On 2017-06-23 01:12, David Hildenbrand wrote:
If we have for example: r3 contains 0x00000000ffffffff
ec 33 3f bf 61 55 risbg %r3,%r3,63,191,97
We want to rotate 33 to the left and only keep MSB bit 63 of that. So the
result is then exactly 1 (we're reading the sign of the 32 bit value).
Current code assumes that we can do that via an extract, which is not
true (at least not that easy) and produces a 0.
I think the mistake there is that the rotation is done to the left,
while in extract the "shift" is done to the right. The following patch
should be enough:
--- a/target/s390x/translate.c
+++ b/target/s390x/translate.c
@@ -3441,8 +3441,8 @@ static ExitStatus op_risbg(DisasContext *s, DisasOps *o)
}
/* In some cases we can implement this with extract. */
- if (imask == 0 && pos == 0 && len > 0 && rot + len <= 64) {
- tcg_gen_extract_i64(o->out, o->in2, rot, len);
+ if (imask == 0 && pos == 0 && len > 0 && rot - len >= 0) {
+ tcg_gen_extract_i64(o->out, o->in2, 64 - rot, len);
return NO_EXIT;