[libcxx-commits] [libcxx] [libcxxabi] [llvm] [runtimes] Unify exception and RTTI configuration for the runtimes (PR #165296)

Louis Dionne via libcxx-commits libcxx-commits at lists.llvm.org
Mon Oct 27 12:00:28 PDT 2025 

https://github.com/ldionne created https://github.com/llvm/llvm-project/pull/165296

This patch introduces a unified mechanism for configuring whether exceptions and RTTI are enabled across the runtimes. It does that by introducing new options named RUNTIMES_ENABLE_{EXCEPTIONS,RTTI} and providing a CMake interface target that can be used by various runtime targets (cxx_shared, cxx_static, etc) to get the relevant flags.

This patch aims to create a precedent and an example that can be followed to unify other similar configuration options across the runtimes.

There are still the following open questions:
- Does it make sense at all to have a unified option for all the runtimes? For example, is it desirable to be able to build libc++ without exception support, but libc++abi with exception support?
- How should we deal with options where one of the runtimes does not allow configuring an option? For example, libunwind currently doesn't allow configuring whether exceptions are enabled: they are always enabled. If libunwind links against the interface target for language-level flags and RUNTIMES_ENABLE_EXCEPTIONS=OFF is used, that won't work.
- Where should we document these new unified options? Should we create a documentation page for all of the runtimes?

>From 987ed32b009a580918f89ac519091288f186e858 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Mon, 27 Oct 2025 11:46:52 -0700
Subject: [PATCH] [runtimes] Unify exception and RTTI configuration for the
 runtimes

This patch introduces a unified mechanism for configuring whether
exceptions and RTTI are enabled across the runtimes. It does that
by introducing new options named RUNTIMES_ENABLE_{EXCEPTIONS,RTTI}
and providing a CMake interface target that can be used by various
runtime targets (cxx_shared, cxx_static, etc) to get the relevant
flags.

This patch aims to create a precedent and an example that can be
followed to unify other similar configuration options across the
runtimes.

There are still the following open questions:
- Does it make sense at all to have a unified option for all the
  runtimes? For example, is it desirable to be able to build libc++
  without exception support, but libc++abi with exception support?
- How should we deal with options where one of the runtimes does not
  allow configuring an option? For example, libunwind currently doesn't
  allow configuring whether exceptions are enabled: they are always
  enabled. If libunwind links against the interface target for
  language-level flags and RUNTIMES_ENABLE_EXCEPTIONS=OFF is used,
  that won't work.
- Where should we document these new unified options? Should we create
  a documentation page for all of the runtimes?
---
 libcxx/CMakeLists.txt                         | 40 ++--------------
 libcxx/cmake/caches/AMDGPU.cmake              |  7 +--
 libcxx/cmake/caches/Armv7M-picolibc.cmake     |  5 +-
 .../caches/Armv7Thumb-no-exceptions.cmake     |  3 +-
 .../caches/Armv8Thumb-no-exceptions.cmake     |  3 +-
 .../cmake/caches/Generic-no-exceptions.cmake  |  3 +-
 libcxx/cmake/caches/Generic-no-rtti.cmake     |  6 +--
 libcxx/cmake/caches/NVPTX.cmake               |  7 +--
 libcxx/docs/Modules.rst                       |  7 +--
 libcxx/docs/VendorDocumentation.rst           | 13 +-----
 libcxx/lib/abi/CMakeLists.txt                 |  2 +-
 libcxx/modules/CMakeLists.txt.in              | 10 +---
 libcxx/test/CMakeLists.txt                    |  4 +-
 libcxx/utils/ci/run-buildbot                  | 10 ++--
 libcxxabi/CMakeLists.txt                      | 16 -------
 libcxxabi/src/CMakeLists.txt                  |  4 +-
 libcxxabi/test/CMakeLists.txt                 |  2 +-
 runtimes/CMakeLists.txt                       |  3 ++
 runtimes/cmake/Modules/HandleFlags.cmake      |  6 +++
 runtimes/cmake/Modules/LanguageFlags.cmake    | 46 +++++++++++++++++++
 20 files changed, 86 insertions(+), 111 deletions(-)
 create mode 100644 runtimes/cmake/Modules/LanguageFlags.cmake

diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index a119850cd808e..f91010591efd0 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -47,10 +47,6 @@ include(HandleCompilerRT)
 # Basic options ---------------------------------------------------------------
 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." ON)
 option(LIBCXX_ENABLE_STATIC "Build libc++ as a static library." ON)
-option(LIBCXX_ENABLE_EXCEPTIONS "Enable exceptions in the built library." ON)
-option(LIBCXX_ENABLE_RTTI
-  "Use runtime type information.
-  This option may only be set to OFF when LIBCXX_ENABLE_EXCEPTIONS=OFF." ON)
 option(LIBCXX_ENABLE_FILESYSTEM
   "Whether to include support for parts of the library that rely on a filesystem being
    available on the platform. This includes things like most parts of <filesystem> and
@@ -164,8 +160,8 @@ if (WIN32 OR MINGW OR ANDROID OR "${CMAKE_SYSTEM_NAME}" MATCHES "AIX"
     OR NOT LIBCXX_ENABLE_THREADS
     OR NOT LIBCXX_ENABLE_FILESYSTEM
     OR NOT LIBCXX_ENABLE_RANDOM_DEVICE
-    OR NOT LIBCXX_ENABLE_EXCEPTIONS
-    OR NOT LIBCXX_ENABLE_RTTI)
+    OR NOT RUNTIMES_ENABLE_EXCEPTIONS
+    OR NOT RUNTIMES_ENABLE_RTTI)
   set(_include_benchmarks OFF)
 else()
   set(_include_benchmarks ON)
@@ -358,12 +354,6 @@ if (LIBCXX_HAS_PTHREAD_API)
   endif()
 endif()
 
-if (NOT LIBCXX_ENABLE_RTTI AND LIBCXX_ENABLE_EXCEPTIONS)
-  message(FATAL_ERROR "Libc++ cannot be built with exceptions enabled but RTTI"
-                      " disabled, since that configuration is broken. See"
-                      " https://llvm.org/PR66117 for details.")
-endif()
-
 if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
     if (APPLE)
       message(FATAL_ERROR "LIBCXX_ENABLE_ABI_LINKER_SCRIPT cannot be used on APPLE targets")
@@ -540,29 +530,6 @@ function(cxx_add_basic_build_flags target)
   target_compile_options(${target} PUBLIC "${LIBCXX_ADDITIONAL_COMPILE_FLAGS}")
 endfunction()
 
-# Exception flags =============================================================
-function(cxx_add_exception_flags target)
-  if (LIBCXX_ENABLE_EXCEPTIONS)
-    # Catches C++ exceptions only and tells the compiler to assume that extern C
-    # functions never throw a C++ exception.
-    target_add_compile_flags_if_supported(${target} PUBLIC -EHsc)
-  else()
-    target_add_compile_flags_if_supported(${target} PUBLIC -EHs- -EHa-)
-    target_add_compile_flags_if_supported(${target} PUBLIC -fno-exceptions)
-  endif()
-endfunction()
-
-# RTTI flags ==================================================================
-function(cxx_add_rtti_flags target)
-  if (NOT LIBCXX_ENABLE_RTTI)
-    if (MSVC)
-      target_add_compile_flags_if_supported(${target} PUBLIC -GR-)
-    else()
-      target_add_compile_flags_if_supported(${target} PUBLIC -fno-rtti)
-    endif()
-  endif()
-endfunction()
-
 # Modules flags ===============================================================
 # FIXME The libc++ sources are fundamentally non-modular. They need special
 # versions of the headers in order to provide C++03 and legacy ABI definitions.
@@ -817,11 +784,10 @@ function(cxx_add_common_build_flags target)
   cxx_add_basic_build_flags(${target})
   cxx_add_warning_flags(${target} ${LIBCXX_ENABLE_WERROR} ${LIBCXX_ENABLE_PEDANTIC})
   cxx_add_windows_flags(${target})
-  cxx_add_exception_flags(${target})
-  cxx_add_rtti_flags(${target})
   cxx_add_module_flags(${target})
   cxx_link_system_libraries(${target})
   target_link_libraries(${target} PRIVATE cxx-sanitizer-flags)
+  target_link_libraries(${target} PRIVATE runtimes-language-flags)
 endfunction()
 
