From: ludo@gnu.org (Ludovic Courtès)
To: guile-user@gnu.org
Subject: Re: smob mark functions in 2.0
Date: Thu, 24 Nov 2011 00:12:05 +0100 [thread overview]
Message-ID: <874nxumo1m.fsf@gnu.org> (raw)
In-Reply-To: 87aa7mmt76.fsf@pobox.com
Hello!
Andy Wingo <wingo@pobox.com> skribis:
> Specifically, there is a warning in gc/gc_mark.h:
>
> /* WARNING: Such a mark procedure may be invoked on an unused object */
> /* residing on a free list. Such objects are cleared, except for a */
> /* free list link field in the first word. Thus mark procedures may */
> /* not count on the presence of a type descriptor, and must handle this */
> /* case correctly somehow. */
Arrgh!
> So, your mark function might see freed objects. This is terrible, but
> it is the way that it is. The key is that, if you touch a Scheme object
> in your mark function, to first do a check on that object, to see that
> it is valid. You can check the TC bits of the first word, or otherwise
> check that other words are non-NULL.
What about making that check in libguile before invoking the user’s mark
function?
Thanks,
Ludo’.
next prev parent reply other threads:[~2011-11-23 23:12 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-23 21:20 smob mark functions in 2.0 Andy Wingo
2011-11-23 23:12 ` Ludovic Courtès [this message]
2011-11-24 10:56 ` Andy Wingo
2011-11-24 23:24 ` Ludovic Courtès
2011-11-30 15:29 ` Mark H Weaver
2014-09-26 4:50 ` Mark H Weaver
2014-09-27 15:29 ` Andy Wingo
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