<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def jarFlags(target, source, env, for_signature):
 """If we have a manifest, make sure that the 'm' flag is specified."""

    jarflags = env.subst('$JARFLAGS', target=target, source=source)
    for src in source:
        contents = src.get_text_contents()
        if contents[:16] == "Manifest-Version":
            if not 'm' in jarflags:
                return jarflags + 'm'
            break
    return jarflags