 #===============================================================================
diff --git a/libcxx/cmake/caches/AMDGPU.cmake b/libcxx/cmake/caches/AMDGPU.cmake
index 5d09a1db8da44..c188788f5dd66 100644
--- a/libcxx/cmake/caches/AMDGPU.cmake
+++ b/libcxx/cmake/caches/AMDGPU.cmake
@@ -1,12 +1,14 @@
+# Configuration options for all the runtimes
+set(RUNTIMES_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_RTTI OFF CACHE BOOL "")
+
 # Configuration options for libcxx.
 set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_LOCALIZATION ON CACHE BOOL "")
 set(LIBCXX_ENABLE_MONOTONIC_CLOCK ON CACHE BOOL "")
 set(LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS ON CACHE BOOL "")
 set(LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")
-set(LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
 set(LIBCXX_ENABLE_STATIC ON CACHE BOOL "")
@@ -21,7 +23,6 @@ set(RUNTIMES_USE_LIBC "llvm-libc" CACHE STRING "")
 
 # Configuration options for libcxxabi.
 set(LIBCXXABI_BAREMETAL ON CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_THREADS OFF CACHE BOOL "")
diff --git a/libcxx/cmake/caches/Armv7M-picolibc.cmake b/libcxx/cmake/caches/Armv7M-picolibc.cmake
index 9df71fba2cadd..75825ad117da5 100644
--- a/libcxx/cmake/caches/Armv7M-picolibc.cmake
+++ b/libcxx/cmake/caches/Armv7M-picolibc.cmake
@@ -6,6 +6,8 @@ set(CMAKE_C_FLAGS "-mfloat-abi=soft" CACHE STRING "")
 set(CMAKE_SYSTEM_NAME Generic CACHE STRING "")
 set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY CACHE STRING "")
 set(LLVM_USE_LINKER "lld" CACHE STRING "")
+set(RUNTIMES_ENABLE_EXCEPTIONS ON CACHE BOOL "")
+set(RUNTIMES_ENABLE_RTTI ON CACHE BOOL "")
 set(COMPILER_RT_BAREMETAL_BUILD ON CACHE BOOL "")
 set(COMPILER_RT_BUILD_LIBFUZZER OFF CACHE BOOL "")
 set(COMPILER_RT_BUILD_PROFILE OFF CACHE BOOL "")
@@ -14,17 +16,14 @@ set(COMPILER_RT_BUILD_XRAY OFF CACHE BOOL "")
 set(COMPILER_RT_DEFAULT_TARGET_ONLY ON CACHE BOOL "")
 set(LIBCXXABI_BAREMETAL ON CACHE BOOL "")
 set(LIBCXXABI_ENABLE_ASSERTIONS OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS ON CACHE BOOL "")
 set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_STATIC ON CACHE BOOL "")
 set(LIBCXXABI_ENABLE_STATIC_UNWINDER ON CACHE BOOL "")
 set(LIBCXXABI_ENABLE_THREADS OFF CACHE BOOL "")
 set(LIBCXXABI_USE_COMPILER_RT ON CACHE BOOL "")
-set(LIBCXX_ENABLE_EXCEPTIONS ON CACHE BOOL "")
 set(LIBCXX_ENABLE_FILESYSTEM OFF CACHE STRING "")
 set(LIBCXX_ENABLE_MONOTONIC_CLOCK OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")
-set(LIBCXX_ENABLE_RTTI ON CACHE BOOL "")
 set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_STATIC ON CACHE BOOL "")
 set(LIBCXX_ENABLE_THREADS OFF CACHE BOOL "")
diff --git a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
index 5ddfa15d77a49..4a059c0a1efb5 100644
--- a/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv7Thumb-no-exceptions.cmake
@@ -1,7 +1,6 @@
 set(CMAKE_CXX_COMPILER_TARGET "armv7l-linux-gnueabihf" CACHE STRING "")
 set(CMAKE_CXX_FLAGS "-mthumb" CACHE STRING "")
 set(CMAKE_C_FLAGS "-mthumb" CACHE STRING "")
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
index b0a53484961e4..1c06ff7c8fbfa 100644
--- a/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Armv8Thumb-no-exceptions.cmake
