diff --git a/libcxx/test/CMakeLists.txt b/libcxx/test/CMakeLists.txt
--- a/libcxx/test/CMakeLists.txt
+++ b/libcxx/test/CMakeLists.txt
@@ -82,7 +82,7 @@
 
 set(LIBCXX_TARGET_INFO "libcxx.test.target_info.LocalTI" CACHE STRING
     "TargetInfo to use when setting up test environment.")
-set(LIBCXX_EXECUTOR "${Python3_EXECUTABLE} ${CMAKE_CURRENT_LIST_DIR}/../utils/run.py" CACHE STRING
+set(LIBCXX_EXECUTOR "${Python3_EXECUTABLE} '${CMAKE_CURRENT_LIST_DIR}/../utils/run.py'" CACHE STRING
     "Executor to use when running tests.")
 
 set(AUTO_GEN_COMMENT "## Autogenerated by libcxx configuration.\n# Do not edit!")
diff --git a/libcxx/test/libcxx/double_include.sh.cpp b/libcxx/test/libcxx/double_include.sh.cpp
--- a/libcxx/test/libcxx/double_include.sh.cpp
+++ b/libcxx/test/libcxx/double_include.sh.cpp
@@ -9,9 +9,9 @@
 
 // Test that we can include each header in two TU's and link them together.
 
-// RUN: %{cxx} -c %s -o %t.first.o %{flags} %{compile_flags}
-// RUN: %{cxx} -c %s -o %t.second.o -DWITH_MAIN %{flags} %{compile_flags}
-// RUN: %{cxx} -o %t.exe %t.first.o %t.second.o %{flags} %{link_flags}
+// RUN: %{cxx} -c "%s" -o "%t.first.o" %{flags} %{compile_flags}
+// RUN: %{cxx} -c "%s" -o "%t.second.o" -DWITH_MAIN %{flags} %{compile_flags}
+// RUN: %{cxx} -o "%t.exe" "%t.first.o" "%t.second.o" %{flags} %{link_flags}
 // RUN: %{run}
 
 // GCC 5 pretends it supports C++17 features, but some features like static_assert
diff --git a/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp b/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
--- a/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
+++ b/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
@@ -11,9 +11,9 @@
 // UNSUPPORTED: libcpp-has-no-localization
 // UNSUPPORTED: c++03
 
-// RUN: %{cxx} %{flags} %s -o %t.exe %{compile_flags} -g %{link_flags}
+// RUN: %{cxx} %{flags} "%s" -o "%t.exe" %{compile_flags} -g %{link_flags}
 // Ensure locale-independence for unicode tests.
-// RUN: %{gdb} -nx -batch -iex "set autoload off" -ex "source %S/../../../utils/gdb/libcxx/printers.py" -ex "python register_libcxx_printer_loader()" -ex "source %S/gdb_pretty_printer_test.py" %t.exe
+// RUN: %{gdb} -nx -batch -iex "set autoload off" -ex "source %S/../../../utils/gdb/libcxx/printers.py" -ex "python register_libcxx_printer_loader()" -ex "source %S/gdb_pretty_printer_test.py" "%t.exe"
 
 #include <bitset>
 #include <deque>
diff --git a/libcxx/test/libcxx/include_as_c.sh.cpp b/libcxx/test/libcxx/include_as_c.sh.cpp
--- a/libcxx/test/libcxx/include_as_c.sh.cpp
+++ b/libcxx/test/libcxx/include_as_c.sh.cpp
@@ -19,7 +19,7 @@
 // NOTE: It's not common or recommended to have libc++ in the header search
 // path when compiling C files, but it does happen often enough.
 
-// RUN: %{cxx} -c -xc %s -fsyntax-only %{flags} %{compile_flags} -std=c99
+// RUN: %{cxx} -c -xc "%s" -fsyntax-only %{flags} %{compile_flags} -std=c99
 
 #include <__config>
 
diff --git a/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp b/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp
--- a/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp
+++ b/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03
-// ADDITIONAL_COMPILE_FLAGS: -I %S/../../../../../../src/filesystem
+// ADDITIONAL_COMPILE_FLAGS: -I "%S/../../../../../../src/filesystem"
 
