code-location code-location))
  (let* ((debug-fun (code-location-debug-fun code-location))
         (blocks (debug-fun-debug-blocks debug-fun)))
    (declare (simple-vector blocks))
    (dotimes (i (length blocks) nil)
      (let* ((block (svref blocks i))
             (locations (compiled-debug-block-code-locations block)))
        (declare (simple-vector locations))
        (dotimes (j (length locations))
          (let ((loc (svref locations j)))
            (when (sub-compiled-code-location= code-location loc)
              (setf (code-location-%debug-block code-location) block)
              (setf (code-location-%tlf-offset code-location)
                    (code-location-%tlf-offset loc))
              (setf (code-location-%form-number code-location)
                    (code-location-%form-number loc))
              (setf (compiled-code-location-%live-set code-location)
                    (compiled-code-location-%live-set loc))
              (setf (compiled-code-location-kind code-location)
                    (compiled-code-location-kind loc))
              (setf (compiled-code-location-step-info code-location)
                    (compiled-code-location-step-info loc))
              (return-from fill-in-code-location t))))))))
\f
;;;; operations on DEBUG-BLOCKs

;;; Execute FORMS in a context with CODE-VAR bound to each
;;; CODE-LOCATION in DEBUG-BLOCK, and return the value of RESULT.
(defmacro do-debug-block-locations ((code-var debug-block &optional result)
                                    &body body)
  (let ((code-locations (gensym))
        (i (gensym)))
    `(let ((,code-locations (debug-block-code-locations ,debug-block)))
       (declare (simple-vector ,code-locations))
       (dotimes (,i (length ,code-locations) ,result)
         (let ((,code-var (svref ,code-locations ,i)))
           ,@body)))))

;;; Return the name of the function represented by DEBUG-FUN.
;;; This may be a string or a cons; do not assume it is a symbol.
(defun debug-block-fun-name (debug-block)
  (etypecase debug-block
    (compiled-debug-block
     (let ((code-locs (compiled-debug-block-code-locations debug-block)))
       (declare (simple-vector code-locs))
       (if (zerop (length code-locs))
           "??? Can't get name of debug-block's function."
           (debug-fun-name
            (code-location-debug-fun (svref code-locs 0))))))
    ;; (There used to be more cases back before sbcl-0.7.0, when we
    ;; did special tricks to debug the IR1 interpreter.)
    ))

(defun debug-block-code-locations (debug-block)
  (etypecase debug-block
    (compiled-debug-block
     (compiled-debug-block-code-locations debug-block))
    ;; (There used to be more cases back before sbcl-0.7.0, when we
    ;; did special tricks to debug the IR1 interpreter.)
    ))
\f
;;;; operations on debug variables

(defun debug-var-symbol-name (debug-var)
  (symbol-name (debug-var-symbol debug-var)))

;;; FIXME: Make sure that this isn't called anywhere that it wouldn't
;;; be acceptable to have NIL returned, or that it's only called on
;;; DEBUG-VARs whose symbols have non-NIL packages.
(defun debug-var-package-name (debug-var)
  (package-name (symbol-package (debug-var-symbol debug-var))))

;;; Return the value stored for DEBUG-VAR in frame, or if the value is
;;; not :VALID, then signal an INVALID-VALUE error.
(defun debug-var-valid-value (debug-var frame)
  (unless (eq (debug-var-validity debug-var (frame-code-location frame))
              :valid)
    (error 'invalid-value :debug-var debug-var :frame frame))
  (debug-var-value debug-var frame))

;;; Returns the value stored for DEBUG-VAR in frame. The value may be
;;; invalid. This is SETFable.
(defun debug-var-value (debug-var frame)
  (aver (typep frame 'compiled-frame))
  (let ((res (access-compiled-debug-var-slot debug-var frame)))
    (if (indirect-value-cell-p res)
        (value-cell-ref res)
        res)))

;;; This returns what is stored for the variable represented by
;;; DEBUG-VAR relative to the FRAME. This may be an indirect value
;;; cell if the variable is both closed over and set.
(defun access-compiled-debug-var-slot (debug-var frame)
  (declare (optimize (speed 1)))
  (let ((escaped (compiled-frame-escaped frame)))
    (if escaped
        (sub-access-debug-var-slot
         (frame-pointer frame)
         (compiled-debug-var-sc-offset debug-var)
         escaped)
      (sub-access-debug-var-slot
       (frame-pointer frame)
       (or (compiled-debug-var-save-sc-offset debug-var)
           (compiled-debug-var-sc-offset debug-var))))))

;;; a helper function for working with possibly-invalid values:
;;; Do (%MAKE-LISP-OBJ VAL) only if the value looks valid.
;;;
;;; (Such values can arise in registers on machines with conservative
;;; GC, and might also arise in debug variable locations when
;;; those variables are invalid.)
(defun make-lisp-obj (val &optional (errorp t))
  (if (or
       ;; fixnum
       (zerop (logand val sb!vm:fixnum-tag-mask))
       ;; immediate single float, 64-bit only
       #!+#.(cl:if (cl:= sb!vm::n-machine-word-bits 64) '(and) '(or))
       (= (logand val #xff) sb!vm:single-float-widetag)
       ;; character
       (and (zerop (logandc2 val #x1fffffff)) ; Top bits zero
            (= (logand val #xff) sb!vm:character-widetag)) ; char tag
       ;; unbound marker
       (= val sb!vm:unbound-marker-widetag)
       ;; pointer
       #!+(or x86 x86-64)
       (not (zerop (valid-lisp-pointer-p (int-sap val))))
       ;; FIXME: There is no fundamental reason not to use the above
       ;; function on other platforms as well, but I didn't have
       ;; others available while doing this. --NS 2007-06-21
       #!-(or x86 x86-64)
       (and (logbitp 0 val)
            (or (< sb!vm:read-only-space-start val
                   (* sb!vm:*read-only-space-free-pointer*
                      sb!vm:n-word-bytes))
                (< sb!vm:static-space-start val
                   (* sb!vm:*static-space-free-pointer*
                      sb!vm:n-word-bytes))
                (< (current-dynamic-space-start) val
                   (sap-int (dynamic-space-free-pointer))))))
      (values (%make-lisp-obj val) t)
      (if errorp
          (error "~S is not a valid argument to ~S"
                 val 'make-lisp-obj)
          (values (make-unprintable-object (format nil "invalid object #x~X" val))
                  nil))))

