SConstruct

   1 # -*- mode:python -*-
   2
   3 # Copyright (c) 2013, 2015-2020 ARM Limited
   4 # All rights reserved.
   5 #
   6 # The license below extends only to copyright in the software and shall
   7 # not be construed as granting a license to any other intellectual
   8 # property including but not limited to intellectual property relating
   9 # to a hardware implementation of the functionality of the software
  10 # licensed hereunder.  You may use the software subject to the license
  11 # terms below provided that you ensure that this notice is replicated
  12 # unmodified and in its entirety in all distributions of the software,
  13 # modified or unmodified, in source code or in binary form.
  14 #
  15 # Copyright (c) 2011 Advanced Micro Devices, Inc.
  16 # Copyright (c) 2009 The Hewlett-Packard Development Company
  17 # Copyright (c) 2004-2005 The Regents of The University of Michigan
  18 # All rights reserved.
  19 #
  20 # Redistribution and use in source and binary forms, with or without
  21 # modification, are permitted provided that the following conditions are
  22 # met: redistributions of source code must retain the above copyright
  23 # notice, this list of conditions and the following disclaimer;
  24 # redistributions in binary form must reproduce the above copyright
  25 # notice, this list of conditions and the following disclaimer in the
  26 # documentation and/or other materials provided with the distribution;
  27 # neither the name of the copyright holders nor the names of its
  28 # contributors may be used to endorse or promote products derived from
  29 # this software without specific prior written permission.
  30 #
  31 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  32 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  33 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  34 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  35 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  36 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  37 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  38 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  39 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  40 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  41 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  42
  43 ###################################################
  44 #
  45 # SCons top-level build description (SConstruct) file.
  46 #
  47 # While in this directory ('gem5'), just type 'scons' to build the default
  48 # configuration (see below), or type 'scons build/<CONFIG>/<binary>'
  49 # to build some other configuration (e.g., 'build/X86/gem5.opt' for
  50 # the optimized full-system version).
  51 #
  52 # You can build gem5 in a different directory as long as there is a
  53 # 'build/<CONFIG>' somewhere along the target path.  The build system
  54 # expects that all configs under the same build directory are being
  55 # built for the same host system.
  56 #
  57 # Examples:
  58 #
  59 #   The following two commands are equivalent.  The '-u' option tells
  60 #   scons to search up the directory tree for this SConstruct file.
  61 #   % cd <path-to-src>/gem5 ; scons build/X86/gem5.debug
  62 #   % cd <path-to-src>/gem5/build/X86; scons -u gem5.debug
  63 #
  64 #   The following two commands are equivalent and demonstrate building
  65 #   in a directory outside of the source tree.  The '-C' option tells
  66 #   scons to chdir to the specified directory to find this SConstruct
  67 #   file.
  68 #   % cd <path-to-src>/gem5 ; scons /local/foo/build/X86/gem5.debug
  69 #   % cd /local/foo/build/X86; scons -C <path-to-src>/gem5 gem5.debug
  70 #
  71 # You can use 'scons -H' to print scons options.  If you're in this
  72 # 'gem5' directory (or use -u or -C to tell scons where to find this
  73 # file), you can use 'scons -h' to print all the gem5-specific build
  74 # options as well.
  75 #
  76 ###################################################
  77
  78 # Global Python includes
  79 import atexit
  80 import itertools
  81 import os
  82 import re
  83 import shutil
  84 import subprocess
  85 import sys
  86
  87 from os import mkdir, environ
  88 from os.path import abspath, basename, dirname, expanduser, normpath
  89 from os.path import exists,  isdir, isfile
  90 from os.path import join as joinpath, split as splitpath
  91 from re import match
  92
  93 # SCons includes
  94 import SCons
  95 import SCons.Node
  96 import SCons.Node.FS
  97
  98 from m5.util import compareVersions, readCommand, readCommandWithReturn
  99
 100 AddOption('--colors', dest='use_colors', action='store_true',
 101           help="Add color to abbreviated scons output")
 102 AddOption('--no-colors', dest='use_colors', action='store_false',
 103           help="Don't add color to abbreviated scons output")
 104 AddOption('--with-cxx-config', action='store_true',
 105           help="Build with support for C++-based configuration")
 106 AddOption('--default',
 107           help='Override which build_opts file to use for defaults')
 108 AddOption('--ignore-style', action='store_true',
 109           help='Disable style checking hooks')
 110 AddOption('--gold-linker', action='store_true', help='Use the gold linker')
 111 AddOption('--no-compress-debug', action='store_true',
 112           help="Don't compress debug info in build files")
 113 AddOption('--no-lto', action='store_true',
 114           help='Disable Link-Time Optimization for fast')
 115 AddOption('--verbose', action='store_true',
 116           help='Print full tool command lines')
 117 AddOption('--without-python', action='store_true',
 118           help='Build without Python configuration support')
 119 AddOption('--without-tcmalloc', action='store_true',
 120           help='Disable linking against tcmalloc')
 121 AddOption('--with-ubsan', action='store_true',
 122           help='Build with Undefined Behavior Sanitizer if available')
 123 AddOption('--with-asan', action='store_true',
 124           help='Build with Address Sanitizer if available')
 125 AddOption('--with-systemc-tests', action='store_true',
 126           help='Build systemc tests')
 127
 128 from gem5_scons import Transform, error, warning, summarize_warnings
 129
 130 ########################################################################
 131 #
 132 # Set up the main build environment.
 133 #
 134 ########################################################################
 135
 136 main = Environment(tools=['default', 'git'])
 137
 138 from gem5_scons.util import get_termcap
 139 termcap = get_termcap()
 140
 141 main_dict_keys = main.Dictionary().keys()
 142
 143 # Check that we have a C/C++ compiler
 144 if not ('CC' in main_dict_keys and 'CXX' in main_dict_keys):
 145     error("No C++ compiler installed (package g++ on Ubuntu and RedHat)")
 146
 147 ###################################################
 148 #
 149 # Figure out which configurations to set up based on the path(s) of
 150 # the target(s).
 151 #
 152 ###################################################
 153
 154 # Find default configuration & binary.
 155 Default(environ.get('M5_DEFAULT_BINARY', 'build/ARM/gem5.debug'))
 156
 157 # helper function: find last occurrence of element in list
 158 def rfind(l, elt, offs = -1):
 159     for i in range(len(l)+offs, 0, -1):
 160         if l[i] == elt:
 161             return i
 162     raise ValueError("element not found")
 163
 164 # Take a list of paths (or SCons Nodes) and return a list with all
 165 # paths made absolute and ~-expanded.  Paths will be interpreted
 166 # relative to the launch directory unless a different root is provided
 167 def makePathListAbsolute(path_list, root=GetLaunchDir()):
 168     return [abspath(joinpath(root, expanduser(str(p))))
 169             for p in path_list]
 170
 171 # Each target must have 'build' in the interior of the path; the
 172 # directory below this will determine the build parameters.  For
 173 # example, for target 'foo/bar/build/X86/arch/x86/blah.do' we
 174 # recognize that X86 specifies the configuration because it
 175 # follow 'build' in the build path.
