Waf: Node is created more than once

Question

Python

I decided to replace Make in my project with something more modern, preferably based on Python. There were few options: Scons and Waf. The first one, on a superficial examination, seemed somewhat chaotic, and, moreover, not very "Pythonic". I liked Waf more, it seemed more thoughtful, and decided to stop on it for now.

What I'm trying to do is:
1. compile boot32.cc (32-bit code passed to grub2)
2. convert boot32.o from elf32 to elf64 for future linking with the rest of the 64-bit code
3. compile all other 64-bit sources (*.cc) in the folder
4. run the linking script template through the C preprocessor
4. link the resulting object files into the kernel binary

I have the following wscript:

APPNAME = 'Toy OS'
VERSION = '0.4'

SUPPORTED_ARCHS = ['x86_64']
DEFAULT_ARCH = 'x86_64'

SUPPORTED_CXXS = ['clang++', 'g++']
DEFAULT_CXX = 'clang++'

SUPPORTED_OPTS = ['0', '1', '3']
DEFAULT_OPT = '3'

def options(opt):
    opt.load('compiler_cxx')

    grp = opt.get_option_group('configure options')
    grp.add_option('', '--arch', dest='arch', default=DEFAULT_ARCH,
                   help="target architecture [default: '%s']" % DEFAULT_ARCH)
    grp.add_option('', '--cxx', dest='CXX', default=DEFAULT_CXX,
                   help="C++ compiler command [default: '%s']" % DEFAULT_CXX)
    grp.add_option('', '--opt', dest='opt', default=DEFAULT_OPT,
                   help="code optimization level [default: '%s']" %DEFAULT_OPT)
    grp.add_option('-d', '--debug', dest='debug', default=False,
                   action='store_true', help='produce debug builds')


def configure(conf):
    conf.load('compiler_cxx')
    conf.find_program('cpp')
    conf.find_program('objcopy')

    options = vars(conf.options)
    cases = [('arch', 'target architecture', SUPPORTED_ARCHS),
             ('CXX', 'C++ compiler', SUPPORTED_CXXS),
             ('opt', 'code optimization level', SUPPORTED_OPTS)]
    for name, desc, supported, in cases:
        if options[name] not in supported:
            conf.fatal('Unsupported %s: %s' % (desc, options[name]))
        conf.env[name] = options[name]
    conf.env.debug = conf.options.debug

    flags = ['-std=c++0x', '-Wall', '-Wextra', '-O%s' % conf.env.opt,
             '-DARCH=%s' % conf.env.arch ]
    if conf.env.debug:
        flags += ['-DDEBUG']
    if conf.env.arch == 'x86_64':
        flags += ['-fno-stack-protector']
        conf.env.cxxflags_boot32 = flags + ['-m32']
        flags += ['-m64']
    conf.env.CXXFLAGS = flags

    conf.env.SHLIB_MARKER, conf.env.STLIB_MARKER = '', ''
    conf.env.LINKFLAGS = ['-nostdlib', '-Wl,--build-id=none',
                          '-Tsrc/%s/linker_script.lds' % conf.env.arch]


def build(bld):
    source, use = [], []
    if bld.env.arch == 'x86_64':
        boot32  = 'src/x86_64/boot32.cc'
        env, env.CXXFLAGS = bld.env.derive(), bld.env.cxxflags_boot32
        bld.objects(source=boot32, target=boot32+'.1.o', env=env)
        bld(rule='objcopy -O elf64-x86-64 ${SRC} ${TGT}',
            source=boot32+'.1.o', target=boot32+'.2.o')
        source += [boot32+'.2.o']

        bld.objects(source=bld.path.ant_glob('src/x86_64/*.cc', excl=boot32),
                    target='objs_x86_64')
        use += ['objs_x86_64']

    lds = 'src/%s/linker_script' % bld.env.arch
    bld(source=lds, target=lds+'.lds', rule='cpp -E -P ${SRC} > ${TGT}')

    bld.program(source=source, use=use, target='toy.bin')

At the output, everything is assembled without errors (sort of), but in verbose mode, waf writes:

* Node /home/ababo/Dropbox/toy/build/src/x86_64/boot32.cc.2.o is created more than once (full message on 'waf -v -v'). The task generators are:
1. 'src/x86_64/boot32.cc.2.o' in /home/ababo/Dropbox/toy
2. 'toy.bin' in /home/ababo/Dropbox/toy

Why does Waf think that does linking recreate boot32.cc.2.o? I have a suspicion that I am doing something wrong (in terms of Waf ideology). In this case, I will be glad if you explain. Thank you.