#!-(or x86 x86-64)
(defun sub-access-debug-var-slot (fp sc-offset &optional escaped)
  (macrolet ((with-escaped-value ((var) &body forms)
               `(if escaped
                    (let ((,var (sb!vm:context-register
                                 escaped
                                 (sb!c:sc-offset-offset sc-offset))))
                      ,@forms)
                    :invalid-value-for-unescaped-register-storage))
             (escaped-float-value (format)
               `(if escaped
                    (sb!vm:context-float-register
                     escaped
                     (sb!c:sc-offset-offset sc-offset)
                     ',format)
                    :invalid-value-for-unescaped-register-storage))
             (with-nfp ((var) &body body)
               `(let ((,var (if escaped
                                (sb!sys:int-sap
                                 (sb!vm:context-register escaped
                                                         sb!vm::nfp-offset))
                                #!-alpha
                                (sb!sys:sap-ref-sap fp (* nfp-save-offset
                                                          sb!vm:n-word-bytes))
                                #!+alpha
                                (sb!vm::make-number-stack-pointer
                                 (sb!sys:sap-ref-32 fp (* nfp-save-offset
                                                          sb!vm:n-word-bytes))))))
                  ,@body)))
    (ecase (sb!c:sc-offset-scn sc-offset)
      ((#.sb!vm:any-reg-sc-number
        #.sb!vm:descriptor-reg-sc-number
        #!+rt #.sb!vm:word-pointer-reg-sc-number)
       (sb!sys:without-gcing
        (with-escaped-value (val)
          (make-lisp-obj val nil))))
      (#.sb!vm:character-reg-sc-number
       (with-escaped-value (val)
         (code-char val)))
      (#.sb!vm:sap-reg-sc-number
       (with-escaped-value (val)
         (sb!sys:int-sap val)))
      (#.sb!vm:signed-reg-sc-number
       (with-escaped-value (val)
         (if (logbitp (1- sb!vm:n-word-bits) val)
             (logior val (ash -1 sb!vm:n-word-bits))
             val)))
      (#.sb!vm:unsigned-reg-sc-number
       (with-escaped-value (val)
         val))
      (#.sb!vm:non-descriptor-reg-sc-number
       (error "Local non-descriptor register access?"))
      (#.sb!vm:interior-reg-sc-number
       (error "Local interior register access?"))
      (#.sb!vm:single-reg-sc-number
       (escaped-float-value single-float))
      (#.sb!vm:double-reg-sc-number
       (escaped-float-value double-float))
      #!+long-float
      (#.sb!vm:long-reg-sc-number
       (escaped-float-value long-float))
      (#.sb!vm:complex-single-reg-sc-number
       (if escaped
           (complex
            (sb!vm:context-float-register
             escaped (sb!c:sc-offset-offset sc-offset) 'single-float)
            (sb!vm:context-float-register
             escaped (1+ (sb!c:sc-offset-offset sc-offset)) 'single-float))
           :invalid-value-for-unescaped-register-storage))
      (#.sb!vm:complex-double-reg-sc-number
       (if escaped
           (complex
            (sb!vm:context-float-register
             escaped (sb!c:sc-offset-offset sc-offset) 'double-float)
            (sb!vm:context-float-register
             escaped (+ (sb!c:sc-offset-offset sc-offset) #!+sparc 2 #!-sparc 1)
             'double-float))
           :invalid-value-for-unescaped-register-storage))
      #!+long-float
      (#.sb!vm:complex-long-reg-sc-number
       (if escaped
           (complex
            (sb!vm:context-float-register
             escaped (sb!c:sc-offset-offset sc-offset) 'long-float)
            (sb!vm:context-float-register
             escaped (+ (sb!c:sc-offset-offset sc-offset) #!+sparc 4)
             'long-float))
           :invalid-value-for-unescaped-register-storage))
      (#.sb!vm:single-stack-sc-number
       (with-nfp (nfp)
         (sb!sys:sap-ref-single nfp (* (sb!c:sc-offset-offset sc-offset)
                                       sb!vm:n-word-bytes))))
      (#.sb!vm:double-stack-sc-number
       (with-nfp (nfp)
         (sb!sys:sap-ref-double nfp (* (sb!c:sc-offset-offset sc-offset)
                                       sb!vm:n-word-bytes))))
      #!+long-float
      (#.sb!vm:long-stack-sc-number
       (with-nfp (nfp)
         (sb!sys:sap-ref-long nfp (* (sb!c:sc-offset-offset sc-offset)
                                     sb!vm:n-word-bytes))))
      (#.sb!vm:complex-single-stack-sc-number
       (with-nfp (nfp)
         (complex
          (sb!sys:sap-ref-single nfp (* (sb!c:sc-offset-offset sc-offset)
                                        sb!vm:n-word-bytes))
          (sb!sys:sap-ref-single nfp (* (1+ (sb!c:sc-offset-offset sc-offset))
                                        sb!vm:n-word-bytes)))))
      (#.sb!vm:complex-double-stack-sc-number
       (with-nfp (nfp)
         (complex
          (sb!sys:sap-ref-double nfp (* (sb!c:sc-offset-offset sc-offset)
                                        sb!vm:n-word-bytes))
          (sb!sys:sap-ref-double nfp (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                                        sb!vm:n-word-bytes)))))
      #!+long-float
      (#.sb!vm:complex-long-stack-sc-number
       (with-nfp (nfp)
         (complex
          (sb!sys:sap-ref-long nfp (* (sb!c:sc-offset-offset sc-offset)
                                      sb!vm:n-word-bytes))
          (sb!sys:sap-ref-long nfp (* (+ (sb!c:sc-offset-offset sc-offset)
                                         #!+sparc 4)
                                      sb!vm:n-word-bytes)))))
      (#.sb!vm:control-stack-sc-number
       (sb!kernel:stack-ref fp (sb!c:sc-offset-offset sc-offset)))
      (#.sb!vm:character-stack-sc-number
       (with-nfp (nfp)
         (code-char (sb!sys:sap-ref-32 nfp (* (sb!c:sc-offset-offset sc-offset)
                                              sb!vm:n-word-bytes)))))
      (#.sb!vm:unsigned-stack-sc-number
       (with-nfp (nfp)
         (sb!sys:sap-ref-32 nfp (* (sb!c:sc-offset-offset sc-offset)
                                   sb!vm:n-word-bytes))))
      (#.sb!vm:signed-stack-sc-number
       (with-nfp (nfp)
         (sb!sys:signed-sap-ref-32 nfp (* (sb!c:sc-offset-offset sc-offset)
                                          sb!vm:n-word-bytes))))
      (#.sb!vm:sap-stack-sc-number
       (with-nfp (nfp)
         (sb!sys:sap-ref-sap nfp (* (sb!c:sc-offset-offset sc-offset)
                                    sb!vm:n-word-bytes)))))))

#!+(or x86 x86-64)
(defun sub-access-debug-var-slot (fp sc-offset &optional escaped)
  (declare (type system-area-pointer fp))
  (macrolet ((with-escaped-value ((var) &body forms)
               `(if escaped
                    (let ((,var (sb!vm:context-register
                                 escaped
                                 (sb!c:sc-offset-offset sc-offset))))
                      ,@forms)
                    :invalid-value-for-unescaped-register-storage))
             (escaped-float-value (format)
               `(if escaped
                    (sb!vm:context-float-register
                     escaped (sb!c:sc-offset-offset sc-offset) ',format)
                    :invalid-value-for-unescaped-register-storage))
             (escaped-complex-float-value (format)
               `(if escaped
                    (complex
                     (sb!vm:context-float-register
                      escaped (sb!c:sc-offset-offset sc-offset) ',format)
                     (sb!vm:context-float-register
                      escaped (1+ (sb!c:sc-offset-offset sc-offset)) ',format))
                    :invalid-value-for-unescaped-register-storage)))
    (ecase (sb!c:sc-offset-scn sc-offset)
      ((#.sb!vm:any-reg-sc-number #.sb!vm:descriptor-reg-sc-number)
       (without-gcing
        (with-escaped-value (val)
          (make-lisp-obj val nil))))
      (#.sb!vm:character-reg-sc-number
       (with-escaped-value (val)
         (code-char val)))
      (#.sb!vm:sap-reg-sc-number
       (with-escaped-value (val)
         (int-sap val)))
      (#.sb!vm:signed-reg-sc-number
       (with-escaped-value (val)
         (if (logbitp (1- sb!vm:n-word-bits) val)
             (logior val (ash -1 sb!vm:n-word-bits))
             val)))
      (#.sb!vm:unsigned-reg-sc-number
       (with-escaped-value (val)
         val))
      (#.sb!vm:single-reg-sc-number
       (escaped-float-value single-float))
      (#.sb!vm:double-reg-sc-number
       (escaped-float-value double-float))
      #!+long-float
      (#.sb!vm:long-reg-sc-number
       (escaped-float-value long-float))
      (#.sb!vm:complex-single-reg-sc-number
       (escaped-complex-float-value single-float))
      (#.sb!vm:complex-double-reg-sc-number
       (escaped-complex-float-value double-float))
      #!+long-float
      (#.sb!vm:complex-long-reg-sc-number
       (escaped-complex-float-value long-float))
      (#.sb!vm:single-stack-sc-number
       (sap-ref-single fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                                sb!vm:n-word-bytes))))
      (#.sb!vm:double-stack-sc-number
       (sap-ref-double fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                                sb!vm:n-word-bytes))))
      #!+long-float
      (#.sb!vm:long-stack-sc-number
       (sap-ref-long fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 3)
                              sb!vm:n-word-bytes))))
      (#.sb!vm:complex-single-stack-sc-number
       (complex
        (sap-ref-single fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                                 sb!vm:n-word-bytes)))
        (sap-ref-single fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                                 sb!vm:n-word-bytes)))))
      (#.sb!vm:complex-double-stack-sc-number
       (complex
        (sap-ref-double fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                                 sb!vm:n-word-bytes)))
        (sap-ref-double fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 4)
                                 sb!vm:n-word-bytes)))))
      #!+long-float
      (#.sb!vm:complex-long-stack-sc-number
       (complex
        (sap-ref-long fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 3)
                               sb!vm:n-word-bytes)))
        (sap-ref-long fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 6)
                               sb!vm:n-word-bytes)))))
      (#.sb!vm:control-stack-sc-number
       (stack-ref fp (sb!c:sc-offset-offset sc-offset)))
      (#.sb!vm:character-stack-sc-number
       (code-char
        (sap-ref-word fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                               sb!vm:n-word-bytes)))))
      (#.sb!vm:unsigned-stack-sc-number
       (sap-ref-word fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                              sb!vm:n-word-bytes))))
      (#.sb!vm:signed-stack-sc-number
       (signed-sap-ref-word fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                                     sb!vm:n-word-bytes))))
      (#.sb!vm:sap-stack-sc-number
       (sap-ref-sap fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                             sb!vm:n-word-bytes)))))))

