[libcxx] Allow linking against the MSVC static CRT

[mstorsjo]

Summary

This respects the CMAKE_MSVC_RUNTIME_LIBRARY option for selecting
the right CRT to use.

Add a CI configuration that tests building this way.

Based on a patch by Andrew Ng.

The test config files end up accumulating and duplicating a fair
bit of cmake-specific logic here; if preferred, we could also add
that in libcxx/test/CMakeLists.txt and export a few more variables
to cmake-bridge.cfg.in instead.

[Mordante]

This SGTM, but I like to see some feedback of the reviewers more familiar with Windows.

[andrewng]

LGTM, although I slightly prefer my patch where it would be possible to build both the shared and static versions of libcxx. However, this patch is more simple which is good too.

[andrewng]

Actually, whilst looking at D155561, I see what you mean by duplication in the test configs. AFAICT, they only differ in the definitions in the compile_flags. I guess it would be good to somehow avoid all this duplication.

[mstorsjo]

In D155560#4515688, @andrewng wrote:

Actually, whilst looking at D155561, I see what you mean by duplication in the test configs. AFAICT, they only differ in the definitions in the compile_flags. I guess it would be good to somehow avoid all this duplication.

Yep. I don’t mind changing it, either in this patch or as a separate later follow-up, to running this logic in cmake and exporting the variables needed in the test config - I’ll leave that call up to the libcxx maintainers.

In D155560#4515188, @andrewng wrote:

although I slightly prefer my patch where it would be possible to build both the shared and static versions of libcxx. However, this patch is more simple which is good too.

Yeah, this is very simple at least. If strictly needed, we can add options later. But due to the dllimport attributes in headers, you can’t really use a build of both static and shared anyway, unless users define the macro for disabling visibility before including libcxx headers. So with clang-cl, you pretty much need to choose either static or shared, not both. And at that point, the single variable CMAKE_MSVC_RUNTIME_LIBRARY gives enough control anyway.

[andrewng]

although I slightly prefer my patch where it would be possible to build both the shared and static versions of libcxx. However, this patch is more simple which is good too.

Yeah, this is very simple at least. If strictly needed, we can add options later. But due to the dllimport attributes in headers, you can’t really use a build of both static and shared anyway, unless users define the macro for disabling visibility before including libcxx headers.

That's basically how I manually switched between "static" and "shared" builds by disabling the "visibility" since I already had to manually add the include paths for the libcxx headers. Ideally, the clang-cl driver would sort this all out based on selected "runtime" type and use of libcxx. But this support is still missing, along with the issues related to compiler-rt. It's very much DIY at the moment...

[mstorsjo]

In D155560#4518237, @andrewng wrote:

although I slightly prefer my patch where it would be possible to build both the shared and static versions of libcxx. However, this patch is more simple which is good too.

Yeah, this is very simple at least. If strictly needed, we can add options later. But due to the dllimport attributes in headers, you can’t really use a build of both static and shared anyway, unless users define the macro for disabling visibility before including libcxx headers.

That's basically how I manually switched between "static" and "shared" builds by disabling the "visibility" since I already had to manually add the include paths for the libcxx headers. Ideally, the clang-cl driver would sort this all out based on selected "runtime" type and use of libcxx. But this support is still missing, along with the issues related to compiler-rt. It's very much DIY at the moment...

Yep - that's why it's probably best to keep things simple and not add more options than necessary for now. One can configure exactly what one wants anyway by doing two separate builds with LIBCXX_ENABLE_SHARED=OFF and LIBCXX_ENABLE_STATIC=OFF.

[Mordante]

LGTM!

libcxx/CMakeLists.txt

message(FATAL_ERROR "Conflicting options given.
         LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY cannot be specified with
         LIBCXX_ENABLE_ABI_LINKER_SCRIPT")
 endif()
 
 if (LIBCXX_ABI_FORCE_ITANIUM AND LIBCXX_ABI_FORCE_MICROSOFT)
   message(FATAL_ERROR "Only one of LIBCXX_ABI_FORCE_ITANIUM and LIBCXX_ABI_FORCE_MICROSOFT can be specified.")
 endif ()
 
+if (LIBCXX_ENABLE_SHARED AND CMAKE_MSVC_RUNTIME_LIBRARY AND
+    (NOT CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$"))
+  message(WARNING "A static CRT linked into a shared libc++ doesn't work correctly.")
+endif()
+
 #===============================================================================
 # Configure System
 #===============================================================================
 
 # TODO: Projects that depend on libc++ should use LIBCXX_GENERATED_INCLUDE_DIR
 # instead of hard-coding include/c++/v1.
 
 set(LIBCXX_INSTALL_INCLUDE_DIR "${CMAKE_INSTALL_INCLUDEDIR}/c++/v1" CACHE PATH

 endif()
 
 #===============================================================================
 # Setup Compiler Flags
 #===============================================================================
 
 include(HandleLibCXXABI) # Setup the ABI library flags
 
-# FIXME: Remove all debug flags and flags that change which Windows
-# default libraries are linked. Currently we only support linking the
-# non-debug DLLs
-remove_flags("/D_DEBUG" "/MTd" "/MDd" "/MT" "/Md")
-
 # FIXME(EricWF): See the FIXME on LIBCXX_ENABLE_PEDANTIC.
 # Remove the -pedantic flag and -Wno-pedantic and -pedantic-errors
 # so they don't get transformed into -Wno and -errors respectively.
 remove_flags(-Wno-pedantic -pedantic-errors -pedantic)
 
