Pass -mtls-use-call when building libraries used in IRT.

src/shared/srpc/nacl.scons

Index: src/shared/srpc/nacl.scons
diff --git a/src/shared/srpc/nacl.scons b/src/shared/srpc/nacl.scons
index 05bfb0c6ea27b4e7288188f1f03fa0462a9e03c7..c56c3758f6d667917e2f21c0be8efe3b68bd3912 100644
--- a/src/shared/srpc/nacl.scons
+++ b/src/shared/srpc/nacl.scons
@@ -1,7 +1,7 @@
 # -*- python -*-
-# Copyright 2008 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.
+# Copyright (c) 2011 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('env')
@@ -9,6 +9,14 @@ Import('env')
 # TODO(robertm): get rid of this if possible
 env.Append(CCFLAGS=['-fno-strict-aliasing'])
 
+# This library is linked into irt.nexe (see src/untrusted/irt/).
+# All IRT code must avoid direct use of the TLS ABI register, which
+# is reserved for user TLS.  Instead, ensure all TLS accesses use a
+# call to __nacl_read_tp, which the IRT code overrides to segregate
+# IRT-private TLS from user TLS.
+if not env.Bit('bitcode'):
+  env.Append(CCFLAGS=['-mtls-use-call'])
+
 
 # NOTE: keep this sync'ed with build.scons
 trusted_untrusted_shared = [