[Chicken-hackers] Reminder (was: more news from the valgrind front)

[Jörg F . Wittenberger]

May I remind you to this simple patch.

It's been quite helpful in locating the other uses of uninitialized
memory, since valgrind would only report so many messages.  All in
the initialization code, one for each static character.

And even under the hope that those never-written bytes will mostly
return zero on read, it's usually bad to depend on that.

BTW: Did anybody try the rather simple patch I posted yesterday?
http://lists.nongnu.org/archive/html/chicken-hackers/2011-10/msg00119.html

/Jörg

---------- Forwarded message ----------
date: 08 Oct 2011 14:09:30 +0200
from: "Jörg F. Wittenberger" <address@hidden>
subject: Re: [Chicken-users] more: news from the valgrind front - another       
test case
to: "Jörg F. Wittenberger" <address@hidden>
cc: Alan Post <address@hidden>, address@hidden

Hi all,

finally I've been able squash that one!
Turns out to be a one line change to chicken.h .
Otherwise valgrind is right to complain.  (It shut up now too.)

The missing cast would allow the compiler to write only sizeof(char).
This turned out to be most often ok (whenever the rest of the word
are already zero bits), but sometimes the compiler might be smarter.
That's way this was highly dependant on various compiler options.
CC-flags that is, not chicken.  And at the same time sensitive to
all sorts of memory management details, which makes it kinda random.

Best Regards

/Jörg

--- /home/jfw/build/Scheme/chicken-core/chicken.h 2011-10-05 
00:03:16.000000000 +0200 +++ chicken.h 2011-10-08 14:01:57.770611923 +0200 
@@ -937,7 +937,7 @@
#define C_demand_2(n) (((C_word *)C_fromspace_top + (n)) < (C_word 
*)C_fromspace_limit)
#define C_fix(n) (((C_word)(n) << C_FIXNUM_SHIFT) | C_FIXNUM_BIT)
#define C_unfix(x) ((x) >> C_FIXNUM_SHIFT) -#define C_make_character(c) 
((((c) & C_CHAR_BIT_MASK) << C_CHAR_SHIFT) | C_CHARACTER_BITS) +#define 
C_make_character(c) ((((C_word)(c) & C_CHAR_BIT_MASK) << C_CHAR_SHIFT) | 
C_CHARACTER_BITS)
#define C_character_code(x) (((C_word)(x) >> C_CHAR_SHIFT) & 
C_CHAR_BIT_MASK)
#define C_flonum_magnitude(x) (*((double *)(((C_SCHEME_BLOCK 
*)(x))->data)))
#define C_c_string(x) ((C_char *)(((C_SCHEME_BLOCK *)(x))->data))




On Oct 7 2011, Jörg F. Wittenberger wrote:

> On Oct 7 2011, Alan Post wrote:
>
> > Given the odd behavior you're experiencing, I would suggest
> > expanding your test case:
>
> Good point.  Here the results:
>
> Now watch the interesting value (should be all 4 true a/a,i/i,a/i,i/a):
> #t#t#f#f
>
> That is:
> (equal? *all-chars* *all-chars*)
> => #t
> (equal? `(/ ,(integer->char 0)
>                      ,(integer->char #xD7FF)
>                      ,(integer->char #xE000)
>                      ,(integer->char #x10FFFF))
>                  `(/ ,(integer->char 0)
>                      ,(integer->char #xD7FF)
>                      ,(integer->char #xE000)
>                      ,(integer->char #x10FFFF)))
> => #t
> (equal? *all-chars*
>                  `(/ ,(integer->char 0)
>                      ,(integer->char #xD7FF)
>                      ,(integer->char #xE000)
>                      ,(integer->char #x10FFFF)))
> => #f
> (equal? `(/ ,(integer->char 0) ,(integer->char #xD7FF)
>      ,(integer->char #xE000) ,(integer->char #x10FFFF))
> *all-chars* )
> => #f
>
> Or: comparison of just initialised value fails to be equal?
> to the literal value.
>
> Can you/anyone reproduce this result?
>
> (So far valgrind not envolved, just this debug code in irregex-core.scm!)
>
>
> /Jörg
>
>
>
>
>
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