scons: Add '-Wl,--as-needed' to default LINKFLAGS

[gem5.git] / SConstruct

diff --git a/SConstruct b/SConstruct
index 9ad589661efc2d4f68a24f7d50b51eefdcd1f05a..d84b91284bde04fc5d52cf90121378465edf2ca7 100755 (executable)
--- a/SConstruct
+++ b/SConstruct
@@ -1,6 +1,6 @@
 # -*- mode:python -*-
 
 # -*- mode:python -*-
 

-# Copyright (c) 2013, 2015 ARM Limited
+# Copyright (c) 2013, 2015-2019 ARM Limited

 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall


@@ -78,40 +78,13 @@
 #
 ###################################################
 
 #
 ###################################################
 

-# Check for recent-enough Python and SCons versions.
-try:
-    # Really old versions of scons only take two options for the
-    # function, so check once without the revision and once with the
-    # revision, the first instance will fail for stuff other than
-    # 0.98, and the second will fail for 0.98.0
-    EnsureSConsVersion(0, 98)
-    EnsureSConsVersion(0, 98, 1)
-except SystemExit, e:
-    print """
-For more details, see:
-    http://gem5.org/Dependencies
-"""
-    raise
-
-# We ensure the python version early because because python-config
-# requires python 2.5
-try:
-    EnsurePythonVersion(2, 5)
-except SystemExit, e:
-    print """
-You can use a non-default installation of the Python interpreter by
-rearranging your PATH so that scons finds the non-default 'python' and
-'python-config' first.
-
-For more details, see:
-    http://gem5.org/wiki/index.php/Using_a_non-default_Python_installation
-"""
-    raise
+from __future__ import print_function

 
 # Global Python includes
 import itertools
 import os
 import re
 
 # Global Python includes
 import itertools
 import os
 import re

+import shutil

 import subprocess
 import sys
 
 import subprocess
 import sys
 


@@ -119,20 +92,14 @@ from os import mkdir, environ
 from os.path import abspath, basename, dirname, expanduser, normpath
 from os.path import exists,  isdir, isfile
 from os.path import join as joinpath, split as splitpath
 from os.path import abspath, basename, dirname, expanduser, normpath
 from os.path import exists,  isdir, isfile
 from os.path import join as joinpath, split as splitpath

+from re import match

 
 # SCons includes
 import SCons
 import SCons.Node
 
 # SCons includes
 import SCons
 import SCons.Node

-
-extra_python_paths = [
-    Dir('src/python').srcnode().abspath, # gem5 includes
-    Dir('ext/ply').srcnode().abspath, # ply is used by several files
-    ]
-
-sys.path[1:1] = extra_python_paths
+import SCons.Node.FS

 
 from m5.util import compareVersions, readCommand
 
 from m5.util import compareVersions, readCommand

-from m5.util.terminal import get_termcap

 
 help_texts = {
     "options" : "",
 
 help_texts = {
     "options" : "",


@@ -180,8 +147,13 @@ AddLocalOption('--default', dest='default', type='string', action='store',
                help='Override which build_opts file to use for defaults')
 AddLocalOption('--ignore-style', dest='ignore_style', action='store_true',
                help='Disable style checking hooks')
                help='Override which build_opts file to use for defaults')
 AddLocalOption('--ignore-style', dest='ignore_style', action='store_true',
                help='Disable style checking hooks')

+AddLocalOption('--gold-linker', dest='gold_linker', action='store_true',
+               help='Use the gold linker')

 AddLocalOption('--no-lto', dest='no_lto', action='store_true',
                help='Disable Link-Time Optimization for fast')
 AddLocalOption('--no-lto', dest='no_lto', action='store_true',
                help='Disable Link-Time Optimization for fast')

+AddLocalOption('--force-lto', dest='force_lto', action='store_true',
+               help='Use Link-Time Optimization instead of partial linking' +
+                    ' when the compiler doesn\'t support using them together.')

 AddLocalOption('--update-ref', dest='update_ref', action='store_true',
                help='Update test reference outputs')
 AddLocalOption('--verbose', dest='verbose', action='store_true',
 AddLocalOption('--update-ref', dest='update_ref', action='store_true',
                help='Update test reference outputs')
 AddLocalOption('--verbose', dest='verbose', action='store_true',


@@ -194,8 +166,13 @@ AddLocalOption('--without-tcmalloc', dest='without_tcmalloc',
                help='Disable linking against tcmalloc')
 AddLocalOption('--with-ubsan', dest='with_ubsan', action='store_true',
                help='Build with Undefined Behavior Sanitizer if available')
                help='Disable linking against tcmalloc')
 AddLocalOption('--with-ubsan', dest='with_ubsan', action='store_true',
                help='Build with Undefined Behavior Sanitizer if available')

+AddLocalOption('--with-asan', dest='with_asan', action='store_true',
+               help='Build with Address Sanitizer if available')
+
+from gem5_scons import Transform, error, warning

 
 

-termcap = get_termcap(GetOption('use_colors'))
+if GetOption('no_lto') and GetOption('force_lto'):
+    error('--no-lto and --force-lto are mutually exclusive')

 
 ########################################################################
 #
 
 ########################################################################
 #


@@ -203,116 +180,16 @@ termcap = get_termcap(GetOption('use_colors'))
 #
 ########################################################################
 
 #
 ########################################################################
 

-# export TERM so that clang reports errors in color
-use_vars = set([ 'AS', 'AR', 'CC', 'CXX', 'HOME', 'LD_LIBRARY_PATH',
-                 'LIBRARY_PATH', 'PATH', 'PKG_CONFIG_PATH', 'PROTOC',
-                 'PYTHONPATH', 'RANLIB', 'SWIG', 'TERM' ])
-
-use_prefixes = [
-    "M5",           # M5 configuration (e.g., path to kernels)
-    "DISTCC_",      # distcc (distributed compiler wrapper) configuration
-    "CCACHE_",      # ccache (caching compiler wrapper) configuration
-    "CCC_",         # clang static analyzer configuration
-    ]
-
-use_env = {}
-for key,val in sorted(os.environ.iteritems()):
-    if key in use_vars or \
-            any([key.startswith(prefix) for prefix in use_prefixes]):
-        use_env[key] = val
-
-# Tell scons to avoid implicit command dependencies to avoid issues
-# with the param wrappes being compiled twice (see
-# http://scons.tigris.org/issues/show_bug.cgi?id=2811)
-main = Environment(ENV=use_env, IMPLICIT_COMMAND_DEPENDENCIES=0)
-main.Decider('MD5-timestamp')
-main.root = Dir(".")         # The current directory (where this file lives).
-main.srcdir = Dir("src")     # The source directory
+main = Environment()
+
+from gem5_scons.util import get_termcap
+termcap = get_termcap()

 
 main_dict_keys = main.Dictionary().keys()
 
 # Check that we have a C/C++ compiler
 if not ('CC' in main_dict_keys and 'CXX' in main_dict_keys):
 
 main_dict_keys = main.Dictionary().keys()
 
 # Check that we have a C/C++ compiler
 if not ('CC' in main_dict_keys and 'CXX' in main_dict_keys):

-    print "No C++ compiler installed (package g++ on Ubuntu and RedHat)"
-    Exit(1)
-
-# Check that swig is present
-if not 'SWIG' in main_dict_keys:
-    print "swig is not installed (package swig on Ubuntu and RedHat)"
-    Exit(1)
-
-# add useful python code PYTHONPATH so it can be used by subprocesses
-# as well
-main.AppendENVPath('PYTHONPATH', extra_python_paths)
-
-########################################################################
-#
-# Mercurial Stuff.
-#
-# If the gem5 directory is a mercurial repository, we should do some
-# extra things.
-#
-########################################################################
-
-hgdir = main.root.Dir(".hg")
-
-mercurial_style_message = """
-You're missing the gem5 style hook, which automatically checks your code
-against the gem5 style rules on hg commit and qrefresh commands.  This
-script will now install the hook in your .hg/hgrc file.
-Press enter to continue, or ctrl-c to abort: """
-
-mercurial_style_hook = """
-# The following lines were automatically added by gem5/SConstruct
-# to provide the gem5 style-checking hooks
-[extensions]
-style = %s/util/style.py
-
-[hooks]
-pretxncommit.style = python:style.check_style
-pre-qrefresh.style = python:style.check_style
-# End of SConstruct additions
-
-""" % (main.root.abspath)
-
-mercurial_lib_not_found = """
-Mercurial libraries cannot be found, ignoring style hook.  If
-you are a gem5 developer, please fix this and run the style
-hook. It is important.
-"""
-
-# Check for style hook and prompt for installation if it's not there.
-# Skip this if --ignore-style was specified, there's no .hg dir to
-# install a hook in, or there's no interactive terminal to prompt.
-if not GetOption('ignore_style') and hgdir.exists() and sys.stdin.isatty():
-    style_hook = True
-    try:
-        from mercurial import ui
-        ui = ui.ui()
-        ui.readconfig(hgdir.File('hgrc').abspath)
-        style_hook = ui.config('hooks', 'pretxncommit.style', None) and \
-                     ui.config('hooks', 'pre-qrefresh.style', None)
-    except ImportError:
-        print mercurial_lib_not_found
-
-    if not style_hook:
-        print mercurial_style_message,
-        # continue unless user does ctrl-c/ctrl-d etc.
-        try:
-            raw_input()
-        except:
-            print "Input exception, exiting scons.\n"
-            sys.exit(1)
-        hgrc_path = '%s/.hg/hgrc' % main.root.abspath
-        print "Adding style hook to", hgrc_path, "\n"
-        try:
-            hgrc = open(hgrc_path, 'a')
-            hgrc.write(mercurial_style_hook)
-            hgrc.close()
-        except:
-            print "Error updating", hgrc_path
-            sys.exit(1)
-
+    error("No C++ compiler installed (package g++ on Ubuntu and RedHat)")