 176
 177 # The funky assignment to "[:]" is needed to replace the list contents
 178 # in place rather than reassign the symbol to a new list, which
 179 # doesn't work (obviously!).
 180 BUILD_TARGETS[:] = makePathListAbsolute(BUILD_TARGETS)
 181
 182 # Generate a list of the unique build roots and configs that the
 183 # collected targets reference.
 184 variant_paths = []
 185 build_root = None
 186 for t in BUILD_TARGETS:
 187     path_dirs = t.split('/')
 188     try:
 189         build_top = rfind(path_dirs, 'build', -2)
 190     except:
 191         error("No non-leaf 'build' dir found on target path.", t)
 192     this_build_root = joinpath('/',*path_dirs[:build_top+1])
 193     if not build_root:
 194         build_root = this_build_root
 195     else:
 196         if this_build_root != build_root:
 197             error("build targets not under same build root\n"
 198                   "  %s\n  %s" % (build_root, this_build_root))
 199     variant_path = joinpath('/',*path_dirs[:build_top+2])
 200     if variant_path not in variant_paths:
 201         variant_paths.append(variant_path)
 202
 203 # Make sure build_root exists (might not if this is the first build there)
 204 if not isdir(build_root):
 205     mkdir(build_root)
 206 main['BUILDROOT'] = build_root
 207
 208 Export('main')
 209
 210 main.SConsignFile(joinpath(build_root, "sconsign"))
 211
 212 # Default duplicate option is to use hard links, but this messes up
 213 # when you use emacs to edit a file in the target dir, as emacs moves
 214 # file to file~ then copies to file, breaking the link.  Symbolic
 215 # (soft) links work better.
 216 main.SetOption('duplicate', 'soft-copy')
 217
 218 #
 219 # Set up global sticky variables... these are common to an entire build
 220 # tree (not specific to a particular build like X86)
 221 #
 222
 223 global_vars_file = joinpath(build_root, 'variables.global')
 224
 225 global_vars = Variables(global_vars_file, args=ARGUMENTS)
 226
 227 global_vars.AddVariables(
 228     ('CC', 'C compiler', environ.get('CC', main['CC'])),
 229     ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),
 230     ('CCFLAGS_EXTRA', 'Extra C and C++ compiler flags', ''),
 231     ('LDFLAGS_EXTRA', 'Extra linker flags', ''),
 232     ('MARSHAL_CCFLAGS_EXTRA', 'Extra C and C++ marshal compiler flags', ''),
 233     ('MARSHAL_LDFLAGS_EXTRA', 'Extra marshal linker flags', ''),
 234     ('PYTHON_CONFIG', 'Python config binary to use',
 235      [ 'python3-config', 'python-config']
 236     ),
 237     ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
 238     ('BATCH', 'Use batch pool for build and tests', False),
 239     ('BATCH_CMD', 'Batch pool submission command name', 'qdo'),
 240     ('M5_BUILD_CACHE', 'Cache built objects in this directory', False),
 241     ('EXTRAS', 'Add extra directories to the compilation', '')
 242     )
 243
 244 # Update main environment with values from ARGUMENTS & global_vars_file
 245 global_vars.Update(main)
 246 Help('''
 247 Global build variables:
 248 {help}
 249 '''.format(help=global_vars.GenerateHelpText(main)), append=True)
 250
 251 # Save sticky variable settings back to current variables file
 252 global_vars.Save(global_vars_file, main)
 253
 254 # Parse EXTRAS variable to build list of all directories where we're
 255 # look for sources etc.  This list is exported as extras_dir_list.
 256 base_dir = Dir('#src').abspath
 257 if main['EXTRAS']:
 258     extras_dir_list = makePathListAbsolute(main['EXTRAS'].split(':'))
 259 else:
 260     extras_dir_list = []
 261
 262 Export('base_dir')
 263 Export('extras_dir_list')
 264
 265 # the ext directory should be on the #includes path
 266 main.Append(CPPPATH=[Dir('ext')])
 267
 268 # Add shared top-level headers
 269 main.Prepend(CPPPATH=Dir('include'))
 270
 271 if GetOption('verbose'):
 272     def MakeAction(action, string, *args, **kwargs):
 273         return Action(action, *args, **kwargs)
 274 else:
 275     MakeAction = Action
 276     main['CCCOMSTR']        = Transform("CC")
 277     main['CXXCOMSTR']       = Transform("CXX")
 278     main['ASCOMSTR']        = Transform("AS")
 279     main['ARCOMSTR']        = Transform("AR", 0)
 280     main['LINKCOMSTR']      = Transform("LINK", 0)
 281     main['SHLINKCOMSTR']    = Transform("SHLINK", 0)
 282     main['RANLIBCOMSTR']    = Transform("RANLIB", 0)
 283     main['M4COMSTR']        = Transform("M4")
 284     main['SHCCCOMSTR']      = Transform("SHCC")
 285     main['SHCXXCOMSTR']     = Transform("SHCXX")
 286 Export('MakeAction')
 287
 288 # Initialize the Link-Time Optimization (LTO) flags
 289 main['LTO_CCFLAGS'] = []
 290 main['LTO_LDFLAGS'] = []
 291
 292 # According to the readme, tcmalloc works best if the compiler doesn't
 293 # assume that we're using the builtin malloc and friends. These flags
 294 # are compiler-specific, so we need to set them after we detect which
 295 # compiler we're using.
 296 main['TCMALLOC_CCFLAGS'] = []
 297
 298 CXX_version = readCommand([main['CXX'],'--version'], exception=False)
 299 CXX_V = readCommand([main['CXX'],'-V'], exception=False)
 300
 301 main['GCC'] = CXX_version and CXX_version.find('g++') >= 0
 302 main['CLANG'] = CXX_version and CXX_version.find('clang') >= 0
 303 if main['GCC'] + main['CLANG'] > 1:
 304     error('Two compilers enabled at once?')
