bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[David Bremner]

1. Save the following as test.el

(let ((inhibit-modification-hooks t))
  (with-temp-buffer
    (insert "P'")
    (goto-char (point-min))
    (while (re-search-forward "\\([^\\]\\)'" nil t)
      (replace-match    "\\1`"))
    (buffer-substring (point-min) (point-max))))

2. run "emacs --batch --quick --load ./test.el"

3. Under docker, with Debian's emacs-nox (but not emacs-lucid or
   emacs-gtk, I get an error "Match data clobbered by buffer modification
   hooks".

I don't think this is Debian specific, as someone was also able to
duplicate it with "nixpkgs.emacs26-nox" (also in Docker).
   
I agree the setup sounds pretty specific, but it is used by a Debian CI
setup, which is why I care.

Here's the build info, copied out of docker:

In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu)
 of 2019-02-03, modified by Debian built on zam904
Recent messages:
Loading /etc/emacs/site-start.d/00debian.el (source)...done
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/sh\
are/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/sh\
are/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-x=no
 --without-gsettings 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-26.1+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[Paul Eggert]

I tried to reproduce the bug and failed, so I'm afraid you'll have to step in 
and help debug it. First, please use 26.2 rather than 26.1. Second, please 
simplify the ./configure arguments (there are some duplicates, and 
--enable-libsystemd isn't the right name for the flag). Third, I suggest running 
it under GDB and seeing what exactly goes wrong, e.g., by putting a watchpoint 
on search_regs.start[sub].

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[Stefan Kangas]

Paul Eggert <eggert@cs.ucla.edu> writes:

> I tried to reproduce the bug and failed, so I'm afraid you'll have to step in
> and help debug it. First, please use 26.2 rather than 26.1. Second, please 
> simplify the ./configure arguments (there are some duplicates, and
> --enable-libsystemd isn't the right name for the flag). Third, I suggest running 
> it under GDB and seeing what exactly goes wrong, e.g., by putting a watchpoint
> on search_regs.start[sub].

I couldn't reproduce this bug either.

David, could you please look into the above suggestions by Paul?

Best regards,
Stefan Kangas

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[David Bremner]

Stefan Kangas <stefan@marxist.se> writes:

> Paul Eggert <eggert@cs.ucla.edu> writes:
>
>> I tried to reproduce the bug and failed, so I'm afraid you'll have to step in
>> and help debug it. First, please use 26.2 rather than 26.1. Second, please 
>> simplify the ./configure arguments (there are some duplicates, and
>> --enable-libsystemd isn't the right name for the flag). Third, I suggest running 
>> it under GDB and seeing what exactly goes wrong, e.g., by putting a watchpoint
>> on search_regs.start[sub].
>
> I couldn't reproduce this bug either.
>
> David, could you please look into the above suggestions by Paul?

FYI I've filed Debian bug 931651 about this. I did duplicate the problem
without docker, and with emacs 26.3, but on an s390x system (and it
seems to be sensitive to _which_ s390x system, so that is a bit
discouraging).

I haven't had time to follow up Paul's suggestions.

d

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[Stefan Kangas]

David Bremner <david@tethera.net> writes:

> Stefan Kangas <stefan@marxist.se> writes:
>
>> Paul Eggert <eggert@cs.ucla.edu> writes:
>>
>>> I tried to reproduce the bug and failed, so I'm afraid you'll have to step in
>>> and help debug it. First, please use 26.2 rather than 26.1. Second, please 
>>> simplify the ./configure arguments (there are some duplicates, and
>>> --enable-libsystemd isn't the right name for the flag). Third, I suggest running 
>>> it under GDB and seeing what exactly goes wrong, e.g., by putting a watchpoint
>>> on search_regs.start[sub].
>>
>> I couldn't reproduce this bug either.
>>
>> David, could you please look into the above suggestions by Paul?
>
> FYI I've filed Debian bug 931651 about this. I did duplicate the problem
> without docker, and with emacs 26.3, but on an s390x system (and it
> seems to be sensitive to _which_ s390x system, so that is a bit
> discouraging).
>
> I haven't had time to follow up Paul's suggestions.

Thank you.  As it seems to be specific to certain s390x machines, I
think we will be dependent on your help to track this down.  When you
find the time, it would be very good if you could try the things
suggested by Paul above.

Thanks in advance.

Best regards,
Stefan Kangas

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[David Bremner]

Stefan Kangas <stefan@marxist.se> writes:

>> I haven't had time to follow up Paul's suggestions.
>
> Thank you.  As it seems to be specific to certain s390x machines, I
> think we will be dependent on your help to track this down.  When you
> find the time, it would be very good if you could try the things
> suggested by Paul above.

Well, no, it was also present in a docker environment on X86 for me, and
someone else on #emacs (IRC) using Nix. 

d

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[Lars Ingebrigtsen]

David Bremner <david@tethera.net> writes:

> 1. Save the following as test.el
>
> (let ((inhibit-modification-hooks t))
>   (with-temp-buffer
>     (insert "P'")
>     (goto-char (point-min))
>     (while (re-search-forward "\\([^\\]\\)'" nil t)
>       (replace-match    "\\1`"))
>     (buffer-substring (point-min) (point-max))))
>
> 2. run "emacs --batch --quick --load ./test.el"

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

I don't seem to be able to reproduce this problem with the current
Emacs.  Are you still seeing this issue in more recent Emacs versions?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[David Bremner]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> David Bremner <david@tethera.net> writes:
>
>> 1. Save the following as test.el
>>
>> (let ((inhibit-modification-hooks t))
>>   (with-temp-buffer
>>     (insert "P'")
>>     (goto-char (point-min))
>>     (while (re-search-forward "\\([^\\]\\)'" nil t)
>>       (replace-match    "\\1`"))
>>     (buffer-substring (point-min) (point-max))))
>>
>> 2. run "emacs --batch --quick --load ./test.el"
>
> (I'm going through old bug reports that unfortunately weren't resolved
> at the time.)
>
> I don't seem to be able to reproduce this problem with the current
> Emacs.  Are you still seeing this issue in more recent Emacs versions?

I can't duplicate it with Debian's 27.1, so it's probably safe to close,

Cheers

David

bug#35557: 26.1; false positive: Match data clobbered by buffer modification hooks

[Lars Ingebrigtsen]

David Bremner <david@tethera.net> writes:

> I can't duplicate it with Debian's 27.1, so it's probably safe to close,

Thanks for checking; I'm closing this bug report, then.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no