 
 ###################################################
 #
 
 ###################################################
 #


@@ -329,7 +206,7 @@ def rfind(l, elt, offs = -1):
     for i in range(len(l)+offs, 0, -1):
         if l[i] == elt:
             return i
     for i in range(len(l)+offs, 0, -1):
         if l[i] == elt:
             return i

-    raise ValueError, "element not found"
+    raise ValueError("element not found")

 
 # Take a list of paths (or SCons Nodes) and return a list with all
 # paths made absolute and ~-expanded.  Paths will be interpreted
 
 # Take a list of paths (or SCons Nodes) and return a list with all
 # paths made absolute and ~-expanded.  Paths will be interpreted


@@ -338,6 +215,19 @@ def makePathListAbsolute(path_list, root=GetLaunchDir()):
     return [abspath(joinpath(root, expanduser(str(p))))
             for p in path_list]
 
     return [abspath(joinpath(root, expanduser(str(p))))
             for p in path_list]
 

+def find_first_prog(prog_names):
+    """Find the absolute path to the first existing binary in prog_names"""
+
+    if not isinstance(prog_names, (list, tuple)):
+        prog_names = [ prog_names ]
+
+    for p in prog_names:
+        p = main.WhereIs(p)
+        if p is not None:
+            return p
+
+    return None
+

 # Each target must have 'build' in the interior of the path; the
 # directory below this will determine the build parameters.  For
 # example, for target 'foo/bar/build/ALPHA_SE/arch/alpha/blah.do' we
 # Each target must have 'build' in the interior of the path; the
 # directory below this will determine the build parameters.  For
 # example, for target 'foo/bar/build/ALPHA_SE/arch/alpha/blah.do' we


@@ -358,16 +248,14 @@ for t in BUILD_TARGETS:
     try:
         build_top = rfind(path_dirs, 'build', -2)
     except:
     try:
         build_top = rfind(path_dirs, 'build', -2)
     except:

-        print "Error: no non-leaf 'build' dir found on target path", t
-        Exit(1)
+        error("No non-leaf 'build' dir found on target path.", t)

     this_build_root = joinpath('/',*path_dirs[:build_top+1])
     if not build_root:
         build_root = this_build_root
     else:
         if this_build_root != build_root:
     this_build_root = joinpath('/',*path_dirs[:build_top+1])
     if not build_root:
         build_root = this_build_root
     else:
         if this_build_root != build_root:

-            print "Error: build targets not under same build root\n"\
-                  "  %s\n  %s" % (build_root, this_build_root)
-            Exit(1)
+            error("build targets not under same build root\n"
+                  "  %s\n  %s" % (build_root, this_build_root))

     variant_path = joinpath('/',*path_dirs[:build_top+2])
     if variant_path not in variant_paths:
         variant_paths.append(variant_path)
     variant_path = joinpath('/',*path_dirs[:build_top+2])
     if variant_path not in variant_paths:
         variant_paths.append(variant_path)


@@ -399,7 +287,10 @@ global_vars = Variables(global_vars_file, args=ARGUMENTS)
 global_vars.AddVariables(
     ('CC', 'C compiler', environ.get('CC', main['CC'])),
     ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),
 global_vars.AddVariables(
     ('CC', 'C compiler', environ.get('CC', main['CC'])),
     ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),

-    ('SWIG', 'SWIG tool', environ.get('SWIG', main['SWIG'])),
+    ('CCFLAGS_EXTRA', 'Extra C and C++ compiler flags', ''),
+    ('LDFLAGS_EXTRA', 'Extra linker flags', ''),
+    ('PYTHON_CONFIG', 'Python config binary to use',
+     [ 'python2.7-config', 'python-config' ]),

     ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
     ('BATCH', 'Use batch pool for build and tests', False),
     ('BATCH_CMD', 'Batch pool submission command name', 'qdo'),
     ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
     ('BATCH', 'Use batch pool for build and tests', False),
     ('BATCH_CMD', 'Batch pool submission command name', 'qdo'),


@@ -428,89 +319,8 @@ Export('extras_dir_list')
 # the ext directory should be on the #includes path
 main.Append(CPPPATH=[Dir('ext')])
 
 # the ext directory should be on the #includes path
 main.Append(CPPPATH=[Dir('ext')])
 

-def strip_build_path(path, env):
-    path = str(path)
-    variant_base = env['BUILDROOT'] + os.path.sep
-    if path.startswith(variant_base):
-        path = path[len(variant_base):]
-    elif path.startswith('build/'):
-        path = path[6:]
-    return path
-
-# Generate a string of the form:
-#   common/path/prefix/src1, src2 -> tgt1, tgt2
-# to print while building.
-class Transform(object):
-    # all specific color settings should be here and nowhere else
-    tool_color = termcap.Normal
-    pfx_color = termcap.Yellow
-    srcs_color = termcap.Yellow + termcap.Bold
-    arrow_color = termcap.Blue + termcap.Bold
-    tgts_color = termcap.Yellow + termcap.Bold
-
-    def __init__(self, tool, max_sources=99):
-        self.format = self.tool_color + (" [%8s] " % tool) \
-                      + self.pfx_color + "%s" \
-                      + self.srcs_color + "%s" \
-                      + self.arrow_color + " -> " \
-                      + self.tgts_color + "%s" \
-                      + termcap.Normal
-        self.max_sources = max_sources
-
-    def __call__(self, target, source, env, for_signature=None):
-        # truncate source list according to max_sources param
-        source = source[0:self.max_sources]
-        def strip(f):
-            return strip_build_path(str(f), env)
-        if len(source) > 0:
-            srcs = map(strip, source)
-        else:
-            srcs = ['']
-        tgts = map(strip, target)
-        # surprisingly, os.path.commonprefix is a dumb char-by-char string
-        # operation that has nothing to do with paths.
-        com_pfx = os.path.commonprefix(srcs + tgts)
-        com_pfx_len = len(com_pfx)
-        if com_pfx:
-            # do some cleanup and sanity checking on common prefix
-            if com_pfx[-1] == ".":
-                # prefix matches all but file extension: ok
-                # back up one to change 'foo.cc -> o' to 'foo.cc -> .o'
-                com_pfx = com_pfx[0:-1]
-            elif com_pfx[-1] == "/":
-                # common prefix is directory path: OK
-                pass
-            else:
-                src0_len = len(srcs[0])
-                tgt0_len = len(tgts[0])
-                if src0_len == com_pfx_len:
-                    # source is a substring of target, OK
-                    pass
-                elif tgt0_len == com_pfx_len:
-                    # target is a substring of source, need to back up to
-                    # avoid empty string on RHS of arrow
-                    sep_idx = com_pfx.rfind(".")
-                    if sep_idx != -1:
-                        com_pfx = com_pfx[0:sep_idx]
-                    else:
-                        com_pfx = ''
-                elif src0_len > com_pfx_len and srcs[0][com_pfx_len] == ".":
-                    # still splitting at file extension: ok
-                    pass
-                else:
-                    # probably a fluke; ignore it
-                    com_pfx = ''
-        # recalculate length in case com_pfx was modified
-        com_pfx_len = len(com_pfx)
-        def fmt(files):
-            f = map(lambda s: s[com_pfx_len:], files)
-            return ', '.join(f)
-        return self.format % (com_pfx, fmt(srcs), fmt(tgts))
-
-Export('Transform')
-
-# enable the regression script to use the termcap
-main['TERMCAP'] = termcap
+# Add shared top-level headers
+main.Prepend(CPPPATH=Dir('include'))

 
 if GetOption('verbose'):
     def MakeAction(action, string, *args, **kwargs):
 
 if GetOption('verbose'):
     def MakeAction(action, string, *args, **kwargs):


@@ -520,9 +330,9 @@ else:
     main['CCCOMSTR']        = Transform("CC")
     main['CXXCOMSTR']       = Transform("CXX")
     main['ASCOMSTR']        = Transform("AS")
     main['CCCOMSTR']        = Transform("CC")
     main['CXXCOMSTR']       = Transform("CXX")
     main['ASCOMSTR']        = Transform("AS")

-    main['SWIGCOMSTR']      = Transform("SWIG")

     main['ARCOMSTR']        = Transform("AR", 0)
     main['LINKCOMSTR']      = Transform("LINK", 0)
     main['ARCOMSTR']        = Transform("AR", 0)
     main['LINKCOMSTR']      = Transform("LINK", 0)

+    main['SHLINKCOMSTR']    = Transform("SHLINK", 0)

     main['RANLIBCOMSTR']    = Transform("RANLIB", 0)
     main['M4COMSTR']        = Transform("M4")
     main['SHCCCOMSTR']      = Transform("SHCC")
     main['RANLIBCOMSTR']    = Transform("RANLIB", 0)
     main['M4COMSTR']        = Transform("M4")
     main['SHCCCOMSTR']      = Transform("SHCC")


@@ -545,88 +355,100 @@ CXX_V = readCommand([main['CXX'],'-V'], exception=False)
 main['GCC'] = CXX_version and CXX_version.find('g++') >= 0
 main['CLANG'] = CXX_version and CXX_version.find('clang') >= 0
 if main['GCC'] + main['CLANG'] > 1:
 main['GCC'] = CXX_version and CXX_version.find('g++') >= 0
 main['CLANG'] = CXX_version and CXX_version.find('clang') >= 0
 if main['GCC'] + main['CLANG'] > 1:

-    print 'Error: How can we have two at the same time?'
-    Exit(1)
+    error('Two compilers enabled at once?')

