Add script to build many glibc configurations.

This patch adds a Python (3.5 or later) script to build many different
configurations of glibc, including building the required cross
compilers first.  It's not intended to change any patch testing
requirements, although some people may wish to use it for high-risk
patches such as adding warning options (and it can also be used to
test building, including compiling tests, for an individual
configuration, if e.g. you wish to do such a compilation test of a
patch for an architecture it touches).

The configurations include all the GNU/Linux ABI variants in
<https://sourceware.org/glibc/wiki/ABIList> (although some do not yet
build cleanly) and it would be desirable to cover enough other
variants e.g. for CPUs using different sysdeps directories to test
building each piece of code in glibc at least once.  It would also be
desirable to extend it to cover Hurd and NaCl, which might best be
done by people familiar with those configurations.

You call the script as

build-many-glibcs.py /some/where thing-to-do <other-arguments>

where /some/where is a working directory for the script.  It will
create and use subdirectories build, install, logs therein.  You can
use it with thing-to-do being "checkout" to create a subdirectory src
therein, with subdirectories binutils, gcc, glibc, gmp, linux, mpc,
mpfr with the sources of those components, or create those directories
manually (all except glibc can be symlinks to sources elsewhere).  In
the checkout case, by default it checks out GCC 6 branch, binutils
2.27 branch, glibc mainline and releases of other components.  You can
specify <component>-<version> to choose a version to check out, where
<version> is "vcs-mainline" or "vcs-<branch>" to check out from
version control (only supported for gcc, binutils, glibc) and
otherwise a release version number to download and use a tarball;
components not specified on the command line have default versions
checked out.  If you rerun "checkout" (with the same version
specifications) it will update checkouts from version control, but
will not detect cases where the location something is expected to be
checked out from has changed.

Other than "checkout", thing-to-do is one of host-libraries,
compilers, glibcs.  So you run, in that order:

build-many-glibcs.py /some/where host-libraries
build-many-glibcs.py /some/where compilers
build-many-glibcs.py /some/where glibcs

host-libraries is run once and then those libraries are used for all
the compilers.  compilers can be run once and then used many times for
testing different glibc versions (so a bot only needs to update glibc
and rerun the glibcs task, if using stable GCC / binutils; if testing
the latest versions of the whole toolchain together including mainline
GCC, it would probably want to update everything and rerun both
compilers and glibcs).  You can also name particular variants after
"compilers" or "glibcs" to build just those variants (the possible
variants are hardcoded in the script).

I may add support for allowing the set of configurations to depend on
the GCC version (to get cleaner default results), and optionally
looping over architecture-independent glibc variants of CFLAGS and
configure options as well, for every glibc configuration listed
(e.g. -Os).

GCC versions before 4.9 are not expected to work (the code uses
--with-glibc-version to get the bootstrap GCC appropriately
configured).  There are various problems for particular configurations
as well.

Command-line options to the script: -jN to run N jobs in parallel
(default the number of CPU cores reported by the system); --keep=all
or --keep=failed to control keeping around build directories (default
--keep=none).

	* scripts/build-many-glibcs.py: New file.

2 files changed, 1144 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 95f983f..7521477 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2016-11-11  Joseph Myers  <joseph@codesourcery.com>
 
+	* scripts/build-many-glibcs.py: New file.
+
 	* stdlib/bug-getcontext.c: Include <libc-internal.h>.
 	(do_test): Disable -Wmaybe-uninitialized around uses of
 	except_mask.
diff --git a/scripts/build-many-glibcs.py b/scripts/build-many-glibcs.py
new file mode 100755
index 0000000..4b4e15c
--- /dev/null
+++ b/scripts/build-many-glibcs.py
@@ -0,0 +1,1142 @@
+#!/usr/bin/python3
+# Build many configurations of glibc.
+# Copyright (C) 2016 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+#
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <http://www.gnu.org/licenses/>.
+
+"""Build many configurations of glibc.
+
+This script takes as arguments a directory name (containing a src
+subdirectory with sources of the relevant toolchain components) and a
+description of what to do: 'checkout', to check out sources into that
+directory, 'host-libraries', to build libraries required by the
+toolchain, 'compilers', to build cross-compilers for various
+configurations, or 'glibcs', to build glibc for various configurations
+and run the compilation parts of the testsuite.  Subsequent arguments
+name the versions of components to check out (<component>-<version),
+for 'checkout', or, for actions other than 'checkout', name
+configurations for which compilers or glibc are to be built.
+"""
+
+import argparse
+import os
+import os.path
+import re
+import shutil
+import stat
+import subprocess
+import sys
+import urllib.request
+
+
+class Context:
+
+    """The global state associated with builds in a given directory."""
+
+    def __init__(self, topdir, parallelism, keep, action):
+        """Initialize the context."""
+        self.topdir = topdir
+        self.parallelism = parallelism
+        self.keep = keep
+        self.srcdir = os.path.join(topdir, 'src')
+        self.installdir = os.path.join(topdir, 'install')
+        self.host_libraries_installdir = os.path.join(self.installdir,
+                                                      'host-libraries')
+        self.builddir = os.path.join(topdir, 'build')
+        self.logsdir = os.path.join(topdir, 'logs')
+        self.makefile = os.path.join(self.builddir, 'Makefile')
+        self.wrapper = os.path.join(self.builddir, 'wrapper')
+        self.save_logs = os.path.join(self.builddir, 'save-logs')
+        if action != 'checkout':
+            self.build_triplet = self.get_build_triplet()
+            self.glibc_version = self.get_glibc_version()
+        self.configs = {}
+        self.glibc_configs = {}
+        self.makefile_pieces = ['.PHONY: all\n']
+        self.add_all_configs()
+
+    def get_build_triplet(self):
+        """Determine the build triplet with config.guess."""
+        config_guess = os.path.join(self.component_srcdir('gcc'),
+                                    'config.guess')
+        cg_out = subprocess.run([config_guess], stdout=subprocess.PIPE,
+                                check=True, universal_newlines=True).stdout
+        return cg_out.rstrip()
+
+    def get_glibc_version(self):
+        """Determine the glibc version number (major.minor)."""
