x86: Add macros to implement ifunce selection in C

These macros are used to implement ifunc selection in C.  To implement
an ifunc function, foo, which returns the address of __foo_sse2 or
__foo_avx2:

   __foo_avx2:

   #define foo __redirect_foo
   #define __foo __redirect___foo
   #include <foo.h>
   #undef foo
   #undef __foo
   #define SYMBOL_NAME foo
   #include <init-arch.h>

   extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2) attribute_hidden;
   extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2) attribute_hidden;

   static inline void *
   foo_selector (void)
   {
     if (use AVX2)
      return OPTIMIZE (avx2);

     return OPTIMIZE (sse2);
   }

   libc_ifunc_redirected (__redirect_foo, foo, foo_selector ());

	* sysdeps/x86/init-arch.h (PASTER1): New.
	(EVALUATOR1): Likewise.
	(PASTER2): Likewise.
	(EVALUATOR2): Likewise.
	(REDIRECT_NAME): Likewise.
	(OPTIMIZE): Likewise.
	(IFUNC_SELECTOR): Likewise.

1 files changed, 40 insertions, 0 deletions

diff --git a/sysdeps/x86/init-arch.h b/sysdeps/x86/init-arch.h
index 6cbc16b7f6..15d3f0975d 100644
--- a/sysdeps/x86/init-arch.h
+++ b/sysdeps/x86/init-arch.h
@@ -21,6 +21,46 @@
 # include <ldsodefs.h>
 #endif
 
+/* These macros are used to implement ifunc selection in C.  To implement
+   an ifunc function, foo, which returns the address of __foo_sse2 or
+   __foo_avx2:
+
+   #define foo __redirect_foo
+   #define __foo __redirect___foo
+   #include <foo.h>
+   #undef foo
+   #undef __foo
+   #define SYMBOL_NAME foo
+   #include <init-arch.h>
+
+   extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2) attribute_hidden;
+   extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2) attribute_hidden;
+
+   static inline void *
+   foo_selector (void)
+   {
+     if (use AVX2)
+      return OPTIMIZE (avx2);
+
+     return OPTIMIZE (sse2);
+   }
+
+   libc_ifunc_redirected (__redirect_foo, foo, foo_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)
+
 #ifndef __x86_64__
 /* Due to the reordering and the other nifty extensions in i686, it is
    not really good to use heavily i586 optimized code on an i686.  It's