 
 # Set up default C++ compiler flags
 if main['GCC'] or main['CLANG']:
     # As gcc and clang share many flags, do the common parts here
     main.Append(CCFLAGS=['-pipe'])
     main.Append(CCFLAGS=['-fno-strict-aliasing'])
 
 # Set up default C++ compiler flags
 if main['GCC'] or main['CLANG']:
     # As gcc and clang share many flags, do the common parts here
     main.Append(CCFLAGS=['-pipe'])
     main.Append(CCFLAGS=['-fno-strict-aliasing'])

-    # Enable -Wall and then disable the few warnings that we
-    # consistently violate
-    main.Append(CCFLAGS=['-Wall', '-Wno-sign-compare', '-Wundef'])
+    # Enable -Wall and -Wextra and then disable the few warnings that
+    # we consistently violate
+    main.Append(CCFLAGS=['-Wall', '-Wundef', '-Wextra',
+                         '-Wno-sign-compare', '-Wno-unused-parameter'])

     # We always compile using C++11
     main.Append(CXXFLAGS=['-std=c++11'])
     # We always compile using C++11
     main.Append(CXXFLAGS=['-std=c++11'])

-    # Add selected sanity checks from -Wextra
-    main.Append(CXXFLAGS=['-Wmissing-field-initializers',
-                          '-Woverloaded-virtual'])
+    if sys.platform.startswith('freebsd'):
+        main.Append(CCFLAGS=['-I/usr/local/include'])
+        main.Append(CXXFLAGS=['-I/usr/local/include'])
+
+    main.Append(LINKFLAGS='-Wl,--as-needed')
+    main['FILTER_PSHLINKFLAGS'] = lambda x: str(x).replace(' -shared', '')
+    main['PSHLINKFLAGS'] = main.subst('${FILTER_PSHLINKFLAGS(SHLINKFLAGS)}')
+    if GetOption('gold_linker'):
+        main.Append(LINKFLAGS='-fuse-ld=gold')
+    main['PLINKFLAGS'] = main.subst('${LINKFLAGS}')
+    shared_partial_flags = ['-r', '-nostdlib']
+    main.Append(PSHLINKFLAGS=shared_partial_flags)
+    main.Append(PLINKFLAGS=shared_partial_flags)
+
+    # Treat warnings as errors but white list some warnings that we
+    # want to allow (e.g., deprecation warnings).
+    main.Append(CCFLAGS=['-Werror',
+                         '-Wno-error=deprecated-declarations',
+                         '-Wno-error=deprecated',
+                        ])

 else:
 else:

-    print termcap.Yellow + termcap.Bold + 'Error' + termcap.Normal,
-    print "Don't know what compiler options to use for your compiler."
-    print termcap.Yellow + '       compiler:' + termcap.Normal, main['CXX']
-    print termcap.Yellow + '       version:' + termcap.Normal,
-    if not CXX_version:
-        print termcap.Yellow + termcap.Bold + "COMMAND NOT FOUND!" +\
-               termcap.Normal
-    else:
-        print CXX_version.replace('\n', '<nl>')
-    print "       If you're trying to use a compiler other than GCC"
-    print "       or clang, there appears to be something wrong with your"
-    print "       environment."
-    print "       "
-    print "       If you are trying to use a compiler other than those listed"
-    print "       above you will need to ease fix SConstruct and "
-    print "       src/SConscript to support that compiler."
-    Exit(1)
+    error('\n'.join(
+          "Don't know what compiler options to use for your compiler.",
+          "compiler: " + main['CXX'],
+          "version: " + CXX_version.replace('\n', '<nl>') if
+                CXX_version else 'COMMAND NOT FOUND!',
+          "If you're trying to use a compiler other than GCC",
+          "or clang, there appears to be something wrong with your",
+          "environment.",
+          "",
+          "If you are trying to use a compiler other than those listed",
+          "above you will need to ease fix SConstruct and ",
+          "src/SConscript to support that compiler."))

 
 if main['GCC']:
 
 if main['GCC']:

-    # Check for a supported version of gcc. >= 4.7 is chosen for its
+    # Check for a supported version of gcc. >= 4.8 is chosen for its

     # level of c++11 support. See
     # http://gcc.gnu.org/projects/cxx0x.html for details.
     gcc_version = readCommand([main['CXX'], '-dumpversion'], exception=False)
     # level of c++11 support. See
     # http://gcc.gnu.org/projects/cxx0x.html for details.
     gcc_version = readCommand([main['CXX'], '-dumpversion'], exception=False)

-    if compareVersions(gcc_version, "4.7") < 0:
-        print 'Error: gcc version 4.7 or newer required.'
-        print '       Installed version:', gcc_version
+    if compareVersions(gcc_version, "4.8") < 0:
+        error('gcc version 4.8 or newer required.\n'
+              'Installed version:', gcc_version)

         Exit(1)
 
     main['GCC_VERSION'] = gcc_version
 
         Exit(1)
 
     main['GCC_VERSION'] = gcc_version
 

-    # gcc from version 4.8 and above generates "rep; ret" instructions
-    # to avoid performance penalties on certain AMD chips. Older
-    # assemblers detect this as an error, "Error: expecting string
-    # instruction after `rep'"
-    if compareVersions(gcc_version, "4.8") > 0:
-        as_version_raw = readCommand([main['AS'], '-v', '/dev/null'],
-                                     exception=False).split()
-
-        # version strings may contain extra distro-specific
-        # qualifiers, so play it safe and keep only what comes before
-        # the first hyphen
-        as_version = as_version_raw[-1].split('-')[0] if as_version_raw \
-            else None
-
-        if not as_version or compareVersions(as_version, "2.23") < 0:
-            print termcap.Yellow + termcap.Bold + \
-                'Warning: This combination of gcc and binutils have' + \
-                ' known incompatibilities.\n' + \
-                '         If you encounter build problems, please update ' + \
-                'binutils to 2.23.' + \
-                termcap.Normal
-
-    # Make sure we warn if the user has requested to compile with the
-    # Undefined Benahvior Sanitizer and this version of gcc does not
-    # support it.
-    if GetOption('with_ubsan') and \
-            compareVersions(gcc_version, '4.9') < 0:
-        print termcap.Yellow + termcap.Bold + \
-            'Warning: UBSan is only supported using gcc 4.9 and later.' + \
-            termcap.Normal
+    if compareVersions(gcc_version, '4.9') >= 0:
+        # Incremental linking with LTO is currently broken in gcc versions
+        # 4.9 and above. A version where everything works completely hasn't
+        # yet been identified.
+        #
+        # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67548
+        main['BROKEN_INCREMENTAL_LTO'] = True
+    if compareVersions(gcc_version, '6.0') >= 0:
+        # gcc versions 6.0 and greater accept an -flinker-output flag which
+        # selects what type of output the linker should generate. This is
+        # necessary for incremental lto to work, but is also broken in
+        # current versions of gcc. It may not be necessary in future
+        # versions. We add it here since it might be, and as a reminder that
+        # it exists. It's excluded if lto is being forced.
+        #
+        # https://gcc.gnu.org/gcc-6/changes.html
+        # https://gcc.gnu.org/ml/gcc-patches/2015-11/msg03161.html
+        # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69866
+        if not GetOption('force_lto'):
+            main.Append(PSHLINKFLAGS='-flinker-output=rel')
+            main.Append(PLINKFLAGS='-flinker-output=rel')
+
+    disable_lto = GetOption('no_lto')
+    if not disable_lto and main.get('BROKEN_INCREMENTAL_LTO', False) and \
+            not GetOption('force_lto'):
+        warning('Warning: Your compiler doesn\'t support incremental linking '
+                'and lto at the same time, so lto is being disabled. To force '
+                'lto on anyway, use the --force-lto option. That will disable '
+                'partial linking.')
+        disable_lto = True

 
     # Add the appropriate Link-Time Optimization (LTO) flags
     # unless LTO is explicitly turned off. Note that these flags
     # are only used by the fast target.
 
     # Add the appropriate Link-Time Optimization (LTO) flags
     # unless LTO is explicitly turned off. Note that these flags
     # are only used by the fast target.

-    if not GetOption('no_lto'):
+    if not disable_lto:

         # Pass the LTO flag when compiling to produce GIMPLE
         # output, we merely create the flags here and only append
         # them later
         # Pass the LTO flag when compiling to produce GIMPLE
         # output, we merely create the flags here and only append
         # them later


@@ -641,28 +463,23 @@ if main['GCC']:
 
 elif main['CLANG']:
     # Check for a supported version of clang, >= 3.1 is needed to
 
 elif main['CLANG']:
     # Check for a supported version of clang, >= 3.1 is needed to

-    # support similar features as gcc 4.7. See
+    # support similar features as gcc 4.8. See

     # http://clang.llvm.org/cxx_status.html for details
     clang_version_re = re.compile(".* version (\d+\.\d+)")
     clang_version_match = clang_version_re.search(CXX_version)
     if (clang_version_match):
         clang_version = clang_version_match.groups()[0]
         if compareVersions(clang_version, "3.1") < 0:
     # http://clang.llvm.org/cxx_status.html for details
     clang_version_re = re.compile(".* version (\d+\.\d+)")
     clang_version_match = clang_version_re.search(CXX_version)
     if (clang_version_match):
         clang_version = clang_version_match.groups()[0]
         if compareVersions(clang_version, "3.1") < 0:

-            print 'Error: clang version 3.1 or newer required.'
-            print '       Installed version:', clang_version
-            Exit(1)
+            error('clang version 3.1 or newer required.\n'
+                  'Installed version:', clang_version)

     else:
     else:

-        print 'Error: Unable to determine clang version.'
-        Exit(1)
+        error('Unable to determine clang version.')