 // <filesystem>
 
diff --git a/libcxx/test/libcxx/input.output/filesystems/convert_file_time.pass.cpp b/libcxx/test/libcxx/input.output/filesystems/convert_file_time.pass.cpp
--- a/libcxx/test/libcxx/input.output/filesystems/convert_file_time.pass.cpp
+++ b/libcxx/test/libcxx/input.output/filesystems/convert_file_time.pass.cpp
@@ -13,7 +13,7 @@
 
 // typedef TrivialClock file_time_type;
 
-// ADDITIONAL_COMPILE_FLAGS: -I %S/../../../../src/filesystem
+// ADDITIONAL_COMPILE_FLAGS: -I "%S/../../../../src/filesystem"
 
 #include <filesystem>
 #include <chrono>
diff --git a/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.merged.sh.cpp b/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.merged.sh.cpp
--- a/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.merged.sh.cpp
+++ b/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.merged.sh.cpp
@@ -8,11 +8,11 @@
 
 // UNSUPPORTED: no-rtti
 
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu1.o -DTU1 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu2.o -DTU2 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.main.o -DMAIN -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
-// RUN: %{cxx} %t.tu1.o %t.tu2.o %t.main.o %{flags} %{link_flags} -o %t.exe
-// RUN: %{exec} %t.exe
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} -c -o "%t.tu1.o" -DTU1 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} -c -o "%t.tu2.o" -DTU2 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} -c -o "%t.main.o" -DMAIN -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=1
+// RUN: %{cxx} "%t.tu1.o" "%t.tu2.o" "%t.main.o" %{flags} %{link_flags} -o "%t.exe"
+// RUN: %{exec} "%t.exe"
 
 #include <cassert>
 #include <typeindex>
diff --git a/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.unmerged.sh.cpp b/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.unmerged.sh.cpp
--- a/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.unmerged.sh.cpp
+++ b/libcxx/test/libcxx/language.support/support.rtti/type.info/type_info.comparison.unmerged.sh.cpp
@@ -8,11 +8,11 @@
 
 // UNSUPPORTED: no-rtti
 
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu1.o -DTU1 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.tu2.o -DTU2 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
-// RUN: %{cxx} %s %{flags} %{compile_flags} -c -o %t.main.o -DMAIN -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
-// RUN: %{cxx} %t.tu1.o %t.tu2.o %t.main.o %{flags} %{link_flags} -o %t.exe
-// RUN: %{exec} %t.exe
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} -c -o "%t.tu1.o" -DTU1 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} -c -o "%t.tu2.o" -DTU2 -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} -c -o "%t.main.o" -DMAIN -D_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION=2
+// RUN: %{cxx} "%t.tu1.o" "%t.tu2.o" "%t.main.o" %{flags} %{link_flags} -o "%t.exe"
+// RUN: %{exec} "%t.exe"
 
 #include <cassert>
 #include <typeindex>
diff --git a/libcxx/test/libcxx/libcpp_freestanding.sh.cpp b/libcxx/test/libcxx/libcpp_freestanding.sh.cpp
--- a/libcxx/test/libcxx/libcpp_freestanding.sh.cpp
+++ b/libcxx/test/libcxx/libcpp_freestanding.sh.cpp
@@ -10,8 +10,8 @@
 // Test that _LIBCPP_FREESTANDING is not defined when -ffreestanding is not passed
 // to the compiler but defined when -ffreestanding is passed to the compiler.
 
-// RUN: %{cxx} %{flags} %{compile_flags} -fsyntax-only %s
-// RUN: %{cxx} %{flags} %{compile_flags} -fsyntax-only -ffreestanding -DFREESTANDING %s
+// RUN: %{cxx} %{flags} %{compile_flags} -fsyntax-only "%s"
+// RUN: %{cxx} %{flags} %{compile_flags} -fsyntax-only -ffreestanding -DFREESTANDING "%s"
 
