bug#34186: 26.1; locking up

bug#34186: 26.1; locking up

[Michael Menefee]

Editing a C header file, I type
'#define AVL_iter(' and it locks up consistently and has to be killed
from another terminal, with CPU at 100%.



In GNU Emacs 26.1 (build 1, amd64-portbld-freebsd11.2)
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
avl.h has auto save data; consider M-x recover-this-file
Making completion list...

Configured using:
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bug#34186: 26.1; locking up

[Eli Zaretskii]

> From: Michael Menefee <mpmenefee@gmail.com>
> Date: Wed, 23 Jan 2019 10:24:09 -0600
> 
> Editing a C header file, I type
> '#define AVL_iter(' and it locks up consistently and has to be killed
> from another terminal, with CPU at 100%.

I cannot reproduce this.  Does the buffer contain anything else in
addition to the text you've shown?  Does it happen in "emacs -Q"?

I invoked "emacs -Q", then typed

  C-x C-f headerhang.h
  #define AVL_iter(

At that point, Emacs was responsive as I'd expect.  Are you doing the
same to reproduce the problem?

Thanks.

bug#34186: 26.1; locking up

[Michael Menefee]

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Hi,

I narrowed it down to a "#define anything(" as the last line in the buffer
will consistently lock up for me.  I'm sure it's the c mode not resolving
something right.  I will experiment more and send you the results if I can
reproduce with minimal buffer content.

Thanks

On Thu, Jan 24, 2019, 8:46 AM Eli Zaretskii <eliz@gnu.org wrote:

> > From: Michael Menefee <mpmenefee@gmail.com>
> > Date: Wed, 23 Jan 2019 10:24:09 -0600
> >
> > Editing a C header file, I type
> > '#define AVL_iter(' and it locks up consistently and has to be killed
> > from another terminal, with CPU at 100%.
>
> I cannot reproduce this.  Does the buffer contain anything else in
> addition to the text you've shown?  Does it happen in "emacs -Q"?
>
> I invoked "emacs -Q", then typed
>
>   C-x C-f headerhang.h
>   #define AVL_iter(
>
> At that point, Emacs was responsive as I'd expect.  Are you doing the
> same to reproduce the problem?
>
> Thanks.
>

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bug#34186: 26.1; locking up

[Michael Menefee]

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I have found the minimum necessary to consistently reproduce.  copy/paste
this into *something.c* to see if you get same results:

void *AVL_first(AVL_t *);
void *AVL_last(AVL_t *);
#define (<--- locks up with pressing open parenthesis

Thanks


On Thu, Jan 24, 2019 at 8:53 AM Michael Menefee <mpmenefee@gmail.com> wrote:

> Hi,
>
> I narrowed it down to a "#define anything(" as the last line in the buffer
> will consistently lock up for me.  I'm sure it's the c mode not resolving
> something right.  I will experiment more and send you the results if I can
> reproduce with minimal buffer content.
>
> Thanks
>
> On Thu, Jan 24, 2019, 8:46 AM Eli Zaretskii <eliz@gnu.org wrote:
>
>> > From: Michael Menefee <mpmenefee@gmail.com>
>> > Date: Wed, 23 Jan 2019 10:24:09 -0600
>> >
>> > Editing a C header file, I type
>> > '#define AVL_iter(' and it locks up consistently and has to be killed
>> > from another terminal, with CPU at 100%.
>>
>> I cannot reproduce this.  Does the buffer contain anything else in
>> addition to the text you've shown?  Does it happen in "emacs -Q"?
>>
>> I invoked "emacs -Q", then typed
>>
>>   C-x C-f headerhang.h
>>   #define AVL_iter(
>>
>> At that point, Emacs was responsive as I'd expect.  Are you doing the
>> same to reproduce the problem?
>>
>> Thanks.
>>
>

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bug#34186: 26.1; locking up

[Eli Zaretskii]

> From: Michael Menefee <mpmenefee@gmail.com>
> Date: Thu, 24 Jan 2019 10:32:34 -0600
> Cc: 34186@debbugs.gnu.org
> 
> I have found the minimum necessary to consistently reproduce.  copy/paste this into something.c to see if you
> get same results:
> 
> void *AVL_first(AVL_t *);
> void *AVL_last(AVL_t *);
> #define (<--- locks up with pressing open parenthesis

Thanks, now I can reproduce this.  Alan, please take a look.

bug#34186: 26.1; locking up

[Alan Mackenzie]

Hello, Eli.