 
 

-    # clang has a few additional warnings that we disable,
-    # tautological comparisons are allowed due to unsigned integers
-    # being compared to constants that happen to be 0, and extraneous
+    # clang has a few additional warnings that we disable, extraneous

     # parantheses are allowed due to Ruby's printing of the AST,
     # finally self assignments are allowed as the generated CPU code
     # is relying on this
     # parantheses are allowed due to Ruby's printing of the AST,
     # finally self assignments are allowed as the generated CPU code
     # is relying on this

-    main.Append(CCFLAGS=['-Wno-tautological-compare',
-                         '-Wno-parentheses',
+    main.Append(CCFLAGS=['-Wno-parentheses',

                          '-Wno-self-assign',
                          # Some versions of libstdc++ (4.8?) seem to
                          # use struct hash and class hash
                          '-Wno-self-assign',
                          # Some versions of libstdc++ (4.8?) seem to
                          # use struct hash and class hash


@@ -678,24 +495,31 @@ elif main['CLANG']:
         main.Append(CXXFLAGS=['-stdlib=libc++'])
         main.Append(LIBS=['c++'])
 
         main.Append(CXXFLAGS=['-stdlib=libc++'])
         main.Append(LIBS=['c++'])
 

-else:
-    print termcap.Yellow + termcap.Bold + 'Error' + termcap.Normal,
-    print "Don't know what compiler options to use for your compiler."
-    print termcap.Yellow + '       compiler:' + termcap.Normal, main['CXX']
-    print termcap.Yellow + '       version:' + termcap.Normal,
-    if not CXX_version:
-        print termcap.Yellow + termcap.Bold + "COMMAND NOT FOUND!" +\
-               termcap.Normal
+    # On FreeBSD we need libthr.
+    if sys.platform.startswith('freebsd'):
+        main.Append(LIBS=['thr'])
+
+# Add sanitizers flags
+sanitizers=[]
+if GetOption('with_ubsan'):
+    # Only gcc >= 4.9 supports UBSan, so check both the version
+    # and the command-line option before adding the compiler and
+    # linker flags.
+    if not main['GCC'] or compareVersions(main['GCC_VERSION'], '4.9') >= 0:
+        sanitizers.append('undefined')
+if GetOption('with_asan'):
+    # Available for gcc >= 4.8 or llvm >= 3.1 both a requirement
+    # by the build system
+    sanitizers.append('address')
+if sanitizers:
+    sanitizers = ','.join(sanitizers)
+    if main['GCC'] or main['CLANG']:
+        main.Append(CCFLAGS=['-fsanitize=%s' % sanitizers,
+                             '-fno-omit-frame-pointer'],
+                    LINKFLAGS='-fsanitize=%s' % sanitizers)

     else:
     else:

-        print CXX_version.replace('\n', '<nl>')
-    print "       If you're trying to use a compiler other than GCC"
-    print "       or clang, there appears to be something wrong with your"
-    print "       environment."
-    print "       "
-    print "       If you are trying to use a compiler other than those listed"
-    print "       above you will need to ease fix SConstruct and "
-    print "       src/SConscript to support that compiler."
-    Exit(1)
+        warning("Don't know how to enable %s sanitizer(s) for your "
+                "compiler." % sanitizers)

 
 # Set up common yacc/bison flags (needed for Ruby)
 main['YACCFLAGS'] = '-d'
 
 # Set up common yacc/bison flags (needed for Ruby)
 main['YACCFLAGS'] = '-d'


@@ -714,137 +538,62 @@ if sys.platform == 'cygwin':
     # cygwin has some header file issues...
     main.Append(CCFLAGS=["-Wno-uninitialized"])
 
     # cygwin has some header file issues...
     main.Append(CCFLAGS=["-Wno-uninitialized"])
 

+
+have_pkg_config = readCommand(['pkg-config', '--version'], exception='')
+

 # Check for the protobuf compiler
 # Check for the protobuf compiler

-protoc_version = readCommand([main['PROTOC'], '--version'],
-                             exception='').split()
-
-# First two words should be "libprotoc x.y.z"
-if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
-    print termcap.Yellow + termcap.Bold + \
-        'Warning: Protocol buffer compiler (protoc) not found.\n' + \
-        '         Please install protobuf-compiler for tracing support.' + \
-        termcap.Normal
-    main['PROTOC'] = False
-else:
-    # Based on the availability of the compress stream wrappers,
-    # require 2.1.0
-    min_protoc_version = '2.1.0'
-    if compareVersions(protoc_version[1], min_protoc_version) < 0:
-        print termcap.Yellow + termcap.Bold + \
-            'Warning: protoc version', min_protoc_version, \
-            'or newer required.\n' + \
-            '         Installed version:', protoc_version[1], \
-            termcap.Normal
-        main['PROTOC'] = False
+try:
+    main['HAVE_PROTOC'] = True
+    protoc_version = readCommand([main['PROTOC'], '--version']).split()
+
+    # First two words should be "libprotoc x.y.z"
+    if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
+        warning('Protocol buffer compiler (protoc) not found.\n'
+                'Please install protobuf-compiler for tracing support.')
+        main['HAVE_PROTOC'] = False

     else:
     else:

-        # Attempt to determine the appropriate include path and
-        # library path using pkg-config, that means we also need to
-        # check for pkg-config. Note that it is possible to use
-        # protobuf without the involvement of pkg-config. Later on we
-        # check go a library config check and at that point the test
-        # will fail if libprotobuf cannot be found.
-        if readCommand(['pkg-config', '--version'], exception=''):
-            try:
-                # Attempt to establish what linking flags to add for protobuf
-                # using pkg-config
-                main.ParseConfig('pkg-config --cflags --libs-only-L protobuf')
-            except:
-                print termcap.Yellow + termcap.Bold + \
-                    'Warning: pkg-config could not get protobuf flags.' + \
-                    termcap.Normal
-
-# Check for SWIG
-if not main.has_key('SWIG'):
-    print 'Error: SWIG utility not found.'
-    print '       Please install (see http://www.swig.org) and retry.'
-    Exit(1)
-
-# Check for appropriate SWIG version
-swig_version = readCommand([main['SWIG'], '-version'], exception='').split()
-# First 3 words should be "SWIG Version x.y.z"
-if len(swig_version) < 3 or \
-        swig_version[0] != 'SWIG' or swig_version[1] != 'Version':
-    print 'Error determining SWIG version.'
-    Exit(1)
-
-min_swig_version = '2.0.4'
-if compareVersions(swig_version[2], min_swig_version) < 0:
-    print 'Error: SWIG version', min_swig_version, 'or newer required.'
-    print '       Installed version:', swig_version[2]
-    Exit(1)
-
-# Check for known incompatibilities. The standard library shipped with
-# gcc >= 4.9 does not play well with swig versions prior to 3.0
-if main['GCC'] and compareVersions(gcc_version, '4.9') >= 0 and \
-        compareVersions(swig_version[2], '3.0') < 0:
-    print termcap.Yellow + termcap.Bold + \
-        'Warning: This combination of gcc and swig have' + \
-        ' known incompatibilities.\n' + \
-        '         If you encounter build problems, please update ' + \
-        'swig to 3.0 or later.' + \
-        termcap.Normal
-
-# Set up SWIG flags & scanner
-swig_flags=Split('-c++ -python -modern -templatereduce $_CPPINCFLAGS')
-main.Append(SWIGFLAGS=swig_flags)
+        # Based on the availability of the compress stream wrappers,
+        # require 2.1.0
+        min_protoc_version = '2.1.0'
+        if compareVersions(protoc_version[1], min_protoc_version) < 0:
+            warning('protoc version', min_protoc_version,
+                    'or newer required.\n'
+                    'Installed version:', protoc_version[1])
+            main['HAVE_PROTOC'] = False
+        else:
+            # Attempt to determine the appropriate include path and
+            # library path using pkg-config, that means we also need to
+            # check for pkg-config. Note that it is possible to use
+            # protobuf without the involvement of pkg-config. Later on we
+            # check go a library config check and at that point the test
+            # will fail if libprotobuf cannot be found.
+            if have_pkg_config:
+                try:
+                    # Attempt to establish what linking flags to add for
+                    # protobuf
+                    # using pkg-config
+                    main.ParseConfig(
+                            'pkg-config --cflags --libs-only-L protobuf')
+                except:
+                    warning('pkg-config could not get protobuf flags.')
+except Exception as e:
+    warning('While checking protoc version:', str(e))
+    main['HAVE_PROTOC'] = False

 
 # Check for 'timeout' from GNU coreutils. If present, regressions will
 # be run with a time limit. We require version 8.13 since we rely on
 # support for the '--foreground' option.
 
 # Check for 'timeout' from GNU coreutils. If present, regressions will
 # be run with a time limit. We require version 8.13 since we rely on
 # support for the '--foreground' option.

