text: #! /usr/bin/env python
  # encoding: utf-8
  
  """
  This tool supports the export_symbols_regex to export the symbols in a shared library.
  by default, all symbols are exported by gcc, and nothing by msvc.
  to use the tool, do something like:
  
  def build(ctx):
  	ctx(features='c cshlib syms', source='a.c b.c', export_symbols_regex='mylib_.*', target='testlib')
  
  only the symbols starting with 'mylib_' will be exported.
  """
  
  import re
  from waflib.Context import STDOUT
  from waflib.Task import Task
  from waflib.Errors import WafError
  from waflib.TaskGen import feature, after_method
  
  class gen_sym(Task):
  	def run(self):
  		obj = self.inputs[0]
  		kw = {}
  
  		reg = getattr(self.generator, 'export_symbols_regex', '.+?')
  		if 'msvc' in (self.env.CC_NAME, self.env.CXX_NAME):
  			re_nm = re.compile(r'External\s+\|\s+_(?P<symbol>%s)\b' % reg)
  			cmd = (self.env.DUMPBIN or ['dumpbin']) + ['/symbols', obj.abspath()]
  		else:
  			if self.env.DEST_BINFMT == 'pe': #gcc uses nm, and has a preceding _ on windows
  				re_nm = re.compile(r'(T|D)\s+_(?P<symbol>%s)\b' % reg)
  			elif self.env.DEST_BINFMT=='mac-o':
  				re_nm=re.compile(r'(T|D)\s+(?P<symbol>_?(%s))\b' % reg)
  			else:
  				re_nm = re.compile(r'(T|D)\s+(?P<symbol>%s)\b' % reg)
  			cmd = (self.env.NM or ['nm']) + ['-g', obj.abspath()]
  		syms = [m.group('symbol') for m in re_nm.finditer(self.generator.bld.cmd_and_log(cmd, quiet=STDOUT, **kw))]
  		self.outputs[0].write('%r' % syms)
  
  class compile_sym(Task):
  	def run(self):
  		syms = {}
  		for x in self.inputs:
  			slist = eval(x.read())
  			for s in slist:
  				syms[s] = 1
  		lsyms = list(syms.keys())
  		lsyms.sort()
  		if self.env.DEST_BINFMT == 'pe':
  			self.outputs[0].write('EXPORTS\n' + '\n'.join(lsyms))
  		elif self.env.DEST_BINFMT == 'elf':
  			self.outputs[0].write('{ global:\n' + ';\n'.join(lsyms) + ";\nlocal: *; };\n")
  		elif self.env.DEST_BINFMT=='mac-o':
  			self.outputs[0].write('\n'.join(lsyms) + '\n')
  		else:
  			raise WafError('NotImplemented')
  
  @feature('syms')
  @after_method('process_source', 'process_use', 'apply_link', 'process_uselib_local', 'propagate_uselib_vars')
  def do_the_symbol_stuff(self):
  	def_node = self.path.find_or_declare(getattr(self, 'sym_file', self.target + '.def'))
  	compiled_tasks = getattr(self, 'compiled_tasks', None)
  	if compiled_tasks:
  		ins = [x.outputs[0] for x in compiled_tasks]
  		self.gen_sym_tasks = [self.create_task('gen_sym', x, x.change_ext('.%d.sym' % self.idx)) for x in ins]
  		self.create_task('compile_sym', [x.outputs[0] for x in self.gen_sym_tasks], def_node)
  
  	link_task = getattr(self, 'link_task', None)
  	if link_task:
  		self.link_task.dep_nodes.append(def_node)
  
  		if 'msvc' in (self.env.CC_NAME, self.env.CXX_NAME):
  			self.link_task.env.append_value('LINKFLAGS', ['/def:' + def_node.bldpath()])
  		elif self.env.DEST_BINFMT == 'pe':
  			# gcc on windows takes *.def as an additional input
  			self.link_task.inputs.append(def_node)
  		elif self.env.DEST_BINFMT == 'elf':
  			self.link_task.env.append_value('LINKFLAGS', ['-Wl,-version-script', '-Wl,' + def_node.bldpath()])
  		elif self.env.DEST_BINFMT=='mac-o':
  			self.link_task.env.append_value('LINKFLAGS',['-Wl,-exported_symbols_list,' + def_node.bldpath()])
  		else:
  			raise WafError('NotImplemented')
  
  