@@ -1,7 +1,6 @@
 set(CMAKE_CXX_COMPILER_TARGET "armv8l-linux-gnueabihf" CACHE STRING "")
 set(CMAKE_CXX_FLAGS "-mthumb" CACHE STRING "")
 set(CMAKE_C_FLAGS "-mthumb" CACHE STRING "")
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
 set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-no-exceptions.cmake b/libcxx/cmake/caches/Generic-no-exceptions.cmake
index c5b2ffd0a36c8..e357bd2ea345b 100644
--- a/libcxx/cmake/caches/Generic-no-exceptions.cmake
+++ b/libcxx/cmake/caches/Generic-no-exceptions.cmake
@@ -1,5 +1,4 @@
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 
 # Speed up the CI
 set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
diff --git a/libcxx/cmake/caches/Generic-no-rtti.cmake b/libcxx/cmake/caches/Generic-no-rtti.cmake
index d080360fe76d7..dd9b876615a7c 100644
--- a/libcxx/cmake/caches/Generic-no-rtti.cmake
+++ b/libcxx/cmake/caches/Generic-no-rtti.cmake
@@ -1,7 +1,5 @@
-set(LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_RTTI OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_RTTI OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 
 # Speed up the CI
 set(LIBCXX_TEST_PARAMS "enable_modules=clang" CACHE STRING "")
diff --git a/libcxx/cmake/caches/NVPTX.cmake b/libcxx/cmake/caches/NVPTX.cmake
index 46fa6e7a1be08..f57904f1ff79c 100644
--- a/libcxx/cmake/caches/NVPTX.cmake
+++ b/libcxx/cmake/caches/NVPTX.cmake
@@ -1,12 +1,14 @@
+# Configuration options for the runtimes.
+set(RUNTIMES_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(RUNTIMES_ENABLE_RTTI OFF CACHE BOOL "")
+
 # Configuration options for libcxx.
 set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_LOCALIZATION ON CACHE BOOL "")
 set(LIBCXX_ENABLE_MONOTONIC_CLOCK ON CACHE BOOL "")
 set(LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS ON CACHE BOOL "")
 set(LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")
-set(LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
 set(LIBCXX_ENABLE_STATIC ON CACHE BOOL "")
@@ -21,7 +23,6 @@ set(RUNTIMES_USE_LIBC "llvm-libc" CACHE STRING "")
 
 # Configuration options for libcxxabi.
 set(LIBCXXABI_BAREMETAL ON CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_THREADS OFF CACHE BOOL "")
diff --git a/libcxx/docs/Modules.rst b/libcxx/docs/Modules.rst
index c8f3e6194fd84..68f0386df6ae2 100644
--- a/libcxx/docs/Modules.rst
+++ b/libcxx/docs/Modules.rst
@@ -48,15 +48,10 @@ What works
    * ``LIBCXX_ENABLE_FILESYSTEM``
    * ``LIBCXX_ENABLE_RANDOM_DEVICE``
    * ``LIBCXX_ENABLE_UNICODE``
-   * ``LIBCXX_ENABLE_EXCEPTIONS`` [#note-no-windows]_
+   * ``RUNTIMES_ENABLE_EXCEPTIONS``
 
  * A C++20 based extension
 
-.. note::
-
-   .. [#note-no-windows] This configuration will probably not work on Windows
-                         due to hard-coded compilation flags.
-
 Some of the current limitations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/libcxx/docs/VendorDocumentation.rst b/libcxx/docs/VendorDocumentation.rst
index 7eba598909a74..0ea66b25a0000 100644
--- a/libcxx/docs/VendorDocumentation.rst
+++ b/libcxx/docs/VendorDocumentation.rst
@@ -227,18 +227,7 @@ General purpose options
 
   Additional libraries libc++ is linked to which can be provided in cache.
 