+        version_h = os.path.join(self.component_srcdir('glibc'), 'version.h')
+        with open(version_h, 'r') as f:
+            lines = f.readlines()
+        starttext = '#define VERSION "'
+        for l in lines:
+            if l.startswith(starttext):
+                l = l[len(starttext):]
+                l = l.rstrip('"\n')
+                m = re.fullmatch('([0-9]+)\.([0-9]+)[.0-9]*', l)
+                return '%s.%s' % m.group(1, 2)
+        print('error: could not determine glibc version')
+        exit(1)
+
+    def add_all_configs(self):
+        """Add all known glibc build configurations."""
+        self.add_config(arch='aarch64',
+                        os_name='linux-gnu')
+        self.add_config(arch='aarch64_be',
+                        os_name='linux-gnu')
+        self.add_config(arch='alpha',
+                        os_name='linux-gnu')
+        self.add_config(arch='arm',
+                        os_name='linux-gnueabi')
+        self.add_config(arch='armeb',
+                        os_name='linux-gnueabi')
+        self.add_config(arch='armeb',
+                        os_name='linux-gnueabi',
+                        variant='be8',
+                        gcc_cfg=['--with-arch=armv7-a'])
+        self.add_config(arch='arm',
+                        os_name='linux-gnueabihf')
+        self.add_config(arch='armeb',
+                        os_name='linux-gnueabihf')
+        self.add_config(arch='armeb',
+                        os_name='linux-gnueabihf',
+                        variant='be8',
+                        gcc_cfg=['--with-arch=armv7-a'])
+        self.add_config(arch='hppa',
+                        os_name='linux-gnu')
+        self.add_config(arch='ia64',
+                        os_name='linux-gnu',
+                        first_gcc_cfg=['--with-system-libunwind'])
+        self.add_config(arch='m68k',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--disable-multilib'])
+        self.add_config(arch='m68k',
+                        os_name='linux-gnu',
+                        variant='coldfire',
+                        gcc_cfg=['--with-arch=cf', '--disable-multilib'])
+        self.add_config(arch='microblaze',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--disable-multilib'])
+        self.add_config(arch='microblazeel',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--disable-multilib'])
+        self.add_config(arch='mips64',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--with-mips-plt'],
+                        glibcs=[{'variant': 'n32'},
+                                {'arch': 'mips',
+                                 'ccopts': '-mabi=32'},
+                                {'variant': 'n64',
+                                 'ccopts': '-mabi=64'}])
+        self.add_config(arch='mips64',
+                        os_name='linux-gnu',
+                        variant='soft',
+                        gcc_cfg=['--with-mips-plt', '--with-float=soft'],
+                        glibcs=[{'variant': 'n32-soft',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'soft',
+                                 'arch': 'mips',
+                                 'ccopts': '-mabi=32',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'n64-soft',
+                                 'ccopts': '-mabi=64',
+                                 'cfg': ['--without-fp']}])
+        self.add_config(arch='mips64',
+                        os_name='linux-gnu',
+                        variant='nan2008',
+                        gcc_cfg=['--with-mips-plt', '--with-nan=2008',
+                                 '--with-arch-64=mips64r2',
+                                 '--with-arch-32=mips32r2'],
+                        glibcs=[{'variant': 'n32-nan2008'},
+                                {'variant': 'nan2008',
+                                 'arch': 'mips',
+                                 'ccopts': '-mabi=32'},
+                                {'variant': 'n64-nan2008',
+                                 'ccopts': '-mabi=64'}])
+        self.add_config(arch='mips64',
+                        os_name='linux-gnu',
+                        variant='nan2008-soft',
+                        gcc_cfg=['--with-mips-plt', '--with-nan=2008',
+                                 '--with-arch-64=mips64r2',
+                                 '--with-arch-32=mips32r2',
+                                 '--with-float=soft'],
+                        glibcs=[{'variant': 'n32-nan2008-soft',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'nan2008-soft',
+                                 'arch': 'mips',
+                                 'ccopts': '-mabi=32',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'n64-nan2008-soft',
+                                 'ccopts': '-mabi=64',
+                                 'cfg': ['--without-fp']}])
+        self.add_config(arch='mips64el',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--with-mips-plt'],
+                        glibcs=[{'variant': 'n32'},
+                                {'arch': 'mipsel',
+                                 'ccopts': '-mabi=32'},
+                                {'variant': 'n64',
+                                 'ccopts': '-mabi=64'}])
+        self.add_config(arch='mips64el',
+                        os_name='linux-gnu',
+                        variant='soft',
+                        gcc_cfg=['--with-mips-plt', '--with-float=soft'],
+                        glibcs=[{'variant': 'n32-soft',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'soft',
+                                 'arch': 'mipsel',
+                                 'ccopts': '-mabi=32',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'n64-soft',
+                                 'ccopts': '-mabi=64',
+                                 'cfg': ['--without-fp']}])
+        self.add_config(arch='mips64el',
+                        os_name='linux-gnu',
+                        variant='nan2008',
+                        gcc_cfg=['--with-mips-plt', '--with-nan=2008',
+                                 '--with-arch-64=mips64r2',
+                                 '--with-arch-32=mips32r2'],
+                        glibcs=[{'variant': 'n32-nan2008'},
+                                {'variant': 'nan2008',
+                                 'arch': 'mipsel',
+                                 'ccopts': '-mabi=32'},
+                                {'variant': 'n64-nan2008',
+                                 'ccopts': '-mabi=64'}])
+        self.add_config(arch='mips64el',
+                        os_name='linux-gnu',
+                        variant='nan2008-soft',
+                        gcc_cfg=['--with-mips-plt', '--with-nan=2008',
+                                 '--with-arch-64=mips64r2',
+                                 '--with-arch-32=mips32r2',
+                                 '--with-float=soft'],
+                        glibcs=[{'variant': 'n32-nan2008-soft',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'nan2008-soft',
+                                 'arch': 'mipsel',
+                                 'ccopts': '-mabi=32',
+                                 'cfg': ['--without-fp']},
+                                {'variant': 'n64-nan2008-soft',
+                                 'ccopts': '-mabi=64',
+                                 'cfg': ['--without-fp']}])
+        self.add_config(arch='nios2',
+                        os_name='linux-gnu')
+        self.add_config(arch='powerpc',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--disable-multilib', '--enable-secureplt'])
+        self.add_config(arch='powerpc',
+                        os_name='linux-gnu',
+                        variant='soft',
+                        gcc_cfg=['--disable-multilib', '--with-float=soft',
+                                 '--enable-secureplt'],
+                        glibcs=[{'variant': 'soft', 'cfg': ['--without-fp']}])
+        self.add_config(arch='powerpc64',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--disable-multilib', '--enable-secureplt'])
+        self.add_config(arch='powerpc64le',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--disable-multilib', '--enable-secureplt'])
+        self.add_config(arch='powerpc',
+                        os_name='linux-gnuspe',
+                        gcc_cfg=['--disable-multilib', '--enable-secureplt',
+                                 '--enable-e500-double'],
+                        glibcs=[{'cfg': ['--without-fp']}])
+        self.add_config(arch='powerpc',
+                        os_name='linux-gnuspe',
+                        variant='e500v1',
+                        gcc_cfg=['--disable-multilib', '--enable-secureplt'],
+                        glibcs=[{'variant': 'e500v1', 'cfg': ['--without-fp']}])
+        self.add_config(arch='s390x',
+                        os_name='linux-gnu',
+                        glibcs=[{},
+                                {'arch': 's390', 'ccopts': '-m31'}])
+        # SH is missing __builtin_trap support, so work around this;
+        # see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70216>.