;;; This stores value as the value of DEBUG-VAR in FRAME. In the
;;; COMPILED-DEBUG-VAR case, access the current value to determine if
;;; it is an indirect value cell. This occurs when the variable is
;;; both closed over and set.
(defun %set-debug-var-value (debug-var frame new-value)
  (aver (typep frame 'compiled-frame))
  (let ((old-value (access-compiled-debug-var-slot debug-var frame)))
    (if (indirect-value-cell-p old-value)
        (value-cell-set old-value new-value)
        (set-compiled-debug-var-slot debug-var frame new-value)))
  new-value)

;;; This stores VALUE for the variable represented by debug-var
;;; relative to the frame. This assumes the location directly contains
;;; the variable's value; that is, there is no indirect value cell
;;; currently there in case the variable is both closed over and set.
(defun set-compiled-debug-var-slot (debug-var frame value)
  (let ((escaped (compiled-frame-escaped frame)))
    (if escaped
        (sub-set-debug-var-slot (frame-pointer frame)
                                (compiled-debug-var-sc-offset debug-var)
                                value escaped)
        (sub-set-debug-var-slot
         (frame-pointer frame)
         (or (compiled-debug-var-save-sc-offset debug-var)
             (compiled-debug-var-sc-offset debug-var))
         value))))

#!-(or x86 x86-64)
(defun sub-set-debug-var-slot (fp sc-offset value &optional escaped)
  (macrolet ((set-escaped-value (val)
               `(if escaped
                    (setf (sb!vm:context-register
                           escaped
                           (sb!c:sc-offset-offset sc-offset))
                          ,val)
                    value))
             (set-escaped-float-value (format val)
               `(if escaped
                    (setf (sb!vm:context-float-register
                           escaped
                           (sb!c:sc-offset-offset sc-offset)
                           ',format)
                          ,val)
                    value))
             (with-nfp ((var) &body body)
               `(let ((,var (if escaped
                                (int-sap
                                 (sb!vm:context-register escaped
                                                         sb!vm::nfp-offset))
                                #!-alpha
                                (sap-ref-sap fp
                                             (* nfp-save-offset
                                                sb!vm:n-word-bytes))
                                #!+alpha
                                (sb!vm::make-number-stack-pointer
                                 (sap-ref-32 fp
                                             (* nfp-save-offset
                                                sb!vm:n-word-bytes))))))
                  ,@body)))
    (ecase (sb!c:sc-offset-scn sc-offset)
      ((#.sb!vm:any-reg-sc-number
        #.sb!vm:descriptor-reg-sc-number
        #!+rt #.sb!vm:word-pointer-reg-sc-number)
       (without-gcing
        (set-escaped-value
          (get-lisp-obj-address value))))
      (#.sb!vm:character-reg-sc-number
       (set-escaped-value (char-code value)))
      (#.sb!vm:sap-reg-sc-number
       (set-escaped-value (sap-int value)))
      (#.sb!vm:signed-reg-sc-number
       (set-escaped-value (logand value (1- (ash 1 sb!vm:n-word-bits)))))
      (#.sb!vm:unsigned-reg-sc-number
       (set-escaped-value value))
      (#.sb!vm:non-descriptor-reg-sc-number
       (error "Local non-descriptor register access?"))
      (#.sb!vm:interior-reg-sc-number
       (error "Local interior register access?"))
      (#.sb!vm:single-reg-sc-number
       (set-escaped-float-value single-float value))
      (#.sb!vm:double-reg-sc-number
       (set-escaped-float-value double-float value))
      #!+long-float
      (#.sb!vm:long-reg-sc-number
       (set-escaped-float-value long-float value))
      (#.sb!vm:complex-single-reg-sc-number
       (when escaped
         (setf (sb!vm:context-float-register escaped
                                             (sb!c:sc-offset-offset sc-offset)
                                             'single-float)
               (realpart value))
         (setf (sb!vm:context-float-register
                escaped (1+ (sb!c:sc-offset-offset sc-offset))
                'single-float)
               (imagpart value)))
       value)
      (#.sb!vm:complex-double-reg-sc-number
       (when escaped
         (setf (sb!vm:context-float-register
                escaped (sb!c:sc-offset-offset sc-offset) 'double-float)
               (realpart value))
         (setf (sb!vm:context-float-register
                escaped
                (+ (sb!c:sc-offset-offset sc-offset) #!+sparc 2 #!-sparc 1)
                'double-float)
               (imagpart value)))
       value)
      #!+long-float
      (#.sb!vm:complex-long-reg-sc-number
       (when escaped
         (setf (sb!vm:context-float-register
                escaped (sb!c:sc-offset-offset sc-offset) 'long-float)
               (realpart value))
         (setf (sb!vm:context-float-register
                escaped
                (+ (sb!c:sc-offset-offset sc-offset) #!+sparc 4)
                'long-float)
               (imagpart value)))
       value)
      (#.sb!vm:single-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-single nfp (* (sb!c:sc-offset-offset sc-offset)
                                      sb!vm:n-word-bytes))
               (the single-float value))))
      (#.sb!vm:double-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-double nfp (* (sb!c:sc-offset-offset sc-offset)
                                      sb!vm:n-word-bytes))
               (the double-float value))))
      #!+long-float
      (#.sb!vm:long-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-long nfp (* (sb!c:sc-offset-offset sc-offset)
                                    sb!vm:n-word-bytes))
               (the long-float value))))
      (#.sb!vm:complex-single-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-single
                nfp (* (sb!c:sc-offset-offset sc-offset) sb!vm:n-word-bytes))
               (the single-float (realpart value)))
         (setf (sap-ref-single
                nfp (* (1+ (sb!c:sc-offset-offset sc-offset))
                       sb!vm:n-word-bytes))
               (the single-float (realpart value)))))
      (#.sb!vm:complex-double-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-double
                nfp (* (sb!c:sc-offset-offset sc-offset) sb!vm:n-word-bytes))
               (the double-float (realpart value)))
         (setf (sap-ref-double
                nfp (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                       sb!vm:n-word-bytes))
               (the double-float (realpart value)))))
      #!+long-float
      (#.sb!vm:complex-long-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-long
                nfp (* (sb!c:sc-offset-offset sc-offset) sb!vm:n-word-bytes))
               (the long-float (realpart value)))
         (setf (sap-ref-long
                nfp (* (+ (sb!c:sc-offset-offset sc-offset) #!+sparc 4)
                       sb!vm:n-word-bytes))
               (the long-float (realpart value)))))
      (#.sb!vm:control-stack-sc-number
       (setf (stack-ref fp (sb!c:sc-offset-offset sc-offset)) value))
      (#.sb!vm:character-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-32 nfp (* (sb!c:sc-offset-offset sc-offset)
                                         sb!vm:n-word-bytes))
               (char-code (the character value)))))
      (#.sb!vm:unsigned-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-32 nfp (* (sb!c:sc-offset-offset sc-offset)
                                  sb!vm:n-word-bytes))
               (the (unsigned-byte 32) value))))
      (#.sb!vm:signed-stack-sc-number
       (with-nfp (nfp)
         (setf (signed-sap-ref-32 nfp (* (sb!c:sc-offset-offset sc-offset)
                                         sb!vm:n-word-bytes))
               (the (signed-byte 32) value))))
      (#.sb!vm:sap-stack-sc-number
       (with-nfp (nfp)
         (setf (sap-ref-sap nfp (* (sb!c:sc-offset-offset sc-offset)
                                   sb!vm:n-word-bytes))
               (the system-area-pointer value)))))))

