Re: [v2.35.0 regression] some PCRE hangs under UTF-8 locale (was: [PATCH 1/2] grep/pcre2: use PCRE2_UTF even with ASCII patterns)

On Sat, Feb 05, 2022 at 06:00:02PM +0100, René Scharfe wrote:

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Subject: [PATCH] grep: disable JIT on PCRE2 before 10.36 to avoid endless loop

Commit e0c6029 (Fix inifinite loop when a single byte newline is
searched in JIT., 2020-05-29) of PCRE2 adds the following point to its
ChangeLog for version 10.36:

  2. Fix inifinite loop when a single byte newline is searched in JIT when
  invalid utf8 mode is enabled.

Avoid that bug on older versions (which are still reportedly found in
the wild) by disabling the JIT when handling UTF-8.

Reported-by: SZEDER Gábor <redacted>
Signed-off-by: René Scharfe <redacted>
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Not sure how to test it.  Killing git grep after a second or so seems a
bit clumsy.  timeout(1) from GNU coreutils at least allows doing that
from the shell, but it's not a standard tool.  Perhaps we need a new
test helper for that purpose?

https://mywiki.wooledge.org/BashFAQ/068 offers a Perl-based Shell
function or aborting a program if it takes too long:

   doalarm() { perl -e 'alarm shift; exec @ARGV' -- "$@"; }

It doesn't waste time when the program finishes faster and seems to work
fine with git grep.

I can't actually test the effectiveness of the patch because PCRE2's
JIT doesn't work on my development machine at all (Apple M1), as I just
discovered. :-/  While we know that disabling JIT helps, we didn't
actually determine, yet, if e0c6029 (Fix inifinite loop when a single
byte newline is searched in JIT., 2020-05-29) really fixes the "^\s"
bug.

So I have to abandon this patch, unfortunately.  Any volunteer to pick
it up?

FWIW, I built Git with your patch and USE_LIBPCRE2=YesPlease and run
the test suite, and it succeeded.  Though I can't judge how much is
this actually worth.