 305
 306 # Set up default C++ compiler flags
 307 if main['GCC'] or main['CLANG']:
 308     # As gcc and clang share many flags, do the common parts here
 309     main.Append(CCFLAGS=['-pipe'])
 310     main.Append(CCFLAGS=['-fno-strict-aliasing'])
 311     # Enable -Wall and -Wextra and then disable the few warnings that
 312     # we consistently violate
 313     main.Append(CCFLAGS=['-Wall', '-Wundef', '-Wextra',
 314                          '-Wno-sign-compare', '-Wno-unused-parameter'])
 315     # We always compile using C++14
 316     main.Append(CXXFLAGS=['-std=c++14'])
 317     if sys.platform.startswith('freebsd'):
 318         main.Append(CCFLAGS=['-I/usr/local/include'])
 319         main.Append(CXXFLAGS=['-I/usr/local/include'])
 320
 321     # On Mac OS X/Darwin the default linker doesn't support the
 322     # option --as-needed
 323     if sys.platform != "darwin":
 324         main.Append(LINKFLAGS='-Wl,--as-needed')
 325     if GetOption('gold_linker'):
 326         main.Append(LINKFLAGS='-fuse-ld=gold')
 327
 328     # Treat warnings as errors but white list some warnings that we
 329     # want to allow (e.g., deprecation warnings).
 330     main.Append(CCFLAGS=['-Werror',
 331                          '-Wno-error=deprecated-declarations',
 332                          '-Wno-error=deprecated',
 333                         ])
 334 else:
 335     error('\n'.join((
 336           "Don't know what compiler options to use for your compiler.",
 337           "compiler: " + main['CXX'],
 338           "version: " + CXX_version.replace('\n', '<nl>') if
 339                 CXX_version else 'COMMAND NOT FOUND!',
 340           "If you're trying to use a compiler other than GCC",
 341           "or clang, there appears to be something wrong with your",
 342           "environment.",
 343           "",
 344           "If you are trying to use a compiler other than those listed",
 345           "above you will need to ease fix SConstruct and ",
 346           "src/SConscript to support that compiler.")))
 347
 348 if main['GCC']:
 349     gcc_version = readCommand([main['CXX'], '-dumpversion'], exception=False)
 350     if compareVersions(gcc_version, "5") < 0:
 351         error('gcc version 5 or newer required.\n'
 352               'Installed version:', gcc_version)
 353         Exit(1)
 354
 355     main['GCC_VERSION'] = gcc_version
 356
 357     # Add the appropriate Link-Time Optimization (LTO) flags
 358     # unless LTO is explicitly turned off. Note that these flags
 359     # are only used by the fast target.
 360     if not GetOption('no_lto'):
 361         # Pass the LTO flag when compiling to produce GIMPLE
 362         # output, we merely create the flags here and only append
 363         # them later
 364         main['LTO_CCFLAGS'] = ['-flto=%d' % GetOption('num_jobs')]
 365
 366         # Use the same amount of jobs for LTO as we are running
 367         # scons with
 368         main['LTO_LDFLAGS'] = ['-flto=%d' % GetOption('num_jobs')]
 369
 370     main.Append(TCMALLOC_CCFLAGS=['-fno-builtin-malloc', '-fno-builtin-calloc',
 371                                   '-fno-builtin-realloc', '-fno-builtin-free'])
 372
 373 elif main['CLANG']:
 374     clang_version_re = re.compile(".* version (\d+\.\d+)")
 375     clang_version_match = clang_version_re.search(CXX_version)
 376     if (clang_version_match):
 377         clang_version = clang_version_match.groups()[0]
 378         if compareVersions(clang_version, "3.9") < 0:
 379             error('clang version 3.9 or newer required.\n'
 380                   'Installed version:', clang_version)
 381     else:
 382         error('Unable to determine clang version.')
 383
 384     # clang has a few additional warnings that we disable, extraneous
 385     # parantheses are allowed due to Ruby's printing of the AST,
 386     # finally self assignments are allowed as the generated CPU code
 387     # is relying on this
 388     main.Append(CCFLAGS=['-Wno-parentheses',
 389                          '-Wno-self-assign',
 390                          # Some versions of libstdc++ (4.8?) seem to
 391                          # use struct hash and class hash
 392                          # interchangeably.
 393                          '-Wno-mismatched-tags',
 394                          ])
 395     if sys.platform != "darwin" and \
 396        compareVersions(clang_version, "10.0") >= 0:
 397         main.Append(CCFLAGS=['-Wno-c99-designator'])
 398
 399     if compareVersions(clang_version, "8.0") >= 0:
 400         main.Append(CCFLAGS=['-Wno-defaulted-function-deleted'])
 401
 402     main.Append(TCMALLOC_CCFLAGS=['-fno-builtin'])
 403
 404     # On Mac OS X/Darwin we need to also use libc++ (part of XCode) as
 405     # opposed to libstdc++, as the later is dated.
 406     if sys.platform == "darwin":
 407         main.Append(CXXFLAGS=['-stdlib=libc++'])
 408         main.Append(LIBS=['c++'])
 409
 410     # On FreeBSD we need libthr.
 411     if sys.platform.startswith('freebsd'):
 412         main.Append(LIBS=['thr'])
 413
 414 # Add sanitizers flags
 415 sanitizers=[]
 416 if GetOption('with_ubsan'):
 417     sanitizers.append('undefined')
 418 if GetOption('with_asan'):
 419     # Available for gcc >= 5 or llvm >= 3.1 both a requirement
 420     # by the build system
 421     sanitizers.append('address')
 422     suppressions_file = Dir('util').File('lsan-suppressions').get_abspath()
 423     suppressions_opt = 'suppressions=%s' % suppressions_file
 424     main['ENV']['LSAN_OPTIONS'] = ':'.join([suppressions_opt,
 425                                             'print_suppressions=0'])
 426     print()
 427     warning('To suppress false positive leaks, set the LSAN_OPTIONS '
 428             'environment variable to "%s" when running gem5' %
 429             suppressions_opt)
 430     warning('LSAN_OPTIONS=suppressions=%s' % suppressions_opt)
 431     print()
 432 if sanitizers:
 433     sanitizers = ','.join(sanitizers)
 434     if main['GCC'] or main['CLANG']:
 435         main.Append(CCFLAGS=['-fsanitize=%s' % sanitizers,
 436                              '-fno-omit-frame-pointer'],
 437                     LINKFLAGS='-fsanitize=%s' % sanitizers)
 438     else:
 439         warning("Don't know how to enable %s sanitizer(s) for your "
 440                 "compiler." % sanitizers)
 441
 442 # Set up common yacc/bison flags (needed for Ruby)
 443 main['YACCFLAGS'] = '-d'
 444 main['YACCHXXFILESUFFIX'] = '.hh'
 445
 446 # Do this after we save setting back, or else we'll tack on an
 447 # extra 'qdo' every time we run scons.