-timeout_lines = readCommand(['timeout', '--version'],
-                            exception='').splitlines()
+if sys.platform.startswith('freebsd'):
+    timeout_lines = readCommand(['gtimeout', '--version'],
+                                exception='').splitlines()
+else:
+    timeout_lines = readCommand(['timeout', '--version'],
+                                exception='').splitlines()

 # Get the first line and tokenize it
 timeout_version = timeout_lines[0].split() if timeout_lines else []
 main['TIMEOUT'] =  timeout_version and \
     compareVersions(timeout_version[-1], '8.13') >= 0
 
 # Get the first line and tokenize it
 timeout_version = timeout_lines[0].split() if timeout_lines else []
 main['TIMEOUT'] =  timeout_version and \
     compareVersions(timeout_version[-1], '8.13') >= 0
 

-# filter out all existing swig scanners, they mess up the dependency
-# stuff for some reason
-scanners = []
-for scanner in main['SCANNERS']:
-    skeys = scanner.skeys
-    if skeys == '.i':
-        continue
-
-    if isinstance(skeys, (list, tuple)) and '.i' in skeys:
-        continue
-
-    scanners.append(scanner)
-
-# add the new swig scanner that we like better
-from SCons.Scanner import ClassicCPP as CPPScanner
-swig_inc_re = '^[ \t]*[%,#][ \t]*(?:include|import)[ \t]*(<|")([^>"]+)(>|")'
-scanners.append(CPPScanner("SwigScan", [ ".i" ], "CPPPATH", swig_inc_re))
-
-# replace the scanners list that has what we want
-main['SCANNERS'] = scanners
-
-# Add a custom Check function to the Configure context so that we can
-# figure out if the compiler adds leading underscores to global
-# variables.  This is needed for the autogenerated asm files that we
-# use for embedding the python code.
-def CheckLeading(context):
-    context.Message("Checking for leading underscore in global variables...")
-    # 1) Define a global variable called x from asm so the C compiler
-    #    won't change the symbol at all.
-    # 2) Declare that variable.
-    # 3) Use the variable
-    #
-    # If the compiler prepends an underscore, this will successfully
-    # link because the external symbol 'x' will be called '_x' which
-    # was defined by the asm statement.  If the compiler does not
-    # prepend an underscore, this will not successfully link because
-    # '_x' will have been defined by assembly, while the C portion of
-    # the code will be trying to use 'x'
-    ret = context.TryLink('''
-        asm(".globl _x; _x: .byte 0");
-        extern int x;
-        int main() { return x; }
-        ''', extension=".c")
-    context.env.Append(LEADING_UNDERSCORE=ret)
-    context.Result(ret)
-    return ret
-

 # Add a custom Check function to test for structure members.
 def CheckMember(context, include, decl, member, include_quotes="<>"):
     context.Message("Checking for member %s in %s..." %
 # Add a custom Check function to test for structure members.
 def CheckMember(context, include, decl, member, include_quotes="<>"):
     context.Message("Checking for member %s in %s..." %


@@ -871,14 +620,9 @@ conf = Configure(main,
                  conf_dir = joinpath(build_root, '.scons_config'),
                  log_file = joinpath(build_root, 'scons_config.log'),
                  custom_tests = {
                  conf_dir = joinpath(build_root, '.scons_config'),
                  log_file = joinpath(build_root, 'scons_config.log'),
                  custom_tests = {

-        'CheckLeading' : CheckLeading,

         'CheckMember' : CheckMember,
         })
 
         'CheckMember' : CheckMember,
         })
 

-# Check for leading underscores.  Don't really need to worry either
-# way so don't need to check the return code.
-conf.CheckLeading()
-

 # Check if we should compile a 64 bit binary on Mac OS X/Darwin
 try:
     import platform
 # Check if we should compile a 64 bit binary on Mac OS X/Darwin
 try:
     import platform


@@ -913,10 +657,11 @@ if not conf:
 
 # Cache build files in the supplied directory.
 if main['M5_BUILD_CACHE']:
 
 # Cache build files in the supplied directory.
 if main['M5_BUILD_CACHE']:

-    print 'Using build cache located at', main['M5_BUILD_CACHE']
+    print('Using build cache located at', main['M5_BUILD_CACHE'])

     CacheDir(main['M5_BUILD_CACHE'])
 
     CacheDir(main['M5_BUILD_CACHE'])
 

-if not GetOption('without_python'):
+main['USE_PYTHON'] = not GetOption('without_python')
+if main['USE_PYTHON']:

     # Find Python include and library directories for embedding the
     # interpreter. We rely on python-config to resolve the appropriate
     # includes and linker flags. ParseConfig does not seem to understand
     # Find Python include and library directories for embedding the
     # interpreter. We rely on python-config to resolve the appropriate
     # includes and linker flags. ParseConfig does not seem to understand


@@ -924,18 +669,20 @@ if not GetOption('without_python'):
     # we add them explicitly below. If you want to link in an alternate
     # version of python, see above for instructions on how to invoke
     # scons with the appropriate PATH set.
     # we add them explicitly below. If you want to link in an alternate
     # version of python, see above for instructions on how to invoke
     # scons with the appropriate PATH set.

-    #
-    # First we check if python2-config exists, else we use python-config
-    python_config = readCommand(['which', 'python2-config'],
-                                exception='').strip()
-    if not os.path.exists(python_config):
-        python_config = readCommand(['which', 'python-config'],
-                                    exception='').strip()
+
+    python_config = find_first_prog(main['PYTHON_CONFIG'])
+    if python_config is None:
+        error("Can't find a suitable python-config, tried %s" % \
+              main['PYTHON_CONFIG'])
+
+    print("Info: Using Python config: %s" % (python_config, ))

     py_includes = readCommand([python_config, '--includes'],
                               exception='').split()
     py_includes = readCommand([python_config, '--includes'],
                               exception='').split()

+    py_includes = filter(lambda s: match(r'.*\/include\/.*',s), py_includes)

     # Strip the -I from the include folders before adding them to the
     # CPPPATH
     # Strip the -I from the include folders before adding them to the
     # CPPPATH

-    main.Append(CPPPATH=map(lambda inc: inc[2:], py_includes))
+    py_includes = map(lambda s: s[2:] if s.startswith('-I') else s, py_includes)
+    main.Append(CPPPATH=py_includes)

 
     # Read the linker flags and split them into libraries and other link
     # flags. The libraries are added later through the call the CheckLib.
 
     # Read the linker flags and split them into libraries and other link
     # flags. The libraries are added later through the call the CheckLib.


@@ -952,44 +699,49 @@ if not GetOption('without_python'):
 
     # verify that this stuff works
     if not conf.CheckHeader('Python.h', '<>'):
 
     # verify that this stuff works
     if not conf.CheckHeader('Python.h', '<>'):

-        print "Error: can't find Python.h header in", py_includes
-        print "Install Python headers (package python-dev on Ubuntu and RedHat)"
-        Exit(1)
+        error("Check failed for Python.h header in",
+                ' '.join(py_includes), "\n"
+              "Two possible reasons:\n"
+              "1. Python headers are not installed (You can install the "
+              "package python-dev on Ubuntu and RedHat)\n"
+              "2. SCons is using a wrong C compiler. This can happen if "
+              "CC has the wrong value.\n"
+              "CC = %s" % main['CC'])

 
     for lib in py_libs:
         if not conf.CheckLib(lib):
 
     for lib in py_libs:
         if not conf.CheckLib(lib):

-            print "Error: can't find library %s required by python" % lib
-            Exit(1)
+            error("Can't find library %s required by python." % lib)

 
 # On Solaris you need to use libsocket for socket ops
 if not conf.CheckLibWithHeader(None, 'sys/socket.h', 'C++', 'accept(0,0,0);'):
 
 # On Solaris you need to use libsocket for socket ops
 if not conf.CheckLibWithHeader(None, 'sys/socket.h', 'C++', 'accept(0,0,0);'):

-   if not conf.CheckLibWithHeader('socket', 'sys/socket.h', 'C++', 'accept(0,0,0);'):
-       print "Can't find library with socket calls (e.g. accept())"
-       Exit(1)
+   if not conf.CheckLibWithHeader('socket', 'sys/socket.h',
+                                  'C++', 'accept(0,0,0);'):
+       error("Can't find library with socket calls (e.g. accept()).")

 
 # Check for zlib.  If the check passes, libz will be automatically
 # added to the LIBS environment variable.
 if not conf.CheckLibWithHeader('z', 'zlib.h', 'C++','zlibVersion();'):
 
 # Check for zlib.  If the check passes, libz will be automatically
 # added to the LIBS environment variable.
 if not conf.CheckLibWithHeader('z', 'zlib.h', 'C++','zlibVersion();'):

-    print 'Error: did not find needed zlib compression library '\
-          'and/or zlib.h header file.'
-    print '       Please install zlib and try again.'
-    Exit(1)
+    error('Did not find needed zlib compression library '
+          'and/or zlib.h header file.\n'
+          'Please install zlib and try again.')

 
 # If we have the protobuf compiler, also make sure we have the
 # development libraries. If the check passes, libprotobuf will be
 # automatically added to the LIBS environment variable. After
 # this, we can use the HAVE_PROTOBUF flag to determine if we have
 # got both protoc and libprotobuf available.
 
 # If we have the protobuf compiler, also make sure we have the
 # development libraries. If the check passes, libprotobuf will be
 # automatically added to the LIBS environment variable. After
 # this, we can use the HAVE_PROTOBUF flag to determine if we have
 # got both protoc and libprotobuf available.

-main['HAVE_PROTOBUF'] = main['PROTOC'] and \
+main['HAVE_PROTOBUF'] = main['HAVE_PROTOC'] and \

     conf.CheckLibWithHeader('protobuf', 'google/protobuf/message.h',
                             'C++', 'GOOGLE_PROTOBUF_VERIFY_VERSION;')
 
     conf.CheckLibWithHeader('protobuf', 'google/protobuf/message.h',
                             'C++', 'GOOGLE_PROTOBUF_VERIFY_VERSION;')
 

+# Valgrind gets much less confused if you tell it when you're using
+# alternative stacks.
+main['HAVE_VALGRIND'] = conf.CheckCHeader('valgrind/valgrind.h')
+

 # If we have the compiler but not the library, print another warning.
 # If we have the compiler but not the library, print another warning.