+        no_isolate = ('-fno-isolate-erroneous-paths-dereference'
+                      ' -fno-isolate-erroneous-paths-attribute')
+        self.add_config(arch='sh3',
+                        os_name='linux-gnu',
+                        glibcs=[{'ccopts': no_isolate}])
+        self.add_config(arch='sh3eb',
+                        os_name='linux-gnu',
+                        glibcs=[{'ccopts': no_isolate}])
+        self.add_config(arch='sh4',
+                        os_name='linux-gnu',
+                        glibcs=[{'ccopts': no_isolate}])
+        self.add_config(arch='sh4eb',
+                        os_name='linux-gnu',
+                        glibcs=[{'ccopts': no_isolate}])
+        self.add_config(arch='sh4',
+                        os_name='linux-gnu',
+                        variant='soft',
+                        gcc_cfg=['--without-fp'],
+                        glibcs=[{'variant': 'soft',
+                                 'cfg': ['--without-fp'],
+                                 'ccopts': no_isolate}])
+        self.add_config(arch='sh4eb',
+                        os_name='linux-gnu',
+                        variant='soft',
+                        gcc_cfg=['--without-fp'],
+                        glibcs=[{'variant': 'soft',
+                                 'cfg': ['--without-fp'],
+                                 'ccopts': no_isolate}])
+        self.add_config(arch='sparc64',
+                        os_name='linux-gnu',
+                        glibcs=[{},
+                                {'arch': 'sparcv9',
+                                 'ccopts': '-m32 -mlong-double-128'}])
+        self.add_config(arch='tilegx',
+                        os_name='linux-gnu',
+                        glibcs=[{},
+                                {'variant': '32', 'ccopts': '-m32'}])
+        self.add_config(arch='tilegxbe',
+                        os_name='linux-gnu',
+                        glibcs=[{},
+                                {'variant': '32', 'ccopts': '-m32'}])
+        self.add_config(arch='tilepro',
+                        os_name='linux-gnu')
+        self.add_config(arch='x86_64',
+                        os_name='linux-gnu',
+                        gcc_cfg=['--with-multilib-list=m64,m32,mx32'],
+                        glibcs=[{},
+                                {'variant': 'x32', 'ccopts': '-mx32'},
+                                {'arch': 'i686', 'ccopts': '-m32 -march=i686'}],
+                        extra_glibcs=[{'variant': 'disable-multi-arch',
+                                       'cfg': ['--disable-multi-arch']},
+                                      {'variant': 'disable-multi-arch',
+                                       'arch': 'i686',
+                                       'ccopts': '-m32 -march=i686',
+                                       'cfg': ['--disable-multi-arch']},
+                                      {'arch': 'i486',
+                                       'ccopts': '-m32 -march=i486'},
+                                      {'arch': 'i586',
+                                       'ccopts': '-m32 -march=i586'}])
+
+    def add_config(self, **args):
+        """Add an individual build configuration."""
+        cfg = Config(self, **args)
+        if cfg.name in self.configs:
+            print('error: duplicate config %s' % cfg.name)
+            exit(1)
+        self.configs[cfg.name] = cfg
+        for c in cfg.all_glibcs:
+            if c.name in self.glibc_configs:
+                print('error: duplicate glibc config %s' % c.name)
+                exit(1)
+            self.glibc_configs[c.name] = c
+
+    def component_srcdir(self, component):
+        """Return the source directory for a given component, e.g. gcc."""
+        return os.path.join(self.srcdir, component)
+
+    def component_builddir(self, action, config, component, subconfig=None):
+        """Return the directory to use for a build."""
+        if config is None:
+            # Host libraries.
+            assert subconfig is None
+            return os.path.join(self.builddir, action, component)
+        if subconfig is None:
+            return os.path.join(self.builddir, action, config, component)
+        else:
+            # glibc build as part of compiler build.
+            return os.path.join(self.builddir, action, config, component,
+                                subconfig)
+
+    def compiler_installdir(self, config):
+        """Return the directory in which to install a compiler."""
+        return os.path.join(self.installdir, 'compilers', config)
+
+    def compiler_bindir(self, config):
+        """Return the directory in which to find compiler binaries."""
+        return os.path.join(self.compiler_installdir(config), 'bin')
+
+    def compiler_sysroot(self, config):
+        """Return the sysroot directory for a compiler."""
+        return os.path.join(self.compiler_installdir(config), 'sysroot')
+
+    def glibc_installdir(self, config):
+        """Return the directory in which to install glibc."""
+        return os.path.join(self.installdir, 'glibcs', config)
+
+    def run_builds(self, action, configs):
+        """Run the requested builds."""
+        if action == 'checkout':
+            self.checkout(configs)
+            return
+        elif action == 'host-libraries':
+            if configs:
+                print('error: configurations specified for host-libraries')
+                exit(1)
+            self.build_host_libraries()
+        elif action == 'compilers':
+            self.build_compilers(configs)
+        else:
+            self.build_glibcs(configs)
+        self.write_files()
+        self.do_build()
+
+    @staticmethod
+    def remove_dirs(*args):
+        """Remove directories and their contents if they exist."""
