Filters: If somebody doesn't like _Thread_local, don't fail for now, just be a little slower.

When the parallel execution comes into place, we'll likely enforce this
C11 feature. It's much simpler and also faster than pthread_[sg]etspecific().

aclocal.m4

@@ -1,6 +1,25 @@
 dnl ** Additional Autoconf tests for BIRD configure script
 dnl ** (c) 1999 Martin Mares <mj@ucw.cz>
 
+AC_DEFUN([BIRD_CHECK_THREAD_LOCAL],
+[
+  AC_CACHE_CHECK(
+    [whether _Thread_local is known],
+    [bird_cv_thread_local],
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM(
+        [
+	  _Thread_local static int x = 42;
+	],
+	[]
+      )
+    ],
+    [bird_cv_thread_local=yes],
+    [bird_cv_thread_local=no]
+    )
+  )
+])
+
 AC_DEFUN([BIRD_CHECK_PTHREADS],
 [
   bird_tmp_cflags="$CFLAGS"
@@ -134,7 +153,7 @@ AC_DEFUN([BIRD_CHECK_ANDROID_LOG],
 AC_DEFUN([BIRD_CHECK_LTO],
 [
   bird_tmp_cflags="$CFLAGS"
-  bird_tmp_ldflags="$CFLAGS"
+  bird_tmp_ldflags="$LDFLAGS"
   CFLAGS="-flto"
   LDFLAGS="-flto"
 

configure.ac

@@ -115,6 +115,11 @@ if test -z "$GCC" ; then
   AC_MSG_ERROR([This program requires the GNU C Compiler.])
 fi
 
+BIRD_CHECK_THREAD_LOCAL
+if test "$bird_cv_thread_local" = yes ; then
+  AC_DEFINE([HAVE_THREAD_LOCAL], [1], [Define to 1 if _Thread_local is available])
+fi
+
 if test "$enable_pthreads" != no ; then
   BIRD_CHECK_PTHREADS
 

filter/filter.c

@@ -51,7 +51,7 @@
 #include "filter/data.h"
 
 /* Internal filter state, to be allocated on stack when executing filters */
-_Thread_local struct filter_state {
+struct filter_state {
   /* The route we are processing. This may be NULL to indicate no route available. */
   struct rte **rte;
 
@@ -63,7 +63,14 @@ _Thread_local struct filter_state {
   struct linpool *pool;
   struct buffer buf;
   int flags;
-} filter_state;
+};
+
+#if HAVE_THREAD_LOCAL
+_Thread_local static struct filter_state filter_state;
+#define FS_INIT(...) filter_state = (struct filter_state) { __VA_ARGS__ }
+#else
+#define FS_INIT(...) struct filter_state filter_state = { __VA_ARGS__ }
+#endif
 
 void (*bt_assert_hook)(int result, const struct f_line_item *assert);
 
@@ -275,11 +282,11 @@ f_run(const struct filter *filter, struct rte **rte, struct linpool *tmp_pool, i
   DBG( "Running filter `%s'...", filter->name );
 
   /* Initialize the filter state */
-  filter_state = (struct filter_state) {
+  FS_INIT(
       .rte = rte,
       .pool = tmp_pool,
       .flags = flags,
-  };
+      );
 
   LOG_BUFFER_INIT(filter_state.buf);
 
@@ -338,10 +345,10 @@ f_run(const struct filter *filter, struct rte **rte, struct linpool *tmp_pool, i
 enum filter_return
 f_eval_rte(const struct f_line *expr, struct rte **rte, struct linpool *tmp_pool)
 {
-  filter_state = (struct filter_state) {
+  FS_INIT(
       .rte = rte,
       .pool = tmp_pool,
-  };
+      );
 
   LOG_BUFFER_INIT(filter_state.buf);
 
@@ -360,9 +367,9 @@ f_eval_rte(const struct f_line *expr, struct rte **rte, struct linpool *tmp_pool
 enum filter_return
 f_eval(const struct f_line *expr, struct linpool *tmp_pool, struct f_val *pres)
 {
-  filter_state = (struct filter_state) {
+  FS_INIT(
       .pool = tmp_pool,
-  };
+      );
 
   LOG_BUFFER_INIT(filter_state.buf);
 
@@ -379,9 +386,9 @@ uint
 f_eval_int(const struct f_line *expr)
 {
   /* Called independently in parse-time to eval expressions */
-  filter_state = (struct filter_state) {
+  FS_INIT(
       .pool = cfg_mem,
-  };
+      );
 
   struct f_val val;
 

lib/birdlib.h

@@ -73,6 +73,12 @@ static inline int u64_cmp(u64 i1, u64 i2)
 #define UNUSED __attribute__((unused))
 #define PACKED __attribute__((packed))
 
+#ifdef HAVE_THREAD_LOCAL
+#define THREAD_LOCAL _Thread_local
+#else
+#define THREAD_LOCAL
+#endif
+
 /* Microsecond time */
 
 typedef s64 btime;