-if main['PROTOC'] and not main['HAVE_PROTOBUF']:
-    print termcap.Yellow + termcap.Bold + \
-        'Warning: did not find protocol buffer library and/or headers.\n' + \
-    '       Please install libprotobuf-dev for tracing support.' + \
-    termcap.Normal
+if main['HAVE_PROTOC'] and not main['HAVE_PROTOBUF']:
+    warning('Did not find protocol buffer library and/or headers.\n'
+            'Please install libprotobuf-dev for tracing support.')

 
 # Check for librt.
 have_posix_clock = \
 
 # Check for librt.
 have_posix_clock = \


@@ -1008,19 +760,45 @@ if not GetOption('without_tcmalloc'):
     elif conf.CheckLib('tcmalloc_minimal'):
         main.Append(CCFLAGS=main['TCMALLOC_CCFLAGS'])
     else:
     elif conf.CheckLib('tcmalloc_minimal'):
         main.Append(CCFLAGS=main['TCMALLOC_CCFLAGS'])
     else:

-        print termcap.Yellow + termcap.Bold + \
-              "You can get a 12% performance improvement by "\
-              "installing tcmalloc (libgoogle-perftools-dev package "\
-              "on Ubuntu or RedHat)." + termcap.Normal
+        warning("You can get a 12% performance improvement by "
+                "installing tcmalloc (libgoogle-perftools-dev package "
+                "on Ubuntu or RedHat).")
+
+
+# Detect back trace implementations. The last implementation in the
+# list will be used by default.
+backtrace_impls = [ "none" ]
+
+backtrace_checker = 'char temp;' + \
+    ' backtrace_symbols_fd((void*)&temp, 0, 0);'
+if conf.CheckLibWithHeader(None, 'execinfo.h', 'C', backtrace_checker):
+    backtrace_impls.append("glibc")
+elif conf.CheckLibWithHeader('execinfo', 'execinfo.h', 'C',
+                             backtrace_checker):
+    # NetBSD and FreeBSD need libexecinfo.
+    backtrace_impls.append("glibc")
+    main.Append(LIBS=['execinfo'])
+
+if backtrace_impls[-1] == "none":
+    default_backtrace_impl = "none"
+    warning("No suitable back trace implementation found.")

 
 if not have_posix_clock:
 
 if not have_posix_clock:

-    print "Can't find library for POSIX clocks."
+    warning("Can't find library for POSIX clocks.")

 
 # Check for <fenv.h> (C99 FP environment control)
 have_fenv = conf.CheckHeader('fenv.h', '<>')
 if not have_fenv:
 
 # Check for <fenv.h> (C99 FP environment control)
 have_fenv = conf.CheckHeader('fenv.h', '<>')
 if not have_fenv:

-    print "Warning: Header file <fenv.h> not found."
-    print "         This host has no IEEE FP rounding mode control."
+    warning("Header file <fenv.h> not found.\n"
+            "This host has no IEEE FP rounding mode control.")
+
+# Check for <png.h> (libpng library needed if wanting to dump
+# frame buffer image in png format)
+have_png = conf.CheckHeader('png.h', '<>')
+if not have_png:
+    warning("Header file <png.h> not found.\n"
+            "This host has no libpng library.\n"
+            "Disabling support for PNG framebuffers.")

 
 # Check if we should enable KVM-based hardware virtualization. The API
 # we rely on exists since version 2.6.36 of the kernel, but somehow
 
 # Check if we should enable KVM-based hardware virtualization. The API
 # we rely on exists since version 2.6.36 of the kernel, but somehow


@@ -1028,8 +806,13 @@ if not have_fenv:
 # the types as a fall back.
 have_kvm = conf.CheckHeader('linux/kvm.h', '<>')
 if not have_kvm:
 # the types as a fall back.
 have_kvm = conf.CheckHeader('linux/kvm.h', '<>')
 if not have_kvm:

-    print "Info: Compatible header file <linux/kvm.h> not found, " \
-        "disabling KVM support."
+    print("Info: Compatible header file <linux/kvm.h> not found, "
+          "disabling KVM support.")
+
+# Check if the TUN/TAP driver is available.
+have_tuntap = conf.CheckHeader('linux/if_tun.h', '<>')
+if not have_tuntap:
+    print("Info: Compatible header file <linux/if_tun.h> not found.")

 
 # x86 needs support for xsave. We test for the structure here since we
 # won't be able to run new tests by the time we know which ISA we're
 
 # x86 needs support for xsave. We test for the structure here since we
 # won't be able to run new tests by the time we know which ISA we're


@@ -1043,12 +826,12 @@ def is_isa_kvm_compatible(isa):
         import platform
         host_isa = platform.machine()
     except:
         import platform
         host_isa = platform.machine()
     except:

-        print "Warning: Failed to determine host ISA."
+        warning("Failed to determine host ISA.")

         return False
 
     if not have_posix_timers:
         return False
 
     if not have_posix_timers:

-        print "Warning: Can not enable KVM, host seems to lack support " \
-            "for POSIX timers"
+        warning("Can not enable KVM, host seems to lack support "
+                "for POSIX timers")

         return False
 
     if isa == "arm":
         return False
 
     if isa == "arm":


@@ -1058,7 +841,7 @@ def is_isa_kvm_compatible(isa):
             return False
 
         if not have_kvm_xsave:
             return False
 
         if not have_kvm_xsave:

-            print "KVM on x86 requires xsave support in kernel headers."
+            warning("KVM on x86 requires xsave support in kernel headers.")

             return False
 
         return True
             return False
 
         return True


@@ -1071,6 +854,42 @@ def is_isa_kvm_compatible(isa):
 main['HAVE_PERF_ATTR_EXCLUDE_HOST'] = conf.CheckMember(
     'linux/perf_event.h', 'struct perf_event_attr', 'exclude_host')
 
 main['HAVE_PERF_ATTR_EXCLUDE_HOST'] = conf.CheckMember(
     'linux/perf_event.h', 'struct perf_event_attr', 'exclude_host')
 

+def check_hdf5():
+    return \
+        conf.CheckLibWithHeader('hdf5', 'hdf5.h', 'C',
+                                'H5Fcreate("", 0, 0, 0);') and \
+        conf.CheckLibWithHeader('hdf5_cpp', 'H5Cpp.h', 'C++',
+                                'H5::H5File("", 0);')
+
+def check_hdf5_pkg(name):
+    print("Checking for %s using pkg-config..." % name, end="")
+    if not have_pkg_config:
+        print(" pkg-config not found")
+        return False
+
+    try:
+        main.ParseConfig('pkg-config --cflags-only-I --libs-only-L %s' % name)
+        print(" yes")
+        return True
+    except:
+        print(" no")
+        return False
+
+# Check if there is a pkg-config configuration for hdf5. If we find
+# it, setup the environment to enable linking and header inclusion. We
+# don't actually try to include any headers or link with hdf5 at this
+# stage.
+if not check_hdf5_pkg('hdf5-serial'):
+    check_hdf5_pkg('hdf5')
+
+# Check if the HDF5 libraries can be found. This check respects the
+# include path and library path provided by pkg-config. We perform
+# this check even if there isn't a pkg-config configuration for hdf5
+# since some installations don't use pkg-config.
+have_hdf5 = check_hdf5()
+if not have_hdf5:
+    print("Warning: Couldn't find any HDF5 C++ libraries. Disabling")
+    print("         HDF5 support.")

 
 ######################################################################
 #
 
 ######################################################################
 #


@@ -1085,7 +904,9 @@ main = conf.Finish()
 
 # Define the universe of supported ISAs
 all_isa_list = [ ]
 
 # Define the universe of supported ISAs
 all_isa_list = [ ]

+all_gpu_isa_list = [ ]

 Export('all_isa_list')
 Export('all_isa_list')

+Export('all_gpu_isa_list')

 
 class CpuModel(object):
     '''The CpuModel class encapsulates everything the ISA parser needs to
 
 class CpuModel(object):
     '''The CpuModel class encapsulates everything the ISA parser needs to


@@ -1103,7 +924,7 @@ class CpuModel(object):
 
         # Add self to dict
         if name in CpuModel.dict:
 
         # Add self to dict
         if name in CpuModel.dict:

-            raise AttributeError, "CpuModel '%s' already registered" % name
+            raise AttributeError("CpuModel '%s' already registered" % name)

         CpuModel.dict[name] = self
 
 Export('CpuModel')
         CpuModel.dict[name] = self
 
 Export('CpuModel')


@@ -1129,21 +950,22 @@ Export('slicc_includes')
 # Walk the tree and execute all SConsopts scripts that wil add to the
 # above variables
 if GetOption('verbose'):
 # Walk the tree and execute all SConsopts scripts that wil add to the
 # above variables
 if GetOption('verbose'):

-    print "Reading SConsopts"
+    print("Reading SConsopts")

 for bdir in [ base_dir ] + extras_dir_list:
     if not isdir(bdir):
 for bdir in [ base_dir ] + extras_dir_list:
     if not isdir(bdir):

-        print "Error: directory '%s' does not exist" % bdir
-        Exit(1)
+        error("Directory '%s' does not exist." % bdir)

     for root, dirs, files in os.walk(bdir):
         if 'SConsopts' in files:
             if GetOption('verbose'):
     for root, dirs, files in os.walk(bdir):
         if 'SConsopts' in files:
             if GetOption('verbose'):

-                print "Reading", joinpath(root, 'SConsopts')
+                print("Reading", joinpath(root, 'SConsopts'))