+        for dir in args:
+            shutil.rmtree(dir, ignore_errors=True)
+
+    @staticmethod
+    def remove_recreate_dirs(*args):
+        """Remove directories if they exist, and create them as empty."""
+        Context.remove_dirs(*args)
+        for dir in args:
+            os.makedirs(dir, exist_ok=True)
+
+    def add_makefile_cmdlist(self, target, cmdlist, logsdir):
+        """Add makefile text for a list of commands."""
+        commands = cmdlist.makefile_commands(self.wrapper, logsdir)
+        self.makefile_pieces.append('all: %s\n.PHONY: %s\n%s:\n%s\n' %
+                                    (target, target, target, commands))
+
+    def write_files(self):
+        """Write out the Makefile and wrapper script."""
+        mftext = ''.join(self.makefile_pieces)
+        with open(self.makefile, 'w') as f:
+            f.write(mftext)
+        wrapper_text = (
+            '#!/bin/sh\n'
+            'prev_base=$1\n'
+            'this_base=$2\n'
+            'desc=$3\n'
+            'dir=$4\n'
+            'path=$5\n'
+            'shift 5\n'
+            'prev_status=$prev_base-status.txt\n'
+            'this_status=$this_base-status.txt\n'
+            'this_log=$this_base-log.txt\n'
+            'date > "$this_log"\n'
+            'echo >> "$this_log"\n'
+            'echo "Description: $desc" >> "$this_log"\n'
+            'echo "Command: $*" >> "$this_log"\n'
+            'echo "Directory: $dir" >> "$this_log"\n'
+            'echo "Path addition: $path" >> "$this_log"\n'
+            'echo >> "$this_log"\n'
+            'record_status ()\n'
+            '{\n'
+            '  echo >> "$this_log"\n'
+            '  echo "$1: $desc" > "$this_status"\n'
+            '  echo "$1: $desc" >> "$this_log"\n'
+            '  echo >> "$this_log"\n'
+            '  date >> "$this_log"\n'
+            '  echo "$1: $desc"\n'
+            '  exit 0\n'
+            '}\n'
+            'check_error ()\n'
+            '{\n'
+            '  if [ "$1" != "0" ]; then\n'
+            '    record_status FAIL\n'
+            '  fi\n'
+            '}\n'
+            'if [ "$prev_base" ] && ! grep -q "^PASS" "$prev_status"; then\n'
+            '    record_status UNRESOLVED\n'
+            'fi\n'
+            'if [ "$dir" ]; then\n'
+            '  cd "$dir"\n'
+            '  check_error "$?"\n'
+            'fi\n'
+            'if [ "$path" ]; then\n'
+            '  PATH=$path:$PATH\n'
+            'fi\n'
+            '"$@" < /dev/null >> "$this_log" 2>&1\n'
+            'check_error "$?"\n'
+            'record_status PASS\n')
+        with open(self.wrapper, 'w') as f:
+            f.write(wrapper_text)
+        os.chmod(self.wrapper,
+                 (stat.S_IRWXU|stat.S_IRGRP|stat.S_IXGRP|
+                  stat.S_IROTH|stat.S_IXOTH))
+        save_logs_text = (
+            '#!/bin/sh\n'
+            'if ! [ -f tests.sum ]; then\n'
+            '  echo "No test summary available."\n'
+            '  exit 0\n'
+            'fi\n'
+            'save_file ()\n'
+            '{\n'
+            '  echo "Contents of $1:"\n'
+            '  echo\n'
+            '  cat "$1"\n'
+            '  echo\n'
+            '  echo "End of contents of $1."\n'
+            '  echo\n'
+            '}\n'
+            'save_file tests.sum\n'
+            'non_pass_tests=$(grep -v "^PASS: " tests.sum | sed -e "s/^PASS: //")\n'
+            'for t in $non_pass_tests; do\n'
+            '  if [ -f "$t.out" ]; then\n'
+            '    save_file "$t.out"\n'
+            '  fi\n'
+            'done\n')
+        with open(self.save_logs, 'w') as f:
+            f.write(save_logs_text)
+        os.chmod(self.save_logs,
+                 (stat.S_IRWXU|stat.S_IRGRP|stat.S_IXGRP|
+                  stat.S_IROTH|stat.S_IXOTH))
+
+    def do_build(self):
+        """Do the actual build."""
+        cmd = ['make', '-j%d' % self.parallelism]
+        subprocess.run(cmd, cwd=self.builddir, check=True)
+
+    def build_host_libraries(self):
+        """Build the host libraries."""
+        installdir = self.host_libraries_installdir
+        builddir = os.path.join(self.builddir, 'host-libraries')
+        logsdir = os.path.join(self.logsdir, 'host-libraries')
+        self.remove_recreate_dirs(installdir, builddir, logsdir)
+        cmdlist = CommandList('host-libraries', self.keep)
+        self.build_host_library(cmdlist, 'gmp')
+        self.build_host_library(cmdlist, 'mpfr',
+                                ['--with-gmp=%s' % installdir])
+        self.build_host_library(cmdlist, 'mpc',
+                                ['--with-gmp=%s' % installdir,
+                                '--with-mpfr=%s' % installdir])
+        cmdlist.add_command('done', ['touch', os.path.join(installdir, 'ok')])
+        self.add_makefile_cmdlist('host-libraries', cmdlist, logsdir)
+
+    def build_host_library(self, cmdlist, lib, extra_opts=None):
+        """Build one host library."""
+        srcdir = self.component_srcdir(lib)
+        builddir = self.component_builddir('host-libraries', None, lib)
+        installdir = self.host_libraries_installdir
+        cmdlist.push_subdesc(lib)
+        cmdlist.create_use_dir(builddir)
+        cfg_cmd = [os.path.join(srcdir, 'configure'),
+                   '--prefix=%s' % installdir,
+                   '--disable-shared']
+        if extra_opts:
+            cfg_cmd.extend (extra_opts)
+        cmdlist.add_command('configure', cfg_cmd)
+        cmdlist.add_command('build', ['make'])
+        cmdlist.add_command('check', ['make', 'check'])
+        cmdlist.add_command('install', ['make', 'install'])
+        cmdlist.cleanup_dir()
+        cmdlist.pop_subdesc()
+
+    def build_compilers(self, configs):
+        """Build the compilers."""
