* extract_data_from_object considered dangerous
@ 2019-09-22 13:39 Stefan Monnier
2019-09-22 16:50 ` Eli Zaretskii
0 siblings, 1 reply; 4+ messages in thread
From: Stefan Monnier @ 2019-09-22 13:39 UTC (permalink / raw)
To: emacs-devel
I was just looking at the calling convention of extract_data_from_object
and it seems intrinsically dangerous:
It returns a char* into a Lisp_Object without associating it with
any specific Lisp_Object
In some cases, the Lisp_Object into which the result points is freshly
allocated during the call, so once we return from the function, there is
no Lisp_Object reference to it anywhere any more to keep it from
being GC'd.
Stefan
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: extract_data_from_object considered dangerous
2019-09-22 13:39 extract_data_from_object considered dangerous Stefan Monnier
@ 2019-09-22 16:50 ` Eli Zaretskii
2019-09-22 20:53 ` Stefan Monnier
0 siblings, 1 reply; 4+ messages in thread
From: Eli Zaretskii @ 2019-09-22 16:50 UTC (permalink / raw)
To: Stefan Monnier; +Cc: emacs-devel
> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Sun, 22 Sep 2019 09:39:54 -0400
>
> It returns a char* into a Lisp_Object without associating it with
> any specific Lisp_Object
>
> In some cases, the Lisp_Object into which the result points is freshly
> allocated during the call, so once we return from the function, there is
> no Lisp_Object reference to it anywhere any more to keep it from
> being GC'd.
The original idea was to use the pointer right away, so that GC
couldn't happen. If we want to lift this restriction, I think the
function should return a Lisp object, not a char *.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: extract_data_from_object considered dangerous
2019-09-22 16:50 ` Eli Zaretskii
@ 2019-09-22 20:53 ` Stefan Monnier
2019-09-23 2:28 ` Eli Zaretskii
0 siblings, 1 reply; 4+ messages in thread
From: Stefan Monnier @ 2019-09-22 20:53 UTC (permalink / raw)
To: Eli Zaretskii; +Cc: emacs-devel
> The original idea was to use the pointer right away, so that GC
> couldn't happen.
Indeed, I think that it might be the case that currently this problem is
only hypothetical, but relying on "the GC probably can't happen now" is
too fragile for my taste.
> If we want to lift this restriction, I think the
> function should return a Lisp object, not a char *.
That's also my impression, but I was wondering is there was a good
reason why it wasn't done this way in the first place.
Stefan
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: extract_data_from_object considered dangerous
2019-09-22 20:53 ` Stefan Monnier
@ 2019-09-23 2:28 ` Eli Zaretskii
0 siblings, 0 replies; 4+ messages in thread
From: Eli Zaretskii @ 2019-09-23 2:28 UTC (permalink / raw)
To: Stefan Monnier; +Cc: emacs-devel
> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: emacs-devel@gnu.org
> Date: Sun, 22 Sep 2019 16:53:05 -0400
>
> > If we want to lift this restriction, I think the
> > function should return a Lisp object, not a char *.
>
> That's also my impression, but I was wondering is there was a good
> reason why it wasn't done this way in the first place.
AFAIR, the function was created by consolidating many repeated in-line
code fragments.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-09-23 2:28 UTC | newest]
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2019-09-22 13:39 extract_data_from_object considered dangerous Stefan Monnier
2019-09-22 16:50 ` Eli Zaretskii
2019-09-22 20:53 ` Stefan Monnier
2019-09-23 2:28 ` Eli Zaretskii
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