 448 if main['BATCH']:
 449     main['CC']     = main['BATCH_CMD'] + ' ' + main['CC']
 450     main['CXX']    = main['BATCH_CMD'] + ' ' + main['CXX']
 451     main['AS']     = main['BATCH_CMD'] + ' ' + main['AS']
 452     main['AR']     = main['BATCH_CMD'] + ' ' + main['AR']
 453     main['RANLIB'] = main['BATCH_CMD'] + ' ' + main['RANLIB']
 454
 455 if sys.platform == 'cygwin':
 456     # cygwin has some header file issues...
 457     main.Append(CCFLAGS=["-Wno-uninitialized"])
 458
 459
 460 have_pkg_config = readCommand(['pkg-config', '--version'], exception='')
 461
 462 # Check for the protobuf compiler
 463 try:
 464     main['HAVE_PROTOC'] = True
 465     protoc_version = readCommand([main['PROTOC'], '--version']).split()
 466
 467     # First two words should be "libprotoc x.y.z"
 468     if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
 469         warning('Protocol buffer compiler (protoc) not found.\n'
 470                 'Please install protobuf-compiler for tracing support.')
 471         main['HAVE_PROTOC'] = False
 472     else:
 473         # Based on the availability of the compress stream wrappers,
 474         # require 2.1.0
 475         min_protoc_version = '2.1.0'
 476         if compareVersions(protoc_version[1], min_protoc_version) < 0:
 477             warning('protoc version', min_protoc_version,
 478                     'or newer required.\n'
 479                     'Installed version:', protoc_version[1])
 480             main['HAVE_PROTOC'] = False
 481         else:
 482             # Attempt to determine the appropriate include path and
 483             # library path using pkg-config, that means we also need to
 484             # check for pkg-config. Note that it is possible to use
 485             # protobuf without the involvement of pkg-config. Later on we
 486             # check go a library config check and at that point the test
 487             # will fail if libprotobuf cannot be found.
 488             if have_pkg_config:
 489                 try:
 490                     # Attempt to establish what linking flags to add for
 491                     # protobuf
 492                     # using pkg-config
 493                     main.ParseConfig(
 494                             'pkg-config --cflags --libs-only-L protobuf')
 495                 except:
 496                     warning('pkg-config could not get protobuf flags.')
 497 except Exception as e:
 498     warning('While checking protoc version:', str(e))
 499     main['HAVE_PROTOC'] = False
 500
 501 def CheckCxxFlag(context, flag, autoadd=True):
 502     context.Message("Checking for compiler %s support... " % flag)
 503     last_cxxflags = context.env['CXXFLAGS']
 504     context.env.Append(CXXFLAGS=[flag])
 505     ret = context.TryCompile('', '.cc')
 506     if not autoadd:
 507         context.env['CXXFLAGS'] = last_cxxflags
 508     context.Result(ret)
 509     return ret
 510
 511 def CheckLinkFlag(context, flag, autoadd=True, set_for_shared=True):
 512     context.Message("Checking for linker %s support... " % flag)
 513     last_linkflags = context.env['LINKFLAGS']
 514     context.env.Append(LINKFLAGS=[flag])
 515     ret = context.TryLink('int main(int, char *[]) { return 0; }', '.cc')
 516     if not autoadd:
 517         context.env['LINKFLAGS'] = last_linkflags
 518     if set_for_shared:
 519         assert(autoadd)
 520         context.env.Append(SHLINKFLAGS=[flag])
 521     context.Result(ret)
 522     return ret
 523
 524 # Add a custom Check function to test for structure members.
 525 def CheckMember(context, include, decl, member, include_quotes="<>"):
 526     context.Message("Checking for member %s in %s..." %
 527                     (member, decl))
 528     text = """
 529 #include %(header)s
 530 int main(){
 531   %(decl)s test;
 532   (void)test.%(member)s;
 533   return 0;
 534 };
 535 """ % { "header" : include_quotes[0] + include + include_quotes[1],
 536         "decl" : decl,
 537         "member" : member,
 538         }
 539
 540     ret = context.TryCompile(text, extension=".cc")
 541     context.Result(ret)
 542     return ret
 543
 544 def CheckPythonLib(context):
 545     context.Message('Checking Python version... ')
 546     ret = context.TryRun(r"""
 547 #include <pybind11/embed.h>
 548
 549 int
 550 main(int argc, char **argv) {
 551     pybind11::scoped_interpreter guard{};
 552     pybind11::exec(
 553         "import sys\n"
 554         "vi = sys.version_info\n"
 555         "sys.stdout.write('%i.%i.%i' % (vi.major, vi.minor, vi.micro));\n");
 556     return 0;
 557 }
 558     """, extension=".cc")
 559     context.Result(ret[1] if ret[0] == 1 else 0)
 560     if ret[0] == 0:
 561         return None
 562     else:
 563         return tuple(map(int, ret[1].split(".")))
 564
 565 # Platform-specific configuration.  Note again that we assume that all
 566 # builds under a given build root run on the same host platform.
 567 conf = Configure(main,
 568                  conf_dir = joinpath(build_root, '.scons_config'),
 569                  log_file = joinpath(build_root, 'scons_config.log'),
 570                  custom_tests = {
 571         'CheckMember' : CheckMember,
 572         'CheckPythonLib' : CheckPythonLib,
 573         'CheckCxxFlag' : CheckCxxFlag,
 574         'CheckLinkFlag' : CheckLinkFlag,
 575         })
 576
 577 # Recent versions of scons substitute a "Null" object for Configure()
 578 # when configuration isn't necessary, e.g., if the "--help" option is
 579 # present.  Unfortuantely this Null object always returns false,
 580 # breaking all our configuration checks.  We replace it with our own
 581 # more optimistic null object that returns True instead.
 582 if not conf:
 583     def NullCheck(*args, **kwargs):
 584         return True
 585
 586     class NullConf:
 587         def __init__(self, env):
 588             self.env = env
 589         def Finish(self):
 590             return self.env
 591         def __getattr__(self, mname):
 592             return NullCheck
 593
 594     conf = NullConf(main)
 595
 596 # Cache build files in the supplied directory.
 597 if main['M5_BUILD_CACHE']:
 598     print('Using build cache located at', main['M5_BUILD_CACHE'])
 599     CacheDir(main['M5_BUILD_CACHE'])
 600
 601 if not GetOption('no_compress_debug'):
 602     if not conf.CheckCxxFlag('-gz'):
 603         warning("Can't enable object file debug section compression")
 604     if not conf.CheckLinkFlag('-gz'):
 605         warning("Can't enable executable debug section compression")
 606
 607 main['USE_PYTHON'] = not GetOption('without_python')
 608 if main['USE_PYTHON']:
 609     # Find Python include and library directories for embedding the
 610     # interpreter. We rely on python-config to resolve the appropriate
 611     # includes and linker flags. ParseConfig does not seem to understand
 612     # the more exotic linker flags such as -Xlinker and -export-dynamic so
 613     # we add them explicitly below. If you want to link in an alternate
 614     # version of python, see above for instructions on how to invoke
 615     # scons with the appropriate PATH set.
