Add common ifunc-init.h header

This patch moves the generic definition from x86_64 init-arch
to a common header ifunc-init.h.  No functional changes is expected.

Checked on a x86_64-linux-gnu build.

	* sysdeps/generic/ifunc-init.h: New file.
	* sysdeps/x86/init-arch.h: Use generic ifunc-init.h.

1 files changed, 54 insertions, 0 deletions

diff --git a/sysdeps/generic/ifunc-init.h b/sysdeps/generic/ifunc-init.h
new file mode 100644
index 0000000000..59d5ac6c1c
--- /dev/null
+++ b/sysdeps/generic/ifunc-init.h
@@ -0,0 +1,54 @@
+/* IFUNC generic definitions.
+   This file is part of the GNU C Library.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* These macros are used to implement ifunc selection in C.  To implement
+   an ifunc function, foo, which returns the address of __foo_impl1 or
+   __foo_impl2:
+
+   #define foo __redirect_foo
+   #include <foo.h>
+   #undef foo
+   #define SYMBOL_NAME foo
+   #include <ifunc-init.h>
+
+   extern __typeof (REDIRECT_NAME) OPTIMIZE (impl1) attribute_hidden;
+   extern __typeof (REDIRECT_NAME) OPTIMIZE (impl2) attribute_hidden;
+
+   static inline void *
+   foo_selector (void)
+   {
+     if (condition)
+      return OPTIMIZE (impl2);
+
+     return OPTIMIZE (impl1);
+   }
+
+   libc_ifunc_redirected (__redirect_foo, foo, IFUNC_SELECTOR ());
+*/
+
+#define PASTER1(x,y)	x##_##y
+#define EVALUATOR1(x,y)	PASTER1 (x,y)
+#define PASTER2(x,y)	__##x##_##y
+#define EVALUATOR2(x,y)	PASTER2 (x,y)
+
+/* Basically set '__redirect_<symbol>' to use as type definition,
+   '__<symbol>_<variant>' as the optimized implementation and
+   '<symbol>_ifunc_selector' as the IFUNC selector.  */
+#define REDIRECT_NAME	EVALUATOR1 (__redirect, SYMBOL_NAME)
+#define OPTIMIZE(name)	EVALUATOR2 (SYMBOL_NAME, name)
+#define IFUNC_SELECTOR	EVALUATOR1 (SYMBOL_NAME, ifunc_selector)