#!+(or x86 x86-64)
(defun sub-set-debug-var-slot (fp sc-offset value &optional escaped)
  (macrolet ((set-escaped-value (val)
               `(if escaped
                    (setf (sb!vm:context-register
                           escaped
                           (sb!c:sc-offset-offset sc-offset))
                          ,val)
                    value)))
    (ecase (sb!c:sc-offset-scn sc-offset)
      ((#.sb!vm:any-reg-sc-number #.sb!vm:descriptor-reg-sc-number)
       (without-gcing
        (set-escaped-value
          (get-lisp-obj-address value))))
      (#.sb!vm:character-reg-sc-number
       (set-escaped-value (char-code value)))
      (#.sb!vm:sap-reg-sc-number
       (set-escaped-value (sap-int value)))
      (#.sb!vm:signed-reg-sc-number
       (set-escaped-value (logand value (1- (ash 1 sb!vm:n-word-bits)))))
      (#.sb!vm:unsigned-reg-sc-number
       (set-escaped-value value))
      (#.sb!vm:single-reg-sc-number
        #+nil ;; don't have escaped floats.
       (set-escaped-float-value single-float value))
      (#.sb!vm:double-reg-sc-number
        #+nil ;;  don't have escaped floats -- still in npx?
       (set-escaped-float-value double-float value))
      #!+long-float
      (#.sb!vm:long-reg-sc-number
        #+nil ;;  don't have escaped floats -- still in npx?
       (set-escaped-float-value long-float value))
      (#.sb!vm:single-stack-sc-number
       (setf (sap-ref-single
              fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                       sb!vm:n-word-bytes)))
             (the single-float value)))
      (#.sb!vm:double-stack-sc-number
       (setf (sap-ref-double
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                       sb!vm:n-word-bytes)))
             (the double-float value)))
      #!+long-float
      (#.sb!vm:long-stack-sc-number
       (setf (sap-ref-long
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 3)
                       sb!vm:n-word-bytes)))
             (the long-float value)))
      (#.sb!vm:complex-single-stack-sc-number
       (setf (sap-ref-single
              fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                       sb!vm:n-word-bytes)))
             (realpart (the (complex single-float) value)))
       (setf (sap-ref-single
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                       sb!vm:n-word-bytes)))
             (imagpart (the (complex single-float) value))))
      (#.sb!vm:complex-double-stack-sc-number
       (setf (sap-ref-double
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 2)
                       sb!vm:n-word-bytes)))
             (realpart (the (complex double-float) value)))
       (setf (sap-ref-double
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 4)
                       sb!vm:n-word-bytes)))
             (imagpart (the (complex double-float) value))))
      #!+long-float
      (#.sb!vm:complex-long-stack-sc-number
       (setf (sap-ref-long
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 3)
                       sb!vm:n-word-bytes)))
             (realpart (the (complex long-float) value)))
       (setf (sap-ref-long
              fp (- (* (+ (sb!c:sc-offset-offset sc-offset) 6)
                       sb!vm:n-word-bytes)))
             (imagpart (the (complex long-float) value))))
      (#.sb!vm:control-stack-sc-number
       (setf (stack-ref fp (sb!c:sc-offset-offset sc-offset)) value))
      (#.sb!vm:character-stack-sc-number
       (setf (sap-ref-word fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                                    sb!vm:n-word-bytes)))
             (char-code (the character value))))
      (#.sb!vm:unsigned-stack-sc-number
       (setf (sap-ref-word fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                                    sb!vm:n-word-bytes)))
             (the sb!vm:word value)))
      (#.sb!vm:signed-stack-sc-number
       (setf (signed-sap-ref-word
              fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                       sb!vm:n-word-bytes)))
             (the (signed-byte #.sb!vm:n-word-bits) value)))
      (#.sb!vm:sap-stack-sc-number
       (setf (sap-ref-sap fp (- (* (1+ (sb!c:sc-offset-offset sc-offset))
                                          sb!vm:n-word-bytes)))
             (the system-area-pointer value))))))

;;; The method for setting and accessing COMPILED-DEBUG-VAR values use
;;; this to determine if the value stored is the actual value or an
;;; indirection cell.
(defun indirect-value-cell-p (x)
  (and (= (lowtag-of x) sb!vm:other-pointer-lowtag)
       (= (widetag-of x) sb!vm:value-cell-header-widetag)))

;;; Return three values reflecting the validity of DEBUG-VAR's value
;;; at BASIC-CODE-LOCATION:
;;;   :VALID    The value is known to be available.
;;;   :INVALID  The value is known to be unavailable.
;;;   :UNKNOWN  The value's availability is unknown.
;;;
;;; If the variable is always alive, then it is valid. If the
;;; code-location is unknown, then the variable's validity is
;;; :unknown. Once we've called CODE-LOCATION-UNKNOWN-P, we know the
;;; live-set information has been cached in the code-location.
(defun debug-var-validity (debug-var basic-code-location)
  (etypecase debug-var
    (compiled-debug-var
     (compiled-debug-var-validity debug-var basic-code-location))
    ;; (There used to be more cases back before sbcl-0.7.0, when
    ;; we did special tricks to debug the IR1 interpreter.)
    ))

;;; This is the method for DEBUG-VAR-VALIDITY for COMPILED-DEBUG-VARs.
;;; For safety, make sure basic-code-location is what we think.
(defun compiled-debug-var-validity (debug-var basic-code-location)
  (declare (type compiled-code-location basic-code-location))
  (cond ((debug-var-alive-p debug-var)
         (let ((debug-fun (code-location-debug-fun basic-code-location)))
           (if (>= (compiled-code-location-pc basic-code-location)
                   (sb!c::compiled-debug-fun-start-pc
                    (compiled-debug-fun-compiler-debug-fun debug-fun)))
               :valid
               :invalid)))
        ((code-location-unknown-p basic-code-location) :unknown)
        (t
         (let ((pos (position debug-var
                              (debug-fun-debug-vars
                               (code-location-debug-fun
                                basic-code-location)))))
           (unless pos
             (error 'unknown-debug-var
                    :debug-var debug-var
                    :debug-fun
                    (code-location-debug-fun basic-code-location)))
           ;; There must be live-set info since basic-code-location is known.
           (if (zerop (sbit (compiled-code-location-live-set
                             basic-code-location)
                            pos))
               :invalid
               :valid)))))
\f
;;;; sources

;;; This code produces and uses what we call source-paths. A
;;; source-path is a list whose first element is a form number as
;;; returned by CODE-LOCATION-FORM-NUMBER and whose last element is a
;;; top level form number as returned by
;;; CODE-LOCATION-TOPLEVEL-FORM-NUMBER. The elements from the last to
;;; the first, exclusively, are the numbered subforms into which to
;;; descend. For example:
;;;    (defun foo (x)
;;;      (let ((a (aref x 3)))
;;;     (cons a 3)))
;;; The call to AREF in this example is form number 5. Assuming this
;;; DEFUN is the 11'th top level form, the source-path for the AREF
;;; call is as follows:
;;;    (5 1 0 1 3 11)
;;; Given the DEFUN, 3 gets you the LET, 1 gets you the bindings, 0
;;; gets the first binding, and 1 gets the AREF form.

;;; This returns a table mapping form numbers to source-paths. A
;;; source-path indicates a descent into the TOPLEVEL-FORM form,
;;; going directly to the subform corressponding to the form number.
;;;
;;; The vector elements are in the same format as the compiler's
;;; NODE-SOURCE-PATH; that is, the first element is the form number and
;;; the last is the TOPLEVEL-FORM number.
(defun form-number-translations (form tlf-number)
  (let ((seen nil)
        (translations (make-array 12 :fill-pointer 0 :adjustable t)))
    (labels ((translate1 (form path)
               (unless (member form seen)
                 (push form seen)
                 (vector-push-extend (cons (fill-pointer translations) path)
                                     translations)
                 (let ((pos 0)
                       (subform form)
                       (trail form))
                   (declare (fixnum pos))
                   (macrolet ((frob ()
                                '(progn
                                  (when (atom subform) (return))
                                  (let ((fm (car subform)))
                                    (when (consp fm)
                                      (translate1 fm (cons pos path)))
                                    (incf pos))
                                  (setq subform (cdr subform))
                                  (when (eq subform trail) (return)))))
                     (loop
                       (frob)
                       (frob)
                       (setq trail (cdr trail))))))))
      (translate1 form (list tlf-number)))
    (coerce translations 'simple-vector)))

;;; FORM is a top level form, and path is a source-path into it. This
;;; returns the form indicated by the source-path. Context is the
;;; number of enclosing forms to return instead of directly returning
;;; the source-path form. When context is non-zero, the form returned
;;; contains a marker, #:****HERE****, immediately before the form
;;; indicated by path.
(defun source-path-context (form path context)
  (declare (type unsigned-byte context))
  ;; Get to the form indicated by path or the enclosing form indicated
  ;; by context and path.
  (let ((path (reverse (butlast (cdr path)))))
    (dotimes (i (- (length path) context))
      (let ((index (first path)))
        (unless (and (listp form) (< index (length form)))
          (error "Source path no longer exists."))
        (setq form (elt form index))
        (setq path (rest path))))
    ;; Recursively rebuild the source form resulting from the above
    ;; descent, copying the beginning of each subform up to the next
    ;; subform we descend into according to path. At the bottom of the
    ;; recursion, we return the form indicated by path preceded by our
    ;; marker, and this gets spliced into the resulting list structure
    ;; on the way back up.
    (labels ((frob (form path level)
               (if (or (zerop level) (null path))
                   (if (zerop context)
                       form
                       `(#:***here*** ,form))
                   (let ((n (first path)))
                     (unless (and (listp form) (< n (length form)))
                       (error "Source path no longer exists."))
                     (let ((res (frob (elt form n) (rest path) (1- level))))
                       (nconc (subseq form 0 n)
                              (cons res (nthcdr (1+ n) form))))))))
      (frob form path context))))
\f
;;;; PREPROCESS-FOR-EVAL

