[RFC,0/2] fallback to interpreter if JIT fails with pcre
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Message ID 20181209230024.43444-1-carenas@gmail.com
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  • fallback to interpreter if JIT fails with pcre
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Carlo Arenas Dec. 9, 2018, 11 p.m. UTC
while testing in NetBSD 8, was surprised to find that most test cases
using PCRE2 where failing with some cryptic error from git :

  fatal: Couldn't JIT the PCRE2 pattern '$PATTERN', got '-48'

interestingly enough, using a JIT enabled PCRE1 library (not the default)
will show a similar error but a different error code.

the underlying problem is the same though; NetBSD includes PAX support
which restricts the use of memory that is both writeable and executable
and that prevents the JIT to create a compiled expression to jump into,
and while the "fix" for NetBSD is simple it would seem the user experience
could be improved if instead of aborting, git will instead return the matches
using the slower interpreter (which seem to be also the recomendation from
the library developers)

it is important to note that the problem is not unique to NetBSD and had
reproduced it in OpenBSD where working around the issue is more complicated
as WˆX exceptions require a filesystem mount option, and I can see it being
problematic with linux (as shown by the open bug[1] and the development of
an alternative allocator to workaround the issue with seLinux) and with
macOS (specially versions older than 10.14) where there are restrictions to
the number of maps allowed with those flags.

I am also curious if expanding NO_LIBPCRE1_JIT as an option to disable JIT
with PCRE2 (with a different name) might be worth pursuing? as well as some
ways to narrow the failures that will trigger the fallback, but the later
is likely to need library changes which might not be possible with the old
version anyway.

[1] https://bugs.exim.org/show_bug.cgi?id=1749

Carlo Marcelo Arenas Belón (2):
  grep: fallback to interpreter if JIT fails with pcre1
  grep: fallback to interpreter if JIT fails with pcre2

 Makefile | 12 ++++++------
 grep.c   | 13 +++++++++++--
 2 files changed, 17 insertions(+), 8 deletions(-)