[Qemu-devel] [PULL 19/28] target-ppc: kvm: fix floating point registers sync on little-endian hosts

[David Gibson <david@gibson.dropbear.id.au>]

From: Greg Kurz <gkurz@linux.vnet.ibm.com>

On VSX capable CPUs, the 32 FP registers are mapped to the high-bits
of the 32 first VSX registers. So if you have:

VSR31 = (uint128) 0x0102030405060708090a0b0c0d0e0f00

then

FPR31 = (uint64) 0x0102030405060708

The kernel stores the VSX registers in the fp_state struct following the
host endian element ordering.

On big-endian:

fp_state.fpr[31][0] = 0x0102030405060708
fp_state.fpr[31][1] = 0x090a0b0c0d0e0f00

On little-endian:

fp_state.fpr[31][0] = 0x090a0b0c0d0e0f00
fp_state.fpr[31][1] = 0x0102030405060708

The KVM_GET_ONE_REG and KVM_SET_ONE_REG ioctls preserve this ordering, but
QEMU considers it as big-endian and always copies element [0] to the
fpr[] array and element [1] to the vsr[] array. This does not work with
little-endian hosts, and you will get:

(qemu) p $f31
0x90a0b0c0d0e0f00

instead of:

(qemu) p $f31
0x102030405060708

This patch fixes the element ordering for little-endian hosts.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 target-ppc/kvm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 9940a90..4524999 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -650,8 +650,13 @@ static int kvm_put_fp(CPUState *cs)
         for (i = 0; i < 32; i++) {
             uint64_t vsr[2];
 
+#ifdef HOST_WORDS_BIGENDIAN
             vsr[0] = float64_val(env->fpr[i]);
             vsr[1] = env->vsr[i];
+#else
+            vsr[0] = env->vsr[i];
+            vsr[1] = float64_val(env->fpr[i]);
+#endif
             reg.addr = (uintptr_t) &vsr;
             reg.id = vsx ? KVM_REG_PPC_VSR(i) : KVM_REG_PPC_FPR(i);
 
@@ -721,10 +726,17 @@ static int kvm_get_fp(CPUState *cs)
                         vsx ? "VSR" : "FPR", i, strerror(errno));
                 return ret;
             } else {
+#ifdef HOST_WORDS_BIGENDIAN
                 env->fpr[i] = vsr[0];
                 if (vsx) {
                     env->vsr[i] = vsr[1];
                 }
+#else
+                env->fpr[i] = vsr[1];
+                if (vsx) {
+                    env->vsr[i] = vsr[0];
+                }
+#endif
             }
         }
     }
-- 
2.5.0