 #include <__config>
 
diff --git a/libcxx/test/libcxx/modules/stds_include.sh.cpp b/libcxx/test/libcxx/modules/stds_include.sh.cpp
--- a/libcxx/test/libcxx/modules/stds_include.sh.cpp
+++ b/libcxx/test/libcxx/modules/stds_include.sh.cpp
@@ -25,11 +25,11 @@
 // NOTE: The -std=XXX flag is present in %{flags}, so we overwrite it by passing it after %{flags}.
 // FIXME: Remove the `-DINVALIDATE_CACHE_FOO` macros. Their purpose is to workaround a bug in older Clang versions
 //        the same modules caches were reused across standard dialects.
-// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++03 -DINVALIDATE_CACHE_CXX03 %s
-// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++11 -DINVALIDATE_CACHE_CXX11 %s
-// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++14 -DINVALIDATE_CACHE_CKK14 %s
-// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++17 -DINVALIDATE_CACHE_CXX17 %s
-// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++2a -DINVALIDATE_CACHE_CXX2A %s
+// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++03 -DINVALIDATE_CACHE_CXX03 "%s"
+// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++11 -DINVALIDATE_CACHE_CXX11 "%s"
+// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++14 -DINVALIDATE_CACHE_CKK14 "%s"
+// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++17 -DINVALIDATE_CACHE_CXX17 "%s"
+// RUN: %{cxx} %{flags} %{compile_flags} -fmodules -fcxx-modules -fsyntax-only -std=c++2a -DINVALIDATE_CACHE_CXX2A "%s"
 
 #include <vector>
 
diff --git a/libcxx/test/libcxx/selftest/dsl/dsl.sh.py b/libcxx/test/libcxx/selftest/dsl/dsl.sh.py
--- a/libcxx/test/libcxx/selftest/dsl/dsl.sh.py
+++ b/libcxx/test/libcxx/selftest/dsl/dsl.sh.py
@@ -8,8 +8,8 @@
 
 # Note: We prepend arguments with 'x' to avoid thinking there are too few
 #       arguments in case an argument is an empty string.
-# RUN: %{python} %s x%S \
-# RUN:              x%T \
+# RUN: %{python} "%s" "x%S" \
+# RUN:              "x%T" \
 # RUN:              x%{escaped_exec} \
 # RUN:              x%{escaped_cxx} \
 # RUN:              x%{escaped_flags} \
diff --git a/libcxx/test/libcxx/selftest/file_dependencies/absolute-and-relative-paths.sh.cpp b/libcxx/test/libcxx/selftest/file_dependencies/absolute-and-relative-paths.sh.cpp
--- a/libcxx/test/libcxx/selftest/file_dependencies/absolute-and-relative-paths.sh.cpp
+++ b/libcxx/test/libcxx/selftest/file_dependencies/absolute-and-relative-paths.sh.cpp
@@ -8,8 +8,8 @@
 
 // Make sure that FILE_DEPENDENCIES work with relative AND absolute paths.
 
-// FILE_DEPENDENCIES: %S/a.txt
-// RUN: test -e %T/a.txt
+// FILE_DEPENDENCIES: "%S/a.txt"
+// RUN: test -e "%T/a.txt"
 
 // FILE_DEPENDENCIES: dir/b.txt
-// RUN: test -e %T/b.txt
+// RUN: test -e "%T/b.txt"
diff --git a/libcxx/test/libcxx/selftest/file_dependencies/substitute-in-dependencies.sh.cpp b/libcxx/test/libcxx/selftest/file_dependencies/substitute-in-dependencies.sh.cpp
--- a/libcxx/test/libcxx/selftest/file_dependencies/substitute-in-dependencies.sh.cpp
+++ b/libcxx/test/libcxx/selftest/file_dependencies/substitute-in-dependencies.sh.cpp
@@ -8,5 +8,5 @@
 
 // Make sure that lit substitutions are expanded inside FILE_DEPENDENCIES lines.
 
-// FILE_DEPENDENCIES: %s
-// RUN: test -e %T/substitute-in-dependencies.sh.cpp
+// FILE_DEPENDENCIES: "%s"
+// RUN: test -e "%T/substitute-in-dependencies.sh.cpp"
diff --git a/libcxx/test/libcxx/selftest/remote-substitutions.sh.cpp b/libcxx/test/libcxx/selftest/remote-substitutions.sh.cpp
--- a/libcxx/test/libcxx/selftest/remote-substitutions.sh.cpp
+++ b/libcxx/test/libcxx/selftest/remote-substitutions.sh.cpp
@@ -15,9 +15,9 @@
 // We also check that the path of test-executables is replaced whether they
 // appear first in the command-line or not.
 
