To include another source file in an assembler source file, use the ‘include’ directive:
Argument string_literal specifies a (quoted) full or relative path to an included file. A relative path is interpreted by using for the base directory a directory that contains a file with the ‘include’ directive, a base directory specified as a parameter of preprocessing if the name of that file is unknown, or current working directory if the base directory is not specified as a parameter of preprocessing. The directive must be written on a separate line after at least one whitespace character at the beginning of the line. The directive must not occur within a macro definition. The maximum nesting level of ‘include’ directives is equal to 100.