target/s390x: fix PACK reading 1 byte less and writing 1 byte more

PACK fails on the test from the Principles of Operation: F1F2F3F4
becomes 0000234C instead of 0001234C due to an off-by-one error.
Furthermore, it overwrites one extra byte to the left of F1.

If len_dest is 0, then we only want to flip the 1st byte and never loop
over the rest. Therefore, the loop condition should be > and not >=.

If len_src is 1, then we should flip the 1st byte and pack the 2nd.
Since len_src is already decremented before the loop, the first
condition should be >=, and not >.

Likewise for len_src == 2 and the second condition.

Signed-off-by: Pavel Zbitskiy <pavel.zbitskiy@gmail.com>
Message-Id: <20180821025104.19604-7-pavel.zbitskiy@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

2 files changed, 22 insertions, 0 deletions

diff --git a/tests/tcg/s390x/Makefile.target b/tests/tcg/s390x/Makefile.target
index 7de4376f52..151dc075aa 100644
--- a/tests/tcg/s390x/Makefile.target
+++ b/tests/tcg/s390x/Makefile.target
@@ -5,3 +5,4 @@ TESTS+=csst
 TESTS+=ipm
 TESTS+=exrl-trt
 TESTS+=exrl-trtr
+TESTS+=pack
diff --git a/tests/tcg/s390x/pack.c b/tests/tcg/s390x/pack.c
new file mode 100644
index 0000000000..4be36f29a7
--- /dev/null
+++ b/tests/tcg/s390x/pack.c
@@ -0,0 +1,21 @@
+#include <unistd.h>
+
+int main(void)
+{
+    char data[] = {0xaa, 0xaa, 0xf1, 0xf2, 0xf3, 0xc4, 0xaa, 0xaa};
+    char exp[] = {0xaa, 0xaa, 0x00, 0x01, 0x23, 0x4c, 0xaa, 0xaa};
+    int i;
+
+    asm volatile(
+        "    pack 2(4,%[data]),2(4,%[data])\n"
+        :
+        : [data] "r" (&data[0])
+        : "memory");
+    for (i = 0; i < 8; i++) {
+        if (data[i] != exp[i]) {
+            write(1, "bad data\n", 9);
+            return 1;
+        }
+    }
+    return 0;
+}