+        if not configs:
+            self.remove_dirs(os.path.join(self.builddir, 'compilers'))
+            self.remove_dirs(os.path.join(self.installdir, 'compilers'))
+            self.remove_dirs(os.path.join(self.logsdir, 'compilers'))
+            configs = sorted(self.configs.keys())
+        for c in configs:
+            self.configs[c].build()
+
+    def build_glibcs(self, configs):
+        """Build the glibcs."""
+        if not configs:
+            self.remove_dirs(os.path.join(self.builddir, 'glibcs'))
+            self.remove_dirs(os.path.join(self.installdir, 'glibcs'))
+            self.remove_dirs(os.path.join(self.logsdir, 'glibcs'))
+            configs = sorted(self.glibc_configs.keys())
+        for c in configs:
+            self.glibc_configs[c].build()
+
+    def checkout(self, versions):
+        """Check out the desired component versions."""
+        default_versions = {'binutils': 'vcs-2.27',
+                            'gcc': 'vcs-6',
+                            'glibc': 'vcs-mainline',
+                            'gmp': '6.1.1',
+                            'linux': '4.8.6',
+                            'mpc': '1.0.3',
+                            'mpfr': '3.1.5'}
+        use_versions = {}
+        for v in versions:
+            found_v = False
+            for k in default_versions.keys():
+                kx = k + '-'
+                if v.startswith(kx):
+                    vx = v[len(kx):]
+                    if k in use_versions:
+                        print('error: multiple versions for %s' % k)
+                        exit(1)
+                    use_versions[k] = vx
+                    found_v = True
+                    break
+            if not found_v:
+                print('error: unknown component in %s' % v)
+                exit(1)
+        for k in default_versions.keys():
+            if k not in use_versions:
+                use_versions[k] = default_versions[k]
+        os.makedirs(self.srcdir, exist_ok=True)
+        for k in sorted(default_versions.keys()):
+            update = os.access(self.component_srcdir(k), os.F_OK)
+            v = use_versions[k]
+            if v.startswith('vcs-'):
+                self.checkout_vcs(k, v[4:], update)
+            else:
+                self.checkout_tar(k, v, update)
+
+    def checkout_vcs(self, component, version, update):
+        """Check out the given version of the given component from version
+        control."""
+        if component == 'binutils':
+            git_url = 'git://sourceware.org/git/binutils-gdb.git'
+            if version == 'mainline':
+                git_branch = 'master'
+            else:
+                trans = str.maketrans({'.': '_'})
+                git_branch = 'binutils-%s-branch' % version.translate(trans)
+            self.git_checkout(component, git_url, git_branch, update)
+        elif component == 'gcc':
+            if version == 'mainline':
+                branch = 'trunk'
+            else:
+                trans = str.maketrans({'.': '_'})
+                branch = 'branches/gcc-%s-branch' % version.translate(trans)
+            svn_url = 'svn://gcc.gnu.org/svn/gcc/%s' % branch
+            self.gcc_checkout(svn_url, update)
+        elif component == 'glibc':
+            git_url = 'git://sourceware.org/git/glibc.git'
+            if version == 'mainline':
+                git_branch = 'master'
+            else:
+                git_branch = 'release/%s/master' % version
+            self.git_checkout(component, git_url, git_branch, update)
+            self.fix_glibc_timestamps()
+        else:
+            print('error: component %s coming from VCS' % component)
+            exit(1)
+
+    def git_checkout(self, component, git_url, git_branch, update):
+        """Check out a component from git."""
+        if update:
+            subprocess.run(['git', 'remote', 'prune', 'origin'],
+                           cwd=self.component_srcdir(component), check=True)
+            subprocess.run(['git', 'pull', '-q'],
+                           cwd=self.component_srcdir(component), check=True)
+        else:
+            subprocess.run(['git', 'clone', '-q', '-b', git_branch, git_url,
+                            self.component_srcdir(component)], check=True)
+
+    def fix_glibc_timestamps(self):
+        """Fix timestamps in a glibc checkout."""
+        # Ensure that builds do not try to regenerate generated files
+        # in the source tree.
+        srcdir = self.component_srcdir('glibc')
+        for dirpath, dirnames, filenames in os.walk(srcdir):
+            for f in filenames:
+                if (f == 'configure' or
+                    f == 'preconfigure' or
+                    f.endswith('-kw.h')):
+                    to_touch = os.path.join(dirpath, f)
+                    subprocess.run(['touch', to_touch], check=True)
+
+    def gcc_checkout(self, svn_url, update):
+        """Check out GCC from SVN."""
+        if not update:
+            subprocess.run(['svn', 'co', '-q', svn_url,
+                            self.component_srcdir('gcc')], check=True)
+        subprocess.run(['contrib/gcc_update', '--silent'],
+                       cwd=self.component_srcdir('gcc'), check=True)
+
+    def checkout_tar(self, component, version, update):
+        """Check out the given version of the given component from a
+        tarball."""
+        if update:
+            return
+        url_map = {'binutils': 'https://ftp.gnu.org/gnu/binutils/binutils-%(version)s.tar.bz2',
+                   'gcc': 'https://ftp.gnu.org/gnu/gcc/gcc-%(version)s/gcc-%(version)s.tar.bz2',
+                   'gmp': 'https://ftp.gnu.org/gnu/gmp/gmp-%(version)s.tar.xz',
+                   'linux': 'https://www.kernel.org/pub/linux/kernel/v4.x/linux-%(version)s.tar.xz',
+                   'mpc': 'https://ftp.gnu.org/gnu/mpc/mpc-%(version)s.tar.gz',
+                   'mpfr': 'https://ftp.gnu.org/gnu/mpfr/mpfr-%(version)s.tar.xz'}
+        if component not in url_map:
+            print('error: component %s coming from tarball' % component)
+            exit(1)
+        url = url_map[component] % {'version': version}
+        filename = os.path.join(self.srcdir, url.split('/')[-1])
+        response = urllib.request.urlopen(url)
+        data = response.read()
+        with open(filename, 'wb') as f:
+            f.write(data)
+        subprocess.run(['tar', '-C', self.srcdir, '-x', '-f', filename],
+                       check=True)
+        os.rename(os.path.join(self.srcdir, '%s-%s' % (component, version)),
+                  self.component_srcdir(component))
+        os.remove(filename)
+
+
+class Config:
+
+    """A configuration for building a compiler and associated libraries."""