;;; Return a function of one argument that evaluates form in the
;;; lexical context of the BASIC-CODE-LOCATION LOC, or signal a
;;; NO-DEBUG-VARS condition when the LOC's DEBUG-FUN has no
;;; DEBUG-VAR information available.
;;;
;;; The returned function takes the frame to get values from as its
;;; argument, and it returns the values of FORM. The returned function
;;; can signal the following conditions: INVALID-VALUE,
;;; AMBIGUOUS-VAR-NAME, and FRAME-FUN-MISMATCH.
(defun preprocess-for-eval (form loc)
  (declare (type code-location loc))
  (let ((n-frame (gensym))
        (fun (code-location-debug-fun loc)))
    (unless (debug-var-info-available fun)
      (debug-signal 'no-debug-vars :debug-fun fun))
    (sb!int:collect ((binds)
                     (specs))
      (do-debug-fun-vars (var fun)
        (let ((validity (debug-var-validity var loc)))
          (unless (eq validity :invalid)
            (let* ((sym (debug-var-symbol var))
                   (found (assoc sym (binds))))
              (if found
                  (setf (second found) :ambiguous)
                  (binds (list sym validity var)))))))
      (dolist (bind (binds))
        (let ((name (first bind))
              (var (third bind)))
          (ecase (second bind)
            (:valid
             (specs `(,name (debug-var-value ',var ,n-frame))))
            (:unknown
             (specs `(,name (debug-signal 'invalid-value
                                          :debug-var ',var
                                          :frame ,n-frame))))
            (:ambiguous
             (specs `(,name (debug-signal 'ambiguous-var-name
                                          :name ',name
                                          :frame ,n-frame)))))))
      (let ((res (coerce `(lambda (,n-frame)
                            (declare (ignorable ,n-frame))
                            (symbol-macrolet ,(specs) ,form))
                         'function)))
        (lambda (frame)
          ;; This prevents these functions from being used in any
          ;; location other than a function return location, so maybe
          ;; this should only check whether FRAME's DEBUG-FUN is the
          ;; same as LOC's.
          (unless (code-location= (frame-code-location frame) loc)
            (debug-signal 'frame-fun-mismatch
                          :code-location loc :form form :frame frame))
          (funcall res frame))))))
\f
;;;; breakpoints

;;;; user-visible interface

;;; Create and return a breakpoint. When program execution encounters
;;; the breakpoint, the system calls HOOK-FUN. HOOK-FUN takes the
;;; current frame for the function in which the program is running and
;;; the breakpoint object.
;;;
;;; WHAT and KIND determine where in a function the system invokes
;;; HOOK-FUN. WHAT is either a code-location or a DEBUG-FUN. KIND is
;;; one of :CODE-LOCATION, :FUN-START, or :FUN-END. Since the starts
;;; and ends of functions may not have code-locations representing
;;; them, designate these places by supplying WHAT as a DEBUG-FUN and
;;; KIND indicating the :FUN-START or :FUN-END. When WHAT is a
;;; DEBUG-FUN and kind is :FUN-END, then HOOK-FUN must take two
;;; additional arguments, a list of values returned by the function
;;; and a FUN-END-COOKIE.
;;;
;;; INFO is information supplied by and used by the user.
;;;
;;; FUN-END-COOKIE is a function. To implement :FUN-END
;;; breakpoints, the system uses starter breakpoints to establish the
;;; :FUN-END breakpoint for each invocation of the function. Upon
;;; each entry, the system creates a unique cookie to identify the
;;; invocation, and when the user supplies a function for this
;;; argument, the system invokes it on the frame and the cookie. The
;;; system later invokes the :FUN-END breakpoint hook on the same
;;; cookie. The user may save the cookie for comparison in the hook
;;; function.
;;;
;;; Signal an error if WHAT is an unknown code-location.
(defun make-breakpoint (hook-fun what
                        &key (kind :code-location) info fun-end-cookie)
  (etypecase what
    (code-location
     (when (code-location-unknown-p what)
       (error "cannot make a breakpoint at an unknown code location: ~S"
              what))
     (aver (eq kind :code-location))
     (let ((bpt (%make-breakpoint hook-fun what kind info)))
       (etypecase what
         (compiled-code-location
          ;; This slot is filled in due to calling CODE-LOCATION-UNKNOWN-P.
          (when (eq (compiled-code-location-kind what) :unknown-return)
            (let ((other-bpt (%make-breakpoint hook-fun what
                                               :unknown-return-partner
                                               info)))
              (setf (breakpoint-unknown-return-partner bpt) other-bpt)
              (setf (breakpoint-unknown-return-partner other-bpt) bpt))))
         ;; (There used to be more cases back before sbcl-0.7.0,,
         ;; when we did special tricks to debug the IR1
         ;; interpreter.)
         )
       bpt))
    (compiled-debug-fun
     (ecase kind
       (:fun-start
        (%make-breakpoint hook-fun what kind info))
       (:fun-end
        (unless (eq (sb!c::compiled-debug-fun-returns
                     (compiled-debug-fun-compiler-debug-fun what))
                    :standard)
          (error ":FUN-END breakpoints are currently unsupported ~
                  for the known return convention."))

        (let* ((bpt (%make-breakpoint hook-fun what kind info))
               (starter (compiled-debug-fun-end-starter what)))
          (unless starter
            (setf starter (%make-breakpoint #'list what :fun-start nil))
            (setf (breakpoint-hook-fun starter)
                  (fun-end-starter-hook starter what))
            (setf (compiled-debug-fun-end-starter what) starter))
          (setf (breakpoint-start-helper bpt) starter)
          (push bpt (breakpoint-%info starter))
          (setf (breakpoint-cookie-fun bpt) fun-end-cookie)
          bpt))))))

;;; These are unique objects created upon entry into a function by a
;;; :FUN-END breakpoint's starter hook. These are only created
;;; when users supply :FUN-END-COOKIE to MAKE-BREAKPOINT. Also,
;;; the :FUN-END breakpoint's hook is called on the same cookie
;;; when it is created.
(defstruct (fun-end-cookie
            (:print-object (lambda (obj str)
                             (print-unreadable-object (obj str :type t))))
            (:constructor make-fun-end-cookie (bogus-lra debug-fun))
            (:copier nil))
  ;; a pointer to the bogus-lra created for :FUN-END breakpoints
  bogus-lra
  ;; the DEBUG-FUN associated with this cookie
  debug-fun)

;;; This maps bogus-lra-components to cookies, so that
;;; HANDLE-FUN-END-BREAKPOINT can find the appropriate cookie for the
;;; breakpoint hook.
(defvar *fun-end-cookies* (make-hash-table :test 'eq :synchronized t))

;;; This returns a hook function for the start helper breakpoint
;;; associated with a :FUN-END breakpoint. The returned function
;;; makes a fake LRA that all returns go through, and this piece of
;;; fake code actually breaks. Upon return from the break, the code
;;; provides the returnee with any values. Since the returned function
;;; effectively activates FUN-END-BPT on each entry to DEBUG-FUN's
;;; function, we must establish breakpoint-data about FUN-END-BPT.
(defun fun-end-starter-hook (starter-bpt debug-fun)
  (declare (type breakpoint starter-bpt)
           (type compiled-debug-fun debug-fun))
  (lambda (frame breakpoint)
    (declare (ignore breakpoint)
             (type frame frame))
    (let ((lra-sc-offset
           (sb!c::compiled-debug-fun-return-pc
            (compiled-debug-fun-compiler-debug-fun debug-fun))))
      (multiple-value-bind (lra component offset)
          (make-bogus-lra
           (get-context-value frame
                              lra-save-offset
                              lra-sc-offset))
        (setf (get-context-value frame
                                 lra-save-offset
                                 lra-sc-offset)
              lra)
        (let ((end-bpts (breakpoint-%info starter-bpt)))
          (let ((data (breakpoint-data component offset)))
            (setf (breakpoint-data-breakpoints data) end-bpts)
            (dolist (bpt end-bpts)
              (setf (breakpoint-internal-data bpt) data)))
          (let ((cookie (make-fun-end-cookie lra debug-fun)))
            (setf (gethash component *fun-end-cookies*) cookie)
            (dolist (bpt end-bpts)
              (let ((fun (breakpoint-cookie-fun bpt)))
                (when fun (funcall fun frame cookie))))))))))

