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;;; Guile VM code converters
;; Copyright (C) 2001, 2009 Free Software Foundation, Inc.
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Code:
(define-module (language assembly decompile-bytecode)
#:use-module (system vm instruction)
#:use-module (system base pmatch)
#:use-module (srfi srfi-4)
#:use-module (rnrs bytevector)
#:use-module (language assembly)
#:use-module ((system vm objcode) #:select (byte-order))
#:export (decompile-bytecode))
(define (decompile-bytecode x env opts)
(let ((i 0) (size (u8vector-length x)))
(define (pop)
(let ((b (cond ((< i size) (u8vector-ref x i))
((= i size) #f)
(else (error "tried to decode too many bytes")))))
(if b (set! i (1+ i)))
b))
(let ((ret (decode-load-program pop)))
(if (= i size)
(values ret env)
(error "bad bytecode: only decoded ~a out of ~a bytes" i size)))))
(define (br-instruction? x)
(memq x '(br br-if br-if-not br-if-eq br-if-not-eq br-if-null br-if-not-null)))
(define (bytes->s16 a b)
(let ((x (+ (ash a 8) b)))
(if (zero? (logand (ash 1 15) x))
x
(- x (ash 1 16)))))
;; FIXME: this is a little-endian disassembly!!!
(define (decode-load-program pop)
(let* ((nargs (pop)) (nrest (pop)) (nlocs0 (pop)) (nlocs1 (pop))
(nlocs (+ nlocs0 (ash nlocs1 8)))
(a (pop)) (b (pop)) (c (pop)) (d (pop))
(e (pop)) (f (pop)) (g (pop)) (h (pop))
(len (+ a (ash b 8) (ash c 16) (ash d 24)))
(metalen (+ e (ash f 8) (ash g 16) (ash h 24)))
(totlen (+ len metalen))
(pad0 (pop)) (pad1 (pop)) (pad2 (pop)) (pad3 (pop))
(labels '())
(i 0))
(define (ensure-label rel1 rel2)
(let ((where (+ (logand i (lognot #x7))
(* (bytes->s16 rel1 rel2) 8))))
(or (assv-ref labels where)
(begin
(let ((l (gensym ":L")))
(set! labels (acons where l labels))
l)))))
(define (sub-pop) ;; ...records. ha. ha.
(let ((b (cond ((< i len) (pop))
((= i len) #f)
(else (error "tried to decode too many bytes")))))
(if b (set! i (1+ i)))
b))
(let lp ((out '()))
(cond ((> i len)
(error "error decoding program -- read too many bytes" out))
((= i len)
`(load-program ,nargs ,nrest ,nlocs
,(map (lambda (x) (cons (cdr x) (car x)))
(reverse labels))
,len
,(if (zero? metalen) #f (decode-load-program pop))
,@(reverse! out)))
(else
(let ((exp (decode-bytecode sub-pop)))
(pmatch exp
((,br ,rel1 ,rel2) (guard (br-instruction? br))
(lp (cons `(,br ,(ensure-label rel1 rel2)) out)))
((mv-call ,n ,rel1 ,rel2)
(lp (cons `(mv-call ,n ,(ensure-label rel1 rel2)) out)))
(else
(lp (cons exp out))))))))))
(define (decode-bytecode pop)
(define (get1 bytes-per-char)
(if (= bytes-per-char 1)
(pop)
(let* ((a (pop))
(b (pop))
(c (pop))
(d (pop)))
(if (= byte-order 1234)
(+ (ash d 24) (ash c 16) (ash b 8) a)
(+ (ash a 24) (ash b 16) (ash c 8) d)))))
(and=> (pop)
(lambda (opcode)
(let ((inst (opcode->instruction opcode)))
(cond
((eq? inst 'load-program)
(decode-load-program pop))
((< (instruction-length inst) 0)
;; the negative length indicates a variable length
;; instruction
(let* ((make-sequence
(if (eq? inst 'load-array)
make-bytevector
make-string))
(sequence-set!
(if (eq? inst 'load-array)
bytevector-u8-set!
(lambda (str pos value)
(string-set! str pos (integer->char value)))))
(len (let* ((a (pop)) (b (pop)) (c (pop)))
(+ (ash a 16) (ash b 8) c)))
(bytes-per-count
(if (or (eq? inst 'load-string)
(eq? inst 'load-symbol)
(eq? inst 'load-keyword)
(eq? inst 'define))
(pop)
1))
(seq (make-sequence len)))
(let lp ((i 0))
(if (= i len)
`(,inst ,seq)
(begin
(sequence-set! seq i (get1 bytes-per-count))
(lp (1+ i)))))))
(else
;; fixed length
(let lp ((n (instruction-length inst)) (out (list inst)))
(if (zero? n)
(reverse! out)
(lp (1- n) (cons (pop) out))))))))))
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