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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Carlo Arenas <carenas@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 14:38:39 +0200
Message-ID: <87wog15834.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <CAPUEspgQNCENviPYP6X790DvSgj_RpJVo2KP_39voLQnVc65pQ@mail.gmail.com>


On Mon, Jul 29 2019, Carlo Arenas wrote:

> 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)

Ah of course, I was reading this as "regexp
compile-time". I.e. something like (*NO_JIT). No *such* thing exists for
PCRE v1 JIT AFAIK as exposed by git-grep.

>> > 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

...because OpenBSD PCRE v1 was compiled with --disable-jit before, but
their v2 package has --enable-jit, it just doesn't work at all? Is this
your custom built git + OpenBSD packages of PCRE coming with the OS?

I don't use OpenBSD, but isn't this their recipe? Seems they use "make
test", and don't compile with PCRE at all if I'm reading it right:
https://github.com/openbsd/ports/blob/master/devel/git/Makefile

> 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

Right, no arguments at all about ab/no-kwset making this worse (re: your
#1). I just really prefer not to expose/document config for what
*should* be something purely internal if the X-Y problem is a bug being
exposed that we should just fix.

Particularly because I think it's a losing battle to provide run-time
options for what are surely a *lot* of "make test" failures.

If it really is unavoidable to detect this until runtime in some common
configurations I have no problem with it, I just haven't encountered
that so far.

> 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.

patches = your recent
https://public-inbox.org/git/20181209230024.43444-2-carenas@gmail.com/
or something earlier?

That patch seems sane without having tested it. Seems like the
equivalent of what we do with v1 with PCRE2_JIT_COMPLETE.

I *am* curious if there's setups where fixing the code for PCRE v1 isn't
purely an academic exercise. Is there a reason for why these platforms
can't just move to PCRE v2 in principle (dumpster fires in "next"
non-withstanding)?

>> 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.

  reply	other threads:[~2019-07-29 12:38 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
2019-07-29 12:38     ` Ævar Arnfjörð Bjarmason [this message]
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

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