diff --git a/Runtimes/Core/CMakeLists.txt b/Runtimes/Core/CMakeLists.txt
index 54c25b0bbb5aa..a69845cb0dbe6 100644
--- a/Runtimes/Core/CMakeLists.txt
+++ b/Runtimes/Core/CMakeLists.txt
@@ -118,6 +118,8 @@ option(SwiftCore_INSTALL_NESTED_SUBDIR "Install libraries under a platform and a
 set(SwiftCore_INSTALL_LIBDIR "${CMAKE_INSTALL_LIBDIR}/swift$<$<NOT:$<BOOL:${BUILD_SHARED_LIBS}>>:_static>$<$<BOOL:${SwiftCore_INSTALL_NESTED_SUBDIR}>:/${SwiftCore_PLATFORM_SUBDIR}/${SwiftCore_ARCH_SUBDIR}>")
 set(SwiftCore_INSTALL_SWIFTMODULEDIR "${CMAKE_INSTALL_LIBDIR}/swift$<$<NOT:$<BOOL:${BUILD_SHARED_LIBS}>>:_static>$<$<BOOL:${SwiftCore_INSTALL_NESTED_SUBDIR}>:/${SwiftCore_PLATFORM_SUBDIR}>")
 
+option(SwiftCore_ENABLE_ONONESUPPORT "Enable Onone Support" YES)
+
 # TODO: Most of these should be attached to specific targets rather than applied
 #       globally. They can be applied as part of the library interface if they
 #       affect the behavior of libraries that build against a given target.
@@ -193,3 +195,6 @@ add_subdirectory(runtime)
 add_subdirectory(stubs)
 add_subdirectory(CommandLineSupport)
 add_subdirectory(core)
+if(SwiftCore_ENABLE_ONONESUPPORT)
+  add_subdirectory(SwiftOnoneSupport)
+endif()
diff --git a/Runtimes/Core/SwiftOnoneSupport/CMakeLists.txt b/Runtimes/Core/SwiftOnoneSupport/CMakeLists.txt
new file mode 100644
index 0000000000000..c7437d94ea8b6
--- /dev/null
+++ b/Runtimes/Core/SwiftOnoneSupport/CMakeLists.txt
@@ -0,0 +1,45 @@
+add_library(swiftSwiftOnoneSupport
+  SwiftOnoneSupport.swift
+  "${PROJECT_SOURCE_DIR}/linker-support/magic-symbols-for-install-name.c")
+
+set_target_properties(swiftSwiftOnoneSupport PROPERTIES
+ Swift_MODULE_NAME SwiftOnoneSupport)
+
+if(APPLE AND BUILD_SHARED_LIBS)
+  target_link_options(swiftSwiftOnoneSupport PRIVATE "SHELL:-Xlinker -headerpad_max_install_names")
+endif()
+
+target_compile_options(swiftSwiftOnoneSupport PRIVATE
+  $<$<COMPILE_LANGUAGE:Swift>:-parse-stdlib>
+  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xllvm -sil-inline-generics=false>"
+
+  # We have to disable validation of TBD files, because this module is
+  # _explicitly_ special-cased to result in extra symbols generated by the
+  # optimizer, meaning TBDGen can't (and shouldn't: it has to run
+  # pre-optimization for performance) list them.
+  # See also caa3dd4d291ec93c1a59f1db62604e703bff8468
+  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -validate-tbd-against-ir=none>"
+
+  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -check-onone-completeness>"
+  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -disable-access-control>")
+
+target_compile_definitions(swiftSwiftOnoneSupport PRIVATE
+  $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_TARGET_LIBRARY_NAME=swiftSwiftOnoneSupport>)
+
+target_link_libraries(swiftSwiftOnoneSupport
+  PRIVATE
+    swiftShims
+    swiftCore)
+
+install(TARGETS swiftSwiftOnoneSupport
+    ARCHIVE DESTINATION "${SwiftCore_INSTALL_LIBDIR}"
+    LIBRARY DESTINATION "${SwiftCore_INSTALL_LIBDIR}"
+    RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/SwiftOnoneSupport.swiftmodule"
+  DESTINATION "${SwiftCore_INSTALL_SWIFTMODULEDIR}/SwiftOnoneSupport.swiftmodule"
+  RENAME "${SwiftCore_MODULE_TRIPLE}.swiftmodule")
+emit_swift_interface(swiftSwiftOnoneSupport)
+install_swift_interface(swiftSwiftOnoneSupport)
+
+# Configure plist creation for Darwin platforms.
+generate_plist("${CMAKE_PROJECT_NAME}" "${CMAKE_PROJECT_VERSION}" swiftSwiftOnoneSupport)
diff --git a/Runtimes/Core/cmake/caches/Vendors/Apple/apple-common.cmake b/Runtimes/Core/cmake/caches/Vendors/Apple/apple-common.cmake
index b5a335cc4f4e0..803d26a1b1239 100644
--- a/Runtimes/Core/cmake/caches/Vendors/Apple/apple-common.cmake
+++ b/Runtimes/Core/cmake/caches/Vendors/Apple/apple-common.cmake
@@ -13,6 +13,8 @@ set(SwiftCore_ENABLE_RUNTIME_FUNCTION_COUNTERS ON CACHE BOOL "")
 set(SwiftCore_ENABLE_BACKDEPLOYMENT_SUPPORT ON CACHE BOOL "")
 set(SwiftCore_ENABLE_FILESYSTEM_SUPPORT ON CACHE BOOL "")
 
+set(SwiftCore_ENABLE_ONONESUPPORT OFF CACHE BOOL "")
+
 set(SwiftCore_INSTALL_NESTED_SUBDIR OFF CACHE BOOL "")
 
 set(CMAKE_CXX_FLAGS_MINSIZEREL "-Os -g -DNDEBUG" CACHE STRING "")
diff --git a/Runtimes/Resync.cmake b/Runtimes/Resync.cmake
index 2fb3584ab6bce..c412b17197626 100644
--- a/Runtimes/Resync.cmake
+++ b/Runtimes/Resync.cmake
@@ -78,15 +78,11 @@ set(CoreLibs
   CompatibilityOverride
   stubs
   CommandLineSupport
-  core)
+  core
+  SwiftOnoneSupport)
 
   # Add these as we get them building
-  # core
-  # Concurrency
-  # SwiftOnoneSUpport
-  # CommandLineSupport
   # Demangling
-  # runtime)
 
 foreach(library ${CoreLibs})
   copy_library_sources(${library} "public" "Core")