-.. option:: LIBCXX_ENABLE_EXCEPTIONS:BOOL
-
-  **Default**: ``ON``
-
-  Build libc++ with exception support.
-
-.. option:: LIBCXX_ENABLE_RTTI:BOOL
-
-  **Default**: ``ON``
-
-  Build libc++ with run time type information.
-  This option may only be set to OFF when LIBCXX_ENABLE_EXCEPTIONS=OFF.
+.. TODO: Where should we document the runtimes build options?
 
 .. option:: LIBCXX_INCLUDE_TESTS:BOOL
 
diff --git a/libcxx/lib/abi/CMakeLists.txt b/libcxx/lib/abi/CMakeLists.txt
index 8f277aad2dcd5..d848df424d5ba 100644
--- a/libcxx/lib/abi/CMakeLists.txt
+++ b/libcxx/lib/abi/CMakeLists.txt
@@ -53,7 +53,7 @@ cxx_abi_list_identifier(abi_list_identifier
   "${LIBCXX_CXX_ABI}"
   "${LIBCXX_ABI_VERSION}"
   "${LIBCXX_ABI_UNSTABLE}"
-  "${LIBCXX_ENABLE_EXCEPTIONS}"
+  "${RUNTIMES_ENABLE_EXCEPTIONS}"
   "${LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS}"
 )
 
diff --git a/libcxx/modules/CMakeLists.txt.in b/libcxx/modules/CMakeLists.txt.in
index 9fef16e9cefde..421f9dcd00669 100644
--- a/libcxx/modules/CMakeLists.txt.in
+++ b/libcxx/modules/CMakeLists.txt.in
@@ -43,10 +43,6 @@ target_sources(std
 
 target_include_directories(std SYSTEM PUBLIC @LIBCXX_CONFIGURED_INCLUDE_DIRS@)
 
-if (NOT @LIBCXX_ENABLE_EXCEPTIONS@)
-  target_compile_options(std PUBLIC -fno-exceptions)
-endif()
-
 target_compile_options(std
   PUBLIC
     -nostdinc++
@@ -58,7 +54,7 @@ target_compile_options(std
     -Wno-reserved-user-defined-literal
 )
 target_link_options(std PUBLIC -nostdlib++ -Wl,-rpath, at LIBCXX_LIBRARY_DIR@ -L at LIBCXX_LIBRARY_DIR@)
-target_link_libraries(std c++)
+target_link_libraries(std c++ runtimes-language-flags)
 set_target_properties(std
   PROPERTIES
     OUTPUT_NAME   "c++std"
@@ -74,10 +70,6 @@ target_sources(std.compat
 
 target_include_directories(std.compat SYSTEM PUBLIC @LIBCXX_CONFIGURED_INCLUDE_DIRS@)
 
-if (NOT @LIBCXX_ENABLE_EXCEPTIONS@)
-  target_compile_options(std.compat PUBLIC -fno-exceptions)
-endif()
-
 target_compile_options(std.compat
   PUBLIC
     -nostdinc++
diff --git a/libcxx/test/CMakeLists.txt b/libcxx/test/CMakeLists.txt
index f4e577aed57de..ba5086e41eb33 100644
--- a/libcxx/test/CMakeLists.txt
+++ b/libcxx/test/CMakeLists.txt
@@ -70,11 +70,11 @@ else()
   set(_libcxx_benchmark_mode "no")
 endif()
 
-if (NOT LIBCXX_ENABLE_EXCEPTIONS)
+if (NOT RUNTIMES_ENABLE_EXCEPTIONS)
   serialize_lit_param(SERIALIZED_LIT_PARAMS enable_exceptions False)
 endif()
 