-// RUN: %{cxx} %s %{flags} %{compile_flags} %{link_flags} -o %t.exe
-// RUN: %{exec} %t.exe 0
-// RUN: %{exec} bash -c '! %t.exe 1'
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} %{link_flags} -o "%t.exe"
+// RUN: %{exec} "%t.exe" 0
+// RUN: %{exec} bash -c '! "%t.exe" 1'
 
 #include <cassert>
 #include <cstdlib>
diff --git a/libcxx/test/libcxx/selftest/sh.cpp/substitutions.sh.cpp b/libcxx/test/libcxx/selftest/sh.cpp/substitutions.sh.cpp
--- a/libcxx/test/libcxx/selftest/sh.cpp/substitutions.sh.cpp
+++ b/libcxx/test/libcxx/selftest/sh.cpp/substitutions.sh.cpp
@@ -13,8 +13,8 @@
 // - %{link_flags}
 // - %{exec}
 
-// RUN: %{cxx} %s %{flags} %{compile_flags} %{link_flags} -o %t.exe
-// RUN: %{exec} %t.exe "HELLO"
+// RUN: %{cxx} "%s" %{flags} %{compile_flags} %{link_flags} -o "%t.exe"
+// RUN: %{exec} "%t.exe" "HELLO"
 
 #include <cassert>
 #include <string>
diff --git a/libcxx/test/libcxx/selftest/tmpdir-exists.sh.cpp b/libcxx/test/libcxx/selftest/tmpdir-exists.sh.cpp
--- a/libcxx/test/libcxx/selftest/tmpdir-exists.sh.cpp
+++ b/libcxx/test/libcxx/selftest/tmpdir-exists.sh.cpp
@@ -8,4 +8,4 @@
 
 // Make sure that the directory represented by %T exists when we run the test.
 
-// RUN: test -d %T
+// RUN: test -d "%T"
diff --git a/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp b/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp
--- a/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp
+++ b/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp
@@ -8,7 +8,7 @@
 
 // Regression test for PR42676.
 
-// RUN: %{cxx} %{flags} %s -o %t.exe %{compile_flags} %{link_flags} -D_LIBCPP_HIDE_FROM_ABI_PER_TU
+// RUN: %{cxx} %{flags} "%s" -o "%t.exe" %{compile_flags} %{link_flags} -D_LIBCPP_HIDE_FROM_ABI_PER_TU
 // RUN: %{run}
 
 #include <memory>
diff --git a/libcxx/test/libcxx/utilities/function.objects/abi_bug_cxx03_cxx11_example.sh.cpp b/libcxx/test/libcxx/utilities/function.objects/abi_bug_cxx03_cxx11_example.sh.cpp
--- a/libcxx/test/libcxx/utilities/function.objects/abi_bug_cxx03_cxx11_example.sh.cpp
+++ b/libcxx/test/libcxx/utilities/function.objects/abi_bug_cxx03_cxx11_example.sh.cpp
@@ -13,9 +13,9 @@
 // This tests is meant to demonstrate an existing ABI bug between the
 // C++03 and C++11 implementations of std::function. It is not a real test.
 
-// RUN: %{cxx} -c %s -o %t.first.o %{flags} %{compile_flags} -std=c++03 -g
-// RUN: %{cxx} -c %s -o %t.second.o -DWITH_MAIN %{flags} %{compile_flags} -g -std=c++11
-// RUN: %{cxx} -o %t.exe %t.first.o %t.second.o %{flags} %{link_flags} -g
+// RUN: %{cxx} -c "%s" -o "%t.first.o" %{flags} %{compile_flags} -std=c++03 -g
+// RUN: %{cxx} -c "%s" -o "%t.second.o" -DWITH_MAIN %{flags} %{compile_flags} -g -std=c++11
+// RUN: %{cxx} -o "%t.exe" "%t.first.o" "%t.second.o" %{flags} %{link_flags} -g
 // RUN: %{run}
 
 #include <functional>
diff --git a/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_is_same.sh.cpp b/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_is_same.sh.cpp
--- a/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_is_same.sh.cpp
+++ b/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_is_same.sh.cpp
@@ -17,8 +17,8 @@
 // std::_IsSame:    689.634 ms     356 K
 // std::is_same:  8,129.180 ms     560 K
 //
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %S/orig.o -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -std=c++17
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %S/new.o -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -std=c++17 -DTEST_NEW
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%S/orig.o" -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -std=c++17
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%S/new.o" -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -std=c++17 -DTEST_NEW
 
 #include <type_traits>
 #include <cassert>
diff --git a/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_metafunctions.sh.cpp b/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_metafunctions.sh.cpp
--- a/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_metafunctions.sh.cpp
+++ b/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_metafunctions.sh.cpp
@@ -19,9 +19,9 @@
 // __and_:      14,181.851 ms     648 M
 //
 
