From: storm@cua.dk (Kim F. Storm)
Cc: Andreas Schwab <schwab@suse.de>, emacs-devel@gnu.org
Subject: Re: valid_pointer_p
Date: Sat, 12 Aug 2006 22:19:50 +0200 [thread overview]
Message-ID: <m364gxiu55.fsf@kfs-l.imdomain.dk> (raw)
In-Reply-To: <upsf6c925.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 12 Aug 2006 17:39:30 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
>> From: Andreas Schwab <schwab@suse.de>
>> Cc: storm@cua.dk (Kim F. Storm), emacs-devel@gnu.org
>> Date: Sat, 12 Aug 2006 14:36:22 +0200
>>
>> Eli Zaretskii <eliz@gnu.org> writes:
>>
>> > ??? Don't we have macros, like INTEGERP, SUBRP, etc. to do that
>> > without dereferencing? The length of the primitive Lisp types is
>> > known, right?
>>
>> Try to find out the size of a vector object.
>>
>> /* Vector of Lisp objects, or something resembling it.
>> XVECTOR (object) points to a struct Lisp_Vector, which contains
>> the size and contents. The size field also contains the type
>> information, if it's not a real vector object. */
>> Lisp_Vectorlike,
>
> I think something like this should work for such cases:
>
> struct Lisp_Vector *p = XVECTOR (obj);
>
> if (valid_pointer_p (p, offsetof (struct Lisp_Vector, size)
> + sizeof (EMACS_INT))
> && valid_pointer_p (p, p->size))
> return 1; /* valid */
>
> (Modulo the complications of storing other information in the leading
> bits of the `size' field of struct Lisp_Vector.) This is what I meant
> when I wrote:
>
> Even if you are right, dereferencing a pointer accesses a region in
> memory whose length is known in advance, so at most we will need to
> call valid_pointer_p twice.
>
> Am I missing something?
No. My simple approach was simply to assume that if you can access the
size field of a vector, you can access the rest as well. I don't mind
making a more correct implementation, although I didn't see the need --
after all, this is for a corner case of debugging emacs.
--
Kim F. Storm <storm@cua.dk> http://www.cua.dk
next prev parent reply other threads:[~2006-08-12 20:19 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-29 10:27 valid_pointer_p Eli Zaretskii
2006-07-29 10:45 ` valid_pointer_p Andreas Schwab
2006-07-29 12:16 ` valid_pointer_p Eli Zaretskii
2006-07-30 0:05 ` valid_pointer_p Kim F. Storm
2006-07-30 3:16 ` valid_pointer_p Eli Zaretskii
2006-07-30 22:13 ` valid_pointer_p Kim F. Storm
2006-07-31 3:21 ` valid_pointer_p Eli Zaretskii
2006-07-31 8:30 ` valid_pointer_p Andreas Schwab
2006-07-31 17:10 ` valid_pointer_p Eli Zaretskii
2006-07-31 17:56 ` valid_pointer_p Andreas Schwab
2006-07-31 9:01 ` valid_pointer_p Kim F. Storm
2006-08-05 13:04 ` valid_pointer_p Eli Zaretskii
2006-08-05 13:09 ` valid_pointer_p Eli Zaretskii
2006-08-05 22:11 ` valid_pointer_p Kim F. Storm
2006-08-06 3:29 ` valid_pointer_p Eli Zaretskii
2006-08-11 22:58 ` valid_pointer_p Kim F. Storm
2006-08-12 11:06 ` valid_pointer_p Eli Zaretskii
2006-08-12 12:36 ` valid_pointer_p Andreas Schwab
2006-08-12 14:39 ` valid_pointer_p Eli Zaretskii
2006-08-12 20:19 ` Kim F. Storm [this message]
2006-08-12 21:56 ` valid_pointer_p Eli Zaretskii
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