-if (NOT LIBCXX_ENABLE_RTTI)
+if (NOT RUNTIMES_ENABLE_RTTI)
   serialize_lit_param(SERIALIZED_LIT_PARAMS enable_rtti False)
 endif()
 
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index 57ecf1e49dbf2..352f7f8160314 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -617,8 +617,7 @@ aarch64)
 aarch64-no-exceptions)
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AArch64.cmake" \
-                   -DLIBCXX_ENABLE_EXCEPTIONS=OFF \
-                   -DLIBCXXABI_ENABLE_EXCEPTIONS=OFF
+                   -DRUNTIMES_ENABLE_EXCEPTIONS=OFF
     check-runtimes
 ;;
 # Aka Armv8 32 bit
@@ -650,10 +649,9 @@ armv7m-picolibc)
 armv7m-picolibc-no-exceptions)
     test-armv7m-picolibc \
         -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv7M-picolibc.cmake" \
-        -DLIBCXXABI_ENABLE_EXCEPTIONS=OFF \
-        -DLIBCXXABI_ENABLE_STATIC_UNWINDER=OFF \
-        -DLIBCXX_ENABLE_EXCEPTIONS=OFF \
-        -DLIBCXX_ENABLE_RTTI=OFF
+        -DRUNTIMES_ENABLE_EXCEPTIONS=OFF \
+        -DRUNTIMES_ENABLE_RTTI=OFF \
+        -DLIBCXXABI_ENABLE_STATIC_UNWINDER=OFF
 ;;
 clang-cl-dll)
     clean
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index 3dabd87b9c587..055df81a60856 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -46,9 +46,6 @@ include(CMakeDependentOption)
 include(HandleCompilerRT)
 
 # Define options.
-option(LIBCXXABI_ENABLE_EXCEPTIONS
-  "Provide support for exceptions in the runtime.
-  When disabled, libc++abi does not support stack unwinding and other exceptions-related features." ON)
 option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
@@ -325,19 +322,6 @@ add_definitions(-D_LIBCPP_BUILDING_LIBRARY)
 # Get feature flags.
 add_compile_flags_if_supported(-fstrict-aliasing)
 
-# Exceptions
-if (LIBCXXABI_ENABLE_EXCEPTIONS)
-  # Catches C++ exceptions only and tells the compiler to assume that extern C
-  # functions never throw a C++ exception.
-  add_compile_flags_if_supported(-EHsc)
-  # Do we really need to be run through the C compiler ?
-  add_c_compile_flags_if_supported(-funwind-tables)
-else()
-  add_compile_flags_if_supported(-fno-exceptions)
-  add_compile_flags_if_supported(-EHs-)
-  add_compile_flags_if_supported(-EHa-)
-endif()
-
 # Assert
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 if (LIBCXXABI_ENABLE_ASSERTIONS)
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index 38a54b16278a7..b5a6920f51962 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -25,7 +25,7 @@ if (LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS)
   )
 endif()
 
-if (LIBCXXABI_ENABLE_EXCEPTIONS)
+if (RUNTIMES_ENABLE_EXCEPTIONS)
   list(APPEND LIBCXXABI_SOURCES
     cxa_exception.cpp
     cxa_personality.cpp
@@ -258,7 +258,7 @@ endif()
 # whether the exception runtime machinery is provided.
 reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/std-exceptions.exp")
 
-if (LIBCXXABI_ENABLE_EXCEPTIONS)
+if (RUNTIMES_ENABLE_EXCEPTIONS)
   reexport_symbols("${CMAKE_CURRENT_SOURCE_DIR}/../lib/itanium-exceptions.exp")
 
   if ("${CMAKE_OSX_ARCHITECTURES}" MATCHES "^(armv6|armv7|armv7s)$")
diff --git a/libcxxabi/test/CMakeLists.txt b/libcxxabi/test/CMakeLists.txt
index 9eabfb08240b6..dcab5ba42ae56 100644
--- a/libcxxabi/test/CMakeLists.txt
+++ b/libcxxabi/test/CMakeLists.txt
@@ -66,7 +66,7 @@ set(SERIALIZED_LIT_PARAMS "# Lit parameters serialized here for llvm-lit to pick
 
 serialize_lit_string_param(SERIALIZED_LIT_PARAMS compiler "${CMAKE_CXX_COMPILER}")
 
