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bug#41520: 28.0.50; Crash in character.h due to assertion error
From: |
Eli Zaretskii |
Subject: |
bug#41520: 28.0.50; Crash in character.h due to assertion error |
Date: |
Mon, 25 May 2020 17:18:25 +0300 |
> From: Pip Cet <pipcet@gmail.com>
> Date: Mon, 25 May 2020 07:28:23 +0000
> Cc: 41520@debbugs.gnu.org
>
> On Mon, May 25, 2020 at 7:06 AM Stefan Kangas <stefan@marxist.se> wrote:
> > When editing an org-mode document, I saw a crash due to this assertion
> > error:
>
> It's a bug in this code in xdisp.c:
>
> else if (it->bidi_it.charpos == bob
> || (!string_p
> && (FETCH_CHAR (it->bidi_it.bytepos - 1) == '\n'
> || FETCH_CHAR (it->bidi_it.bytepos) == '\n')))
Ouch!
> The first FETCH_CHAR should be a FETCH_BYTE to avoid the assertion error.
>
> There's at least one other place that has the same error, so I'll grep
> some more before sending a patch.
Thanks.
> My suggestion is to drop the "eassume" on emacs-27, and fix FETCH_CHAR
> to FETCH_BYTE on master.
There's no eassume on emacs-27, this is new on master. That is why
these problems were never exposed before: the old versions of macros
didn't signal any errors in these cases, they just produced some wrong
values, which can never be equal to a newline.
So I installed on emacs-27 branch a patch very similar to what you
sent, except that it uses FETCH_BYTE in all cases where we compare to
a newline: this is both more efficient and more correct.
> (I'd like to reiterate my proposal to use a pos_t for bytepos/charpos
> pairs, which would catch or silently fix (which happened in this case
> on my pos_t branch) such bugs. The code on my branch reads:
>
> else if (POS_CHAR_EQUAL (it->bidi_it.pos, bob)
> || (!string_p
> && (FETCH_CHAR (dec_pos (it->bidi_it.pos)) == '\n'
> || FETCH_CHAR (it->bidi_it.pos) == '\n')))
>
> which, while minimally slower, doesn't throw assertion errors.)
That would require us to maintain both character and byte positions
where we use these macros, something that could be redundant
overhead. Moreover, I think we prefer having assertions in the debug
builds rather then silent fixups (and in production eassume compiles
into something that doesn't abort).
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Stefan Kangas, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Pip Cet, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Pip Cet, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error,
Eli Zaretskii <=
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Pip Cet, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Eli Zaretskii, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Pip Cet, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Eli Zaretskii, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Pip Cet, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Eli Zaretskii, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Pip Cet, 2020/05/25
- bug#41520: 28.0.50; Crash in character.h due to assertion error, Eli Zaretskii, 2020/05/26