On Thu, Jan 24, 2019 at 19:41:21 +0200, Eli Zaretskii wrote:
> > From: Michael Menefee <mpmenefee@gmail.com>
> > Date: Thu, 24 Jan 2019 10:32:34 -0600
> > Cc: 34186@debbugs.gnu.org

> > I have found the minimum necessary to consistently reproduce.  copy/paste this into something.c to see if you
> > get same results:

> > void *AVL_first(AVL_t *);
> > void *AVL_last(AVL_t *);
> > #define (<--- locks up with pressing open parenthesis

> Thanks, now I can reproduce this.  Alan, please take a look.

Will do!

Just as a matter of interest, it is not the same bug as #33784 (which
only occurred in the master branch).

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#34186: 26.1; locking up

[Alan Mackenzie]

Hello, Eli and Michael.

On Thu, Jan 24, 2019 at 19:41:21 +0200, Eli Zaretskii wrote:
> > From: Michael Menefee <mpmenefee@gmail.com>
> > Date: Thu, 24 Jan 2019 10:32:34 -0600
> > Cc: 34186@debbugs.gnu.org

> > I have found the minimum necessary to consistently reproduce.  copy/paste this into something.c to see if you
> > get same results:

> > void *AVL_first(AVL_t *);
> > void *AVL_last(AVL_t *);
> > #define (<--- locks up with pressing open parenthesis

> Thanks, now I can reproduce this.  Alan, please take a look.

I've committed the following fix to the emacs-26 branch.  I'm closing
the bug.

@Michael: This patch should apply cleanly to your Emacs 26.1 version (in
directory .../emacs/lisp/progmodes).  If you apply it, please
byte-compile the file before using it.  (If you want any help with the
patching and/or byte-compiling, feel free to send me private email.)



commit 9078f34e84178553cd59bc03ac1b58cb56038436
Author: Alan Mackenzie <acm@muc.de>
Date:   Fri Jan 25 16:14:00 2019 +0000

    Fix a loop in c-fl-decl-start.  This fixes bug #34186.
    
    * lisp/progmodes/cc-mode.el (c-fl-decl-start) In the pair of operations
    c-syntactic-skip-backward and c-forward-syntactic-ws, ensure the latter
    doesn't come back to the position before the former, and break out of the
    enclosing loop if it does.

diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index 8cbb4e8612..5283cfea6e 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -1487,6 +1487,7 @@ c-fl-decl-start
   ;; lock context (etc.) fontification.
   (goto-char pos)
   (let ((lit-start (c-literal-start))
+	old-pos
 	(new-pos pos)
 	capture-opener
 	bod-lim bo-decl)
@@ -1509,12 +1510,14 @@ c-fl-decl-start
     (while
 	;; Go to a less nested declaration each time round this loop.
 	(and
+	 (setq old-pos (point))
 	 (c-syntactic-skip-backward "^;{}" bod-lim t)
 	 (> (point) bod-lim)
 	 (progn (c-forward-syntactic-ws)
 		;; Have we got stuck in a comment at EOB?
 		(not (and (eobp)
 			  (c-literal-start))))
+	 (< (point) old-pos)
 	 (progn (setq bo-decl (point))
 		(or (not (looking-at c-protection-key))
 		    (c-forward-keyword-clause 1)))



-- 
Alan Mackenzie (Nuremberg, Germany).