-if (NOT LIBCXXABI_ENABLE_EXCEPTIONS)
+if (NOT RUNTIMES_ENABLE_EXCEPTIONS)
   serialize_lit_param(SERIALIZED_LIT_PARAMS enable_exceptions False)
 endif()
 
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
index d3280a5867dec..ca29141a2d647 100644
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -33,6 +33,9 @@ list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/../llvm/cmake/modules"
 )
 
+# Include options to configure the runtime projects
+include(cmake/Modules/LanguageFlags.cmake)
+
 # We order libraries to mirror roughly how they are layered, except that compiler-rt can depend
 # on libc++, so we put it after.
 set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;libclc;openmp;offload")
diff --git a/runtimes/cmake/Modules/HandleFlags.cmake b/runtimes/cmake/Modules/HandleFlags.cmake
index 1c744a0aa0ae7..148260013a9cd 100644
--- a/runtimes/cmake/Modules/HandleFlags.cmake
+++ b/runtimes/cmake/Modules/HandleFlags.cmake
@@ -1,3 +1,9 @@
+#
+# This file defines legacy functions to detect and set compiler flags
+# used throughout the runtimes. Please move away from using these
+# functions in favour of using interface targets (see for example
+# LanguageFlags.cmake).
+#
 
 include(CheckCXXCompilerFlag)
 
diff --git a/runtimes/cmake/Modules/LanguageFlags.cmake b/runtimes/cmake/Modules/LanguageFlags.cmake
new file mode 100644
index 0000000000000..62060c4063d87
--- /dev/null
+++ b/runtimes/cmake/Modules/LanguageFlags.cmake
@@ -0,0 +1,46 @@
+#
+# Configure CMake flags related to C++ language.
+#
+# This file defines an interface target named `runtimes-language-flags` which
+# can be linked against to get the language-related flags configured here.
+#
+
+add_library(runtimes-language-flags INTERFACE)
+
+# Exceptions
+option(RUNTIMES_ENABLE_EXCEPTIONS
+  "Whether to enable exceptions (-fexceptions) when building the runtimes.
+   This also controls whether the runtimes provide support for exceptions,
+   for example stack unwinding and other exceptions-related features."
+  ON)
+if (RUNTIMES_ENABLE_EXCEPTIONS)
+  if (MSVC)
+    # Catches C++ exceptions only and tells the compiler to assume that extern C
+    # functions never throw a C++ exception.
+    target_compile_options(runtimes-language-flags INTERFACE "-EHsc")
+  endif()
+else()
+  if (MSVC)
+    target_compile_options(runtimes-language-flags INTERFACE "-EHs-" "-EHa-")
+  else()
+    target_compile_options(runtimes-language-flags INTERFACE "-fno-exceptions")
+  endif()
+endif()
+
+# RTTI
+option(RUNTIMES_ENABLE_RTTI
+  "Whether to enable runtime type information (-frtti) when building the runtimes.
+   Note that building the runtimes with support for exceptions requires RTTI to
+   be enabled."
+  ON)
+if (NOT RUNTIMES_ENABLE_RTTI AND RUNTIMES_ENABLE_EXCEPTIONS)
+  message(FATAL_ERROR "The runtimes cannot be built with exceptions enabled but RTTI disabled, since "
+                      "that configuration is broken. See https://llvm.org/PR66117 for details.")
+endif()
+if (NOT RUNTIMES_ENABLE_RTTI)
+  if (MSVC)
+    target_compile_options(runtimes-language-flags INTERFACE -GR-)
+  else()
+    target_compile_options(runtimes-language-flags INTERFACE "-fno-rtti")
+  endif()
+endif()

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