Factor linker flag which sets text segment into a function in SConstruct

SConstruct

 #! -*- python -*-
 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import atexit
 import os
 import platform
 import re
 import subprocess
@@ skipping 2710 matching lines @@
     # With the --build-id option (which the compiler will pass, but pass it
     # here to be doubly sure), the rodata segment starts with the
     # .note.gnu.build-id section; without --build-id it starts with .rodata.
     if via_compiler:
       args = ['--build-id', '--section-start', '.note.gnu.build-id=' + value]
     else:
       # If file is linked directly then it's probably some kind of low-level
       # test so don't use build id and move .rodata to the desired position.
       args = ['--section-start', '.rodata=' + value]
   if via_compiler:
-    args = ','.join(['-Wl'] + args)
+    if env.Bit('bitcode'):
+      # The -Wn flag passes arguments to PNaCl's native linker (as opposed
+      # to the bitcode linker, which gets the -Wl arguments)
+      args = ','.join(['-Wn'] + args)
+    else:
+      args = ','.join(['-Wl'] + args)
   else:
     args = ' '.join(args)
   return args
 
 nacl_env.AddMethod(RodataSwitch)
 
+def TextSwitch(env, value):
+  """ Return a string of arguments to place the text segment at |value|.
+Assume the string is going to the compiler driver, rather than directly
+to the linker. """
+  # The gold linker does not support -Ttext-segment, but -Ttext does the
+  # same thing that -Ttext-segment does in the bfd linker. However,
+  # -Ttext seems to be broken in gold currently (see bug
+  # https://code.google.com/p/nativeclient/issues/detail?id=3573 )
+  # Using --section-start .text= as a workaround works because PNaCl only uses
+  # one text section (no .init etc)
+  if env.Bit('bitcode'):
+    return '-Wn,--section-start,.text=' + value
+  else:
+    return '-Wl,-Ttext-segment=' + value
+
+nacl_env.AddMethod(TextSwitch)
 
 def AllowNonStableBitcode(env):
   """ This modifies the environment to allow features that aren't part
       of PNaCl's stable ABI.  If tests using these features should be
       skipped entirely, this returns False.  Otherwise, on success, it
       returns True.
   """
   if env.Bit('bitcode'):
     env.SetBits('nonstable_bitcode')
   return not env.Bit('skip_nonstable_bitcode')
@@ skipping 905 matching lines @@
   nacl_env.ValidateSdk()
 
 if BROKEN_TEST_COUNT > 0:
   msg = "There are %d broken tests." % BROKEN_TEST_COUNT
   if GetOption('brief_comstr'):
     msg += " Add --verbose to the command line for more information."
   print msg
 
 # separate warnings from actual build output
 Banner('B U I L D - O U T P U T:')