Probe JIT availability at runtime

SELinux or PaX/grsecurity based kernels may deny creating writable and
executable mappings, leading to errors when trying to allocate JIT
memory, even though JIT support is generally available. Instead of
failing hard in this case, allow to use the interpreter fallback by
probing and announcing the availability of JIT mode at runtime through
the PCRE2_CONFIG_JIT hook.

This only happens for configurations using only the default JIT memory
allocator, i.e. not the SELinux aware one. However, we still mark the
latter as experimental and distributions like Debian don't enable it.

The current behaviour leads to nasty user visible errors on such
systems, e.g. when running 'git grep':

  $ git grep peach
  fatal: Couldn't JIT the PCRE2 pattern 'peach', got '-48'

With this change in place, it'll fall back to the interpreter and "just
work", providing a much more pleasant user experience.

Signed-off-by: Mathias Krause <[email protected]>

src/pcre2_config.c

@@ -145,7 +145,7 @@ switch (what)
 
   case PCRE2_CONFIG_JIT:
 #ifdef SUPPORT_JIT
-  *((uint32_t *)where) = 1;
+  *((uint32_t *)where) = PRIV(jit_supported)();
 #else
   *((uint32_t *)where) = 0;
 #endif

src/pcre2_internal.h

@@ -1992,6 +1992,7 @@ is available. */
 #define _pcre2_jit_free              PCRE2_SUFFIX(_pcre2_jit_free_)
 #define _pcre2_jit_get_size          PCRE2_SUFFIX(_pcre2_jit_get_size_)
 #define _pcre2_jit_get_target        PCRE2_SUFFIX(_pcre2_jit_get_target_)
+#define _pcre2_jit_supported         PCRE2_SUFFIX(_pcre2_jit_supported_)
 #define _pcre2_memctl_malloc         PCRE2_SUFFIX(_pcre2_memctl_malloc_)
 #define _pcre2_ord2utf               PCRE2_SUFFIX(_pcre2_ord2utf_)
 #define _pcre2_script_run            PCRE2_SUFFIX(_pcre2_script_run_)
@@ -2019,6 +2020,7 @@ extern void         _pcre2_jit_free_rodata(void *, void *);
 extern void         _pcre2_jit_free(void *, pcre2_memctl *);
 extern size_t       _pcre2_jit_get_size(void *);
 const char *        _pcre2_jit_get_target(void);
+extern int          _pcre2_jit_supported(void);
 extern void *       _pcre2_memctl_malloc(size_t, pcre2_memctl *);
 extern unsigned int _pcre2_ord2utf(uint32_t, PCRE2_UCHAR *);
 extern BOOL         _pcre2_script_run(PCRE2_SPTR, PCRE2_SPTR, BOOL);

src/pcre2_jit_misc.c

@@ -197,6 +197,21 @@ if (jit_stack != NULL)
 }
 
 
+/*************************************************
+*             Test runtime JIT support           *
+*************************************************/
+
+int
+PRIV(jit_supported)(void)
+{
+#ifndef SUPPORT_JIT
+return 0;
+#else  /* SUPPORT_JIT */
+return sljit_get_runtime_support();
+#endif  /* SUPPORT_JIT */
+}
+
+
 /*************************************************
 *               Get target CPU type              *
 *************************************************/