[PATCH] Fix MPX tests on systems with MPX disabled

[Andi Kleen]

From: Andi Kleen <a...@linux.intel.com>

I have a Skylake system with MPX in the CPU, but MPX is disabled
in the kernel configuration.

This makes all the MPX tests fail because they assume if MPX
is in CPUID it works

Check the output of XGETBV too to detect non MPX kernels.

gcc/testsuite/:

2016-06-25  Andi Kleen  <a...@linux.intel.com>

        * gcc.target/i386/mpx/mpx-check.h: Check XGETBV output
        if kernel supports MPX.
---
 gcc/testsuite/gcc.target/i386/mpx/mpx-check.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.target/i386/mpx/mpx-check.h 
b/gcc/testsuite/gcc.target/i386/mpx/mpx-check.h
index 3afa460..73aa01f 100644
--- a/gcc/testsuite/gcc.target/i386/mpx/mpx-check.h
+++ b/gcc/testsuite/gcc.target/i386/mpx/mpx-check.h
@@ -16,6 +16,16 @@ mpx_test (int, const char **);
 
 #define DEBUG
 
+#define XSTATE_BNDREGS (1 << 3)
+
+/* This should be an intrinsic, but isn't.  */
+static int xgetbv (unsigned x)
+{
+   unsigned eax, edx;
+   asm ("xgetbv" : "=a" (eax), "=d" (edx) : "c" (x)); 
+   return eax;
+}
+
 int
 main (int argc, const char **argv)
 {
@@ -27,7 +37,7 @@ main (int argc, const char **argv)
   __cpuid_count (7, 0, eax, ebx, ecx, edx);
 
   /* Run MPX test only if host has MPX support.  */
-  if (ebx & bit_MPX)
+  if ((ebx & bit_MPX) && (xgetbv (0) & XSTATE_BNDREGS))
     mpx_test (argc, argv);
   else
     {
-- 
2.8.3