Index: libcxx/test/CMakeLists.txt
===================================================================
--- libcxx/test/CMakeLists.txt
+++ libcxx/test/CMakeLists.txt
@@ -34,6 +34,10 @@
   serialize_lit_param(target_triple "\"${LLVM_DEFAULT_TARGET_TRIPLE}\"")
 endif()
 
+if (CMAKE_SYSROOT)
+  serialize_lit_param(sysroot "\"${CMAKE_SYSROOT}\"")
+endif()
+
 if (LLVM_USE_SANITIZER)
   serialize_lit_param(use_sanitizer "\"${LLVM_USE_SANITIZER}\"")
 endif()
Index: libcxx/test/configs/llvm-libc++-shared.cfg.in
===================================================================
--- libcxx/test/configs/llvm-libc++-shared.cfg.in
+++ libcxx/test/configs/llvm-libc++-shared.cfg.in
@@ -3,8 +3,10 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-pthread' + (' -isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else '')
+    '-pthread' + ('{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else '')
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support'
Index: libcxx/test/configs/llvm-libc++-static.cfg.in
===================================================================
--- libcxx/test/configs/llvm-libc++-static.cfg.in
+++ libcxx/test/configs/llvm-libc++-static.cfg.in
@@ -3,8 +3,10 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-pthread' + (' -isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else '')
+    '-pthread' + ('{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else '')
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support'
Index: libcxx/utils/libcxx/test/params.py
===================================================================
--- libcxx/utils/libcxx/test/params.py
+++ libcxx/utils/libcxx/test/params.py
@@ -215,4 +215,8 @@
               AddFeature('transitive-includes-disabled'),
               AddCompileFlag('-D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES')
             ]),
+
+  Parameter(name='sysroot', type=str, default='',
+            help="sysroot to use",
+            actions=lambda sysroot: [AddCompileFlag(f"--sysroot={sysroot}")] if sysroot else []),
 ]
Index: libcxxabi/test/CMakeLists.txt
===================================================================
--- libcxxabi/test/CMakeLists.txt
+++ libcxxabi/test/CMakeLists.txt
@@ -53,6 +53,10 @@
   serialize_lit_param(target_triple "\"${LLVM_DEFAULT_TARGET_TRIPLE}\"")
 endif()
 
+if (CMAKE_SYSROOT)
+  serialize_lit_param(sysroot "\"${CMAKE_SYSROOT}\"")
+endif()
+
 foreach(param IN LISTS LIBCXXABI_TEST_PARAMS)
   string(REGEX REPLACE "(.+)=(.+)" "\\1" name "${param}")
   string(REGEX REPLACE "(.+)=(.+)" "\\2" value "${param}")
Index: libcxxabi/test/configs/llvm-libc++abi-shared.cfg.in
===================================================================
--- libcxxabi/test/configs/llvm-libc++abi-shared.cfg.in
+++ libcxxabi/test/configs/llvm-libc++abi-shared.cfg.in
@@ -3,8 +3,10 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+    '{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{cxx-include} -I %{cxx-target-include} %{maybe-include-libunwind} -I %{libcxx}/test/support -I %{libcxx}/src -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS'
Index: libcxxabi/test/configs/llvm-libc++abi-static.cfg.in
===================================================================
--- libcxxabi/test/configs/llvm-libc++abi-static.cfg.in
+++ libcxxabi/test/configs/llvm-libc++abi-static.cfg.in
@@ -3,8 +3,10 @@
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
+local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+    '{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{cxx-include} -I %{cxx-target-include} %{maybe-include-libunwind} -I %{libcxx}/test/support -I %{libcxx}/src -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS'
Index: libunwind/test/configs/llvm-libunwind-merged.cfg.in
===================================================================
--- libunwind/test/configs/llvm-libunwind-merged.cfg.in
+++ libunwind/test/configs/llvm-libunwind-merged.cfg.in
@@ -18,8 +18,9 @@
 compile_flags.append('-funwind-tables')
 
 local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format(local_sysroot) if local_sysroot else ''
+    '{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{{include}} {}'.format(' '.join(compile_flags))
Index: libunwind/test/configs/llvm-libunwind-shared.cfg.in
===================================================================
--- libunwind/test/configs/llvm-libunwind-shared.cfg.in
+++ libunwind/test/configs/llvm-libunwind-shared.cfg.in
@@ -17,8 +17,9 @@
 compile_flags.append('-funwind-tables')
 
 local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format(local_sysroot) if local_sysroot else ''
+    '{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{{include}} {}'.format(' '.join(compile_flags))
Index: libunwind/test/configs/llvm-libunwind-static.cfg.in
===================================================================
--- libunwind/test/configs/llvm-libunwind-static.cfg.in
+++ libunwind/test/configs/llvm-libunwind-static.cfg.in
@@ -20,8 +20,9 @@
 compile_flags.append('-funwind-tables')
 
 local_sysroot = '@CMAKE_OSX_SYSROOT@' or '@CMAKE_SYSROOT@'
+sysroot_flag = '--sysroot=' if '@CMAKE_SYSROOT@' else '-isysroot '
 config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format(local_sysroot) if local_sysroot else ''
+    '{}{}'.format(sysroot_flag, local_sysroot) if local_sysroot else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{{include}} {}'.format(' '.join(compile_flags))