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[debbugs-tracker] bug#31888: closed (27.0.50; Segmentation fault in repl

From: GNU bug Tracking System
Subject: [debbugs-tracker] bug#31888: closed (27.0.50; Segmentation fault in replace-buffer-contents)
Date: Sat, 23 Jun 2018 11:16:03 +0000

Your message dated Sat, 23 Jun 2018 14:15:23 +0300
with message-id <address@hidden>
and subject line Re: bug#31888: 27.0.50; Segmentation fault in 
has caused the debbugs.gnu.org bug report #31888,
regarding 27.0.50; Segmentation fault in replace-buffer-contents
to be marked as done.

(If you believe you have received this mail in error, please contact

31888: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=31888
GNU Bug Tracking System
Contact address@hidden with problems
--- Begin Message --- Subject: 27.0.50; Segmentation fault in replace-buffer-contents Date: Sun, 17 Jun 2018 15:12:10 +0200 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0
Run this shell command in Emacs source tree (the file contents.c was
generated with clang-format):

emacs -Q src/dispnew.c contents.c --eval '(with-current-buffer
"dispnew.c" (replace-buffer-contents "contents.c"))'

Backtrace (full backtrace in attachment):
Thread 1 "emacs" received signal SIGSEGV, Segmentation fault.
0x00000000005b34cb in find_interval (tree=0x0, address@hidden) at ../../src/intervals.c:616
616           if (relative_position < LEFT_TOTAL_LENGTH (tree))
#0 0x00000000005b34cb in find_interval (tree=0x0, address@hidden) at ../../src/intervals.c:616
        relative_position = -13
#1 0x00000000005b4dfd in set_point_both (charpos=-12, bytepos=-12) at ../../src/intervals.c:1864
        to = <optimized out>
        from = <optimized out>
        toprev = <optimized out>
        fromprev = <optimized out>
        buffer_point = <optimized out>
        old_position = 160
        backwards = true
        original_position = <optimized out>
#2 0x00000000005b5586 in set_point (charpos=<optimized out>) at ../../src/intervals.c:1754
No locals.
#3 0x000000000055c40d in Freplace_buffer_contents (source=0x184d9a4) at ../../src/editfns.c:3267
        end_a = <optimized out>
        end_b = <optimized out>
        beg_b = <optimized out>
        a = <optimized out>
        source_buffer = <optimized out>
        min_a = 1
        min_b = 1
        size_a = <optimized out>
        a_empty = <optimized out>
        b_empty = false
        diags = <optimized out>
        buffer = <optimized out>
        sa_avail = <optimized out>
        sa_must_free = <optimized out>
        del_bytes = <optimized out>
        ins_bytes = <optimized out>
ctx = {buffer_a = 0x1727fa0, buffer_b = 0x177d180, deletions = 0x184db90 "\254^", insertions = 0x1853ac0 "B\327\v", fdiag = 0x7fffe336f158, bdiag = 0x7fffe36828e8, too_expensive = 1000000}
        i = <optimized out>
        j = <optimized out>

Lisp backtrace:
"replace-buffer-contents" (0xffffc9f0)
"save-current-buffer" (0xffffcad8)
"with-current-buffer" (0xffffcb98)
"eval" (0xffffcd28)
"command-line-1" (0xffffd340)
"command-line" (0xffffdb48)
"normal-top-level" (0xffffde60)

In GNU Emacs 27.0.50 (build 4, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2018-06-17 built on mkc
Repository revision: fa9679ca488a17b2b6b9f31299d69c190aa86642
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description: Linux Mint 18.2

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-x-toolkit=lucid'

Configured features:

Important settings:
  value of $LC_MONETARY: pl_PL.UTF-8
  value of $LC_NUMERIC: pl_PL.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
easymenu mml-sec password-cache epa derived epg epg-config gnus-util
rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 94745 9710)
 (symbols 48 20133 1)
 (miscs 40 35 86)
 (strings 32 28988 1919)
 (string-bytes 1 755246)
 (vectors 16 14157)
 (vector-slots 8 503184 11636)
 (floats 8 50 67)
 (intervals 56 232 0)
 (buffers 992 11)
 (heap 1024 14329 1068))

Attachment: gdb.txt
Description: Text document

Attachment: contents.c
Description: Text Data

--- End Message ---
--- Begin Message --- Subject: Re: bug#31888: 27.0.50; Segmentation fault in replace-buffer-contents Date: Sat, 23 Jun 2018 14:15:23 +0300
> Date: Fri, 22 Jun 2018 16:03:02 +0300
> From: Eli Zaretskii <address@hidden>
> Cc: address@hidden
> The command is still too slow (takes about 2.5 min for the above use
> case in my unoptimized build, about 30 sec of which is spent in
> compareseq).  I will try to look into speeding it up.

I could find only a minor speedup (about 10%), by slightly changing
buffer_chars_equal per suggestion in another bug report.

In this particular case, replacing the contents of dispnew.c with that
of contents.c takes 2018 deletions and 2781 insertions, each one of
these operations takes about 20 msec in the unoptimized build where I
timed them; the call to compareseq takes another 26 sec (expect the
times to be lower by a factor of 3 in an optimized build).  My
conclusion from various attempts to speed up the code was that most of
this time is taken by making small changes to buffer text, which
involves moving the gap, which in turn requires shuffling of buffer
text to and fro.  I don't see how can we speed that up if we stay with
the current idea of the function, and want to preserve text properties
and overlays as much as possible.

So I ended up inserting a few calls to maybe_quit into the inner loops
of the function, to allow users bail out of lengthy execution, and
warning about the potential slowness in the doc string.

I'm closing this bug; if someone has ideas for how to speed up the
function significantly, please reopen, or file a new bug.

--- End Message ---

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