+
+    def __init__(self, ctx, arch, os_name, variant=None, gcc_cfg=None,
+                 first_gcc_cfg=None, glibcs=None, extra_glibcs=None):
+        """Initialize a Config object."""
+        self.ctx = ctx
+        self.arch = arch
+        self.os = os_name
+        self.variant = variant
+        if variant is None:
+            self.name = '%s-%s' % (arch, os_name)
+        else:
+            self.name = '%s-%s-%s' % (arch, os_name, variant)
+        self.triplet = '%s-glibc-%s' % (arch, os_name)
+        if gcc_cfg is None:
+            self.gcc_cfg = []
+        else:
+            self.gcc_cfg = gcc_cfg
+        if first_gcc_cfg is None:
+            self.first_gcc_cfg = []
+        else:
+            self.first_gcc_cfg = first_gcc_cfg
+        if glibcs is None:
+            glibcs = [{'variant': variant}]
+        if extra_glibcs is None:
+            extra_glibcs = []
+        glibcs = [Glibc(self, **g) for g in glibcs]
+        extra_glibcs = [Glibc(self, **g) for g in extra_glibcs]
+        self.all_glibcs = glibcs + extra_glibcs
+        self.compiler_glibcs = glibcs
+        self.installdir = ctx.compiler_installdir(self.name)
+        self.bindir = ctx.compiler_bindir(self.name)
+        self.sysroot = ctx.compiler_sysroot(self.name)
+        self.builddir = os.path.join(ctx.builddir, 'compilers', self.name)
+        self.logsdir = os.path.join(ctx.logsdir, 'compilers', self.name)
+
+    def component_builddir(self, component):
+        """Return the directory to use for a (non-glibc) build."""
+        return self.ctx.component_builddir('compilers', self.name, component)
+
+    def build(self):
+        """Generate commands to build this compiler."""
+        self.ctx.remove_recreate_dirs(self.installdir, self.builddir,
+                                      self.logsdir)
+        cmdlist = CommandList('compilers-%s' % self.name, self.ctx.keep)
+        cmdlist.add_command('check-host-libraries',
+                            ['test', '-f',
+                             os.path.join(self.ctx.host_libraries_installdir,
+                                          'ok')])
+        cmdlist.use_path(self.bindir)
+        self.build_cross_tool(cmdlist, 'binutils', 'binutils',
+                              ['--disable-gdb',
+                               '--disable-libdecnumber',
+                               '--disable-readline',
+                               '--disable-sim'])
+        if self.os.startswith('linux'):
+            self.install_linux_headers(cmdlist)
+        self.build_gcc(cmdlist, True)
+        for g in self.compiler_glibcs:
+            cmdlist.push_subdesc('glibc')
+            cmdlist.push_subdesc(g.name)
+            g.build_glibc(cmdlist, True)
+            cmdlist.pop_subdesc()
+            cmdlist.pop_subdesc()
+        self.build_gcc(cmdlist, False)
+        cmdlist.add_command('done', ['touch',
+                                     os.path.join(self.installdir, 'ok')])
+        self.ctx.add_makefile_cmdlist('compilers-%s' % self.name, cmdlist,
+                                      self.logsdir)
+
+    def build_cross_tool(self, cmdlist, tool_src, tool_build, extra_opts=None):
+        """Build one cross tool."""
+        srcdir = self.ctx.component_srcdir(tool_src)
+        builddir = self.component_builddir(tool_build)
+        cmdlist.push_subdesc(tool_build)
+        cmdlist.create_use_dir(builddir)
+        cfg_cmd = [os.path.join(srcdir, 'configure'),
+                   '--prefix=%s' % self.installdir,
+                   '--build=%s' % self.ctx.build_triplet,
+                   '--host=%s' % self.ctx.build_triplet,
+                   '--target=%s' % self.triplet,
+                   '--with-sysroot=%s' % self.sysroot]
+        if extra_opts:
+            cfg_cmd.extend(extra_opts)
+        cmdlist.add_command('configure', cfg_cmd)
+        cmdlist.add_command('build', ['make'])
+        cmdlist.add_command('install', ['make', 'install'])
+        cmdlist.cleanup_dir()
+        cmdlist.pop_subdesc()
+
+    def install_linux_headers(self, cmdlist):
+        """Install Linux kernel headers."""
+        arch_map = {'aarch64': 'arm64',
+                    'alpha': 'alpha',
+                    'arm': 'arm',
+                    'hppa': 'parisc',
+                    'i486': 'x86',
+                    'i586': 'x86',
+                    'i686': 'x86',
+                    'i786': 'x86',
+                    'ia64': 'ia64',
+                    'm68k': 'm68k',
+                    'microblaze': 'microblaze',
+                    'mips': 'mips',
+                    'nios2': 'nios2',
+                    'powerpc': 'powerpc',
+                    's390': 's390',
+                    'sh': 'sh',
+                    'sparc': 'sparc',
+                    'tile': 'tile',
+                    'x86_64': 'x86'}
+        linux_arch = None
+        for k in arch_map:
+            if self.arch.startswith(k):
+                linux_arch = arch_map[k]
+                break
+        assert linux_arch is not None
+        srcdir = self.ctx.component_srcdir('linux')
+        builddir = self.component_builddir('linux')
+        headers_dir = os.path.join(self.sysroot, 'usr')
+        cmdlist.push_subdesc('linux')
+        cmdlist.create_use_dir(builddir)
+        cmdlist.add_command('install-headers',
+                            ['make', '-C', srcdir, 'O=%s' % builddir,
+                             'ARCH=%s' % linux_arch,
+                             'INSTALL_HDR_PATH=%s' % headers_dir,
+                             'headers_install'])
+        cmdlist.cleanup_dir()
+        cmdlist.pop_subdesc()
+
+    def build_gcc(self, cmdlist, bootstrap):
+        """Build GCC."""
+        # libsanitizer commonly breaks because of glibc header
+        # changes, or on unusual targets.  libssp is of little
+        # relevance with glibc's own stack checking support.
+        cfg_opts = list(self.gcc_cfg)
+        cfg_opts += ['--disable-libsanitizer', '--disable-libssp']
+        if bootstrap:
+            tool_build = 'gcc-first'
+            # Building a static-only, C-only compiler that is
+            # sufficient to build glibc.  Various libraries and
+            # features that may require libc headers must be disabled.