 616
 617     python_config = main.Detect(main['PYTHON_CONFIG'])
 618     if python_config is None:
 619         error("Can't find a suitable python-config, tried %s" % \
 620               main['PYTHON_CONFIG'])
 621
 622     print("Info: Using Python config: %s" % (python_config, ))
 623
 624     py_includes = readCommand([python_config, '--includes'],
 625                               exception='').split()
 626     py_includes = list(filter(
 627         lambda s: match(r'.*\/include\/.*',s), py_includes))
 628     # Strip the -I from the include folders before adding them to the
 629     # CPPPATH
 630     py_includes = list(map(
 631         lambda s: s[2:] if s.startswith('-I') else s, py_includes))
 632     main.Append(CPPPATH=py_includes)
 633
 634     # Read the linker flags and split them into libraries and other link
 635     # flags. The libraries are added later through the call the CheckLib.
 636     # Note: starting in Python 3.8 the --embed flag is required to get the
 637     # -lpython3.8 linker flag
 638     retcode, cmd_stdout = readCommandWithReturn(
 639         [python_config, '--ldflags', '--embed'], exception='')
 640     if retcode != 0:
 641         # If --embed isn't detected then we're running python <3.8
 642         retcode, cmd_stdout = readCommandWithReturn(
 643             [python_config, '--ldflags'], exception='')
 644
 645     # Checking retcode again
 646     if retcode != 0:
 647         error("Failing on python-config --ldflags command")
 648
 649     py_ld_flags = cmd_stdout.split()
 650
 651     py_libs = []
 652     for lib in py_ld_flags:
 653          if not lib.startswith('-l'):
 654              main.Append(LINKFLAGS=[lib])
 655          else:
 656              lib = lib[2:]
 657              if lib not in py_libs:
 658                  py_libs.append(lib)
 659
 660     # verify that this stuff works
 661     if not conf.CheckHeader('Python.h', '<>'):
 662         error("Check failed for Python.h header in",
 663                 ' '.join(py_includes), "\n"
 664               "Two possible reasons:\n"
 665               "1. Python headers are not installed (You can install the "
 666               "package python-dev on Ubuntu and RedHat)\n"
 667               "2. SCons is using a wrong C compiler. This can happen if "
 668               "CC has the wrong value.\n"
 669               "CC = %s" % main['CC'])
 670
 671     for lib in py_libs:
 672         if not conf.CheckLib(lib):
 673             error("Can't find library %s required by python." % lib)
 674
 675     main.Prepend(CPPPATH=Dir('ext/pybind11/include/'))
 676
 677     marshal_env = main.Clone()
 678
 679     # Bare minimum environment that only includes python
 680     marshal_env.Append(CCFLAGS='$MARSHAL_CCFLAGS_EXTRA')
 681     marshal_env.Append(LINKFLAGS='$MARSHAL_LDFLAGS_EXTRA')
 682
 683     py_version = conf.CheckPythonLib()
 684     if not py_version:
 685         error("Can't find a working Python installation")
 686
 687     # Found a working Python installation. Check if it meets minimum
 688     # requirements.
 689     if py_version[0] < 3 or \
 690     (py_version[0] == 3 and py_version[1] < 6):
 691         error('Python version too old. Version 3.6 or newer is required.')
 692     elif py_version[0] > 3:
 693         warning('Python version too new. Python 3 expected.')
 694
 695 # On Solaris you need to use libsocket for socket ops
 696 if not conf.CheckLibWithHeader(None, 'sys/socket.h', 'C++', 'accept(0,0,0);'):
 697    if not conf.CheckLibWithHeader('socket', 'sys/socket.h',
 698                                   'C++', 'accept(0,0,0);'):
 699        error("Can't find library with socket calls (e.g. accept()).")
 700
 701 # Check for zlib.  If the check passes, libz will be automatically
 702 # added to the LIBS environment variable.
 703 if not conf.CheckLibWithHeader('z', 'zlib.h', 'C++','zlibVersion();'):
 704     error('Did not find needed zlib compression library '
 705           'and/or zlib.h header file.\n'
 706           'Please install zlib and try again.')
 707
 708 # If we have the protobuf compiler, also make sure we have the
 709 # development libraries. If the check passes, libprotobuf will be
 710 # automatically added to the LIBS environment variable. After
 711 # this, we can use the HAVE_PROTOBUF flag to determine if we have
 712 # got both protoc and libprotobuf available.
 713 main['HAVE_PROTOBUF'] = main['HAVE_PROTOC'] and \
 714     conf.CheckLibWithHeader('protobuf', 'google/protobuf/message.h',
 715                             'C++', 'GOOGLE_PROTOBUF_VERIFY_VERSION;')
 716
 717 # Valgrind gets much less confused if you tell it when you're using
 718 # alternative stacks.
 719 main['HAVE_VALGRIND'] = conf.CheckCHeader('valgrind/valgrind.h')
 720
 721 # If we have the compiler but not the library, print another warning.
 722 if main['HAVE_PROTOC'] and not main['HAVE_PROTOBUF']:
 723     warning('Did not find protocol buffer library and/or headers.\n'
 724             'Please install libprotobuf-dev for tracing support.')
 725
 726 # Check for librt.
 727 have_posix_clock = \
 728     conf.CheckLibWithHeader(None, 'time.h', 'C',
 729                             'clock_nanosleep(0,0,NULL,NULL);') or \
 730     conf.CheckLibWithHeader('rt', 'time.h', 'C',
 731                             'clock_nanosleep(0,0,NULL,NULL);')
 732
 733 have_posix_timers = \
 734     conf.CheckLibWithHeader([None, 'rt'], [ 'time.h', 'signal.h' ], 'C',
 735                             'timer_create(CLOCK_MONOTONIC, NULL, NULL);')
 736
 737 if not GetOption('without_tcmalloc'):
 738     if conf.CheckLib('tcmalloc'):
 739         main.Append(CCFLAGS=main['TCMALLOC_CCFLAGS'])
 740     elif conf.CheckLib('tcmalloc_minimal'):
 741         main.Append(CCFLAGS=main['TCMALLOC_CCFLAGS'])
 742     else:
 743         warning("You can get a 12% performance improvement by "
 744                 "installing tcmalloc (libgoogle-perftools-dev package "
 745                 "on Ubuntu or RedHat).")