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %S/new.o -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -std=c++17
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %S/lazy.o -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace  -std=c++17 -DTEST_LAZY_AND
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %S/std.o -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace   -std=c++17 -DTEST_STD_AND
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%S/new.o" -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -std=c++17
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%S/lazy.o" -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace  -std=c++17 -DTEST_LAZY_AND
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%S/std.o" -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace   -std=c++17 -DTEST_STD_AND
 
 #include <type_traits>
 #include <cassert>
diff --git a/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_variant_overloads_impl.sh.cpp b/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_variant_overloads_impl.sh.cpp
--- a/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_variant_overloads_impl.sh.cpp
+++ b/libcxx/test/libcxx/utilities/meta/stress_tests/stress_test_variant_overloads_impl.sh.cpp
@@ -24,15 +24,15 @@
 // variant_new:     1,105 ms        828 KiB
 
 
-// RUN: %{cxx} %{flags} %{compile_flags} -std=c++17 -c %s \
+// RUN: %{cxx} %{flags} %{compile_flags} -std=c++17 -c "%s" \
 // RUN:    -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -g \
-// RUN:    -DTEST_NS=flat_impl -o %S/flat.o
-// RUN: %{cxx} %{flags} %{compile_flags} -std=c++17 -c %s \
+// RUN:    -DTEST_NS=flat_impl -o "%S/flat.o"
+// RUN: %{cxx} %{flags} %{compile_flags} -std=c++17 -c "%s" \
 // RUN:    -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -g \
-// RUN:    -DTEST_NS=rec_impl -o %S/rec.o
-// RUN: %{cxx} %{flags} %{compile_flags} -std=c++17 -c %s \
+// RUN:    -DTEST_NS=rec_impl -o "%S/rec.o"
+// RUN: %{cxx} %{flags} %{compile_flags} -std=c++17 -c "%s" \
 // RUN:    -ggdb  -ggnu-pubnames -ftemplate-depth=5000 -ftime-trace -g \
-// RUN:    -DTEST_NS=variant_impl -o %S/variant.o
+// RUN:    -DTEST_NS=variant_impl -o "%S/variant.o"
 
 #include <type_traits>
 #include <tuple>
diff --git a/libcxx/test/std/input.output/iostream.objects/check-stderr.sh b/libcxx/test/std/input.output/iostream.objects/check-stderr.sh
--- a/libcxx/test/std/input.output/iostream.objects/check-stderr.sh
+++ b/libcxx/test/std/input.output/iostream.objects/check-stderr.sh
@@ -1,4 +1,4 @@
 program=${1}
 expected_stderr=${2}
-${program} 2>stderr.log >stdout.log
+"${program}" 2>stderr.log >stdout.log
 [ "${expected_stderr}" == "$(cat stderr.log)" ]
diff --git a/libcxx/test/std/input.output/iostream.objects/check-stdout.sh b/libcxx/test/std/input.output/iostream.objects/check-stdout.sh
--- a/libcxx/test/std/input.output/iostream.objects/check-stdout.sh
+++ b/libcxx/test/std/input.output/iostream.objects/check-stdout.sh
@@ -1,4 +1,4 @@
 program=${1}
 expected_stdout=${2}
-${program} 2>stderr.log >stdout.log
+"${program}" 2>stderr.log >stdout.log
 [ "${expected_stdout}" == "$(cat stdout.log)" ]
diff --git a/libcxx/test/std/input.output/iostream.objects/send-stdin.sh b/libcxx/test/std/input.output/iostream.objects/send-stdin.sh
--- a/libcxx/test/std/input.output/iostream.objects/send-stdin.sh
+++ b/libcxx/test/std/input.output/iostream.objects/send-stdin.sh
@@ -1,3 +1,3 @@
 program=${1}
 input=${2}
-echo -n ${input} | ${program}
+echo -n ${input} | "${program}"
diff --git a/libcxx/test/std/namespace/addressable_functions.sh.cpp b/libcxx/test/std/namespace/addressable_functions.sh.cpp
--- a/libcxx/test/std/namespace/addressable_functions.sh.cpp
+++ b/libcxx/test/std/namespace/addressable_functions.sh.cpp
@@ -12,10 +12,10 @@
 // in C++20, we test it in all standard modes because it's basic QOI to provide
 // a consistent behavior for that across standard modes.
 
