From: "Ævar Arnfjörð Bjarmason" <email@example.com> To: Johannes Schindelin <Johannes.Schindelin@gmx.de> Cc: "Carlo Marcelo Arenas Belón" <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Re: [RFC PATCH v2] grep: allow for run time disabling of JIT in PCRE Date: Wed, 31 Jul 2019 16:57:54 +0200 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <nycvar.QRO.firstname.lastname@example.org> On Wed, Jul 31 2019, Johannes Schindelin wrote: > Hi, > > On Mon, 29 Jul 2019, Carlo Marcelo Arenas Belón wrote: > >> $ git grep 'foo bar' >> fatal: Couldn't JIT the PCRE2 pattern 'foo bar', got '-48' > > My immediate reaction to this error message was: That's not helpful. > What is `-48` supposed to mean? Why do we even think it sensible to > throw such an error message at the end user? Can't we do a much better > job translating that into something that makes actual sense without > knowing implementation details? > > But then, I realized that -48 must be a well-known constant in PCRE2, > and my reaction transformed into something much more hopeful: why don't > we detect the situation where the JIT'ed code was not actually > executable [*1*], and fall back to the non-JIT'ed code path ourselves, > without troubling the end user (maybe warning, but maybe better not lest > we annoy the user with something pointless)? > > Even after finding out that -48 disappointingly means > PCRE2_ERROR_NOMEMORY (as opposed to something like > PCRE2_ERROR_CANNOT_EXECUTE_JIT_CODE), I like the idea of not bothering > end users and doing the sensible fallback under the hood. > > Ciao, > Dscho > > Footnote *1*: Why anybody would think it sensible to build a PCRE2 with > JIT on an OS that does not allow executing code that was written by the > same process is beyond me. Or is there a mode in OpenBSD that *does* > allow JIT'ed code to be executed? We do detect if JIT isn't supported and fall back. That's what the pcre2_config(PCRE2_CONFIG_JIT, &p->pcre2_jit_on) code in grep.c does. This and is the subsequent pcre2_pattern_info() call is how PCRE documents that you should do this. What hasn't been supported is all of that saying "yes, I support JIT" and the feature then fail whaling. I had not encountered that before. So far that seems like because Carlo just built a completely broken PCRE v2 package, so I don't know if that's worth supporting on our side. I.e. this isn't something I think could plausibly happen in the wild. That should *not* be confused with me thinking other stuff Carlo's raised is a non-issue, e.g. running into the JIT stack limit etc. Some of that's clearly bugs in our/my grep.c code that need fixing.
next prev parent reply other threads:[~2019-07-31 14:57 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-07-28 23:54 [RFC PATCH] " 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 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 [this message] 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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