git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
From: Carlo Arenas <carenas@gmail.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, sandals@crustytoothpaste.net
Subject: Re: [RFC PATCH] grep: allow for run time disabling of JIT in PCRE
Date: Mon, 29 Jul 2019 03:26:42 -0700	[thread overview]
Message-ID: <CAPUEspgQNCENviPYP6X790DvSgj_RpJVo2KP_39voLQnVc65pQ@mail.gmail.com> (raw)
In-Reply-To: <8736ip6wzk.fsf@evledraar.gmail.com>

On Mon, Jul 29, 2019 at 1:55 AM Ævar Arnfjörð Bjarmason
<avarab@gmail.com> wrote:
>
> On Mon, Jul 29 2019, Carlo Marcelo Arenas Belón wrote:
>
> > PCRE1 allowed for a compile time flag to disable JIT, but PCRE2 never
> > had one, forcing the use of JIT if -P was requested.
>
> What's that PCRE1 compile-time flag?

NO_LIBPCRE1_JIT at GIT compile time (regardless of JIT support in the
PCRE1 library you are using)

> > After ed0479ce3d (Merge branch 'ab/no-kwset' into next, 2019-07-15)
> > the PCRE2 engine will be used more broadly and therefore adding this
> > knob will give users a fallback for situations like the one observed
> > in OpenBSD with a JIT enabled PCRE2, because of W^X restrictions:
> >
> >   $ git grep 'foo bar'
> >   fatal: Couldn't JIT the PCRE2 pattern 'foo bar', got '-48'
> >   $ git grep -G 'foo bar'
> >   fatal: Couldn't JIT the PCRE2 pattern 'foo bar', got '-48'
> >   $ git grep -E 'foo bar'
> >   fatal: Couldn't JIT the PCRE2 pattern 'foo bar', got '-48'
> >   $ git grep -F 'foo bar'
> >   fatal: Couldn't JIT the PCRE2 pattern 'foo bar', got '-48'
>
> Yeah that obviously sucks more with ab/no-kwset, but that seems like a
> case where -P would have been completely broken before, and therefore I
> can't imagine the package ever passed "make test". Or is W^X also
> exposed as some run-time option on OpenBSD?

ironically, you could use PCRE1 since that is not using the JIT fast
path and therefore will fallback automatically to the interpreter

there is also a convoluted way to make your binary work by moving
it into a mount point that has been specially exempted from that W^X
restriction.

> I.e. aside from the merits of such a setting in general these examples
> seem like just working around something that should be fixed at make
> all/test time, or maybe I'm missing something.

1) before you could just avoid using -P and still be able to grep
2) there is no way to tell PCRE2 to get out of the way even if you are
    not using -P

you are right though that this is not a new problem and was reported
before with patches and the last comment saying a configuration
should be provided.

> To the extent that we'd want to make this sort of thing configurable, I
> wonder if a continuation of my (*NO_JIT) patch isn't better, i.e. just
> adding the ability to configure some string we'd inject at the start of
> every pattern.

looking at the number of lines of code, it would seem the configuration
approach is simpler.

> That would allow for setting any other number of options in
> pcre2syntax(3) without us needing to carry config for each one,
> e.g. (*LIMIT_HEAP=d), (*LIMIT_DEPTH=d) etc. It does present a larger
> foot-gun surface though...

the parameters I suspect users might need are not really accessible through
that (ex: jit stacksize).

it is important to note that currently we are not preventing any user to use
those flags themselves in their patterns either.

Carlo

  reply	other threads:[~2019-07-29 10:26 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-28 23:54 Carlo Marcelo Arenas Belón
2019-07-29  0:09 ` Carlo Arenas
2019-07-29  4:57 ` Junio C Hamano
2019-07-29  5:29   ` Carlo Arenas
2019-07-29  8:55 ` Ævar Arnfjörð Bjarmason
2019-07-29 10:26   ` Carlo Arenas [this message]
2019-07-29 12:38     ` Ævar Arnfjörð Bjarmason
2019-07-30 13:01       ` Carlo Arenas
2019-07-29 10:59 ` [RFC PATCH v2] " Carlo Marcelo Arenas Belón
2019-07-29 11:33   ` Carlo Arenas
2019-07-29 15:11   ` René Scharfe
2019-07-29 17:47     ` Junio C Hamano
2019-07-30  0:49       ` Carlo Arenas
2019-07-30 17:55         ` René Scharfe
2019-07-31 12:36         ` Johannes Schindelin
2019-07-31 16:18           ` Junio C Hamano
2019-07-31 12:32   ` Johannes Schindelin
2019-07-31 14:57     ` Ævar Arnfjörð Bjarmason
2019-08-04  0:25       ` Carlo Arenas
2019-08-04  3:14   ` [RFC PATCH v3] grep: treat PCRE2 jit compilation memory error as non fatal Carlo Marcelo Arenas Belón
2019-08-04  7:43     ` Carlo Arenas
2019-08-05 20:16       ` Junio C Hamano
2019-07-31 12:24 ` [RFC PATCH] grep: allow for run time disabling of JIT in PCRE Johannes Schindelin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAPUEspgQNCENviPYP6X790DvSgj_RpJVo2KP_39voLQnVc65pQ@mail.gmail.com \
    --to=carenas@gmail.com \
    --cc=avarab@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=sandals@crustytoothpaste.net \
    --subject='Re: [RFC PATCH] grep: allow for run time disabling of JIT in PCRE' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Code repositories for project(s) associated with this inbox:

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).