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %t.tu1.o -DTU1
-// RUN: %{cxx} %{flags} %{compile_flags} -c %s -o %t.tu2.o -DTU2
-// RUN: %{cxx} %t.tu1.o %t.tu2.o %{flags} %{link_flags} -o %t.exe
-// RUN: %{exec} %t.exe
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%t.tu1.o" -DTU1
+// RUN: %{cxx} %{flags} %{compile_flags} -c "%s" -o "%t.tu2.o" -DTU2
+// RUN: %{cxx} "%t.tu1.o" "%t.tu2.o" %{flags} %{link_flags} -o "%t.exe"
+// RUN: %{exec} "%t.exe"
 
 // The functions checked below come from <iostream> & friends
 // UNSUPPORTED: libcpp-has-no-localization
diff --git a/libcxx/utils/libcxx/test/config.py b/libcxx/utils/libcxx/test/config.py
--- a/libcxx/utils/libcxx/test/config.py
+++ b/libcxx/utils/libcxx/test/config.py
@@ -589,7 +589,7 @@
         codesign_ident = self.get_lit_conf('llvm_codesign_identity', '')
         env_vars = ' '.join('%s=%s' % (k, pipes.quote(v)) for (k, v) in self.exec_env.items())
         exec_args = [
-            '--execdir %T',
+            '--execdir "%T"',
             '--codesign_identity "{}"'.format(codesign_ident),
             '--env {}'.format(env_vars)
         ]
diff --git a/libcxx/utils/libcxx/test/dsl.py b/libcxx/utils/libcxx/test/dsl.py
--- a/libcxx/utils/libcxx/test/dsl.py
+++ b/libcxx/utils/libcxx/test/dsl.py
@@ -95,7 +95,7 @@
     with open(test.getSourcePath(), 'w') as sourceFile:
       sourceFile.write(source)
     out, err, exitCode, timeoutInfo = _executeScriptInternal(test, ['%{build}'])
-    _executeScriptInternal(test, ['rm %t.exe'])
+    _executeScriptInternal(test, ['rm "%t.exe"'])
     return exitCode == 0
 
 @_memoizeExpensiveOperation(lambda c, p, args=None, testPrefix='': (c.substitutions, c.environment, p, args))
@@ -127,7 +127,7 @@
       return actualOut
 
     finally:
-      _executeScriptInternal(test, ['rm %t.exe'])
+      _executeScriptInternal(test, ['rm "%t.exe"'])
 
 @_memoizeExpensiveOperation(lambda c, f: (c.substitutions, c.environment, f))
 def hasCompileFlag(config, flag):
@@ -190,7 +190,7 @@
       # additional macros.
       sourceFile.write("#include <cstddef>")
     unparsedOutput, err, exitCode, timeoutInfo = _executeScriptInternal(test, [
-      "%{{cxx}} %s -dM -E %{{flags}} %{{compile_flags}} {}".format(flags)
+      "%{{cxx}} \"%s\" -dM -E %{{flags}} %{{compile_flags}} {}".format(flags)
     ])
     parsedMacros = dict()
     defines = (l.strip() for l in unparsedOutput.split('\n') if l.startswith('#define '))
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -48,7 +48,7 @@
   #       build against now-invalid cached headers from a previous build.
   Feature(name='modules-support',
           when=lambda cfg: hasCompileFlag(cfg, '-fmodules'),
-          actions=lambda cfg: [AddCompileFlag('-fmodules-cache-path=%t/ModuleCache')]),
+          actions=lambda cfg: [AddCompileFlag('-fmodules-cache-path="%t/ModuleCache"')]),
 
   Feature(name='non-lockfree-atomics',
           when=lambda cfg: sourceBuilds(cfg, """
diff --git a/libcxx/utils/libcxx/test/format.py b/libcxx/utils/libcxx/test/format.py
--- a/libcxx/utils/libcxx/test/format.py
+++ b/libcxx/utils/libcxx/test/format.py
@@ -70,8 +70,8 @@
 
     # Check base substitutions and add the %{build} and %{run} convenience substitutions
     _checkBaseSubstitutions(substitutions)
-    substitutions.append(('%{build}', '%{cxx} %s %{flags} %{compile_flags} %{link_flags} -o %t.exe'))
-    substitutions.append(('%{run}', '%{exec} %t.exe'))
+    substitutions.append(('%{build}', '%{cxx} "%s" %{flags} %{compile_flags} %{link_flags} -o "%t.exe"'))
+    substitutions.append(('%{run}', '%{exec} "%t.exe"'))
 
