[librm] Add rm stack copying functions

src/arch/i386/transitions/librm_mgmt.c

@@ -0,0 +1,45 @@
+/*
+ * librm: a library for interfacing to real-mode code
+ *
+ * Michael Brown <mbrown@fensystems.co.uk>
+ *
+ */
+
+#include <stdint.h>
+#include <librm.h>
+
+/*
+ * This file provides functions for managing librm.
+ *
+ */
+
+/**
+ * Allocate space on the real-mode stack and copy data there from a
+ * user buffer
+ *
+ * @v data			User buffer
+ * @v size			Size of stack data
+ * @ret sp			New value of real-mode stack pointer
+ */
+uint16_t copy_user_to_rm_stack ( userptr_t data, size_t size ) {
+	userptr_t rm_stack;
+	rm_sp -= size;
+	rm_stack = real_to_user ( rm_ss, rm_sp );
+	memcpy_user ( rm_stack, 0, data, 0, size );
+	return rm_sp;
+};
+
+/**
+ * Deallocate space on the real-mode stack, optionally copying back
+ * data to a user buffer.
+ *
+ * @v data			User buffer
+ * @v size			Size of stack data
+ */
+void remove_user_from_rm_stack ( userptr_t data, size_t size ) {
+	if ( data ) {
+		userptr_t rm_stack = real_to_user ( rm_ss, rm_sp );
+		memcpy_user ( rm_stack, 0, data, 0, size );
+	}
+	rm_sp += size;
+};