tests/tcg/s390x: Test MXDB and MXDBR

Add a small test to prevent regressions.

Cc: qemu-stable@nongnu.org
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230601223027.795501-3-iii@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/tcg/s390x/Makefile.target

@@ -35,6 +35,7 @@ TESTS+=chrl
 TESTS+=rxsbg
 TESTS+=ex-relative-long
 TESTS+=ex-branch
+TESTS+=mxdb
 
 cdsg: CFLAGS+=-pthread
 cdsg: LDFLAGS+=-pthread

tests/tcg/s390x/mxdb.c

@@ -0,0 +1,30 @@
+/*
+ * Test the MXDB and MXDBR instructions.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <stdlib.h>
+
+int main(void)
+{
+    union {
+        double d[2];
+        long double ld;
+    } a;
+    double b;
+
+    a.d[0] = 1.2345;
+    a.d[1] = 999;
+    b = 6.789;
+    asm("mxdb %[a],%[b]" : [a] "+f" (a.ld) : [b] "R" (b));
+    assert(a.ld > 8.38 && a.ld < 8.39);
+
+    a.d[0] = 1.2345;
+    a.d[1] = 999;
+    b = 6.789;
+    asm("mxdbr %[a],%[b]" : [a] "+f" (a.ld) : [b] "f" (b));
+    assert(a.ld > 8.38 && a.ld < 8.39);
+
+    return EXIT_SUCCESS;
+}