acpi: add helper routines to initialize ACPI tables

Patch introduces acpi_table_begin()/ acpi_table_end() API
that hides pointer/offset arithmetic from user as opposed
to build_header(), to prevent errors caused by it [1].

 acpi_table_begin():
     initializes table header and keeps track of
     table data/offsets
 acpi_table_end():
     sets actual table length and tells bios loader
     where table is for the later initialization on
     guest side.

1) commits
   bb9feea431 x86: acpi: use offset instead of pointer when using build_header()
   4d027afeb3 Virt: ACPI: fix qemu assert due to re-assigned table data address

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210924122802.1455362-2-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Yanan Wang <wangyanan55@huawei.com>

hw/acpi/aml-build.c

@@ -52,6 +52,19 @@ static void build_append_byte(GArray *array, uint8_t val)
     g_array_append_val(array, val);
 }
 
+static void build_append_padded_str(GArray *array, const char *str,
+                                    size_t maxlen, char pad)
+{
+    size_t i;
+    size_t len = strlen(str);
+
+    g_assert(len <= maxlen);
+    g_array_append_vals(array, str, len);
+    for (i = maxlen - len; i > 0; i--) {
+        g_array_append_val(array, pad);
+    }
+}
+
 static void build_append_array(GArray *array, GArray *val)
 {
     g_array_append_vals(array, val->data, val->len);
@@ -1692,6 +1705,55 @@ Aml *aml_object_type(Aml *object)
     return var;
 }
 
+void acpi_table_begin(AcpiTable *desc, GArray *array)
+{
+
+    desc->array = array;
+    desc->table_offset = array->len;
+
+    /*
+     * ACPI spec 1.0b
+     * 5.2.3 System Description Table Header
+     */
+    g_assert(strlen(desc->sig) == 4);
+    g_array_append_vals(array, desc->sig, 4); /* Signature */
+    /*
+     * reserve space for Length field, which will be patched by
+     * acpi_table_end() when the table creation is finished.
+     */
+    build_append_int_noprefix(array, 0, 4); /* Length */
+    build_append_int_noprefix(array, desc->rev, 1); /* Revision */
+    build_append_int_noprefix(array, 0, 1); /* Checksum */
+    build_append_padded_str(array, desc->oem_id, 6, ' '); /* OEMID */
+    /* OEM Table ID */
+    build_append_padded_str(array, desc->oem_table_id, 8, ' ');
+    build_append_int_noprefix(array, 1, 4); /* OEM Revision */
+    g_array_append_vals(array, ACPI_BUILD_APPNAME8, 4); /* Creator ID */
+    build_append_int_noprefix(array, 1, 4); /* Creator Revision */
+}
+
+void acpi_table_end(BIOSLinker *linker, AcpiTable *desc)
+{
+    /*
+     * ACPI spec 1.0b
+     * 5.2.3 System Description Table Header
+     * Table 5-2 DESCRIPTION_HEADER Fields
+     */
+    const unsigned checksum_offset = 9;
+    uint32_t table_len = desc->array->len - desc->table_offset;
+    uint32_t table_len_le = cpu_to_le32(table_len);
+    gchar *len_ptr = &desc->array->data[desc->table_offset + 4];
+
+    /* patch "Length" field that has been reserved by acpi_table_begin()
+     * to the actual length, i.e. accumulated table length from
+     * acpi_table_begin() till acpi_table_end()
+     */
+    memcpy(len_ptr, &table_len_le, sizeof table_len_le);
+
+    bios_linker_loader_add_checksum(linker, ACPI_BUILD_TABLE_FILE,
+        desc->table_offset, table_len, desc->table_offset + checksum_offset);
+}
+
 void
 build_header(BIOSLinker *linker, GArray *table_data,
              AcpiTableHeader *h, const char *sig, int len, uint8_t rev,

include/hw/acpi/aml-build.h

@@ -413,6 +413,37 @@ Aml *aml_concatenate(Aml *source1, Aml *source2, Aml *target);
 Aml *aml_object_type(Aml *object);
 
 void build_append_int_noprefix(GArray *table, uint64_t value, int size);
+
+typedef struct AcpiTable {
+    const char *sig;
+    const uint8_t rev;
+    const char *oem_id;
+    const char *oem_table_id;
+    /* private vars tracking table state */
+    GArray *array;
+    unsigned table_offset;
+} AcpiTable;
+
+/**
+ * acpi_table_begin:
+ * initializes table header and keeps track of
+ * table data/offsets
+ * @desc: ACPI table descriptor
+ * @array: blob where the ACPI table will be composed/stored.
+ */
+void acpi_table_begin(AcpiTable *desc, GArray *array);
+
+/**
+ * acpi_table_end:
+ * sets actual table length and tells bios loader
+ * where table is for the later initialization on
+ * guest side.
+ * @linker: reference to BIOSLinker object to use for the table
+ * @table: ACPI table descriptor that was used with @acpi_table_begin
+ * counterpart
+ */
+void acpi_table_end(BIOSLinker *linker, AcpiTable *table);
+
 void
 build_header(BIOSLinker *linker, GArray *table_data,
              AcpiTableHeader *h, const char *sig, int len, uint8_t rev,