diff --git a/SConstruct b/SConstruct
index 679315e165..fe7b3abf73 100755
--- a/SConstruct
+++ b/SConstruct
@@ -641,23 +641,6 @@ sticky_vars.Add(BoolVariable('USE_EFENCE',
     'Link with Electric Fence malloc debugger', False))
 
 
-########################################################################
-#
-# Find and process all the SConscript files in ext. These are shared by
-# all variants in a build root.
-#
-########################################################################
-
-ext_dir = Dir('#ext').abspath
-ext_build_dirs = []
-for root, dirs, files in os.walk(ext_dir):
-    if 'SConscript' in files:
-        build_dir = os.path.relpath(root, ext_dir)
-        ext_build_dirs.append(build_dir)
-        main.SConscript(os.path.join(root, 'SConscript'),
-                        variant_dir=os.path.join(build_root, build_dir))
-
-
 ########################################################################
 #
 # Define build environments for required variants.
@@ -686,9 +669,6 @@ for variant_path in variant_paths:
         sticky_vars.files.append(current_vars_file)
         if not GetOption('silent'):
             print("Using saved variables file %s" % current_vars_file)
-    elif variant_dir in ext_build_dirs:
-        # Things in ext are built without a variant directory.
-        continue
     else:
         # Variant specific variables file doesn't exist.
 
@@ -741,6 +721,15 @@ Build variables for {dir}:
 
     exports=['env', 'gem5py_env']
 
+    ext_dir = Dir('#ext').abspath
+    variant_ext = os.path.join(variant_path, 'ext')
+    for root, dirs, files in os.walk(ext_dir):
+        if 'SConscript' in files:
+            build_dir = os.path.relpath(root, ext_dir)
+            SConscript(os.path.join(root, 'SConscript'),
+                       variant_dir=os.path.join(variant_ext, build_dir),
+                       exports=exports)
+
     # The src/SConscript file sets up the build rules in 'env' according
     # to the configured variables.  It returns a list of environments,
     # one for each variant build (debug, opt, etc.)
diff --git a/ext/drampower/SConscript b/ext/drampower/SConscript
index 0518197bc8..870d0504c7 100644
--- a/ext/drampower/SConscript
+++ b/ext/drampower/SConscript
@@ -39,9 +39,9 @@
 
 import os
 
-Import('main')
+Import('env')
 
-main.Prepend(CPPPATH=Dir('./src'))
+env.Prepend(CPPPATH=Dir('./src'))
 
 # Add the appropriate files for the library
 drampower_files = []
@@ -63,7 +63,7 @@ DRAMPowerFile('CAHelpers.cc')
 DRAMPowerFile('CmdHandlers.cc')
 DRAMPowerFile('MemBankWiseParams.cc')
 
-main.Library('drampower', [main.SharedObject(f) for f in drampower_files])
+env.Library('drampower', [env.SharedObject(f) for f in drampower_files])
 
-main.Append(LIBS=['drampower'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Append(LIBS=['drampower'])
+env.Prepend(LIBPATH=[Dir('.')])
diff --git a/ext/dramsim2/SConscript b/ext/dramsim2/SConscript
index b4355fa693..95b999dc4c 100644
--- a/ext/dramsim2/SConscript
+++ b/ext/dramsim2/SConscript
@@ -38,16 +38,16 @@
 
 import os
 
-Import('main')
+Import('env')
 
 # See if we got a cloned DRAMSim2 repo as a subdirectory and set the
 # HAVE_DRAMSIM flag accordingly
 if not os.path.exists(Dir('.').srcnode().abspath + '/DRAMSim2'):
-    main['HAVE_DRAMSIM'] = False
+    env['HAVE_DRAMSIM'] = False
     Return()
 
 # We have got the folder, so add the library and build the wrappers
-main['HAVE_DRAMSIM'] = True
+env['HAVE_DRAMSIM'] = True
 
 # Add the appropriate files. We leave out the trace driven simulator
 dram_files = []
@@ -59,7 +59,7 @@ DRAMFile('AddressMapping.cpp')
 DRAMFile('Bank.cpp')
 DRAMFile('BankState.cpp')
 DRAMFile('BusPacket.cpp')
-DRAMFile('ClockDomain.cpp')
+DRAMFile('ClockDoenv.cpp')
 DRAMFile('CommandQueue.cpp')
 DRAMFile('IniReader.cpp')
 DRAMFile('MemoryController.cpp')
@@ -71,11 +71,11 @@ DRAMFile('Transaction.cpp')
 
