/usr/share/scsh-0.6/link/transport.scm is in scsh-common-0.6 0.6.7-8.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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; This is file transport.scm.
; System builder for bootstrapping and debugging.
; Things that have to be written out:
; Made by the compiler
; closures
; templates
; code-vectors
; locations
; Quoted data
; symbols
; pairs
; vectors
; strings
; booleans
; characters
; Convert THING to the Scheme 48 virtual machine's representation and
; return it. Locations and symbols may have multiple references in
; the image. Their transported addresses are kept in a table.
(define (transport thing)
(let transport ((thing thing))
(cond ((immediate? thing)
(transport-immediate thing))
((closure? thing)
(transport-closure thing))
((code-vector? thing)
(allocate-b-vector thing code-vector-length))
((location? thing)
(let ((address (table-ref *locations* thing)))
(cond (address address)
(else
(let ((desc (transport-location thing)))
(table-set! *locations* thing desc)
desc)))))
((symbol? thing)
(let ((address (table-ref *symbols* thing)))
(cond (address address)
(else
(let ((desc (transport-symbol thing)))
(table-set! *symbols* thing desc)
desc)))))
((pair? thing)
(transport-pair thing))
((template? thing)
(transport-template thing))
((vector? thing)
(transport-vector thing))
((string? thing)
(allocate-b-vector thing (lambda (x) (+ 1 (string-length x)))))
(else
(error "cannot transport object" thing)))))
; Transport the things that are not allocated from the heap.
(define (transport-immediate thing)
(cond ((integer? thing)
(make-descriptor (enum tag fixnum) thing))
((char? thing)
(make-immediate (enum imm char) (char->ascii thing)))
((eq? thing '())
vm-null)
((eq? thing #f)
vm-false)
((eq? thing #t)
vm-true)
((eq? thing (unspecific))
vm-unspecific)
(else
(error "cannot transport literal" thing))))
;==============================================================================
; The heap is a list of transported stored objects, each of which is either a
; string, a code-vector, or a vector of length N+1 representing a stored object
; with N cells. The last slot of the vector is the object's header.
(define *heap* '())
(define *hp* 0) ; Current heap-pointer (in a-units)
(define *symbols* #f) ; Table of already-transported symbols
(define *locations* #f) ; Table of already-transported locations
(define (initialize-memory)
(set! *hp* 0)
(set! *heap* '())
(set! *symbols* (make-table))
(set! *locations* (make-table location-id)))
; Allocate a new stored object in the heap. DATA is whatever data is
; associated with the object, LEN is the length of the object (not
; including the header) in bytes. A pointer to the new object is
; returned.
(define (allocate-stob data len)
(let ((addr (+ *hp* (cells->a-units 1)))) ; move past header
(set! *hp* (+ addr (bytes->a-units len)))
(set! *heap* (cons data *heap*))
(make-stob-descriptor addr)))
; Allocate a new stored object that contains descriptors. This
; creates a vector to hold the header and the object's tranported
; contents and allocates a stob in the heap. Returns a pair
; containing the stob-pointer and the vector.
(define (allocate-d-vector type cells immutable?)
(let* ((vec (make-vector (+ cells 1) 0))
(ptr (allocate-stob vec (cells->bytes cells)))
(hdr (make-header type (cells->bytes cells))))
(vector-set! vec cells (if immutable? (make-header-immutable hdr) hdr))
(cons ptr vec)))
; Allocate a new stored object that contains data. VEC is either a
; code-vector or a string.
(define (allocate-b-vector vec length)
(let ((len (cells->bytes (bytes->cells (length vec)))))
(allocate-stob vec len)))
;==============================================================================
; Transport an object with two slots. ALLOCATE-D-VECTOR allocates the
; storage and then the two values are transported.
(define (transport-two-slot type accessor1 offset1 accessor2 offset2
immutable?)
(lambda (thing)
(let* ((data (allocate-d-vector type 2 immutable?))
(descriptor (car data))
(vector (cdr data)))
(vector-set! vector offset1 (transport (accessor1 thing)))
(vector-set! vector offset2 (transport (accessor2 thing)))
descriptor)))
; Closures and pairs are transported using TRANSPORT-TWO-SLOT.
