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 <[email protected]> Signed-off-by: Xiao Guangrong <[email protected]> Reviewed-by: Michael S. Tsirkin <[email protected]> Signed-off-by: Michael S. Tsirkin <[email protected]>
cjellick · Mar 11, 2016 · f203549 · f203549
1 parent 3f3009c
commit f203549
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diff --git 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)

diff --git a/include/hw/acpi/aml-build.h b/include/hw/acpi/aml-build.h
@@ -368,4 +368,7 @@ void
 build_rsdt(GArray *table_data, GArray *linker, GArray *table_offsets,
            const char *oem_id, const char *oem_table_id);
 
+int
+build_append_named_dword(GArray *array, const char *name_format, ...);
+
 #endif