[RFC PATCH] grep: allow for run time disabling of JIT in PCRE

[Carlo Marcelo Arenas Belón <carenas@xxxxxxxxx>]

PCRE1 allowed for a compile time flag to disable JIT, but PCRE2 never
had one, forcing the use of JIT if -P was requested.

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'

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@xxxxxxxxx>
---
 Documentation/git-grep.txt |  4 ++++
 grep.c                     | 15 +++++++++++++--
 grep.h                     |  1 +
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index c89fb569e3..ff544bdeec 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -69,6 +69,10 @@ grep.fallbackToNoIndex::
 	If set to true, fall back to git grep --no-index if git grep
 	is executed outside of a git repository.  Defaults to false.
 
+pcre.jit::
+	If set to false, disable JIT when using PCRE.  Defaults to
+	true.
+
 
 OPTIONS
 -------
diff --git a/grep.c b/grep.c
index c7c06ae08d..3524d353dd 100644
--- a/grep.c
+++ b/grep.c
@@ -56,6 +56,7 @@ void init_grep_defaults(struct repository *repo)
 	opt->repo = repo;
 	opt->relative = 1;
 	opt->pathname = 1;
+	opt->pcre_jit = 1;
 	opt->max_depth = -1;
 	opt->pattern_type_option = GREP_PATTERN_TYPE_UNSPECIFIED;
 	color_set(opt->colors[GREP_COLOR_CONTEXT], "");
@@ -125,6 +126,12 @@ int grep_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "pcre.jit")) {
+		int is_bool;
+		opt->pcre_jit = git_config_bool_or_int(var, value, &is_bool);
+		return 0;
+	}
+
 	if (!strcmp(var, "color.grep"))
 		opt->color = git_config_colorbool(var, value);
 	if (!strcmp(var, "color.grep.match")) {
@@ -163,6 +170,7 @@ void grep_init(struct grep_opt *opt, struct repository *repo, const char *prefix
 	opt->pattern_tail = &opt->pattern_list;
 	opt->header_tail = &opt->header_list;
 
+	opt->pcre_jit = def->pcre_jit;
 	opt->only_matching = def->only_matching;
 	opt->color = def->color;
 	opt->extended_regexp_option = def->extended_regexp_option;
@@ -393,7 +401,8 @@ static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 		die("%s", error);
 
 #ifdef GIT_PCRE1_USE_JIT
-	pcre_config(PCRE_CONFIG_JIT, &p->pcre1_jit_on);
+	if (opt->pcre_jit)
+		pcre_config(PCRE_CONFIG_JIT, &p->pcre1_jit_on);
 #endif
 }
 
@@ -489,7 +498,9 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
 		compile_regexp_failed(p, (const char *)&errbuf);
 	}
 
-	pcre2_config(PCRE2_CONFIG_JIT, &p->pcre2_jit_on);
+	if (opt->pcre_jit)
+		pcre2_config(PCRE2_CONFIG_JIT, &p->pcre2_jit_on);
+
 	if (p->pcre2_jit_on) {
 		jitret = pcre2_jit_compile(p->pcre2_pattern, PCRE2_JIT_COMPLETE);
 		if (jitret)
diff --git a/grep.h b/grep.h
index c0c71eb4a9..fff152e606 100644
--- a/grep.h
+++ b/grep.h
@@ -151,6 +151,7 @@ struct grep_opt {
 	int allow_textconv;
 	int extended;
 	int use_reflog_filter;
+	int pcre_jit;
 	int pcre1;
 	int pcre2;
 	int relative;
-- 
2.22.0