[PATCH] powerpc: Expose VSX feature test

[Nathan Phillips <waic9e at protonmail dot com>]

Hope it's OK to submit a small change like this. Trying to familiarize myself
with the patch process.

My copyright assignment is underway.

--

Read the HWCAP auxval key to test for VSX support. Expose result through
the cpu_features interface.

Preliminary change to prepare for PowerPC optimized libmvec implementations
[BZ #20123]. Enables selecting optimized version at load time in ifunc
resolver.

	* sysdeps/powerpc/cpu-features.h (cpu_features): Add vsx field.
	* sysdeps/powerpc/cpu-features.c (init_cpu_features):
	Feature test VSX availability.
---
diff --git a/sysdeps/powerpc/cpu-features.c b/sysdeps/powerpc/cpu-features.c
index 955d4778a6..477c7504b9 100644
--- a/sysdeps/powerpc/cpu-features.c
+++ b/sysdeps/powerpc/cpu-features.c
@@ -16,6 +16,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <errno.h>
+#include <sys/auxv.h>
 #include <stdint.h>
 #include <cpu-features.h>
 
@@ -26,6 +28,9 @@
 static inline void
 init_cpu_features (struct cpu_features *cpu_features)
 {
+  errno = 0;
+  unsigned long int hwcap = getauxval (AT_HWCAP);
+
   /* Default is to use aligned memory access on optimized function unless
      tunables is enable, since for this case user can explicit disable
      unaligned optimizations.  */
@@ -36,4 +41,13 @@ init_cpu_features (struct cpu_features *cpu_features)
 #else
   cpu_features->use_cached_memopt = false;
 #endif
+
+  if (errno == ENOENT)
+    {
+      cpu_features->vsx = false;
+    }
+  else
+    {
+      cpu_features->vsx = ((hwcap & PPC_FEATURE_HAS_VSX) != 0);
+    }
 }
diff --git a/sysdeps/powerpc/cpu-features.h b/sysdeps/powerpc/cpu-features.h
index e596385b4b..0248862b8a 100644
--- a/sysdeps/powerpc/cpu-features.h
+++ b/sysdeps/powerpc/cpu-features.h
@@ -23,6 +23,7 @@
 struct cpu_features
 {
   bool use_cached_memopt;
+  bool vsx;
 };
 
 #endif /* __CPU_FEATURES_H  */