Re: [RFC PATCH v3] grep: treat PCRE2 jit compilation memory error as non fatal

[Carlo Arenas <carenas@gmail.com>]

PROs:
* it works (only for PCRE2) and tested in OpenBSD, NetBSD, macOS, Linux (Debian)
* it applies everywhere (even pu) without conflicts
* it doesn't introduce any regressions in tests (tested in Debian with
SElinux in enforcing mode)
* it is simple

CONs:
* HardenedBSD still segfaults (bugfix proposed[1] to sljit/pcre)
* warning is noisy (at least once per thread) and might be even
ineffective as it goes to stderr while stdout with most the output
goes to a pager
* too conservative (pcre2grep shows all errors from pcre2_jit_compile
should be ignored)
* no tests

Known Issues:
* code is ugly (it even triggers a warning if you have the right compiler)
* code is suspiciously similar to one[2] that was rejected, but
hopefully commit message is better
* code is incomplete (PCRE1 has too many conflicting changes in flight
to attempt a similar fix)
* there are obvious blind spots in the tests that need fixing, and a
lot more testing in other platforms/architectures
* git still will sometimes die because the non fast path has UTF-8 issues

I still think the pcre.jit flag knob might be useful to workaround
some of the issues detailed in CONs but probably with a different
definition:
unset -> fallback (try JIT but use interpreter if that didn't work)
false -> don't even try to use JIT
true -> print warning and maybe even die (if we really think that is useful)

some performance numbers below for the perl tests

with JIT enabled (in non enforcing SELinux)

Test                                            this tree
---------------------------------------------------------------
7820.3: perl grep 'how.to'                      0.56(0.29+0.60)
7820.7: perl grep '^how to'                     0.49(0.29+0.54)
7820.11: perl grep '[how] to'                   0.54(0.39+0.51)
7820.15: perl grep '(e.t[^ ]*|v.ry) rare'       0.60(0.45+0.58)
7820.19: perl grep 'm(ú|u)lt.b(æ|y)te'          0.58(0.30+0.61)

with "fallback to interpreter" (in enforcing SELinux)

Test                                            this tree
---------------------------------------------------------------
7820.3: perl grep 'how.to'                      0.64(0.59+0.56)
7820.7: perl grep '^how to'                     1.83(2.91+0.56)
7820.11: perl grep '[how] to'                   2.07(3.33+0.61)
7820.15: perl grep '(e.t[^ ]*|v.ry) rare'       2.89(4.91+0.66)
7820.19: perl grep 'm(ú|u)lt.b(æ|y)te'          0.78(0.86+0.55)

[1] https://github.com/zherczeg/sljit/pull/2
[2] https://public-inbox.org/git/20181209230024.43444-3-carenas@gmail.com/