(define transport-closure
(transport-two-slot (enum stob closure)
closure-template closure-template-offset
closure-env closure-env-offset
#t)) ; ***
(define transport-pair
(transport-two-slot (enum stob pair)
car car-offset
cdr cdr-offset
#t)) ; *** ?
; Transporting a location requires some care so as to avoid calling CONTENTS
; when the location is unbound.
(define (transport-location loc)
(let* ((data (allocate-d-vector (enum stob location) 2 #f))
(descriptor (car data))
(vector (cdr data)))
(vector-set! vector
location-contents-offset
(if (location-defined? loc)
(transport (contents loc))
vm-unbound))
(vector-set! vector
location-id-offset
(transport (location-id loc)))
descriptor))
; Symbols have two slots, the string containing the symbol's name and a slot
; used in building the symbol table.
; Characters in the symbol name are made to be lower case.
(define (transport-symbol symbol)
(let* ((data (allocate-d-vector (enum stob symbol) 2 #t))
(descriptor (car data))
(vector (cdr data)))
(vector-set! vector
0
(transport (symbol-case-converter (symbol->string symbol))))
(vector-set! vector
1
(transport #f))
descriptor))
(define (string-case-converter string)
(let ((new (make-string (string-length string) #\x)))
(do ((i 0 (+ i 1)))
((>= i (string-length new))
new)
(string-set! new i (preferred-case (string-ref string i))))))
;(define preferred-case ;Copied from rts/read.scm
; (if (char=? (string-ref (symbol->string 't) 0) #\T)
; char-upcase
; char-downcase))
(define preferred-case char-downcase)
(define symbol-case-converter
(if (char=? (string-ref (symbol->string 't) 0)
(preferred-case #\t))
(lambda (string) string)
string-case-converter))
; Templates and vectors have an arbitrary number of slots but are otherwise
; the same as pairs and closures.
(define (transport-template template)
(transport-vector-like template
(enum stob template)
(template-length template)
template-ref
#f))
(define (transport-vector vector)
(transport-vector-like vector
(enum stob vector)
(vector-length vector)
vector-ref
#t)) ;***
(define (transport-vector-like vector type length ref immutable?)
(let* ((data (allocate-d-vector type length immutable?))
(descriptor (car data))
(new (cdr data)))
(do ((i 0 (+ i 1)))
((>= i length))
(vector-set! new i (transport (ref vector i))))
descriptor))
;==============================================================================
; Writing the heap out to a port.
(define (write-heap port)
(do ((heap (reverse *heap*) (cdr heap)))
((null? heap))
(write-heap-stob (car heap) port)))
; Dispatch on the type of THING and call WRITE-STOB.
(define (write-heap-stob thing port)
(cond ((string? thing)
(let ((len (+ 1 (string-length thing))))
(write-stob (make-header-immutable ; ***
(make-header (enum stob string) len))
thing len nulled-string-ref write-char port)
(align-port len port)))
((code-vector? thing)
(let ((len (code-vector-length thing)))
(write-stob (make-header-immutable ; ***
(make-header (enum stob byte-vector) len))
thing len code-vector-ref write-byte port)
(align-port len port)))
((vector? thing)
(let ((len (vector-length thing)))
(write-stob (vector-ref thing (- len 1))
thing (- len 1) vector-ref write-descriptor port)))
(else
(error "do not know how to write stob" thing))))
(define (nulled-string-ref string i)
(if (= i (string-length string))
(ascii->char 0)
(string-ref string i)))
; Write out a transported STOB to PORT. HEADER is the header, LENGTH is the
; number of objects the STOB contains, ACCESSOR and WRITER access the contents
; and write them to the heap.
(define (write-stob header contents length accessor writer port)
(write-descriptor header port)
(do ((i 0 (+ i 1)))
((>= i length))
(writer (accessor contents i) port)))
; Write out zeros to align the port on a four-byte boundary.
(define (align-port len port)
(let ((count (- (cells->bytes (bytes->cells len)) len)))
(do ((count count (- count 1)))
((<= count 0))
(write-byte 0 port))))
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