s390/sclp: use cpu offset to locate cpu entries

The start of the CPU entry region in the Read SCP Info response data is
denoted by the offset_cpu field. As such, QEMU needs to begin creating
entries at this address.

This is in preparation for when Read SCP Info inevitably introduces new
bytes that push the start of the CPUEntry field further away.

Read CPU Info is unlikely to ever change, so let's not bother
accounting for the offset there.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20200915194416.107460-6-walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index 0d54075309..1df67c99bf 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -89,6 +89,8 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
     int rnsize, rnmax;
     IplParameterBlock *ipib = s390_ipl_get_iplb();
     int required_len = SCCB_REQ_LEN(ReadInfo, machine->possible_cpus->len);
+    int offset_cpu = offsetof(ReadInfo, entries);
+    CPUEntry *entries_start = (void *)sccb + offset_cpu;
 
     if (be16_to_cpu(sccb->h.length) < required_len) {
         sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
@@ -96,9 +98,9 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
     }
 
     /* CPU information */
-    prepare_cpu_entries(machine, read_info->entries, &cpu_count);
+    prepare_cpu_entries(machine, entries_start, &cpu_count);
     read_info->entries_cpu = cpu_to_be16(cpu_count);
-    read_info->offset_cpu = cpu_to_be16(offsetof(ReadInfo, entries));
+    read_info->offset_cpu = cpu_to_be16(offset_cpu);
     read_info->highest_cpu = cpu_to_be16(machine->smp.max_cpus - 1);
 
     read_info->ibc_val = cpu_to_be32(s390_get_ibc_val());