;;; This takes a FUN-END-COOKIE and a frame, and it returns
;;; whether the cookie is still valid. A cookie becomes invalid when
;;; the frame that established the cookie has exited. Sometimes cookie
;;; holders are unaware of cookie invalidation because their
;;; :FUN-END breakpoint hooks didn't run due to THROW'ing.
;;;
;;; This takes a frame as an efficiency hack since the user probably
;;; has a frame object in hand when using this routine, and it saves
;;; repeated parsing of the stack and consing when asking whether a
;;; series of cookies is valid.
(defun fun-end-cookie-valid-p (frame cookie)
  (let ((lra (fun-end-cookie-bogus-lra cookie))
        (lra-sc-offset (sb!c::compiled-debug-fun-return-pc
                        (compiled-debug-fun-compiler-debug-fun
                         (fun-end-cookie-debug-fun cookie)))))
    (do ((frame frame (frame-down frame)))
        ((not frame) nil)
      (when (and (compiled-frame-p frame)
                 (#!-(or x86 x86-64) eq #!+(or x86 x86-64) sap=
                  lra
                  (get-context-value frame lra-save-offset lra-sc-offset)))
        (return t)))))
\f
;;;; ACTIVATE-BREAKPOINT

;;; Cause the system to invoke the breakpoint's hook function until
;;; the next call to DEACTIVATE-BREAKPOINT or DELETE-BREAKPOINT. The
;;; system invokes breakpoint hook functions in the opposite order
;;; that you activate them.
(defun activate-breakpoint (breakpoint)
  (when (eq (breakpoint-status breakpoint) :deleted)
    (error "cannot activate a deleted breakpoint: ~S" breakpoint))
  (unless (eq (breakpoint-status breakpoint) :active)
    (ecase (breakpoint-kind breakpoint)
      (:code-location
       (let ((loc (breakpoint-what breakpoint)))
         (etypecase loc
           (compiled-code-location
            (activate-compiled-code-location-breakpoint breakpoint)
            (let ((other (breakpoint-unknown-return-partner breakpoint)))
              (when other
                (activate-compiled-code-location-breakpoint other))))
           ;; (There used to be more cases back before sbcl-0.7.0, when
           ;; we did special tricks to debug the IR1 interpreter.)
           )))
      (:fun-start
       (etypecase (breakpoint-what breakpoint)
         (compiled-debug-fun
          (activate-compiled-fun-start-breakpoint breakpoint))
         ;; (There used to be more cases back before sbcl-0.7.0, when
         ;; we did special tricks to debug the IR1 interpreter.)
         ))
      (:fun-end
       (etypecase (breakpoint-what breakpoint)
         (compiled-debug-fun
          (let ((starter (breakpoint-start-helper breakpoint)))
            (unless (eq (breakpoint-status starter) :active)
              ;; may already be active by some other :FUN-END breakpoint
              (activate-compiled-fun-start-breakpoint starter)))
          (setf (breakpoint-status breakpoint) :active))
         ;; (There used to be more cases back before sbcl-0.7.0, when
         ;; we did special tricks to debug the IR1 interpreter.)
         ))))
  breakpoint)

(defun activate-compiled-code-location-breakpoint (breakpoint)
  (declare (type breakpoint breakpoint))
  (let ((loc (breakpoint-what breakpoint)))
    (declare (type compiled-code-location loc))
    (sub-activate-breakpoint
     breakpoint
     (breakpoint-data (compiled-debug-fun-component
                       (code-location-debug-fun loc))
                      (+ (compiled-code-location-pc loc)
                         (if (or (eq (breakpoint-kind breakpoint)
                                     :unknown-return-partner)
                                 (eq (compiled-code-location-kind loc)
                                     :single-value-return))
                             sb!vm:single-value-return-byte-offset
                             0))))))

(defun activate-compiled-fun-start-breakpoint (breakpoint)
  (declare (type breakpoint breakpoint))
  (let ((debug-fun (breakpoint-what breakpoint)))
    (sub-activate-breakpoint
     breakpoint
     (breakpoint-data (compiled-debug-fun-component debug-fun)
                      (sb!c::compiled-debug-fun-start-pc
                       (compiled-debug-fun-compiler-debug-fun
                        debug-fun))))))

(defun sub-activate-breakpoint (breakpoint data)
  (declare (type breakpoint breakpoint)
           (type breakpoint-data data))
  (setf (breakpoint-status breakpoint) :active)
  (without-interrupts
   (unless (breakpoint-data-breakpoints data)
     (setf (breakpoint-data-instruction data)
           (without-gcing
            (breakpoint-install (get-lisp-obj-address
                                 (breakpoint-data-component data))
                                (breakpoint-data-offset data)))))
   (setf (breakpoint-data-breakpoints data)
         (append (breakpoint-data-breakpoints data) (list breakpoint)))
   (setf (breakpoint-internal-data breakpoint) data)))
\f
;;;; DEACTIVATE-BREAKPOINT

;;; Stop the system from invoking the breakpoint's hook function.
(defun deactivate-breakpoint (breakpoint)
  (when (eq (breakpoint-status breakpoint) :active)
    (without-interrupts
     (let ((loc (breakpoint-what breakpoint)))
       (etypecase loc
         ((or compiled-code-location compiled-debug-fun)
          (deactivate-compiled-breakpoint breakpoint)
          (let ((other (breakpoint-unknown-return-partner breakpoint)))
            (when other
              (deactivate-compiled-breakpoint other))))
         ;; (There used to be more cases back before sbcl-0.7.0, when
         ;; we did special tricks to debug the IR1 interpreter.)
         ))))
  breakpoint)

(defun deactivate-compiled-breakpoint (breakpoint)
  (if (eq (breakpoint-kind breakpoint) :fun-end)
      (let ((starter (breakpoint-start-helper breakpoint)))
        (unless (find-if (lambda (bpt)
                           (and (not (eq bpt breakpoint))
                                (eq (breakpoint-status bpt) :active)))
                         (breakpoint-%info starter))
          (deactivate-compiled-breakpoint starter)))
      (let* ((data (breakpoint-internal-data breakpoint))
             (bpts (delete breakpoint (breakpoint-data-breakpoints data))))
        (setf (breakpoint-internal-data breakpoint) nil)
        (setf (breakpoint-data-breakpoints data) bpts)
        (unless bpts
          (without-gcing
           (breakpoint-remove (get-lisp-obj-address
                               (breakpoint-data-component data))
                              (breakpoint-data-offset data)
                              (breakpoint-data-instruction data)))
          (delete-breakpoint-data data))))
  (setf (breakpoint-status breakpoint) :inactive)
  breakpoint)
\f
;;;; BREAKPOINT-INFO

;;; Return the user-maintained info associated with breakpoint. This
;;; is SETF'able.
(defun breakpoint-info (breakpoint)
  (breakpoint-%info breakpoint))
(defun %set-breakpoint-info (breakpoint value)
  (setf (breakpoint-%info breakpoint) value)
  (let ((other (breakpoint-unknown-return-partner breakpoint)))
    (when other
      (setf (breakpoint-%info other) value))))
\f
;;;; BREAKPOINT-ACTIVE-P and DELETE-BREAKPOINT

(defun breakpoint-active-p (breakpoint)
  (ecase (breakpoint-status breakpoint)
    (:active t)
    ((:inactive :deleted) nil)))

;;; Free system storage and remove computational overhead associated
;;; with breakpoint. After calling this, breakpoint is completely
;;; impotent and can never become active again.
(defun delete-breakpoint (breakpoint)
  (let ((status (breakpoint-status breakpoint)))
    (unless (eq status :deleted)
      (when (eq status :active)
        (deactivate-breakpoint breakpoint))
      (setf (breakpoint-status breakpoint) :deleted)
      (let ((other (breakpoint-unknown-return-partner breakpoint)))
        (when other
          (setf (breakpoint-status other) :deleted)))
      (when (eq (breakpoint-kind breakpoint) :fun-end)
        (let* ((starter (breakpoint-start-helper breakpoint))
               (breakpoints (delete breakpoint
                                    (the list (breakpoint-info starter)))))
          (setf (breakpoint-info starter) breakpoints)
          (unless breakpoints
            (delete-breakpoint starter)
            (setf (compiled-debug-fun-end-starter
                   (breakpoint-what breakpoint))
                  nil))))))
  breakpoint)
\f
;;;; C call out stubs