     # Parse the test file, including custom directives
     additionalCompileFlags = []
@@ -96,7 +96,7 @@
     # that file to the execution directory. Execute the copy from %S to allow
     # relative paths from the test directory.
     for dep in fileDependencies:
-        script += ['%dbg(SETUP) cd %S && cp {} %T'.format(dep)]
+        script += ['%dbg(SETUP) cd "%S" && cp {} "%T"'.format(dep)]
     script += preamble
     script += scriptInTest
 
@@ -235,23 +235,23 @@
             return self._executeShTest(test, litConfig, steps)
         elif filename.endswith('.compile.pass.cpp'):
             steps = [
-                "%dbg(COMPILED WITH) %{cxx} %s %{flags} %{compile_flags} -fsyntax-only"
+                "%dbg(COMPILED WITH) %{cxx} \"%s\" %{flags} %{compile_flags} -fsyntax-only"
             ]
             return self._executeShTest(test, litConfig, steps)
         elif filename.endswith('.compile.fail.cpp'):
             steps = [
-                "%dbg(COMPILED WITH) ! %{cxx} %s %{flags} %{compile_flags} -fsyntax-only"
+                "%dbg(COMPILED WITH) ! %{cxx} \"%s\" %{flags} %{compile_flags} -fsyntax-only"
             ]
             return self._executeShTest(test, litConfig, steps)
         elif filename.endswith('.link.pass.cpp'):
             steps = [
-                "%dbg(COMPILED WITH) %{cxx} %s %{flags} %{compile_flags} %{link_flags} -o %t.exe"
+                "%dbg(COMPILED WITH) %{cxx} \"%s\" %{flags} %{compile_flags} %{link_flags} -o \"%t.exe\""
             ]
             return self._executeShTest(test, litConfig, steps)
         elif filename.endswith('.link.fail.cpp'):
             steps = [
-                "%dbg(COMPILED WITH) %{cxx} %s %{flags} %{compile_flags} -c -o %t.o",
-                "%dbg(LINKED WITH) ! %{cxx} %t.o %{flags} %{link_flags} -o %t.exe"
+                "%dbg(COMPILED WITH) %{cxx} \"%s\" %{flags} %{compile_flags} -c -o \"%t.o\"",
+                "%dbg(LINKED WITH) ! %{cxx} \"%t.o\" %{flags} %{link_flags} -o \"%t.exe\""
             ]
             return self._executeShTest(test, litConfig, steps)
         elif filename.endswith('.verify.cpp'):
@@ -261,15 +261,15 @@
             steps = [
                 # Note: Use -Wno-error to make sure all diagnostics are not treated as errors,
                 #       which doesn't make sense for clang-verify tests.
-                "%dbg(COMPILED WITH) %{{cxx}} %s %{{flags}} %{{compile_flags}} -fsyntax-only -Wno-error {}".format(VERIFY_FLAGS)
+                "%dbg(COMPILED WITH) %{{cxx}} \"%s\" %{{flags}} %{{compile_flags}} -fsyntax-only -Wno-error {}".format(VERIFY_FLAGS)
             ]
             return self._executeShTest(test, litConfig, steps)
         # Make sure to check these ones last, since they will match other
         # suffixes above too.
         elif filename.endswith('.pass.cpp') or filename.endswith('.pass.mm'):
             steps = [
-                "%dbg(COMPILED WITH) %{cxx} %s %{flags} %{compile_flags} %{link_flags} -o %t.exe",
-                "%dbg(EXECUTED AS) %{exec} %t.exe"
+                "%dbg(COMPILED WITH) %{cxx} \"%s\" %{flags} %{compile_flags} %{link_flags} -o \"%t.exe\"",
+                "%dbg(EXECUTED AS) %{exec} \"%t.exe\""
             ]
             return self._executeShTest(test, litConfig, steps)
         # This is like a .verify.cpp test when clang-verify is supported,
@@ -278,11 +278,11 @@
         elif filename.endswith('.fail.cpp'):
             if supportsVerify:
                 steps = [
-                    "%dbg(COMPILED WITH) %{{cxx}} %s %{{flags}} %{{compile_flags}} -fsyntax-only -Wno-error {}".format(VERIFY_FLAGS)
+                    "%dbg(COMPILED WITH) %{{cxx}} \"%s\" %{{flags}} %{{compile_flags}} -fsyntax-only -Wno-error {}".format(VERIFY_FLAGS)
                 ]
             else:
                 steps = [
-                    "%dbg(COMPILED WITH) ! %{cxx} %s %{flags} %{compile_flags} -fsyntax-only"
+                    "%dbg(COMPILED WITH) ! %{cxx} \"%s\" %{flags} %{compile_flags} -fsyntax-only"
                 ]
             return self._executeShTest(test, litConfig, steps)
         else:
diff --git a/libcxxabi/test/CMakeLists.txt b/libcxxabi/test/CMakeLists.txt
--- a/libcxxabi/test/CMakeLists.txt
+++ b/libcxxabi/test/CMakeLists.txt
@@ -50,7 +50,7 @@
 pythonize_bool(LIBCXXABI_LINK_TESTS_WITH_SHARED_LIBCXXABI)
 set(LIBCXXABI_TARGET_INFO "libcxx.test.target_info.LocalTI" CACHE STRING
     "TargetInfo to use when setting up test environment.")
-set(LIBCXXABI_EXECUTOR "${Python3_EXECUTABLE} ${LIBCXXABI_LIBCXX_PATH}/utils/run.py" CACHE STRING
+set(LIBCXXABI_EXECUTOR "${Python3_EXECUTABLE} '${LIBCXXABI_LIBCXX_PATH}/utils/run.py'" CACHE STRING
     "Executor to use when running tests.")
 
