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jumps encoded using 24 bits, not 19; blocks no longer aligned

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* libguile/_scm.h (SCM_OBJCODE_MINOR_VERSION): Bump.
* libguile/vm-i-system.c (FETCH_OFFSET, BR): Labels are no longer 8-byte
  aligned; instead, jumps are encoded into 3 bytes instead of 2.
  (br, br-if, br-if-not, br-if-eq, br-if-not-eq, br-if-null)
  (br-if-not-null, mv-call): Adapt for new length of br instructions (3
  bytes instead of 2).

* libguile/vm.c (really_make_boot_program): Adapt hand-coded bytecode
  for new offset regime.

* module/language/assembly.scm (align-block): No alignment necessary.

* module/language/assembly/compile-bytecode.scm (write-bytecode): Write
  out breaks as 24-bit relative jumps.
* module/language/assembly/decompile-bytecode.scm (decode-load-program):
  Decompile break instructions.
This commit is contained in:
Andy Wingo 2009-09-17 14:58:31 +02:00
parent f95f82f8e1
commit 97fcf583b7
6 changed files with 40 additions and 39 deletions
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2
module/language/assembly.scm
View file

@ -72,7 +72,7 @@
'(nop)))
(define (align-block addr)
(code-alignment addr *block-alignment* 0))
'())
(define (align-code code addr alignment header-len)
`(,@(code-alignment addr alignment header-len)

14
module/language/assembly/compile-bytecode.scm
View file

@ -55,6 +55,10 @@
(define (write-uint16-le x)
(write-byte (logand x 255))
(write-byte (logand (ash x -8) 255)))
(define (write-uint24-be x)
(write-byte (logand (ash x -16) 255))
(write-byte (logand (ash x -8) 255))
(write-byte (logand x 255)))
(define (write-uint32-be x)
(write-byte (logand (ash x -24) 255))
(write-byte (logand (ash x -16) 255))
@ -85,12 +89,10 @@
;; Ew!
(for-each write-byte (bytevector->u8-list bv)))
(define (write-break label)
(let ((offset (- (assq-ref labels label)
(logand (+ (get-addr) 2) (lognot #x7)))))
(cond ((not (= 0 (modulo offset 8))) (error "unaligned jump" offset))
((>= offset (ash 1 18)) (error "jump too far forward" offset))
((< offset (- (ash 1 18))) (error "jump too far backwards" offset))
(else (write-uint16-be (ash offset -3))))))
(let ((offset (- (assq-ref labels label) (+ (get-addr) 3))))
(cond ((>= offset (ash 1 23)) (error "jump too far forward" offset))
((< offset (- (ash 1 23))) (error "jump too far backwards" offset))
(else (write-uint24-be offset)))))
(let ((inst (car asm))
(args (cdr asm))

19
module/language/assembly/decompile-bytecode.scm
View file

@ -43,11 +43,11 @@
(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))
(define (bytes->s24 a b c)
(let ((x (+ (ash a 16) (ash b 8) c)))
(if (zero? (logand (ash 1 23) x))
x
(- x (ash 1 16)))))
(- x (ash 1 24)))))
;; FIXME: this is a little-endian disassembly!!!
(define (decode-load-program pop)
@ -60,9 +60,8 @@
(%unused-pad (begin (pop) (pop) (pop) (pop)))
(labels '())
(i 0))
(define (ensure-label rel1 rel2)
(let ((where (+ (logand i (lognot #x7))
(* (bytes->s16 rel1 rel2) 8))))
(define (ensure-label rel1 rel2 rel3)
(let ((where (+ i (bytes->s24 rel1 rel2 rel3))))
(or (assv-ref labels where)
(begin
(let ((l (gensym ":L")))
@ -87,9 +86,9 @@
(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)
((,br ,rel1 ,rel2 ,rel3) (guard (br-instruction? br))
(lp (cons `(,br ,(ensure-label rel1 rel2 rel3)) out)))
((mv-call ,n ,rel1 ,rel2 ,rel3)
(lp (cons `(mv-call ,n ,(ensure-label rel1 rel2)) out)))
(else
(lp (cons exp out))))))))))