             SConscript(joinpath(root, 'SConsopts'))
 
 all_isa_list.sort()
             SConscript(joinpath(root, 'SConsopts'))
 
 all_isa_list.sort()

+all_gpu_isa_list.sort()

 
 sticky_vars.AddVariables(
     EnumVariable('TARGET_ISA', 'Target ISA', 'alpha', all_isa_list),
 
 sticky_vars.AddVariables(
     EnumVariable('TARGET_ISA', 'Target ISA', 'alpha', all_isa_list),

+    EnumVariable('TARGET_GPU_ISA', 'Target GPU ISA', 'hsail', all_gpu_isa_list),

     ListVariable('CPU_MODELS', 'CPU models',
                  sorted(n for n,m in CpuModel.dict.iteritems() if m.default),
                  sorted(CpuModel.dict.keys())),
     ListVariable('CPU_MODELS', 'CPU models',
                  sorted(n for n,m in CpuModel.dict.iteritems() if m.default),
                  sorted(CpuModel.dict.keys())),


@@ -1157,16 +979,30 @@ sticky_vars.AddVariables(
                  False),
     BoolVariable('USE_POSIX_CLOCK', 'Use POSIX Clocks', have_posix_clock),
     BoolVariable('USE_FENV', 'Use <fenv.h> IEEE mode control', have_fenv),
                  False),
     BoolVariable('USE_POSIX_CLOCK', 'Use POSIX Clocks', have_posix_clock),
     BoolVariable('USE_FENV', 'Use <fenv.h> IEEE mode control', have_fenv),

-    BoolVariable('CP_ANNOTATE', 'Enable critical path annotation capability', False),
-    BoolVariable('USE_KVM', 'Enable hardware virtualized (KVM) CPU models', have_kvm),
+    BoolVariable('USE_PNG',  'Enable support for PNG images', have_png),
+    BoolVariable('CP_ANNOTATE', 'Enable critical path annotation capability',
+                 False),
+    BoolVariable('USE_KVM', 'Enable hardware virtualized (KVM) CPU models',
+                 have_kvm),
+    BoolVariable('USE_TUNTAP',
+                 'Enable using a tap device to bridge to the host network',
+                 have_tuntap),
+    BoolVariable('BUILD_GPU', 'Build the compute-GPU model', False),

     EnumVariable('PROTOCOL', 'Coherence protocol for Ruby', 'None',
                   all_protocols),
     EnumVariable('PROTOCOL', 'Coherence protocol for Ruby', 'None',
                   all_protocols),

+    EnumVariable('BACKTRACE_IMPL', 'Post-mortem dump implementation',
+                 backtrace_impls[-1], backtrace_impls),
+    ('NUMBER_BITS_PER_SET', 'Max elements in set (default 64)',
+                 64),
+    BoolVariable('USE_HDF5', 'Enable the HDF5 support', have_hdf5),

     )
 
 # These variables get exported to #defines in config/*.hh (see src/SConscript).
     )
 
 # These variables get exported to #defines in config/*.hh (see src/SConscript).

-export_vars += ['USE_FENV', 'SS_COMPATIBLE_FP', 'TARGET_ISA', 'CP_ANNOTATE',
-                'USE_POSIX_CLOCK', 'USE_KVM', 'PROTOCOL', 'HAVE_PROTOBUF',
-                'HAVE_PERF_ATTR_EXCLUDE_HOST']
+export_vars += ['USE_FENV', 'SS_COMPATIBLE_FP', 'TARGET_ISA', 'TARGET_GPU_ISA',
+                'CP_ANNOTATE', 'USE_POSIX_CLOCK', 'USE_KVM', 'USE_TUNTAP',
+                'PROTOCOL', 'HAVE_PROTOBUF', 'HAVE_VALGRIND',
+                'HAVE_PERF_ATTR_EXCLUDE_HOST', 'USE_PNG',
+                'NUMBER_BITS_PER_SET', 'USE_HDF5']

 
 ###################################################
 #
 
 ###################################################
 #


@@ -1181,7 +1017,7 @@ export_vars += ['USE_FENV', 'SS_COMPATIBLE_FP', 'TARGET_ISA', 'CP_ANNOTATE',
 def build_config_file(target, source, env):
     (variable, value) = [s.get_contents() for s in source]
     f = file(str(target[0]), 'w')
 def build_config_file(target, source, env):
     (variable, value) = [s.get_contents() for s in source]
     f = file(str(target[0]), 'w')

-    print >> f, '#define', variable, value
+    print('#define', variable, value, file=f)

     f.close()
     return None
 
     f.close()
     return None
 


@@ -1209,92 +1045,102 @@ config_builder = Builder(emitter = config_emitter, action = config_action)
 
 main.Append(BUILDERS = { 'ConfigFile' : config_builder })
 
 
 main.Append(BUILDERS = { 'ConfigFile' : config_builder })
 

-# libelf build is shared across all configs in the build root.
-main.SConscript('ext/libelf/SConscript',
-                variant_dir = joinpath(build_root, 'libelf'))
-
-# gzstream build is shared across all configs in the build root.
-main.SConscript('ext/gzstream/SConscript',
-                variant_dir = joinpath(build_root, 'gzstream'))
-
-# libfdt build is shared across all configs in the build root.
-main.SConscript('ext/libfdt/SConscript',
-                variant_dir = joinpath(build_root, 'libfdt'))
-
-# fputils build is shared across all configs in the build root.
-main.SConscript('ext/fputils/SConscript',
-                variant_dir = joinpath(build_root, 'fputils'))
-
-# DRAMSim2 build is shared across all configs in the build root.
-main.SConscript('ext/dramsim2/SConscript',
-                variant_dir = joinpath(build_root, 'dramsim2'))
+###################################################
+#
+# Builders for static and shared partially linked object files.
+#
+###################################################

 
 

-# DRAMPower build is shared across all configs in the build root.
-main.SConscript('ext/drampower/SConscript',
-                variant_dir = joinpath(build_root, 'drampower'))
+partial_static_builder = Builder(action=SCons.Defaults.LinkAction,
+                                 src_suffix='$OBJSUFFIX',
+                                 src_builder=['StaticObject', 'Object'],
+                                 LINKFLAGS='$PLINKFLAGS',
+                                 LIBS='')
+
+def partial_shared_emitter(target, source, env):
+    for tgt in target:
+        tgt.attributes.shared = 1
+    return (target, source)
+partial_shared_builder = Builder(action=SCons.Defaults.ShLinkAction,
+                                 emitter=partial_shared_emitter,
+                                 src_suffix='$SHOBJSUFFIX',
+                                 src_builder='SharedObject',
+                                 SHLINKFLAGS='$PSHLINKFLAGS',
+                                 LIBS='')
+
+main.Append(BUILDERS = { 'PartialShared' : partial_shared_builder,
+                         'PartialStatic' : partial_static_builder })
+
+def add_local_rpath(env, *targets):
+    '''Set up an RPATH for a library which lives in the build directory.
+
+    The construction environment variable BIN_RPATH_PREFIX should be set to
+    the relative path of the build directory starting from the location of the
+    binary.'''
+    for target in targets:
+        target = env.Entry(target)
+        if not isinstance(target, SCons.Node.FS.Dir):
+            target = target.dir
+        relpath = os.path.relpath(target.abspath, env['BUILDDIR'])
+        components = [
+            '\\$$ORIGIN',
+            '${BIN_RPATH_PREFIX}',
+            relpath
+        ]
+        env.Append(RPATH=[env.Literal(os.path.join(*components))])
+
+if sys.platform != "darwin":
+    main.Append(LINKFLAGS=Split('-z origin'))
+
+main.AddMethod(add_local_rpath, 'AddLocalRPATH')
+
+# builds in ext are shared across all configs in the build root.
+ext_dir = abspath(joinpath(str(main.root), 'ext'))
+ext_build_dirs = []
+for root, dirs, files in os.walk(ext_dir):
+    if 'SConscript' in files:
+        build_dir = os.path.relpath(root, ext_dir)
+        ext_build_dirs.append(build_dir)
+        main.SConscript(joinpath(root, 'SConscript'),
+                        variant_dir=joinpath(build_root, build_dir))
+
+gdb_xml_dir = joinpath(ext_dir, 'gdb-xml')
+Export('gdb_xml_dir')
+
+main.Prepend(CPPPATH=Dir('ext/pybind11/include/'))

 
 ###################################################
 #
 
 ###################################################
 #

-# This function is used to set up a directory with switching headers
+# This builder and wrapper method are used to set up a directory with
+# switching headers. Those are headers which are in a generic location and
+# that include more specific headers from a directory chosen at build time
+# based on the current build settings.