 746
 747
 748 # Detect back trace implementations. The last implementation in the
 749 # list will be used by default.
 750 backtrace_impls = [ "none" ]
 751
 752 backtrace_checker = 'char temp;' + \
 753     ' backtrace_symbols_fd((void*)&temp, 0, 0);'
 754 if conf.CheckLibWithHeader(None, 'execinfo.h', 'C', backtrace_checker):
 755     backtrace_impls.append("glibc")
 756 elif conf.CheckLibWithHeader('execinfo', 'execinfo.h', 'C',
 757                              backtrace_checker):
 758     # NetBSD and FreeBSD need libexecinfo.
 759     backtrace_impls.append("glibc")
 760     main.Append(LIBS=['execinfo'])
 761
 762 if backtrace_impls[-1] == "none":
 763     default_backtrace_impl = "none"
 764     warning("No suitable back trace implementation found.")
 765
 766 if not have_posix_clock:
 767     warning("Can't find library for POSIX clocks.")
 768
 769 # Check for <fenv.h> (C99 FP environment control)
 770 have_fenv = conf.CheckHeader('fenv.h', '<>')
 771 if not have_fenv:
 772     warning("Header file <fenv.h> not found.\n"
 773             "This host has no IEEE FP rounding mode control.")
 774
 775 # Check for <png.h> (libpng library needed if wanting to dump
 776 # frame buffer image in png format)
 777 have_png = conf.CheckHeader('png.h', '<>')
 778 if not have_png:
 779     warning("Header file <png.h> not found.\n"
 780             "This host has no libpng library.\n"
 781             "Disabling support for PNG framebuffers.")
 782
 783 # Check if we should enable KVM-based hardware virtualization. The API
 784 # we rely on exists since version 2.6.36 of the kernel, but somehow
 785 # the KVM_API_VERSION does not reflect the change. We test for one of
 786 # the types as a fall back.
 787 have_kvm = conf.CheckHeader('linux/kvm.h', '<>')
 788 if not have_kvm:
 789     print("Info: Compatible header file <linux/kvm.h> not found, "
 790           "disabling KVM support.")
 791
 792 # Check if the TUN/TAP driver is available.
 793 have_tuntap = conf.CheckHeader('linux/if_tun.h', '<>')
 794 if not have_tuntap:
 795     print("Info: Compatible header file <linux/if_tun.h> not found.")
 796
 797 # x86 needs support for xsave. We test for the structure here since we
 798 # won't be able to run new tests by the time we know which ISA we're
 799 # targeting.
 800 have_kvm_xsave = conf.CheckTypeSize('struct kvm_xsave',
 801                                     '#include <linux/kvm.h>') != 0
 802
 803 # Check if the requested target ISA is compatible with the host
 804 def is_isa_kvm_compatible(isa):
 805     try:
 806         import platform
 807         host_isa = platform.machine()
 808     except:
 809         warning("Failed to determine host ISA.")
 810         return False
 811
 812     if not have_posix_timers:
 813         warning("Can not enable KVM, host seems to lack support "
 814                 "for POSIX timers")
 815         return False
 816
 817     if isa == "arm":
 818         return host_isa in ( "armv7l", "aarch64" )
 819     elif isa == "x86":
 820         if host_isa != "x86_64":
 821             return False
 822
 823         if not have_kvm_xsave:
 824             warning("KVM on x86 requires xsave support in kernel headers.")
 825             return False
 826
 827         return True
 828     else:
 829         return False
 830
 831
 832 # Check if the exclude_host attribute is available. We want this to
 833 # get accurate instruction counts in KVM.
 834 main['HAVE_PERF_ATTR_EXCLUDE_HOST'] = conf.CheckMember(
 835     'linux/perf_event.h', 'struct perf_event_attr', 'exclude_host')
 836
 837 def check_hdf5():
 838     return \
 839         conf.CheckLibWithHeader('hdf5', 'hdf5.h', 'C',
 840                                 'H5Fcreate("", 0, 0, 0);') and \
 841         conf.CheckLibWithHeader('hdf5_cpp', 'H5Cpp.h', 'C++',
 842                                 'H5::H5File("", 0);')
 843
 844 def check_hdf5_pkg(name):
 845     print("Checking for %s using pkg-config..." % name, end="")
 846     if not have_pkg_config:
 847         print(" pkg-config not found")
 848         return False
 849
 850     try:
 851         main.ParseConfig('pkg-config --cflags-only-I --libs-only-L %s' % name)
 852         print(" yes")
 853         return True
 854     except:
 855         print(" no")
 856         return False
 857
 858 # Check if there is a pkg-config configuration for hdf5. If we find
 859 # it, setup the environment to enable linking and header inclusion. We
 860 # don't actually try to include any headers or link with hdf5 at this
 861 # stage.
 862 if not check_hdf5_pkg('hdf5-serial'):
 863     check_hdf5_pkg('hdf5')
 864
 865 # Check if the HDF5 libraries can be found. This check respects the
 866 # include path and library path provided by pkg-config. We perform
 867 # this check even if there isn't a pkg-config configuration for hdf5
 868 # since some installations don't use pkg-config.
 869 have_hdf5 = check_hdf5()
 870 if not have_hdf5:
 871     print("Warning: Couldn't find any HDF5 C++ libraries. Disabling")
 872     print("         HDF5 support.")
 873
 874 ######################################################################
 875 #
 876 # Finish the configuration
 877 #
 878 main = conf.Finish()
 879
 880 ######################################################################
 881 #
 882 # Collect all non-global variables
 883 #
 884
 885 # Define the universe of supported ISAs
 886 all_isa_list = [ ]
 887 all_gpu_isa_list = [ ]
 888 Export('all_isa_list')
 889 Export('all_gpu_isa_list')
 890
 891 class CpuModel(object):
 892     '''The CpuModel class encapsulates everything the ISA parser needs to
 893     know about a particular CPU model.'''
 894
 895     # Dict of available CPU model objects.  Accessible as CpuModel.dict.
 896     dict = {}
 897
 898     # Constructor.  Automatically adds models to CpuModel.dict.
 899     def __init__(self, name, default=False):
 900         self.name = name           # name of model
 901
 902         # This cpu is enabled by default
 903         self.default = default
 904
 905         # Add self to dict
 906         if name in CpuModel.dict:
 907             raise AttributeError("CpuModel '%s' already registered" % name)
 908         CpuModel.dict[name] = self
 909
 910 Export('CpuModel')
 911
 912 # Sticky variables get saved in the variables file so they persist from
 913 # one invocation to the next (unless overridden, in which case the new
 914 # value becomes sticky).
