zdtm/x86: Add a mxcsr preserving fpu test

It helped a bit to debug Skylake ptrace() bug, let's put it in.

Signed-off-by: Dmitry Safonov <dima@arista.com>

test/zdtm/static/Makefile

@@ -13,6 +13,7 @@ TST_NOFILE	:=				\
 		zombie01			\
 		fpu00				\
 		fpu01				\
+		fpu02				\
 		arm-neon00			\
 		futex				\
 		futex-rl			\

test/zdtm/static/fpu02.c

@@ -0,0 +1,88 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <sys/types.h>
+
+#include "zdtmtst.h"
+
+#if defined(__i386__) || defined(__x86_64__)
+
+#include "cpuid.h"
+
+const char *test_doc	= "Test preserve of mxcsr in FPU";
+const char *test_author	= "Dmitry Safonov <0x7f454c46@gmail.com>";
+
+static int verify_cpu(void)
+{
+	unsigned int eax, ebx, ecx, edx;
+
+	/* Do we have xsave? */
+	cpuid(1, &eax, &ebx, &ecx, &edx);
+	if (!(ecx & (1u << 27)))
+		return -1;
+
+	/* Is YMM here? */
+	cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
+	if ((eax & (0x4)) != 0x4)
+		return -1;
+
+	return 0;
+}
+
+#define __aligned __attribute__((aligned(64)))
+
+static int fpu_test(void)
+{
+	uint32_t before, after;
+
+	asm volatile("stmxcsr %0\n"
+		     : "+m"(before));
+
+	test_daemon();
+	test_waitsig();
+
+	asm volatile("stmxcsr %0\n"
+		     : "+m"(after));
+
+	test_msg("before: %x, after: %x\n", before, after);
+
+	return (before != after);
+}
+
+static int bare_run(void)
+{
+	test_msg("Your cpu doesn't support ymm registers, skipping\n");
+
+	test_daemon();
+	test_waitsig();
+
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	int ret = 0;
+
+	test_init(argc, argv);
+
+	ret = verify_cpu() ? bare_run() : fpu_test();
+
+	if (!ret)
+		pass();
+	else
+		fail();
+
+	return 0;
+}
+
+#else
+
+int main(int argc, char *argv[])
+{
+	test_init(argc, argv);
+	skip("Unsupported arch");
+	return 0;
+}
+
+#endif