;;; This actually installs the break instruction in the component. It
;;; returns the overwritten bits. You must call this in a context in
;;; which GC is disabled, so that Lisp doesn't move objects around
;;; that C is pointing to.
(sb!alien:define-alien-routine "breakpoint_install" sb!alien:unsigned-int
  (code-obj sb!alien:unsigned-long)
  (pc-offset sb!alien:int))

;;; This removes the break instruction and replaces the original
;;; instruction. You must call this in a context in which GC is disabled
;;; so Lisp doesn't move objects around that C is pointing to.
(sb!alien:define-alien-routine "breakpoint_remove" sb!alien:void
  (code-obj sb!alien:unsigned-long)
  (pc-offset sb!alien:int)
  (old-inst sb!alien:unsigned-int))

(sb!alien:define-alien-routine "breakpoint_do_displaced_inst" sb!alien:void
  (scp (* os-context-t))
  (orig-inst sb!alien:unsigned-int))

;;;; breakpoint handlers (layer between C and exported interface)

;;; This maps components to a mapping of offsets to BREAKPOINT-DATAs.
(defvar *component-breakpoint-offsets* (make-hash-table :test 'eq :synchronized t))

;;; This returns the BREAKPOINT-DATA object associated with component cross
;;; offset. If none exists, this makes one, installs it, and returns it.
(defun breakpoint-data (component offset &optional (create t))
  (flet ((install-breakpoint-data ()
           (when create
             (let ((data (make-breakpoint-data component offset)))
               (push (cons offset data)
                     (gethash component *component-breakpoint-offsets*))
               data))))
    (let ((offsets (gethash component *component-breakpoint-offsets*)))
      (if offsets
          (let ((data (assoc offset offsets)))
            (if data
                (cdr data)
                (install-breakpoint-data)))
          (install-breakpoint-data)))))

;;; We use this when there are no longer any active breakpoints
;;; corresponding to DATA.
(defun delete-breakpoint-data (data)
  ;; Again, this looks brittle. Is there no danger of being interrupted
  ;; here?
  (let* ((component (breakpoint-data-component data))
         (offsets (delete (breakpoint-data-offset data)
                          (gethash component *component-breakpoint-offsets*)
                          :key #'car)))
    (if offsets
        (setf (gethash component *component-breakpoint-offsets*) offsets)
        (remhash component *component-breakpoint-offsets*)))
  (values))

;;; The C handler for interrupts calls this when it has a
;;; debugging-tool break instruction. This does *not* handle all
;;; breaks; for example, it does not handle breaks for internal
;;; errors.
(defun handle-breakpoint (offset component signal-context)
  (let ((data (breakpoint-data component offset nil)))
    (unless data
      (error "unknown breakpoint in ~S at offset ~S"
              (debug-fun-name (debug-fun-from-pc component offset))
              offset))
    (let ((breakpoints (breakpoint-data-breakpoints data)))
      (if (or (null breakpoints)
              (eq (breakpoint-kind (car breakpoints)) :fun-end))
          (handle-fun-end-breakpoint-aux breakpoints data signal-context)
          (handle-breakpoint-aux breakpoints data
                                 offset component signal-context)))))

;;; This holds breakpoint-datas while invoking the breakpoint hooks
;;; associated with that particular component and location. While they
;;; are executing, if we hit the location again, we ignore the
;;; breakpoint to avoid infinite recursion. fun-end breakpoints
;;; must work differently since the breakpoint-data is unique for each
;;; invocation.
(defvar *executing-breakpoint-hooks* nil)

;;; This handles code-location and DEBUG-FUN :FUN-START
;;; breakpoints.
(defun handle-breakpoint-aux (breakpoints data offset component signal-context)
  (unless breakpoints
    (bug "breakpoint that nobody wants"))
  (unless (member data *executing-breakpoint-hooks*)
    (let ((*executing-breakpoint-hooks* (cons data
                                              *executing-breakpoint-hooks*)))
      (invoke-breakpoint-hooks breakpoints signal-context)))
  ;; At this point breakpoints may not hold the same list as
  ;; BREAKPOINT-DATA-BREAKPOINTS since invoking hooks may have allowed
  ;; a breakpoint deactivation. In fact, if all breakpoints were
  ;; deactivated then data is invalid since it was deleted and so the
  ;; correct one must be looked up if it is to be used. If there are
  ;; no more breakpoints active at this location, then the normal
  ;; instruction has been put back, and we do not need to
  ;; DO-DISPLACED-INST.
  (setf data (breakpoint-data component offset nil))
  (when (and data (breakpoint-data-breakpoints data))
    ;; The breakpoint is still active, so we need to execute the
    ;; displaced instruction and leave the breakpoint instruction
    ;; behind. The best way to do this is different on each machine,
    ;; so we just leave it up to the C code.
    (breakpoint-do-displaced-inst signal-context
                                  (breakpoint-data-instruction data))
    ;; Some platforms have no usable sigreturn() call.  If your
    ;; implementation of arch_do_displaced_inst() _does_ sigreturn(),
    ;; it's polite to warn here
    #!+(and sparc solaris)
    (error "BREAKPOINT-DO-DISPLACED-INST returned?")))

(defun invoke-breakpoint-hooks (breakpoints signal-context)
  (let* ((frame (signal-context-frame signal-context)))
    (dolist (bpt breakpoints)
      (funcall (breakpoint-hook-fun bpt)
               frame
               ;; If this is an :UNKNOWN-RETURN-PARTNER, then pass the
               ;; hook function the original breakpoint, so that users
               ;; aren't forced to confront the fact that some
               ;; breakpoints really are two.
               (if (eq (breakpoint-kind bpt) :unknown-return-partner)
                   (breakpoint-unknown-return-partner bpt)
                   bpt)))))

(defun signal-context-frame (signal-context)
  (let* ((scp
          (locally
            (declare (optimize (inhibit-warnings 3)))
            (sb!alien:sap-alien signal-context (* os-context-t))))
         (cfp (int-sap (sb!vm:context-register scp sb!vm::cfp-offset))))
    (compute-calling-frame cfp
                           (sb!vm:context-pc scp)
                           nil)))

(defun handle-fun-end-breakpoint (offset component context)
  (let ((data (breakpoint-data component offset nil)))
    (unless data
      (error "unknown breakpoint in ~S at offset ~S"
              (debug-fun-name (debug-fun-from-pc component offset))
              offset))
    (let ((breakpoints (breakpoint-data-breakpoints data)))
      (when breakpoints
        (aver (eq (breakpoint-kind (car breakpoints)) :fun-end))
        (handle-fun-end-breakpoint-aux breakpoints data context)))))

;;; Either HANDLE-BREAKPOINT calls this for :FUN-END breakpoints
;;; [old C code] or HANDLE-FUN-END-BREAKPOINT calls this directly
;;; [new C code].
(defun handle-fun-end-breakpoint-aux (breakpoints data signal-context)
  ;; FIXME: This looks brittle: what if we are interrupted somewhere
  ;; here? ...or do we have interrupts disabled here?
  (delete-breakpoint-data data)
  (let* ((scp
          (locally
            (declare (optimize (inhibit-warnings 3)))
            (sb!alien:sap-alien signal-context (* os-context-t))))
         (frame (signal-context-frame signal-context))
         (component (breakpoint-data-component data))
         (cookie (gethash component *fun-end-cookies*)))
    (remhash component *fun-end-cookies*)
    (dolist (bpt breakpoints)
      (funcall (breakpoint-hook-fun bpt)
               frame bpt
               (get-fun-end-breakpoint-values scp)
               cookie))))

(defun get-fun-end-breakpoint-values (scp)
  (let ((ocfp (int-sap (sb!vm:context-register
                        scp
                        #!-(or x86 x86-64) sb!vm::ocfp-offset
                        #!+(or x86 x86-64) sb!vm::ebx-offset)))
        (nargs (make-lisp-obj
                (sb!vm:context-register scp sb!vm::nargs-offset)))
        (reg-arg-offsets '#.sb!vm::*register-arg-offsets*)
        (results nil))
    (without-gcing
     (dotimes (arg-num nargs)
       (push (if reg-arg-offsets
                 (make-lisp-obj
                  (sb!vm:context-register scp (pop reg-arg-offsets)))
               (stack-ref ocfp arg-num))
             results)))
    (nreverse results)))
\f
;;;; MAKE-BOGUS-LRA (used for :FUN-END breakpoints)

