From: "René Scharfe" <l.s.r@web.de>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: "Carlo Arenas" <carenas@gmail.com>,
git@vger.kernel.org, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: improve performance of PCRE2 bug 2642 bug workaround
Date: Tue, 22 Mar 2022 21:26:10 +0100 [thread overview]
Message-ID: <99b0adb6-26ba-293c-3a8f-679f59e7cb4d@web.de> (raw)
In-Reply-To: <bd751d5c-2f8b-4c52-72ec-f2b7268a30a8@cs.ucla.edu>
Am 22.03.22 um 17:38 schrieb Paul Eggert:
> Today, Carlo Arenas pointed out[1] that GNU grep didn't work around
> PCRE2 bug 2642, which Git grep has a workaround for. While installing
> a GNU grep patch to fix this[2] I noticed that Git's workaround
> appears to be too pessimistic: on older PCRE2 libraries Git grep sets
> PCRE2_NO_START_OPTIMIZE even when PCRE2_CASELESS is not set.
>
> Attached is a patch to Git that I just now cobbled up and have not
> even compiled, much less tested. Please feel free to ignore it, as it
> would merely improve performance on older, buggy PCRE2 libraries and
> that might not be worth your trouble. I'm sending this email as more
> of a thank-you for letting us know indirectly of the PCRE2 bug.
>
> [1]: https://lists.gnu.org/r/grep-devel/2022-03/msg00004.html
> [2]: https://lists.gnu.org/r/grep-devel/2022-03/msg00005.html
Interesting. So you say bug 2642 [3] requires the flag PCRE2_CASELESS
(i.e. --ignore-case) to be triggered. (That's probably documented in
Bugzilla, but I'm not authorized to access it.)
However, the looser check works around another bug, if only by accident.
I believe it was fixed upstream by [4]. That other bug was discussed in
the thread Carlo linked to, which started at [5]. You should be able to
reproduce it with something like this (search for leading white-space in
a Unicode haystack):
$ echo ' Halló' | grep -P '^\s'
An affected version of PCRE2 would loop forever.
However, I can only test any of that with CI jobs, not locally, so
please take my findings with a heap of salt.
René
[3] https://bugs.exim.org/show_bug.cgi?id=2642
[4] https://github.com/PhilipHazel/pcre2/commit/e0c6029
[5] https://lore.kernel.org/git/20220129172542.GB2581@szeder.dev/
next prev parent reply other threads:[~2022-03-22 20:26 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-22 16:38 improve performance of PCRE2 bug 2642 bug workaround Paul Eggert
2022-03-22 20:26 ` René Scharfe [this message]
2022-03-22 21:12 ` Paul Eggert
2022-03-23 1:09 ` Carlo Marcelo Arenas Belón
2022-03-23 4:06 ` Paul Eggert
2022-03-23 18:37 ` René Scharfe
2022-03-23 20:24 ` Carlo Arenas
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