GNU bug report logs - #18361
New 'sort' implementation can crash Emacs

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From: Dmitry Antipov <dmantipov <at> yandex.ru>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 18361 <at> debbugs.gnu.org
Subject: bug#18361: New 'sort' implementation can crash Emacs
Date: Sat, 30 Aug 2014 09:07:46 +0400

On 08/30/2014 03:07 AM, Paul Eggert wrote:

> Sure, a comparison function that returns a new random value every
> time you call it.  Such a function is most likely not well formed
> that is, it most likely does not define a total order.

If an undefined behavior doesn't cause crash, I don't see a problem
if this is well-documented (probably in lispref).

I gave this function a solid run on GNU/Linux (glibc 2.18) and FreeBSD
10.0, and was unable to crash:

(defun sort-run ()
  (interactive)
  (let* ((max 1000000)
         (size 1000)
         (p (make-progress-reporter "Sorted: " 0 max)))
    (dotimes (loops max)
      (let ((v (make-vector size 0)))
        (dotimes (i size) (aset v i (% (random) (* size 2))))
        (sort v (lambda (x y) (random)))
        (progress-reporter-update p loops)))
    (progress-reporter-done p)))

I don't have any reasons to not trust in your experience, but I'm
really curious to look at the real example crashing qsort(_r) due
to ill-formed comparison function.

Dmitry

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