Add 'first link flags' for building tests

[bcain]

Summary

In order to build test executables with a link line that explicitly includes init.o, fini.o, etc we need to have greater control over the order of the link args from the target_info class.

[EricWF]

Are the changes that actually use this feature going to be upstreamed as well? Or are they specific to an internal build? It's never great to introduce seemingly dead or unused code.

libcxx/utils/libcxx/compiler.py

32

If we just need this to pass object files to the link, then I think making it specific to that purpose might be better. IE link_objects instead of first_link_flags.

[bcain]

In D38635#917435, @EricWF wrote:

Are the changes that actually use this feature going to be upstreamed as well? Or are they specific to an internal build? It's never great to introduce seemingly dead or unused code.

I will find out if I can upstream the build configuration that leverages this feature.

libcxx/utils/libcxx/compiler.py

32

The order of the items on the link line is critical and it's important that the items in first_link_flags appear before -lc++ -lc++abi. I don't think link_objects conveys that same sort of interface/guarantee. If first_link_flags is not clear or generic enough, it could be before_cxx_libs or something else more appropriate.

libcxx/utils/libcxx/compiler.py

def __init__(self, path, flags=None, compile_flags=None, link_flags=None,
                  modules_flags=None, use_modules=False,
                  use_ccache=False, use_warnings=False, compile_env=None,
                  cxx_type=None, cxx_version=None):
         self.source_lang = 'c++'
         self.path = path
         self.flags = list(flags or [])
         self.compile_flags = list(compile_flags or [])
         self.link_flags = list(link_flags or [])
+        self.first_link_flags = []
         self.warning_flags = list(warning_flags or [])
         self.verify_supported = verify_supported
         self.use_verify = use_verify
         self.verify_flags = list(verify_flags or [])
         assert not use_verify or verify_supported
         assert not use_verify or verify_flags is not None
         self.modules_flags = list(modules_flags or [])
         self.use_modules = use_modules
def _initTypeAndVersion(self):
             compiler_type = 'gcc'
             major_ver = macros['__GNUC__']
             minor_ver = macros['__GNUC_MINOR__']
             patchlevel = macros['__GNUC_PATCHLEVEL__']
         self.type = compiler_type
         self.version = (major_ver, minor_ver, patchlevel)
 
     def _basicCmd(self, source_files, out, mode=CM_Default, flags=[],
-                  input_is_cxx=False):
+                  input_is_cxx=False, first_flags=[]):
         cmd = []
         if self.use_ccache \
                 and not mode == self.CM_Link \
                 and not mode == self.CM_PreProcess:
             cmd += ['ccache']
         cmd += [self.path]
+        cmd += first_flags
         if out is not None:
             cmd += ['-o', out]
         if input_is_cxx:
             cmd += ['-x', self.source_lang]
         if isinstance(source_files, list):
             cmd += source_files
         elif isinstance(source_files, str):
             cmd += [source_files]
class CXXCompiler(object):
 
     def compileCmd(self, source_files, out=None, flags=[]):
         return self._basicCmd(source_files, out, flags=flags,
                              mode=self.CM_Compile,
                              input_is_cxx=True) + ['-c']
 
     def linkCmd(self, source_files, out=None, flags=[]):
         return self._basicCmd(source_files, out, flags=flags,
-                              mode=self.CM_Link)
+                              mode=self.CM_Link,
+                              first_flags=self.first_link_flags)
 
     def compileLinkCmd(self, source_files, out=None, flags=[]):
-        return self._basicCmd(source_files, out, flags=flags)
+        return self._basicCmd(source_files, out, flags=flags,
+                              first_flags=self.first_link_flags)
 
     def preprocess(self, source_files, out=None, flags=[], cwd=None):
         cmd = self.preprocessCmd(source_files, out, flags)
         out, err, rc = libcxx.util.executeCommand(cmd, env=self.compile_env,
                                                   cwd=cwd)
         return cmd, out, err, rc
 
     def compile(self, source_files, out=None, flags=[], cwd=None):