From: Pip Cet <pipcet@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 41520@debbugs.gnu.org, stefan@marxist.se
Subject: bug#41520: 28.0.50; Crash in character.h due to assertion error
Date: Mon, 25 May 2020 17:54:01 +0000 [thread overview]
Message-ID: <CAOqdjBdMhH2eOM8if3B8HO2VrTc4V8As370BG51FA3rXro09Wg@mail.gmail.com> (raw)
In-Reply-To: <83tv04uhca.fsf@gnu.org>
On Mon, May 25, 2020 at 4:09 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Mon, 25 May 2020 15:16:09 +0000
> > Cc: stefan@marxist.se, 41520@debbugs.gnu.org
> >
> > > But wouldn't it be strange to see a macro that accepts a struct, but
> > > only uses one member of that struct?
> >
> > I don't think so. CHARPOS and BYTEPOS already exist, and that's
> > precisely what they do.
> >
> > What is a little strange is that the ancient convention of not
> > returning struct types is still followed in much of Emacs.
>
> It's more expensive.
Only for very large structs, or on old architectures.
> That's what I meant when I said "strange": why
> would we fill 2 fields of a struct, but use only one?
As I said, I'm not talking about cases in which one variable suffices.
It's those cases where we have:
ptrdiff_t charpos;
ptrdiff_t bytepos;
(not usually named like that, or indeed consistently).
My suggestion is we use
pos_t pos;
and then pos.charpos and pos.bytepos as appropriate.
> > > I mean we already have assertions: that's what eassume does in a debug
> > > build.
> >
> > Yes, but we could do with some stricter checking, I think.
>
> It cannot catch the cases where we put a character position into the
> byte position slot. That's the general problem with using simple
> scalars.
Incorrect code becomes way more obvious.
bytepos = PT;
is incorrect but shorter than the correct version.
pos.bytepos = PT_POS.charpos;
pos.charpos = PT_POS.bytepos;
is much more obviously wrong, and the correct version is simply:
pos = PT_POS;
On non-obsolescent architectures, returning a two-word struct is
cheaper than accessing two parameters through pointers, too; and
that's only relevant for those few cases in which the function isn't
inlined, anyway.
All I'm hoping for, at this point, is a "maybe, show me a patch".
next prev parent reply other threads:[~2020-05-25 17:54 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-25 7:05 bug#41520: 28.0.50; Crash in character.h due to assertion error Stefan Kangas
2020-05-25 7:28 ` Pip Cet
2020-05-25 7:41 ` Pip Cet
2020-05-25 14:18 ` Eli Zaretskii
2020-05-25 14:30 ` Pip Cet
2020-05-25 15:07 ` Eli Zaretskii
2020-05-25 15:16 ` Pip Cet
2020-05-25 16:09 ` Eli Zaretskii
2020-05-25 17:54 ` Pip Cet [this message]
2020-05-25 19:30 ` Eli Zaretskii
2020-05-25 20:39 ` Pip Cet
2020-05-26 16:17 ` Eli Zaretskii
2020-09-27 14:36 ` Lars Ingebrigtsen
2020-09-27 15:15 ` Eli Zaretskii
2020-09-27 15:42 ` Lars Ingebrigtsen
2020-09-27 16:00 ` Eli Zaretskii
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