 # DRAMSim2 violates some of the warning flags used by gem5, so
 # we explicitly disable them here
-dramenv = main.Clone()
+dramenv = env.Clone()
 dramenv.Append(CCFLAGS=['-Wno-unused-value', '-Wno-error=nonnull-compare'])
 
 # If we are using clang, there are more flags to disable
-if main['CLANG']:
+if env['CLANG']:
     dramenv.Append(CCFLAGS=['-Wno-unused-private-field',
                             '-Wno-tautological-undefined-compare'])
 
@@ -85,6 +85,6 @@ dramenv.Append(CCFLAGS=['-DNO_STORAGE'])
 
 dramenv.Library('dramsim2', [dramenv.SharedObject(f) for f in dram_files])
 
-main.Prepend(CPPPATH=Dir('.'))
-main.Append(LIBS=['dramsim2'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Prepend(CPPPATH=Dir('.'))
+env.Append(LIBS=['dramsim2'])
+env.Prepend(LIBPATH=[Dir('.')])
diff --git a/ext/dramsim3/SConscript b/ext/dramsim3/SConscript
index 9e5a3a1a2c..b7178161f7 100644
--- a/ext/dramsim3/SConscript
+++ b/ext/dramsim3/SConscript
@@ -38,32 +38,32 @@
 
 import os
 
-Import('main')
+Import('env')
 
 thermal = False
 
 # See if we got a cloned DRAMSim3 repo as a subdirectory and set the
 # HAVE_DRAMSIM flag accordingly
 if not os.path.exists(Dir('.').srcnode().abspath + '/DRAMsim3'):
-    main['HAVE_DRAMSIM3'] = False
+    env['HAVE_DRAMSIM3'] = False
     Return()
 
 # We have got the folder, so add the library and build the wrappers
-main['HAVE_DRAMSIM3'] = True
+env['HAVE_DRAMSIM3'] = True
 
 
 dramsim_path = os.path.join(Dir('#').abspath, 'ext/dramsim3/DRAMsim3/')
 
 if thermal:
     superlu_path = os.path.join(dramsim_path, 'ext/SuperLU_MT_3.1/lib')
-    main.Prepend(CPPPATH=Dir('.'))
-    main.Append(LIBS=['dramsim3', 'superlu_mt_OPENMP', 'm', 'f77blas',
+    env.Prepend(CPPPATH=Dir('.'))
+    env.Append(LIBS=['dramsim3', 'superlu_mt_OPENMP', 'm', 'f77blas',
                       'atlas', 'gomp'],
                 LIBPATH=[dramsim_path, superlu_path])
 else:
-    main.Prepend(CPPPATH=Dir('.'))
+    env.Prepend(CPPPATH=Dir('.'))
     # a littel hacky but can get a shared library working
-    main.Append(LIBS=['dramsim3', 'gomp'],
+    env.Append(LIBS=['dramsim3', 'gomp'],
                 LIBPATH=[dramsim_path],  # compile-time lookup
                 RPATH=[dramsim_path],  # runtime lookup
                 CPPPATH=[dramsim_path+'/src/'])
diff --git a/ext/fputils/SConscript b/ext/fputils/SConscript
index 6d3f1ff8d7..6a8e44f4af 100644
--- a/ext/fputils/SConscript
+++ b/ext/fputils/SConscript
@@ -28,11 +28,11 @@
 #
 # Authors: Andreas Sandberg
 
-Import('main')
+Import('env')
 
-main.Prepend(CPPPATH=Dir('./include'))
+env.Prepend(CPPPATH=Dir('./include'))
 
-fpenv = main.Clone()
+fpenv = env.Clone()
 
 # By default gcc uses c89 and clang uses c99. For fputils to compile
 # we need to use c99.
@@ -44,6 +44,6 @@ fpenv.Library('fputils', [
         fpenv.SharedObject('fp80.c'),
     ])
 
-main.Append(LIBS=['fputils'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Append(LIBS=['fputils'])
+env.Prepend(LIBPATH=[Dir('.')])
 
