s390x/tcg: MVC: Increment the length once

Let's increment the length once.

While at it, cleanup the comment. The memset() example is given as a
programming note in the PoP, so drop the description.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
index 58ab2e48e3..013e8d6045 100644
--- a/target/s390x/mem_helper.c
+++ b/target/s390x/mem_helper.c
@@ -320,16 +320,20 @@ static uint32_t do_helper_mvc(CPUS390XState *env, uint32_t l, uint64_t dest,
     HELPER_LOG("%s l %d dest %" PRIx64 " src %" PRIx64 "\n",
                __func__, l, dest, src);
 
-    /* mvc and memmove do not behave the same when areas overlap! */
-    /* mvc with source pointing to the byte after the destination is the
-       same as memset with the first source byte */
+    /* MVC always copies one more byte than specified - maximum is 256 */
+    l++;
+
+    /*
+     * "When the operands overlap, the result is obtained as if the operands
+     * were processed one byte at a time". Only non-destructive overlaps
+     * behave like memmove().
+     */
     if (dest == src + 1) {
-        fast_memset(env, dest, cpu_ldub_data_ra(env, src, ra), l + 1, ra);
-    } else if (dest < src || src + l < dest) {
-        fast_memmove(env, dest, src, l + 1, ra);
+        fast_memset(env, dest, cpu_ldub_data_ra(env, src, ra), l, ra);
+    } else if (dest < src || src + l <= dest) {
+        fast_memmove(env, dest, src, l, ra);
     } else {
-        /* slow version with byte accesses which always work */
-        for (i = 0; i <= l; i++) {
+        for (i = 0; i < l; i++) {
             uint8_t x = cpu_ldub_data_ra(env, src + i, ra);
             cpu_stb_data_ra(env, dest + i, x, ra);
         }