bug#12095: Protecting pointer on bytevector with guardian does not protect memory

[Daniel Hartwig <mandyke@gmail.com>]

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On 7 August 2012 00:37, Ian Price <ianprice90@googlemail.com> wrote:
> Patrick Bernaud <patrickb@chez.com> writes:
>
>> With auto compilation turned on, it looks like the problem can not be
>> reproduced.

That is to say, when using --fresh-auto-compile.

>
> I cannot reproduce this on 32 bit fedora 16 with guile (GNU Guile)
> 2.0.6-dirty (commit 1321a36ed61deb9431b41768dc92cb7230c9afa1). However,
> there was one caveat, as I didn't have html prag, I substituted for
> various other libraries (ice-9 regex)/(ice-9 threads)/(sxml simple)/ and
> my own (pfds queues).
>
> Is this bug somehow particular to htmlprag, or can you confirm it with others?

On x86 Debian sid I reproduced the bug by loading (web server) with
the original test.scm from the mailing list.

The bug report copy differs from the original by replacing
parse-c-struct with pointer->bytevector.

I attach test1.scm, with a loop to load many modules one at a time.
Curiously, when using pointer->bytevector the contents change (for me)
only when freshly compiling:

$ guile --fresh-auto-compile test1.scm
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /home/daniel/Downloads/test1.scm
;;; compiled /home/daniel/.cache/guile/ccache/2.0-LE-4-2.0/home/daniel/Downloads/test1.scm.go
#<pointer 0xa1cdb7c>
#vu8(1 1 1 1 1 1 1 1 1 1)
Contents differ after (web http)
#vu8(110 116 104 101 115 105 122 101 0 1)
#<pointer 0xa1cdb7c>
$ guile test1.scm
#<pointer 0x82c754c>
#vu8(1 1 1 1 1 1 1 1 1 1)
#<pointer 0x82c754c>

With the original (using parse-c-struct) it was the other way around.

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(use-modules (system foreign) (rnrs bytevectors))
(define my-guardian (make-guardian))
(define len 10)
(define x (bytevector->pointer (make-bytevector len 1)))
(define a (pointer-address x))
(display x)(newline)
(my-guardian x)
;(my-guardian (pointer->bytevector x len))
(set! x #f)

(define (dump-struct)
  (write (pointer->bytevector (make-pointer a) len))(newline))

(dump-struct)

(let lp ((s1 (with-output-to-string dump-struct))
         (m '((web uri) (web http) (web request) (web response)
              (web client) (web server) (sxml apply-templates)
              (sxml fold) (sxml simple) (sxml ssax)
              (ice-9 popen) (ice-9 getopt-long) (srfi srfi-42))))
  (gc)
  (primitive-eval `(use-modules ,(car m)))
  (let ((s2 (with-output-to-string dump-struct)))
    (if (not (string=? s1 s2))
        (begin
          (display "Contents differ after ")
          (display (car m))
          (newline)
          (display s2))
        (if (pair? (cdr m))
            (lp s2 (cdr m))))))

(display (my-guardian))(newline)