acpi: add build_append_named_dword, returning an offset in buffer

This is a very limited form of support for runtime patching -
similar in functionality to what we can do with ACPI_EXTRACT
macros in python, but implemented in C.

This is to allow ACPI code direct access to data tables -
which is exactly what DataTableRegion is there for, except
no known windows release so far implements DataTableRegion.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
index f26fa26802..ab89ca6380 100644
--- a/hw/acpi/aml-build.c
+++ b/hw/acpi/aml-build.c
@@ -258,6 +258,34 @@ static void build_append_int(GArray *table, uint64_t value)
     }
 }
 
+/*
+ * Build NAME(XXXX, 0x00000000) where 0x00000000 is encoded as a dword,
+ * and return the offset to 0x00000000 for runtime patching.
+ *
+ * Warning: runtime patching is best avoided. Only use this as
+ * a replacement for DataTableRegion (for guests that don't
+ * support it).
+ */
+int
+build_append_named_dword(GArray *array, const char *name_format, ...)
+{
+    int offset;
+    va_list ap;
+
+    build_append_byte(array, 0x08); /* NameOp */
+    va_start(ap, name_format);
+    build_append_namestringv(array, name_format, ap);
+    va_end(ap);
+
+    build_append_byte(array, 0x0C); /* DWordPrefix */
+
+    offset = array->len;
+    build_append_int_noprefix(array, 0x00000000, 4);
+    assert(array->len == offset + 4);
+
+    return offset;
+}
+
 static GPtrArray *alloc_list;
 
 static Aml *aml_alloc(void)