[RFC PATCH 1/2] grep: fallback to interpreter if JIT fails with pcre1

["Carlo Marcelo Arenas Belón" <carenas@gmail.com>]

JIT support was added to 8.20 but the interface we rely on is only
enabled after 8.32 so try to make the message clearer.

in systems where there are restrictions against creating executable
pages programatically (like OpenBSD, NetBSD, macOS or seLinux) JIT
will fail, resulting in a error message to the user.

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
---
 Makefile | 12 ++++++------
 grep.c   |  6 ++++++
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 1a44c811aa..62b0cb6ee6 100644
--- a/Makefile
+++ b/Makefile
@@ -32,14 +32,14 @@ all::
 # USE_LIBPCRE is a synonym for USE_LIBPCRE2, define USE_LIBPCRE1
 # instead if you'd like to use the legacy version 1 of the PCRE
 # library. Support for version 1 will likely be removed in some future
-# release of Git, as upstream has all but abandoned it.
+# release of Git, as upstream is focusing all development for new
+# features in the newer version instead.
 #
 # When using USE_LIBPCRE1, define NO_LIBPCRE1_JIT if the PCRE v1
-# library is compiled without --enable-jit. We will auto-detect
-# whether the version of the PCRE v1 library in use has JIT support at
-# all, but we unfortunately can't auto-detect whether JIT support
-# hasn't been compiled in in an otherwise JIT-supporting version. If
-# you have link-time errors about a missing `pcre_jit_exec` define
+# library is newer than 8.32 but compiled without --enable-jit or
+# you want to disable JIT
+#
+# If you have link-time errors about a missing `pcre_jit_exec` define
 # this, or recompile PCRE v1 with --enable-jit.
 #
 # Define LIBPCREDIR=/foo/bar if your PCRE header and library files are
diff --git a/grep.c b/grep.c
index 4db1510d16..5ccc0421a1 100644
--- a/grep.c
+++ b/grep.c
@@ -405,6 +405,12 @@ static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 		die("%s", error);
 
 #ifdef GIT_PCRE1_USE_JIT
+	if (p->pcre1_extra_info &&
+		!(p->pcre1_extra_info->flags & PCRE_EXTRA_EXECUTABLE_JIT)) {
+		/* JIT failed so fallback to the interpreter */
+		p->pcre1_jit_on = 0;
+		return;
+	}
 	pcre_config(PCRE_CONFIG_JIT, &p->pcre1_jit_on);
 	if (p->pcre1_jit_on == 1) {
 		p->pcre1_jit_stack = pcre_jit_stack_alloc(1, 1024 * 1024);
-- 
2.20.0