 915 sticky_vars = Variables(args=ARGUMENTS)
 916 Export('sticky_vars')
 917
 918 # Sticky variables that should be exported
 919 export_vars = []
 920 Export('export_vars')
 921
 922 # For Ruby
 923 all_protocols = []
 924 Export('all_protocols')
 925 protocol_dirs = []
 926 Export('protocol_dirs')
 927 slicc_includes = []
 928 Export('slicc_includes')
 929
 930 # Walk the tree and execute all SConsopts scripts that wil add to the
 931 # above variables
 932 if GetOption('verbose'):
 933     print("Reading SConsopts")
 934 for bdir in [ base_dir ] + extras_dir_list:
 935     if not isdir(bdir):
 936         error("Directory '%s' does not exist." % bdir)
 937     for root, dirs, files in os.walk(bdir):
 938         if 'SConsopts' in files:
 939             if GetOption('verbose'):
 940                 print("Reading", joinpath(root, 'SConsopts'))
 941             SConscript(joinpath(root, 'SConsopts'))
 942
 943 all_isa_list.sort()
 944 all_gpu_isa_list.sort()
 945
 946 sticky_vars.AddVariables(
 947     EnumVariable('TARGET_ISA', 'Target ISA', 'null', all_isa_list),
 948     EnumVariable('TARGET_GPU_ISA', 'Target GPU ISA', 'gcn3', all_gpu_isa_list),
 949     ListVariable('CPU_MODELS', 'CPU models',
 950                  sorted(n for n,m in CpuModel.dict.items() if m.default),
 951                  sorted(CpuModel.dict.keys())),
 952     BoolVariable('EFENCE', 'Link with Electric Fence malloc debugger',
 953                  False),
 954     BoolVariable('USE_SSE2',
 955                  'Compile for SSE2 (-msse2) to get IEEE FP on x86 hosts',
 956                  False),
 957     BoolVariable('USE_POSIX_CLOCK', 'Use POSIX Clocks', have_posix_clock),
 958     BoolVariable('USE_FENV', 'Use <fenv.h> IEEE mode control', have_fenv),
 959     BoolVariable('USE_PNG',  'Enable support for PNG images', have_png),
 960     BoolVariable('USE_KVM', 'Enable hardware virtualized (KVM) CPU models',
 961                  have_kvm),
 962     BoolVariable('USE_TUNTAP',
 963                  'Enable using a tap device to bridge to the host network',
 964                  have_tuntap),
 965     BoolVariable('BUILD_GPU', 'Build the compute-GPU model', False),
 966     EnumVariable('PROTOCOL', 'Coherence protocol for Ruby', 'None',
 967                   all_protocols),
 968     EnumVariable('BACKTRACE_IMPL', 'Post-mortem dump implementation',
 969                  backtrace_impls[-1], backtrace_impls),
 970     ('NUMBER_BITS_PER_SET', 'Max elements in set (default 64)',
 971                  64),
 972     BoolVariable('USE_HDF5', 'Enable the HDF5 support', have_hdf5),
 973     )
 974
 975 # These variables get exported to #defines in config/*.hh (see src/SConscript).
 976 export_vars += ['USE_FENV', 'TARGET_ISA', 'TARGET_GPU_ISA',
 977                 'USE_POSIX_CLOCK', 'USE_KVM', 'USE_TUNTAP', 'PROTOCOL',
 978                 'HAVE_PROTOBUF', 'HAVE_VALGRIND',
 979                 'HAVE_PERF_ATTR_EXCLUDE_HOST', 'USE_PNG',
 980                 'NUMBER_BITS_PER_SET', 'USE_HDF5']
 981
 982 ###################################################
 983 #
 984 # Define a SCons builder for configuration flag headers.
 985 #
 986 ###################################################
 987
 988 # This function generates a config header file that #defines the
 989 # variable symbol to the current variable setting (0 or 1).  The source
 990 # operands are the name of the variable and a Value node containing the
 991 # value of the variable.
 992 def build_config_file(target, source, env):
 993     (variable, value) = [s.get_contents().decode('utf-8') for s in source]
 994     with open(str(target[0].abspath), 'w') as f:
 995         print('#define', variable, value, file=f)
 996     return None
 997
 998 # Combine the two functions into a scons Action object.
 999 config_action = MakeAction(build_config_file, Transform("CONFIG H", 2))
1000
1001 # The emitter munges the source & target node lists to reflect what
1002 # we're really doing.
1003 def config_emitter(target, source, env):
1004     # extract variable name from Builder arg
1005     variable = str(target[0])
1006     # True target is config header file
1007     target = Dir('config').File(variable.lower() + '.hh')
1008     val = env[variable]
1009     if isinstance(val, bool):
1010         # Force value to 0/1
1011         val = int(val)
1012     elif isinstance(val, str):
1013         val = '"' + val + '"'
1014
1015     # Sources are variable name & value (packaged in SCons Value nodes)
1016     return [target], [Value(variable), Value(val)]
1017
1018 config_builder = Builder(emitter=config_emitter, action=config_action)
1019
1020 main.Append(BUILDERS = { 'ConfigFile' : config_builder })
1021
1022 def add_local_rpath(env, *targets):
1023     '''Set up an RPATH for a library which lives in the build directory.
1024
1025     The construction environment variable BIN_RPATH_PREFIX should be set to
1026     the relative path of the build directory starting from the location of the
1027     binary.'''
1028     for target in targets:
1029         target = env.Entry(target)
1030         if not isinstance(target, SCons.Node.FS.Dir):
1031             target = target.dir
1032         relpath = os.path.relpath(target.abspath, env['BUILDDIR'])
1033         components = [
1034             '\\$$ORIGIN',
1035             '${BIN_RPATH_PREFIX}',
1036             relpath
1037         ]
1038         env.Append(RPATH=[env.Literal(os.path.join(*components))])
1039
1040 if sys.platform != "darwin":
1041     main.Append(LINKFLAGS=Split('-z origin'))
1042
1043 main.AddMethod(add_local_rpath, 'AddLocalRPATH')
1044
1045 # builds in ext are shared across all configs in the build root.
1046 ext_dir = Dir('#ext').abspath
1047 ext_build_dirs = []
1048 for root, dirs, files in os.walk(ext_dir):
1049     if 'SConscript' in files:
1050         build_dir = os.path.relpath(root, ext_dir)
1051         ext_build_dirs.append(build_dir)
1052         main.SConscript(joinpath(root, 'SConscript'),
1053                         variant_dir=joinpath(build_root, build_dir))
1054
1055 gdb_xml_dir = joinpath(ext_dir, 'gdb-xml')
1056 Export('gdb_xml_dir')
1057
1058 ###################################################
1059 #
1060 # This builder and wrapper method are used to set up a directory with
1061 # switching headers. Those are headers which are in a generic location and
1062 # that include more specific headers from a directory chosen at build time
1063 # based on the current build settings.