+            # When configuring with a sysroot, --with-newlib is
+            # required to define inhibit_libc (to stop some parts of
+            # libgcc including libc headers); --without-headers is not
+            # sufficient.
+            cfg_opts += ['--enable-languages=c', '--disable-shared',
+                         '--disable-threads',
+                         '--disable-libatomic',
+                         '--disable-decimal-float',
+                         '--disable-libffi',
+                         '--disable-libgomp',
+                         '--disable-libitm',
+                         '--disable-libmpx',
+                         '--disable-libquadmath',
+                         '--without-headers', '--with-newlib',
+                         '--with-glibc-version=%s' % self.ctx.glibc_version
+                         ]
+            cfg_opts += self.first_gcc_cfg
+        else:
+            tool_build = 'gcc'
+            cfg_opts += ['--enable-languages=c,c++', '--enable-shared',
+                         '--enable-threads']
+        self.build_cross_tool(cmdlist, 'gcc', tool_build, cfg_opts)
+
+
+class Glibc:
+
+    """A configuration for building glibc."""
+
+    def __init__(self, compiler, arch=None, os_name=None, variant=None,
+                 cfg=None, ccopts=None):
+        """Initialize a Glibc object."""
+        self.ctx = compiler.ctx
+        self.compiler = compiler
+        if arch is None:
+            self.arch = compiler.arch
+        else:
+            self.arch = arch
+        if os_name is None:
+            self.os = compiler.os
+        else:
+            self.os = os_name
+        self.variant = variant
+        if variant is None:
+            self.name = '%s-%s' % (self.arch, self.os)
+        else:
+            self.name = '%s-%s-%s' % (self.arch, self.os, variant)
+        self.triplet = '%s-glibc-%s' % (self.arch, self.os)
+        if cfg is None:
+            self.cfg = []
+        else:
+            self.cfg = cfg
+        self.ccopts = ccopts
+
+    def tool_name(self, tool):
+        """Return the name of a cross-compilation tool."""
+        ctool = '%s-%s' % (self.compiler.triplet, tool)
+        if self.ccopts and (tool == 'gcc' or tool == 'g++'):
+            ctool = '%s %s' % (ctool, self.ccopts)
+        return ctool
+
+    def build(self):
+        """Generate commands to build this glibc."""
+        builddir = self.ctx.component_builddir('glibcs', self.name, 'glibc')
+        installdir = self.ctx.glibc_installdir(self.name)
+        logsdir = os.path.join(self.ctx.logsdir, 'glibcs', self.name)
+        self.ctx.remove_recreate_dirs(installdir, builddir, logsdir)
+        cmdlist = CommandList('glibcs-%s' % self.name, self.ctx.keep)
+        cmdlist.add_command('check-compilers',
+                            ['test', '-f',
+                             os.path.join(self.compiler.installdir, 'ok')])
+        cmdlist.use_path(self.compiler.bindir)
+        self.build_glibc(cmdlist, False)
+        self.ctx.add_makefile_cmdlist('glibcs-%s' % self.name, cmdlist,
+                                      logsdir)
+
+    def build_glibc(self, cmdlist, for_compiler):
+        """Generate commands to build this glibc, either as part of a compiler
+        build or with the bootstrapped compiler (and in the latter case, run
+        tests as well)."""
+        srcdir = self.ctx.component_srcdir('glibc')
+        if for_compiler:
+            builddir = self.ctx.component_builddir('compilers',
+                                                   self.compiler.name, 'glibc',
+                                                   self.name)
+            installdir = self.compiler.sysroot
+            srcdir_copy = self.ctx.component_builddir('compilers',
+                                                      self.compiler.name,
+                                                      'glibc-src',
+                                                      self.name)
+        else:
+            builddir = self.ctx.component_builddir('glibcs', self.name,
+                                                   'glibc')
+            installdir = self.ctx.glibc_installdir(self.name)
+            srcdir_copy = self.ctx.component_builddir('glibcs', self.name,
+                                                      'glibc-src')
+        cmdlist.create_use_dir(builddir)
+        # glibc builds write into the source directory, and even if
+        # not intentionally there is a risk of bugs that involve
+        # writing into the working directory.  To avoid possible
+        # concurrency issues, copy the source directory.
+        cmdlist.create_copy_dir(srcdir, srcdir_copy)
+        cfg_cmd = [os.path.join(srcdir_copy, 'configure'),
+                   '--prefix=/usr',
+                   '--enable-add-ons',
+                   '--build=%s' % self.ctx.build_triplet,
+                   '--host=%s' % self.triplet,
+                   'CC=%s' % self.tool_name('gcc'),
+                   'CXX=%s' % self.tool_name('g++'),
+                   'AR=%s' % self.tool_name('ar'),
+                   'AS=%s' % self.tool_name('as'),
+                   'LD=%s' % self.tool_name('ld'),
+                   'NM=%s' % self.tool_name('nm'),
+                   'OBJCOPY=%s' % self.tool_name('objcopy'),
+                   'OBJDUMP=%s' % self.tool_name('objdump'),
+                   'RANLIB=%s' % self.tool_name('ranlib'),
+                   'READELF=%s' % self.tool_name('readelf'),
+                   'STRIP=%s' % self.tool_name('strip')]
+        cfg_cmd += self.cfg
+        cmdlist.add_command('configure', cfg_cmd)
+        cmdlist.add_command('build', ['make'])
+        cmdlist.add_command('install', ['make', 'install',
+                                        'install_root=%s' % installdir])
+        # GCC uses paths such as lib/../lib64, so make sure lib
+        # directories always exist.
+        cmdlist.add_command('mkdir-lib', ['mkdir', '-p',
+                                          os.path.join(installdir, 'lib'),
+                                          os.path.join(installdir,
+                                                       'usr', 'lib')])
+        if not for_compiler:
+            cmdlist.add_command('check', ['make', 'check'])
+            cmdlist.add_command('save-logs', [self.ctx.save_logs],
+                                always_run=True)
+        cmdlist.cleanup_dir('cleanup-src', srcdir_copy)
+        cmdlist.cleanup_dir()
+
+
+class Command:
+
+    """A command run in the build process."""
+
+    def __init__(self, desc, num, dir, path, command, always_run=False):
+        """Initialize a Command object."""