diff --git a/ext/googletest/SConscript b/ext/googletest/SConscript
index 5a4b691f0c..21830f0308 100644
--- a/ext/googletest/SConscript
+++ b/ext/googletest/SConscript
@@ -26,7 +26,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-Import('main')
+Import('env')
 
 # The root of the build directory.
 build = Dir('.')
@@ -40,18 +40,18 @@ gmock_include = gmock_base.Dir('include')
 gtest_src = Dir('googletest/src')
 gmock_src = Dir('googlemock/src')
 
-main.Append(CPPPATH=[gtest_include, gmock_include])
-main.Append(LIBPATH=[build])
+env.Append(CPPPATH=[gtest_include, gmock_include])
+env.Append(LIBPATH=[build])
 
-env = main.Clone(CCFLAGS=['-g', '-pthread', '-Wno-undef', '-isystem',
+genv = env.Clone(CCFLAGS=['-g', '-pthread', '-Wno-undef', '-isystem',
                           str(gtest_include), '-isystem', str(gmock_include)])
-env.Append(CPPPATH=[gtest_base, gmock_base])
+genv.Append(CPPPATH=[gtest_base, gmock_base])
 
-gtest_all = env.Object(gtest_src.File('gtest-all.cc'))
-gmock_all = env.Object(gmock_src.File('gmock-all.cc'))
-gtest_main = env.StaticLibrary(target='libgtest', source=[
+gtest_all = genv.Object(gtest_src.File('gtest-all.cc'))
+gmock_all = genv.Object(gmock_src.File('gmock-all.cc'))
+gtest_main = genv.StaticLibrary(target='libgtest', source=[
         gtest_all, gmock_all, gtest_src.File('gtest_main.cc')])
 
-main['GTEST_LIBS'] = ['libgtest', 'pthread']
-main['GTEST_CPPFLAGS'] = [
+env['GTEST_LIBS'] = ['libgtest', 'pthread']
+env['GTEST_CPPFLAGS'] = [
     '-pthread', '-DUSE_GMOCK', '-Wno-undef', '-isystem', gtest_include.abspath]
diff --git a/ext/iostream3/SConscript b/ext/iostream3/SConscript
index f8b5461a25..df0b2132f2 100644
--- a/ext/iostream3/SConscript
+++ b/ext/iostream3/SConscript
@@ -37,10 +37,10 @@
 #
 # Authors: Andreas Hansson
 
-Import('main')
+Import('env')
 
-main.Library('iostream3', [main.SharedObject('zfstream.cc')])
+env.Library('iostream3', [env.SharedObject('zfstream.cc')])
 
-main.Prepend(CPPPATH=Dir('.'))
-main.Append(LIBS=['iostream3'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Prepend(CPPPATH=Dir('.'))
+env.Append(LIBS=['iostream3'])
+env.Prepend(LIBPATH=[Dir('.')])
diff --git a/ext/libelf/SConscript b/ext/libelf/SConscript
index ccc1f64466..535e216ddf 100644
--- a/ext/libelf/SConscript
+++ b/ext/libelf/SConscript
@@ -30,7 +30,7 @@
 
 import os, subprocess
 
-Import('main')
+Import('env')
 
 elf_files = []
 def ElfFile(filename):
@@ -97,7 +97,7 @@ ElfFile('libelf_convert.c')
 ElfFile('libelf_fsize.c')
 ElfFile('libelf_msize.c')
 
-m4env = main.Clone()
+m4env = env.Clone()
 if m4env['GCC']:
     m4env.Append(CCFLAGS=['-Wno-pointer-sign',
                           '-Wno-unused-but-set-variable',
@@ -146,6 +146,6 @@ m4env.Library('elf', [m4env.SharedObject(f) for f in elf_files])
 m4env.Command(File('native-elf-format.h'), File('native-elf-format'),
               '${SOURCE} > ${TARGET}')
 
-main.Prepend(CPPPATH=Dir('.'))
-main.Append(LIBS=[File('libelf.a')])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Prepend(CPPPATH=Dir('.'))
+env.Append(LIBS=[File('libelf.a')])
+env.Prepend(LIBPATH=[Dir('.')])
diff --git a/ext/libfdt/SConscript b/ext/libfdt/SConscript
index fb4411535b..64573b78c8 100644
--- a/ext/libfdt/SConscript
+++ b/ext/libfdt/SConscript
@@ -28,7 +28,7 @@
 #
 # Authors: Anthony Gutierrez
 