1064 #
1065 ###################################################
1066
1067 def build_switching_header(target, source, env):
1068     path = str(target[0])
1069     subdir = str(source[0])
1070     dp, fp = os.path.split(path)
1071     dp = os.path.relpath(os.path.realpath(dp),
1072                          os.path.realpath(env['BUILDDIR']))
1073     with open(path, 'w') as hdr:
1074         print('#include "%s/%s/%s"' % (dp, subdir, fp), file=hdr)
1075
1076 switching_header_action = MakeAction(build_switching_header,
1077                                      Transform('GENERATE'))
1078
1079 switching_header_builder = Builder(action=switching_header_action,
1080                                    source_factory=Value,
1081                                    single_source=True)
1082
1083 main.Append(BUILDERS = { 'SwitchingHeader': switching_header_builder })
1084
1085 def switching_headers(self, headers, source):
1086     for header in headers:
1087         self.SwitchingHeader(header, source)
1088
1089 main.AddMethod(switching_headers, 'SwitchingHeaders')
1090
1091 ###################################################
1092 #
1093 # Define build environments for selected configurations.
1094 #
1095 ###################################################
1096
1097 for variant_path in variant_paths:
1098     if not GetOption('silent'):
1099         print("Building in", variant_path)
1100
1101     # Make a copy of the build-root environment to use for this config.
1102     env = main.Clone()
1103     env['BUILDDIR'] = variant_path
1104
1105     # variant_dir is the tail component of build path, and is used to
1106     # determine the build parameters (e.g., 'X86')
1107     (build_root, variant_dir) = splitpath(variant_path)
1108
1109     # Set env variables according to the build directory config.
1110     sticky_vars.files = []
1111     # Variables for $BUILD_ROOT/$VARIANT_DIR are stored in
1112     # $BUILD_ROOT/variables/$VARIANT_DIR so you can nuke
1113     # $BUILD_ROOT/$VARIANT_DIR without losing your variables settings.
1114     current_vars_file = joinpath(build_root, 'variables', variant_dir)
1115     if isfile(current_vars_file):
1116         sticky_vars.files.append(current_vars_file)
1117         if not GetOption('silent'):
1118             print("Using saved variables file %s" % current_vars_file)
1119     elif variant_dir in ext_build_dirs:
1120         # Things in ext are built without a variant directory.
1121         continue
1122     else:
1123         # Build dir-specific variables file doesn't exist.
1124
1125         # Make sure the directory is there so we can create it later
1126         opt_dir = dirname(current_vars_file)
1127         if not isdir(opt_dir):
1128             mkdir(opt_dir)
1129
1130         # Get default build variables from source tree.  Variables are
1131         # normally determined by name of $VARIANT_DIR, but can be
1132         # overridden by '--default=' arg on command line.
1133         default = GetOption('default')
1134         opts_dir = Dir('#build_opts').abspath
1135         if default:
1136             default_vars_files = [joinpath(build_root, 'variables', default),
1137                                   joinpath(opts_dir, default)]
1138         else:
1139             default_vars_files = [joinpath(opts_dir, variant_dir)]
1140         existing_files = list(filter(isfile, default_vars_files))
1141         if existing_files:
1142             default_vars_file = existing_files[0]
1143             sticky_vars.files.append(default_vars_file)
1144             print("Variables file %s not found,\n  using defaults in %s"
1145                   % (current_vars_file, default_vars_file))
1146         else:
1147             error("Cannot find variables file %s or default file(s) %s"
1148                   % (current_vars_file, ' or '.join(default_vars_files)))
1149             Exit(1)
1150
1151     # Apply current variable settings to env
1152     sticky_vars.Update(env)
1153
1154     Help('''
1155 Build variables for {dir}:
1156 {help}
1157 '''.format(dir=variant_dir, help=sticky_vars.GenerateHelpText(env)),
1158          append=True)
1159
1160     # Process variable settings.
1161
1162     if not have_fenv and env['USE_FENV']:
1163         warning("<fenv.h> not available; forcing USE_FENV to False in",
1164                 variant_dir + ".")
1165         env['USE_FENV'] = False
1166
1167     if not env['USE_FENV']:
1168         warning("No IEEE FP rounding mode control in", variant_dir + ".\n"
1169                 "FP results may deviate slightly from other platforms.")
1170
1171     if not have_png and env['USE_PNG']:
1172         warning("<png.h> not available; forcing USE_PNG to False in",
1173                 variant_dir + ".")
1174         env['USE_PNG'] = False
1175
1176     if env['USE_PNG']:
1177         env.Append(LIBS=['png'])
1178
1179     if env['EFENCE']:
1180         env.Append(LIBS=['efence'])
1181
1182     if env['USE_KVM']:
1183         if not have_kvm:
1184             warning("Can not enable KVM, host seems to lack KVM support")
1185             env['USE_KVM'] = False
1186         elif not is_isa_kvm_compatible(env['TARGET_ISA']):
1187             print("Info: KVM support disabled due to unsupported host and "
1188                   "target ISA combination")
1189             env['USE_KVM'] = False
1190
1191     if env['USE_TUNTAP']:
1192         if not have_tuntap:
1193             warning("Can't connect EtherTap with a tap device.")
1194             env['USE_TUNTAP'] = False
1195
1196     if env['BUILD_GPU']:
1197         env.Append(CPPDEFINES=['BUILD_GPU'])
1198
1199     # Warn about missing optional functionality
1200     if env['USE_KVM']:
1201         if not main['HAVE_PERF_ATTR_EXCLUDE_HOST']:
1202             warning("perf_event headers lack support for the exclude_host "
1203                     "attribute. KVM instruction counts will be inaccurate.")
1204
1205     # Save sticky variable settings back to current variables file
1206     sticky_vars.Save(current_vars_file, env)
1207
1208     if env['USE_SSE2']:
1209         env.Append(CCFLAGS=['-msse2'])
1210
1211     env.Append(CCFLAGS='$CCFLAGS_EXTRA')
1212     env.Append(LINKFLAGS='$LDFLAGS_EXTRA')
1213
1214     exports=['env']
1215     if main['USE_PYTHON']:
1216         exports.append('marshal_env')
1217
1218     # The src/SConscript file sets up the build rules in 'env' according
1219     # to the configured variables.  It returns a list of environments,
1220     # one for each variant build (debug, opt, etc.)
1221     SConscript('src/SConscript', variant_dir=variant_path, exports=exports)
1222
1223 atexit.register(summarize_warnings)