[PATCH, rs6000] Modify libgcc's float128 IFUNC resolver functions to use __builtin_cpu_supports()

[Peter Bergner <peter at bergner dot org>]

Usage of getauxval() within the float128 libgcc IFUNC resolver functions is
causing problems:

    https://sourceware.org/bugzilla/show_bug.cgi?id=21707

Alan describes why we can't have relocations in IFUNC resolver functions here:

    https://gcc.gnu.org/PR81193

With the addition of __builtin_cpu_supports (), we no longer need to call
getauxval() to query the HWCAP/HWCAP2 masks, so let's use that instead.

I have verified with some small test cases, that we do call the correct
__{add,sub,...}k3_hw() functions instead of the *_sw versions.  I did that
by running the test cases in GDB and manually setting the IEEE128 bit in
the HWCAP2 mask stored in the TCB before the resolvers were run.

This bootstrapps and regtests with no regressions, ok for trunk?

I will note that this patch causes issues in some tests in the GLIBC testsiute,
which Tulio is working on fixing (it's a GLIBC issue, not a GCC issue), so if
this patch is "ok", I plan on holding off on committing this, until the GLIBC
fix is committed.

Peter

	* config/rs6000/float128-ifunc.c: Don't include auxv.h.
	(have_ieee_hw_p): Delete function.
	(SW_OR_HW) Use __builtin_cpu_supports().

Index: libgcc/config/rs6000/float128-ifunc.c
===================================================================
--- libgcc/config/rs6000/float128-ifunc.c	(revision 249850)
+++ libgcc/config/rs6000/float128-ifunc.c	(working copy)
@@ -45,47 +45,7 @@
 #error "This module must not be compiled with IEEE 128-bit hardware support"
 #endif
 
-#include <sys/auxv.h>
-
-/* Use the namespace clean version of getauxval.  However, not all versions of
-   sys/auxv.h declare it, so declare it here.  This code is intended to be
-   temporary until a suitable version of __builtin_cpu_supports is added that
-   allows us to tell quickly if the machine supports IEEE 128-bit hardware.  */
-extern unsigned long __getauxval (unsigned long);
-
-static int
-have_ieee_hw_p (void)
-{
-  static int ieee_hw_p = -1;
-
-  if (ieee_hw_p < 0)
-    {
-      char *p = (char *) __getauxval (AT_PLATFORM);
-
-      ieee_hw_p = 0;
-
-      /* Don't use atoi/strtol/strncmp/etc.  These may require the normal
-	 environment to be setup to set errno to 0, and the ifunc resolvers run
-	 before the whole glibc environment is initialized.  */
-      if (p && p[0] == 'p' && p[1] == 'o' && p[2] == 'w' && p[3] == 'e'
-	  && p[4] == 'r')
-	{
-	  long n = 0;
-	  char ch;
-
-	  p += 5;
-	  while ((ch = *p++) >= '0' && (ch <= '9'))
-	    n = (n * 10) + (ch - '0');
-
-	  if (n >= 9)
-	    ieee_hw_p = 1;
-	}
-    }
-
-  return ieee_hw_p;
-}
-
-#define SW_OR_HW(SW, HW) (have_ieee_hw_p () ? HW : SW)
+#define SW_OR_HW(SW, HW) (__builtin_cpu_supports ("ieee128") ? HW : SW)
 
 /* Resolvers.  */