-Import('main')
+Import('env')
 
 fdt_files = []
 
@@ -43,7 +43,7 @@ FdtFile('fdt_wip.c')
 FdtFile('fdt_empty_tree.c')
 FdtFile('fdt_strerror.c')
 
-main.Library('fdt', [main.SharedObject(f) for f in fdt_files])
-main.Prepend(CPPPATH=Dir('.'))
-main.Append(LIBS=['fdt'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Library('fdt', [env.SharedObject(f) for f in fdt_files])
+env.Prepend(CPPPATH=Dir('.'))
+env.Append(LIBS=['fdt'])
+env.Prepend(LIBPATH=[Dir('.')])
diff --git a/ext/nomali/SConscript b/ext/nomali/SConscript
index 2810f6d51e..b156ab0b3e 100644
--- a/ext/nomali/SConscript
+++ b/ext/nomali/SConscript
@@ -37,11 +37,11 @@
 #
 # Authors: Andreas Sandberg
 
-Import('main')
+Import('env')
 
-main.Prepend(CPPPATH=Dir('./include'))
+env.Prepend(CPPPATH=Dir('./include'))
 
-nomali = main.Clone()
+nomali = env.Clone()
 nomali.Append(CCFLAGS=['-Wno-ignored-qualifiers'])
 
 nomali_sources = [
@@ -60,6 +60,6 @@ nomali_sources = [
 
 nomali.Library('nomali', [  nomali.SharedObject(f) for f in nomali_sources ])
 
-main.Append(LIBS=['nomali'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Append(LIBS=['nomali'])
+env.Prepend(LIBPATH=[Dir('.')])
 
diff --git a/ext/softfloat/SConscript b/ext/softfloat/SConscript
index f08a0225cd..bfa2b285b1 100644
--- a/ext/softfloat/SConscript
+++ b/ext/softfloat/SConscript
@@ -31,19 +31,19 @@
 
 import os
 
-Import('main')
+Import('env')
 
-env = main.Clone()
-if env['GCC']:
-    env.Append(CCFLAGS=['-Wno-unused-variable',
-                        '-Wno-unused-label',
-                        '-Wno-implicit-fallthrough',
-                        '-g'])
+sf_env = env.Clone()
+if sf_env['GCC']:
+    sf_env.Append(CCFLAGS=['-Wno-unused-variable',
+                           '-Wno-unused-label',
+                           '-Wno-implicit-fallthrough',
+                           '-g'])
 
-elif env['CLANG']:
-    env.Append(CCFLAGS=['-Wno-unused-variable',
-                        '-Wno-unused-label',
-                        '-g'])
+elif sf_env['CLANG']:
+    sf_env.Append(CCFLAGS=['-Wno-unused-variable',
+                           '-Wno-unused-label',
+                           '-g'])
 
 # Add the appropriate files for the library
 softfloat_files = []
@@ -271,8 +271,8 @@ SoftfloatFile('ui64_to_f16.c')
 SoftfloatFile('ui64_to_f32.c')
 SoftfloatFile('ui64_to_f64.c')
 
-env.Library('softfloat', [env.SharedObject(f) for f in softfloat_files])
+sf_env.Library('softfloat', [sf_env.SharedObject(f) for f in softfloat_files])
 
-main.Prepend(CPPPATH=Dir('./'))
-main.Append(LIBS=['softfloat'])
-main.Prepend(LIBPATH=[Dir('.')])
+env.Prepend(CPPPATH=Dir('./'))
+env.Append(LIBS=['softfloat'])
+env.Prepend(LIBPATH=[Dir('.')])
diff --git a/ext/systemc/SConscript b/ext/systemc/SConscript
index d0cb6f83fc..89ef9202bd 100644
--- a/ext/systemc/SConscript
+++ b/ext/systemc/SConscript
@@ -26,8 +26,8 @@
 import os
 from m5.util.terminal import get_termcap
 
-Import('main')
-systemc = main.Clone()
+Import('env')
+systemc = env.Clone()
 
 build_root = Dir('.').abspath
 src_root = Dir('.').srcdir.abspath