+        self.dir = dir
+        self.path = path
+        self.desc = desc
+        trans = str.maketrans({' ': '-'})
+        self.logbase = '%03d-%s' % (num, desc.translate(trans))
+        self.command = command
+        self.always_run = always_run
+
+    @staticmethod
+    def shell_make_quote_string(s):
+        """Given a string not containing a newline, quote it for use by the
+        shell and make."""
+        assert '\n' not in s
+        if re.fullmatch('[]+,./0-9@A-Z_a-z-]+', s):
+            return s
+        strans = str.maketrans({"'": "'\\''"})
+        s = "'%s'" % s.translate(strans)
+        mtrans = str.maketrans({'$': '$$'})
+        return s.translate(mtrans)
+
+    @staticmethod
+    def shell_make_quote_list(l, translate_make):
+        """Given a list of strings not containing newlines, quote them for use
+        by the shell and make, returning a single string.  If translate_make
+        is true and the first string is 'make', change it to $(MAKE)."""
+        l = [Command.shell_make_quote_string(s) for s in l]
+        if translate_make and l[0] == 'make':
+            l[0] = '$(MAKE)'
+        return ' '.join(l)
+
+    def shell_make_quote(self):
+        """Return this command quoted for the shell and make."""
+        return self.shell_make_quote_list(self.command, True)
+
+
+class CommandList:
+
+    """A list of commands run in the build process."""
+
+    def __init__(self, desc, keep):
+        """Initialize a CommandList object."""
+        self.cmdlist = []
+        self.dir = None
+        self.path = None
+        self.desc = [desc]
+        self.keep = keep
+
+    def desc_txt(self, desc):
+        """Return the description to use for a command."""
+        return '%s %s' % (' '.join(self.desc), desc)
+
+    def use_dir(self, dir):
+        """Set the default directory for subsequent commands."""
+        self.dir = dir
+
+    def use_path(self, path):
+        """Set a directory to be prepended to the PATH for subsequent
+        commands."""
+        self.path = path
+
+    def push_subdesc(self, subdesc):
+        """Set the default subdescription for subsequent commands (e.g., the
+        name of a component being built, within the series of commands
+        building it)."""
+        self.desc.append(subdesc)
+
+    def pop_subdesc(self):
+        """Pop a subdescription from the list of descriptions."""
+        self.desc.pop()
+
+    def create_use_dir(self, dir):
+        """Remove and recreate a directory and use it for subsequent
+        commands."""
+        self.add_command_dir('rm', None, ['rm', '-rf', dir])
+        self.add_command_dir('mkdir', None, ['mkdir', '-p', dir])
+        self.use_dir(dir)
+
+    def create_copy_dir(self, src, dest):
+        """Remove a directory and recreate it as a copy from the given
+        source."""
+        self.add_command_dir('copy-rm', None, ['rm', '-rf', dest])
+        parent = os.path.dirname(dest)
+        self.add_command_dir('copy-mkdir', None, ['mkdir', '-p', parent])
+        self.add_command_dir('copy', None, ['cp', '-a', src, dest])
+
+    def add_command_dir(self, desc, dir, command, always_run=False):
+        """Add a command to run in a given directory."""
+        cmd = Command(self.desc_txt(desc), len(self.cmdlist), dir, self.path,
+                      command, always_run)
+        self.cmdlist.append(cmd)
+
+    def add_command(self, desc, command, always_run=False):
+        """Add a command to run in the default directory."""
+        cmd = Command(self.desc_txt(desc), len(self.cmdlist), self.dir,
+                      self.path, command, always_run)
+        self.cmdlist.append(cmd)
+
+    def cleanup_dir(self, desc='cleanup', dir=None):
+        """Clean up a build directory.  If no directory is specified, the
+        default directory is cleaned up and ceases to be the default
+        directory."""
+        if dir is None:
+            dir = self.dir
+            self.use_dir(None)
+        if self.keep != 'all':
+            self.add_command_dir(desc, None, ['rm', '-rf', dir],
+                                 always_run=(self.keep == 'none'))
+
+    def makefile_commands(self, wrapper, logsdir):
+        """Return the sequence of commands in the form of text for a Makefile.
+        The given wrapper script takes arguments: base of logs for
+        previous command, or empty; base of logs for this command;
+        description; directory; PATH addition; the command itself."""
+        # prev_base is the base of the name for logs of the previous
+        # command that is not always-run (that is, a build command,
+        # whose failure should stop subsequent build commands from
+        # being run, as opposed to a cleanup command, which is run
+        # even if previous commands failed).
+        prev_base = ''
+        cmds = []
+        for c in self.cmdlist:
+            ctxt = c.shell_make_quote()
+            if prev_base and not c.always_run:
+                prev_log = os.path.join(logsdir, prev_base)
+            else:
+                prev_log = ''
+            this_log = os.path.join(logsdir, c.logbase)
+            if not c.always_run:
+                prev_base = c.logbase
+            if c.dir is None:
+                dir = ''
+            else:
+                dir = c.dir
+            if c.path is None:
+                path = ''
+            else:
+                path = c.path
+            prelims = [wrapper, prev_log, this_log, c.desc, dir, path]
+            prelim_txt = Command.shell_make_quote_list(prelims, False)
+            cmds.append('\t@%s %s' % (prelim_txt, ctxt))
+        return '\n'.join(cmds)
+
+
+def get_parser():
+    """Return an argument parser for this module."""
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('-j', dest='parallelism',
+                        help='Run this number of jobs in parallel',
+                        type=int, default=os.cpu_count())
+    parser.add_argument('--keep', dest='keep',
+                        help='Whether to keep all build directories, '
+                        'none or only those from failed builds',
+                        default='none', choices=('none', 'all', 'failed'))
+    parser.add_argument('topdir',
+                        help='Toplevel working directory')
+    parser.add_argument('action',
+                        help='What to do',
+                        choices=('checkout', 'host-libraries', 'compilers',
+                                 'glibcs'))
+    parser.add_argument('configs',
+                        help='Versions to check out or configurations to build',
+                        nargs='*')
+    return parser
+
+
+def main(argv):
+    """The main entry point."""
+    parser = get_parser()
+    opts = parser.parse_args(argv)
+    topdir = os.path.abspath(opts.topdir)
+    ctx = Context(topdir, opts.parallelism, opts.keep, opts.action)
+    ctx.run_builds(opts.action, opts.configs)
+
+
+if __name__ == '__main__':
+    main(sys.argv[1:])