(defconstant bogus-lra-constants
  #!-(or x86 x86-64) 2 #!+(or x86 x86-64) 3)
(defconstant known-return-p-slot
  (+ sb!vm:code-constants-offset #!-(or x86 x86-64) 1 #!+(or x86 x86-64) 2))

;;; Make a bogus LRA object that signals a breakpoint trap when
;;; returned to. If the breakpoint trap handler returns, REAL-LRA is
;;; returned to. Three values are returned: the bogus LRA object, the
;;; code component it is part of, and the PC offset for the trap
;;; instruction.
(defun make-bogus-lra (real-lra &optional known-return-p)
  (without-gcing
   ;; These are really code labels, not variables: but this way we get
   ;; their addresses.
   (let* ((src-start (foreign-symbol-sap "fun_end_breakpoint_guts"))
          (src-end (foreign-symbol-sap "fun_end_breakpoint_end"))
          (trap-loc (foreign-symbol-sap "fun_end_breakpoint_trap"))
          (length (sap- src-end src-start))
          (code-object
           (%primitive sb!c:allocate-code-object (1+ bogus-lra-constants)
                       length))
          (dst-start (code-instructions code-object)))
     (declare (type system-area-pointer
                    src-start src-end dst-start trap-loc)
              (type index length))
     (setf (%code-debug-info code-object) :bogus-lra)
     (setf (code-header-ref code-object sb!vm:code-trace-table-offset-slot)
           length)
     #!-(or x86 x86-64)
     (setf (code-header-ref code-object real-lra-slot) real-lra)
     #!+(or x86 x86-64)
     (multiple-value-bind (offset code) (compute-lra-data-from-pc real-lra)
       (setf (code-header-ref code-object real-lra-slot) code)
       (setf (code-header-ref code-object (1+ real-lra-slot)) offset))
     (setf (code-header-ref code-object known-return-p-slot)
           known-return-p)
     (system-area-ub8-copy src-start 0 dst-start 0 length)
     (sb!vm:sanctify-for-execution code-object)
     #!+(or x86 x86-64)
     (values dst-start code-object (sap- trap-loc src-start))
     #!-(or x86 x86-64)
     (let ((new-lra (make-lisp-obj (+ (sap-int dst-start)
                                      sb!vm:other-pointer-lowtag))))
       (set-header-data
        new-lra
        (logandc2 (+ sb!vm:code-constants-offset bogus-lra-constants 1)
                  1))
       (sb!vm:sanctify-for-execution code-object)
       (values new-lra code-object (sap- trap-loc src-start))))))
\f
;;;; miscellaneous

;;; This appears here because it cannot go with the DEBUG-FUN
;;; interface since DO-DEBUG-BLOCK-LOCATIONS isn't defined until after
;;; the DEBUG-FUN routines.

;;; Return a code-location before the body of a function and after all
;;; the arguments are in place; or if that location can't be
;;; determined due to a lack of debug information, return NIL.
(defun debug-fun-start-location (debug-fun)
  (etypecase debug-fun
    (compiled-debug-fun
     (code-location-from-pc debug-fun
                            (sb!c::compiled-debug-fun-start-pc
                             (compiled-debug-fun-compiler-debug-fun
                              debug-fun))
                            nil))
    ;; (There used to be more cases back before sbcl-0.7.0, when
    ;; we did special tricks to debug the IR1 interpreter.)
    ))

\f
;;;; Single-stepping

;;; The single-stepper works by inserting conditional trap instructions
;;; into the generated code (see src/compiler/*/call.lisp), currently:
;;;
;;;   1) Before the code generated for a function call that was
;;;      translated to a VOP
;;;   2) Just before the call instruction for a full call
;;;
;;; In both cases, the trap will only be executed if stepping has been
;;; enabled, in which case it'll ultimately be handled by
;;; HANDLE-SINGLE-STEP-TRAP, which will either signal a stepping condition,
;;; or replace the function that's about to be called with a wrapper
;;; which will signal the condition.

(defun handle-single-step-trap (kind callee-register-offset)
  (let ((context (nth-interrupt-context (1- *free-interrupt-context-index*))))
    ;; The following calls must get tail-call eliminated for
    ;; *STEP-FRAME* to get set correctly on non-x86.
    (if (= kind single-step-before-trap)
        (handle-single-step-before-trap context)
        (handle-single-step-around-trap context callee-register-offset))))

(defvar *step-frame* nil)

(defun handle-single-step-before-trap (context)
  (let ((step-info (single-step-info-from-context context)))
    ;; If there was not enough debug information available, there's no
    ;; sense in signaling the condition.
    (when step-info
      (let ((*step-frame*
             #!+(or x86 x86-64)
             (signal-context-frame (sb!alien::alien-sap context))
             #!-(or x86 x86-64)
             ;; KLUDGE: Use the first non-foreign frame as the
             ;; *STACK-TOP-HINT*. Getting the frame from the signal
             ;; context as on x86 would be cleaner, but
             ;; SIGNAL-CONTEXT-FRAME doesn't seem seem to work at all
             ;; on non-x86.
             (loop with frame = (frame-down (top-frame))
                   while frame
                   for dfun = (frame-debug-fun frame)
                   do (when (typep dfun 'compiled-debug-fun)
                        (return frame))
                   do (setf frame (frame-down frame)))))
        (sb!impl::step-form step-info
                            ;; We could theoretically store information in
                            ;; the debug-info about to determine the
                            ;; arguments here, but for now let's just pass
                            ;; on it.
                            :unknown)))))

;;; This function will replace the fdefn / function that was in the
;;; register at CALLEE-REGISTER-OFFSET with a wrapper function. To
;;; ensure that the full call will use the wrapper instead of the
;;; original, conditional trap must be emitted before the fdefn /
;;; function is converted into a raw address.
(defun handle-single-step-around-trap (context callee-register-offset)
  ;; Fetch the function / fdefn we're about to call from the
  ;; appropriate register.
  (let* ((callee (make-lisp-obj
                  (context-register context callee-register-offset)))
         (step-info (single-step-info-from-context context)))
    ;; If there was not enough debug information available, there's no
    ;; sense in signaling the condition.
    (unless step-info
      (return-from handle-single-step-around-trap))
    (let* ((fun (lambda (&rest args)
                  (flet ((call ()
                           (apply (typecase callee
                                    (fdefn (fdefn-fun callee))
                                    (function callee))
                                  args)))
                    ;; Signal a step condition
                    (let* ((step-in
                            (let ((*step-frame* (frame-down (top-frame))))
                              (sb!impl::step-form step-info args))))
                      ;; And proceed based on its return value.
                      (if step-in
                          ;; STEP-INTO was selected. Use *STEP-OUT* to
                          ;; let the stepper know that selecting the
                          ;; STEP-OUT restart is valid inside this
                          (let ((sb!impl::*step-out* :maybe))
                            ;; Pass the return values of the call to
                            ;; STEP-VALUES, which will signal a
                            ;; condition with them in the VALUES slot.
                            (unwind-protect
                                 (multiple-value-call #'sb!impl::step-values
                                   step-info
                                   (call))
                              ;; If the user selected the STEP-OUT
                              ;; restart during the call, resume
                              ;; stepping
                              (when (eq sb!impl::*step-out* t)
                                (sb!impl::enable-stepping))))
                          ;; STEP-NEXT / CONTINUE / OUT selected:
                          ;; Disable the stepper for the duration of
                          ;; the call.
                          (sb!impl::with-stepping-disabled
                            (call)))))))
           (new-callee (etypecase callee
                         (fdefn
                          (let ((fdefn (make-fdefn (gensym))))
                            (setf (fdefn-fun fdefn) fun)
                            fdefn))
                         (function fun))))
      ;; And then store the wrapper in the same place.
      (setf (context-register context callee-register-offset)
            (get-lisp-obj-address new-callee)))))

;;; Given a signal context, fetch the step-info that's been stored in
;;; the debug info at the trap point.
(defun single-step-info-from-context (context)
  (multiple-value-bind (pc-offset code)
      (compute-lra-data-from-pc (context-pc context))
    (let* ((debug-fun (debug-fun-from-pc code pc-offset))
           (location (code-location-from-pc debug-fun
                                            pc-offset
                                            nil)))
      (handler-case
          (progn
            (fill-in-code-location location)
            (code-location-debug-source location)
            (compiled-code-location-step-info location))
        (debug-condition ()
          nil)))))

;;; Return the frame that triggered a single-step condition. Used to
;;; provide a *STACK-TOP-HINT*.
(defun find-stepped-frame ()
  (or *step-frame*
      (top-frame)))