acpi: build_fadt: use acpi_table_begin()/acpi_table_end() instead of build_header()

it replaces error-prone pointer arithmetic for build_header() API,
with 2 calls to start and finish table creation,
which hides offsets magic from API user.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210924122802.1455362-6-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/acpi/aml-build.c

@@ -1982,9 +1982,10 @@ void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData *f,
                 const char *oem_id, const char *oem_table_id)
 {
     int off;
-    int fadt_start = tbl->len;
+    AcpiTable table = { .sig = "FACP", .rev = f->rev,
+                        .oem_id = oem_id, .oem_table_id = oem_table_id };
 
-    acpi_data_push(tbl, sizeof(AcpiTableHeader));
+    acpi_table_begin(&table, tbl);
 
     /* FACS address to be filled by Guest linker at runtime */
     off = tbl->len;
@@ -2048,7 +2049,7 @@ void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData *f,
     build_append_int_noprefix(tbl, f->flags, 4); /* Flags */
 
     if (f->rev == 1) {
-        goto build_hdr;
+        goto done;
     }
 
     build_append_gas_from_struct(tbl, &f->reset_reg); /* RESET_REG */
@@ -2085,7 +2086,7 @@ void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData *f,
     build_append_gas(tbl, AML_AS_SYSTEM_MEMORY, 0 , 0, 0, 0); /* X_GPE1_BLK */
 
     if (f->rev <= 4) {
-        goto build_hdr;
+        goto done;
     }
 
     /* SLEEP_CONTROL_REG */
@@ -2096,9 +2097,8 @@ void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData *f,
     /* TODO: extra fields need to be added to support revisions above rev5 */
     assert(f->rev == 5);
 
-build_hdr:
-    build_header(linker, tbl, (void *)(tbl->data + fadt_start),
-                 "FACP", tbl->len - fadt_start, f->rev, oem_id, oem_table_id);
+done:
+    acpi_table_end(linker, &table);
 }
 
 #ifdef CONFIG_TPM