 if (LIBCXXABI_ENABLE_SHARED)
diff --git a/libcxxabi/test/incomplete_type.sh.cpp b/libcxxabi/test/incomplete_type.sh.cpp
--- a/libcxxabi/test/incomplete_type.sh.cpp
+++ b/libcxxabi/test/incomplete_type.sh.cpp
@@ -20,10 +20,10 @@
 // in the system libc++abi installation on OS X. (DYLD_LIBRARY_PATH is ignored
 // for shell tests because of Apple security features).
 
-// RUN: %{cxx} %{flags} %{compile_flags} -Wno-unreachable-code -c %s -o %t.one.o
-// RUN: %{cxx} %{flags} %{compile_flags} -Wno-unreachable-code -c %s -o %t.two.o -DTU_ONE
-// RUN: %{cxx} %{flags} %t.one.o %t.two.o %{link_libcxxabi} %{link_flags} -o %t.exe
-// RUN: %{exec} %t.exe
+// RUN: %{cxx} %{flags} %{compile_flags} -Wno-unreachable-code -c "%s" -o "%t.one.o"
+// RUN: %{cxx} %{flags} %{compile_flags} -Wno-unreachable-code -c "%s" -o "%t.two.o" -DTU_ONE
+// RUN: %{cxx} %{flags} "%t.one.o" "%t.two.o" %{link_libcxxabi} %{link_flags} -o "%t.exe"
+// RUN: %{exec} "%t.exe"
 
 #include <stdio.h>
 #include <cstring>
diff --git a/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-00.pass.sh.s b/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-00.pass.sh.s
--- a/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-00.pass.sh.s
+++ b/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-00.pass.sh.s
@@ -1,5 +1,5 @@
-@ RUN: %{cxx} %{flags} %{link_flags} %s -o %t.exe
-@ RUN: %t.exe
+@ RUN: %{cxx} %{flags} %{link_flags} "%s" -o "%t.exe"
+@ RUN: "%t.exe"
 @ UNSUPPORTED: no-exceptions
 
 @ PURPOSE: Check that 0x00 is a valid value for ttype encoding.  LLVM and
diff --git a/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-90.pass.sh.s b/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-90.pass.sh.s
--- a/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-90.pass.sh.s
+++ b/libcxxabi/test/native/arm-linux-eabi/ttype-encoding-90.pass.sh.s
@@ -1,5 +1,5 @@
-@ RUN: %{cxx} %{flags} %{link_flags} %s -o %t.exe
-@ RUN: %t.exe
+@ RUN: %{cxx} %{flags} %{link_flags} "%s" -o "%t.exe"
+@ RUN: "%t.exe"
 @ UNSUPPORTED: no-exceptions
 
 @ PURPOSE: Check that 0x90 is a valid value for ttype encoding.