diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 91f8cfe7a8b1..c522cd205fee 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -96,7 +96,6 @@
  *
  * We load our kernel at 4M, leaving space for SLOF initial image
  */
-#define FDT_MAX_SIZE            0x100000
 #define RTAS_MAX_ADDR           0x80000000 /* RTAS must stay below that */
 #define FW_MAX_SIZE             0x400000
 #define FW_FILE_NAME            "slof.bin"
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 9bed659b1a94..b424bca4d2c0 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1665,16 +1665,12 @@ static void spapr_handle_transient_dev_before_cas(SpaprMachineState *spapr)
     spapr_clear_pending_hotplug_events(spapr);
 }
 
-static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
-                                                  SpaprMachineState *spapr,
-                                                  target_ulong opcode,
-                                                  target_ulong *args)
+target_ulong do_client_architecture_support(PowerPCCPU *cpu,
+                                            SpaprMachineState *spapr,
+                                            target_ulong vec,
+                                            target_ulong fdt_bufsize)
 {
-    /* Working address in data buffer */
-    target_ulong addr = ppc64_phys_to_real(args[0]);
-    target_ulong fdt_buf = args[1];
-    target_ulong fdt_bufsize = args[2];
-    target_ulong ov_table;
+    target_ulong ov_table; /* Working address in data buffer */
     uint32_t cas_pvr;
     SpaprOptionVector *ov1_guest, *ov5_guest;
     bool guest_radix;
@@ -1694,7 +1690,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
         }
     }
 
-    cas_pvr = cas_check_pvr(spapr, cpu, &addr, &raw_mode_supported, &local_err);
+    cas_pvr = cas_check_pvr(spapr, cpu, &vec, &raw_mode_supported, &local_err);
     if (local_err) {
         error_report_err(local_err);
         return H_HARDWARE;
@@ -1717,7 +1713,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
     }
 
     /* For the future use: here @ov_table points to the first option vector */
-    ov_table = addr;
+    ov_table = vec;
 
     ov1_guest = spapr_ovec_parse_vector(ov_table, 1);
     if (!ov1_guest) {
@@ -1823,7 +1819,6 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
 
     if (!spapr->cas_reboot) {
         void *fdt;
-        SpaprDeviceTreeUpdateHeader hdr = { .version_id = 1 };
 
         /* If spapr_machine_reset() did not set up a HPT but one is necessary
          * (because the guest isn't going to use radix) then set it up here. */
@@ -1832,21 +1827,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
             spapr_setup_hpt(spapr);
         }
 
-        if (fdt_bufsize < sizeof(hdr)) {
-            error_report("SLOF provided insufficient CAS buffer "
-                         TARGET_FMT_lu " (min: %zu)", fdt_bufsize, sizeof(hdr));
-            exit(EXIT_FAILURE);
-        }
-
-        fdt_bufsize -= sizeof(hdr);
-
         fdt = spapr_build_fdt(spapr, false, fdt_bufsize);
-        _FDT((fdt_pack(fdt)));
-
-        cpu_physical_memory_write(fdt_buf, &hdr, sizeof(hdr));
-        cpu_physical_memory_write(fdt_buf + sizeof(hdr), fdt,
-                                  fdt_totalsize(fdt));
-        trace_spapr_cas_continue(fdt_totalsize(fdt) + sizeof(hdr));
 
         g_free(spapr->fdt_blob);
         spapr->fdt_size = fdt_totalsize(fdt);
@@ -1861,6 +1842,40 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
     return H_SUCCESS;
 }
 
+static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
+                                                  SpaprMachineState *spapr,
+                                                  target_ulong opcode,
+                                                  target_ulong *args)
+{
+    target_ulong vec = ppc64_phys_to_real(args[0]);
+    target_ulong fdt_buf = args[1];
+    target_ulong fdt_bufsize = args[2];
+    target_ulong ret;
+    SpaprDeviceTreeUpdateHeader hdr = { .version_id = 1 };
+
+    if (fdt_bufsize < sizeof(hdr)) {
+        error_report("SLOF provided insufficient CAS buffer "
+                     TARGET_FMT_lu " (min: %zu)", fdt_bufsize, sizeof(hdr));
+        exit(EXIT_FAILURE);
+    }
+
+    fdt_bufsize -= sizeof(hdr);
+
+    ret = do_client_architecture_support(cpu, spapr, vec, fdt_bufsize);
+    if (ret == H_SUCCESS) {
+        _FDT((fdt_pack(spapr->fdt_blob)));
+        spapr->fdt_size = fdt_totalsize(spapr->fdt_blob);
+        spapr->fdt_initial_size = spapr->fdt_size;
+
+        cpu_physical_memory_write(fdt_buf, &hdr, sizeof(hdr));
+        cpu_physical_memory_write(fdt_buf + sizeof(hdr), spapr->fdt_blob,
+                                  spapr->fdt_size);
+        trace_spapr_cas_continue(spapr->fdt_size + sizeof(hdr));
+    }
+
+    return ret;
+}
+
 static target_ulong h_home_node_associativity(PowerPCCPU *cpu,
                                               SpaprMachineState *spapr,
                                               target_ulong opcode,
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index 42d64a036821..b7e13e5aafb7 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -102,6 +102,8 @@ typedef enum {
 #define SPAPR_CAP_FIXED_CCD             0x03
 #define SPAPR_CAP_FIXED_NA              0x10 /* Lets leave a bit of a gap... */
 
+#define FDT_MAX_SIZE                    0x100000
+
 typedef struct SpaprCapabilities SpaprCapabilities;
 struct SpaprCapabilities {
     uint8_t caps[SPAPR_CAP_NUM];
@@ -566,6 +568,11 @@ void spapr_register_hypercall(target_ulong opcode, spapr_hcall_fn fn);
 target_ulong spapr_hypercall(PowerPCCPU *cpu, target_ulong opcode,
                              target_ulong *args);
 
+target_ulong do_client_architecture_support(PowerPCCPU *cpu,
+                                            SpaprMachineState *spapr,
+                                            target_ulong addr,
+                                            target_ulong fdt_bufsize);
+
 /* Virtual Processor Area structure constants */
 #define VPA_MIN_SIZE           640
 #define VPA_SIZE_OFFSET        0x4