 #
 ###################################################
 
 #
 ###################################################
 

-main['ALL_ISA_LIST'] = all_isa_list
-all_isa_deps = {}
-def make_switching_dir(dname, switch_headers, env):
-    # Generate the header.  target[0] is the full path of the output
-    # header to generate.  'source' is a dummy variable, since we get the
-    # list of ISAs from env['ALL_ISA_LIST'].
-    def gen_switch_hdr(target, source, env):
-        fname = str(target[0])
-        isa = env['TARGET_ISA'].lower()
-        try:
-            f = open(fname, 'w')
-            print >>f, '#include "%s/%s/%s"' % (dname, isa, basename(fname))
-            f.close()
-        except IOError:
-            print "Failed to create %s" % fname
-            raise
-
-    # Build SCons Action object. 'varlist' specifies env vars that this
-    # action depends on; when env['ALL_ISA_LIST'] changes these actions
-    # should get re-executed.
-    switch_hdr_action = MakeAction(gen_switch_hdr,
-                          Transform("GENERATE"), varlist=['ALL_ISA_LIST'])
-
-    # Instantiate actions for each header
-    for hdr in switch_headers:
-        env.Command(hdr, [], switch_hdr_action)
-
-    isa_target = Dir('.').up().name.lower().replace('_', '-')
-    env['PHONY_BASE'] = '#'+isa_target
-    all_isa_deps[isa_target] = None
-
-Export('make_switching_dir')
-
-# all-isas -> all-deps -> all-environs -> all_targets
-main.Alias('#all-isas', [])
-main.Alias('#all-deps', '#all-isas')
-
-# Dummy target to ensure all environments are created before telling
-# SCons what to actually make (the command line arguments).  We attach
-# them to the dependence graph after the environments are complete.
-ORIG_BUILD_TARGETS = list(BUILD_TARGETS) # force a copy; gets closure to work.
-def environsComplete(target, source, env):
-    for t in ORIG_BUILD_TARGETS:
-        main.Depends('#all-targets', t)
-
-# Each build/* switching_dir attaches its *-environs target to #all-environs.
-main.Append(BUILDERS = {'CompleteEnvirons' :
-                        Builder(action=MakeAction(environsComplete, None))})
-main.CompleteEnvirons('#all-environs', [])
-
-def doNothing(**ignored): pass
-main.Append(BUILDERS = {'Dummy': Builder(action=MakeAction(doNothing, None))})
-
-# The final target to which all the original targets ultimately get attached.
-main.Dummy('#all-targets', '#all-environs')
-BUILD_TARGETS[:] = ['#all-targets']
+def build_switching_header(target, source, env):
+    path = str(target[0])
+    subdir = str(source[0])
+    dp, fp = os.path.split(path)
+    dp = os.path.relpath(os.path.realpath(dp),
+                         os.path.realpath(env['BUILDDIR']))
+    with open(path, 'w') as hdr:
+        print('#include "%s/%s/%s"' % (dp, subdir, fp), file=hdr)
+
+switching_header_action = MakeAction(build_switching_header,
+                                     Transform('GENERATE'))
+
+switching_header_builder = Builder(action=switching_header_action,
+                                   source_factory=Value,
+                                   single_source=True)
+
+main.Append(BUILDERS = { 'SwitchingHeader': switching_header_builder })
+
+def switching_headers(self, headers, source):
+    for header in headers:
+        self.SwitchingHeader(header, source)
+
+main.AddMethod(switching_headers, 'SwitchingHeaders')

 
 ###################################################
 #
 
 ###################################################
 #


@@ -1304,7 +1150,7 @@ BUILD_TARGETS[:] = ['#all-targets']
 
 for variant_path in variant_paths:
     if not GetOption('silent'):
 
 for variant_path in variant_paths:
     if not GetOption('silent'):

-        print "Building in", variant_path
+        print("Building in", variant_path)

 
     # Make a copy of the build-root environment to use for this config.
     env = main.Clone()
 
     # Make a copy of the build-root environment to use for this config.
     env = main.Clone()


@@ -1323,7 +1169,10 @@ for variant_path in variant_paths:
     if isfile(current_vars_file):
         sticky_vars.files.append(current_vars_file)
         if not GetOption('silent'):
     if isfile(current_vars_file):
         sticky_vars.files.append(current_vars_file)
         if not GetOption('silent'):

-            print "Using saved variables file %s" % current_vars_file
+            print("Using saved variables file %s" % current_vars_file)
+    elif variant_dir in ext_build_dirs:
+        # Things in ext are built without a variant directory.
+        continue

     else:
         # Build dir-specific variables file doesn't exist.
 
     else:
         # Build dir-specific variables file doesn't exist.
 


@@ -1346,12 +1195,11 @@ for variant_path in variant_paths:
         if existing_files:
             default_vars_file = existing_files[0]
             sticky_vars.files.append(default_vars_file)
         if existing_files:
             default_vars_file = existing_files[0]
             sticky_vars.files.append(default_vars_file)

-            print "Variables file %s not found,\n  using defaults in %s" \
-                  % (current_vars_file, default_vars_file)
+            print("Variables file %s not found,\n  using defaults in %s"
+                  % (current_vars_file, default_vars_file))

         else:
         else:

-            print "Error: cannot find variables file %s or " \
-                  "default file(s) %s" \
-                  % (current_vars_file, ' or '.join(default_vars_files))
+            error("Cannot find variables file %s or default file(s) %s"
+                  % (current_vars_file, ' or '.join(default_vars_files)))

             Exit(1)
 
     # Apply current variable settings to env
             Exit(1)
 
     # Apply current variable settings to env


@@ -1364,32 +1212,47 @@ for variant_path in variant_paths:
     # Process variable settings.
 
     if not have_fenv and env['USE_FENV']:
     # Process variable settings.
 
     if not have_fenv and env['USE_FENV']:

-        print "Warning: <fenv.h> not available; " \
-              "forcing USE_FENV to False in", variant_dir + "."
+        warning("<fenv.h> not available; forcing USE_FENV to False in",
+                variant_dir + ".")

         env['USE_FENV'] = False
 
     if not env['USE_FENV']:
         env['USE_FENV'] = False
 
     if not env['USE_FENV']:

-        print "Warning: No IEEE FP rounding mode control in", variant_dir + "."
-        print "         FP results may deviate slightly from other platforms."
+        warning("No IEEE FP rounding mode control in", variant_dir + ".\n"
+                "FP results may deviate slightly from other platforms.")
+
+    if not have_png and env['USE_PNG']:
+        warning("<png.h> not available; forcing USE_PNG to False in",
+                variant_dir + ".")
+        env['USE_PNG'] = False
+
+    if env['USE_PNG']:
+        env.Append(LIBS=['png'])

 
     if env['EFENCE']:
         env.Append(LIBS=['efence'])
 
     if env['USE_KVM']:
         if not have_kvm:
 
     if env['EFENCE']:
         env.Append(LIBS=['efence'])
 
     if env['USE_KVM']:
         if not have_kvm:

-            print "Warning: Can not enable KVM, host seems to lack KVM support"
+            warning("Can not enable KVM, host seems to lack KVM support")

             env['USE_KVM'] = False
         elif not is_isa_kvm_compatible(env['TARGET_ISA']):
             env['USE_KVM'] = False
         elif not is_isa_kvm_compatible(env['TARGET_ISA']):

-            print "Info: KVM support disabled due to unsupported host and " \
-                "target ISA combination"
+            print("Info: KVM support disabled due to unsupported host and "
+                  "target ISA combination")

             env['USE_KVM'] = False
 
             env['USE_KVM'] = False
 

+    if env['USE_TUNTAP']:
+        if not have_tuntap:
+            warning("Can't connect EtherTap with a tap device.")
+            env['USE_TUNTAP'] = False
+
+    if env['BUILD_GPU']:
+        env.Append(CPPDEFINES=['BUILD_GPU'])
+

     # Warn about missing optional functionality
     if env['USE_KVM']:
         if not main['HAVE_PERF_ATTR_EXCLUDE_HOST']:
     # Warn about missing optional functionality
     if env['USE_KVM']:
         if not main['HAVE_PERF_ATTR_EXCLUDE_HOST']:

-            print "Warning: perf_event headers lack support for the " \
-                "exclude_host attribute. KVM instruction counts will " \
-                "be inaccurate."
+            warning("perf_event headers lack support for the exclude_host "
+                    "attribute. KVM instruction counts will be inaccurate.")

 
     # Save sticky variable settings back to current variables file
     sticky_vars.Save(current_vars_file, env)
 
     # Save sticky variable settings back to current variables file
     sticky_vars.Save(current_vars_file, env)


@@ -1397,29 +1260,14 @@ for variant_path in variant_paths:
     if env['USE_SSE2']:
         env.Append(CCFLAGS=['-msse2'])
 
     if env['USE_SSE2']:
         env.Append(CCFLAGS=['-msse2'])
 

+    env.Append(CCFLAGS='$CCFLAGS_EXTRA')
+    env.Append(LINKFLAGS='$LDFLAGS_EXTRA')
+

     # The src/SConscript file sets up the build rules in 'env' according
     # to the configured variables.  It returns a list of environments,
     # one for each variant build (debug, opt, etc.)
     SConscript('src/SConscript', variant_dir = variant_path, exports = 'env')
 
     # The src/SConscript file sets up the build rules in 'env' according
     # to the configured variables.  It returns a list of environments,
     # one for each variant build (debug, opt, etc.)
     SConscript('src/SConscript', variant_dir = variant_path, exports = 'env')
 

-def pairwise(iterable):
-    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
-    a, b = itertools.tee(iterable)
-    b.next()
-    return itertools.izip(a, b)
-
-# Create false dependencies so SCons will parse ISAs, establish
-# dependencies, and setup the build Environments serially. Either
-# SCons (likely) and/or our SConscripts (possibly) cannot cope with -j
-# greater than 1. It appears to be standard race condition stuff; it
-# doesn't always fail, but usually, and the behaviors are different.
-# Every time I tried to remove this, builds would fail in some
-# creative new way. So, don't do that. You'll want to, though, because
-# tests/SConscript takes a long time to make its Environments.
-for t1, t2 in pairwise(sorted(all_isa_deps.iterkeys())):
-    main.Depends('#%s-deps'     % t2, '#%s-deps'     % t1)
-    main.Depends('#%s-environs' % t2, '#%s-environs' % t1)
-

 # base help text
 Help('''
 Usage: scons [scons options] [build variables] [target(s)]
 # base help text
 Help('''
 Usage: scons [scons options] [build variables] [target(s)]