GNU bug report logs -
#33083
27.0.50; Bignums and message-checksum
Previous Next
Reported by: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
Date: Thu, 18 Oct 2018 14:57:01 UTC
Severity: normal
Fixed in version 27.0.50
Done: Paul Eggert <eggert <at> cs.ucla.edu>
Bug is archived. No further changes may be made.
To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 33083 in the body.
You can then email your comments to 33083 AT debbugs.gnu.org in the normal way.
Toggle the display of automated, internal messages from the tracker.
Report forwarded
to
bug-gnu-emacs <at> gnu.org
:
bug#33083
; Package
emacs
.
(Thu, 18 Oct 2018 14:57:02 GMT)
Full text and
rfc822 format available.
Acknowledgement sent
to
Stefan Monnier <monnier <at> IRO.UMontreal.CA>
:
New bug report received and forwarded. Copy sent to
bug-gnu-emacs <at> gnu.org
.
(Thu, 18 Oct 2018 14:57:02 GMT)
Full text and
rfc822 format available.
Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):
Package: Emacs
Version: 27.0.50
I just got this error:
Debugger entered--Lisp error: (overflow-error)
ash(100.....0170 1)
message-checksum()
message--yank-original-internal(nil)
(let nil (message--yank-original-internal 'nil))
eval((let nil (message--yank-original-internal 'nil)))
message-yank-original()
[...]
command-execute(gnus-summary-followup-with-original)
Where the "....." is fairly long. The problem is simple:
In message-checksum we do
(while (not (eobp))
(when (not (looking-at "[ \t\n]"))
(setq sum (logxor (ash sum 1) (if (natnump sum) 0 1)
(char-after))))
(forward-char 1)))
where the code assumes an `ash` where the MSB bit would overflow into
the sign bit when the result can't fit in a fixnum, and the (if (natnump
sum) 0 1) ends up feeding that sign bit back to the LSB, thus doing
a "rotate".
Of course, with bignums we don't overflow until we reach the 65536 bits
and when we do, we signal an error instead of dropping the extra bits.
So the above error is signaled when the yanked text is longer than 20Kchars
(or non-whitespace chars). Note that even before we reach this error,
we have another problem: this function is basically used at one spot
where we do
(not (eq (message-checksum) message-checksum))
and if the checksum is larger than a fixnum, then this `eq` will always
return false even if both numbers are equal.
So, ever since we switched to bignums, this equality is basically always
false (except when yanking less 8 non-whitespace chars).
What should we do:
- just get rid of this message-checksum feature (which has been broken
in master for a few months now).
- replace message-checksum with something like md5 (which will be faster
but won't ignore whitespace chars like the current code does).
- try to get back the original semantics (e.g. by introducing a proper
bit-rotate primitive).
Stefan
Reply sent
to
Paul Eggert <eggert <at> cs.ucla.edu>
:
You have taken responsibility.
(Wed, 26 Dec 2018 09:18:02 GMT)
Full text and
rfc822 format available.
Notification sent
to
Stefan Monnier <monnier <at> IRO.UMontreal.CA>
:
bug acknowledged by developer.
(Wed, 26 Dec 2018 09:18:02 GMT)
Full text and
rfc822 format available.
Message #10 received at 33083-done <at> debbugs.gnu.org (full text, mbox):
[Message part 1 (text/plain, inline)]
Thanks for reporting the bug. I installed the attached, which is a conservative
patch that should fix the bug, though it doesn't address the more-general issues
that you mentioned.
[0001-Port-message-checksum-to-bignums.patch (text/x-patch, attachment)]
bug archived.
Request was from
Debbugs Internal Request <help-debbugs <at> gnu.org>
to
internal_control <at> debbugs.gnu.org
.
(Wed, 23 Jan 2019 12:24:05 GMT)
Full text and
rfc822 format available.
This bug report was last modified 5 years and 94 days ago.
Previous Next
GNU bug tracking system
Copyright (C) 1999 Darren O. Benham,
1997,2003 nCipher Corporation Ltd,
1994-97 Ian Jackson.