 # Required flags ==============================================================
 function(cxx_add_basic_build_flags target)
 
# all libraries but c++ have to be added in manually.
 
   if (MSVC)
     if (uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
       set(LIB_SUFFIX "d")
     else()
       set(LIB_SUFFIX "")
     endif()
 
-    target_link_libraries(${target} PRIVATE msvcrt${LIB_SUFFIX}) # C runtime startup files
-    target_link_libraries(${target} PRIVATE msvcprt${LIB_SUFFIX}) # C++ standard library. Required for exception_ptr internals.
+    if (NOT CMAKE_MSVC_RUNTIME_LIBRARY OR CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$")
+      set(CRT_LIB "msvcrt")
+      set(CXX_LIB "msvcprt")
+    else()
+      set(CRT_LIB "libcmt")
+      set(CXX_LIB "libcpmt")
+    endif()
+
+    target_link_libraries(${target} PRIVATE ${CRT_LIB}${LIB_SUFFIX}) # C runtime startup files
+    target_link_libraries(${target} PRIVATE ${CXX_LIB}${LIB_SUFFIX}) # C++ standard library. Required for exception_ptr internals.
     # Required for standards-complaint wide character formatting functions
     # (e.g. `printfw`/`scanfw`)
     target_link_libraries(${target} PRIVATE iso_stdio_wide_specifiers)
   endif()
 
   if (ANDROID AND ANDROID_PLATFORM_LEVEL LESS 21)
     target_link_libraries(${target} PUBLIC android_support)
   endif()

libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a DLL, with Clang-cl on Windows.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 dbg_include = ''
-lib_suffix = ''
+runtime_library = '@CMAKE_MSVC_RUNTIME_LIBRARY@'
+
+if runtime_library == '' or runtime_library.endswith('DLL'):
+    crt_lib = 'msvcrt'
+    cxx_lib = 'msvcprt'
+else:
+    crt_lib = 'libcmt'
+    cxx_lib = 'libcpmt'
 
 if '@uppercase_CMAKE_BUILD_TYPE@' == 'DEBUG':
     dbg_include = ' -D_DEBUG -include set_windows_crt_report_mode.h'
-    lib_suffix = 'd'
+    crt_lib += 'd'
+    cxx_lib += 'd'
 
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX' + dbg_include
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nostdlib -L %%{lib} -lc++ -lmsvcrt%s -lmsvcprt%s -loldnames' % (lib_suffix, lib_suffix)
+    '-nostdlib -L %%{lib} -lc++ -l%s -l%s -loldnames' % (crt_lib, cxx_lib)
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
 ))
 
 import os, site
 site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
 import libcxx.test.params, libcxx.test.config
 libcxx.test.config.configure(
     libcxx.test.params.DEFAULT_PARAMETERS,
     libcxx.test.features.DEFAULT_FEATURES,
     config,
     lit_config
 )

libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a DLL, with Clang-cl on Windows. This variant sets _HAS_EXCEPTIONS = 0
 # which removes exception class definitions from the vcruntime.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 dbg_include = ''
-lib_suffix = ''
+runtime_library = '@CMAKE_MSVC_RUNTIME_LIBRARY@'
+
+if runtime_library == '' or runtime_library.endswith('DLL'):
+    crt_lib = 'msvcrt'
+    cxx_lib = 'msvcprt'
+else:
+    crt_lib = 'libcmt'
+    cxx_lib = 'libcpmt'
 
 if '@uppercase_CMAKE_BUILD_TYPE@' == 'DEBUG':
     dbg_include = ' -D_DEBUG -include set_windows_crt_report_mode.h'
-    lib_suffix = 'd'
+    crt_lib += 'd'
+    cxx_lib += 'd'
 
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX -D_HAS_EXCEPTIONS=0' + dbg_include
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nostdlib -L %%{lib} -lc++ -lmsvcrt%s -lmsvcprt%s -loldnames' % (lib_suffix, lib_suffix)
+    '-nostdlib -L %%{lib} -lc++ -l%s -l%s -loldnames' % (crt_lib, cxx_lib)
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
 ))
 
 import os, site
 site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
 import libcxx.test.params, libcxx.test.config
 libcxx.test.config.configure(
     libcxx.test.params.DEFAULT_PARAMETERS,
     libcxx.test.features.DEFAULT_FEATURES,
     config,
     lit_config
 )

libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a static library, with Clang-cl on Windows.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 dbg_include = ''
-lib_suffix = ''
+runtime_library = '@CMAKE_MSVC_RUNTIME_LIBRARY@'
+
+if runtime_library == '' or runtime_library.endswith('DLL'):
+    crt_lib = 'msvcrt'
+    cxx_lib = 'msvcprt'
+else:
+    crt_lib = 'libcmt'
+    cxx_lib = 'libcpmt'
 
 if '@uppercase_CMAKE_BUILD_TYPE@' == 'DEBUG':
     dbg_include = ' -D_DEBUG -include set_windows_crt_report_mode.h'
-    lib_suffix = 'd'
+    crt_lib += 'd'
+    cxx_lib += 'd'
 
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX' + dbg_include
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nostdlib -L %%{lib} -llibc++ -lmsvcrt%s -lmsvcprt%s -loldnames' % (lib_suffix, lib_suffix)
+    '-nostdlib -L %%{lib} -llibc++ -l%s -l%s -loldnames' % (crt_lib, cxx_lib)
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T -- '
 ))
 
 import os, site
 site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
 import libcxx.test.params, libcxx.test.config
 libcxx.test.config.configure(
     libcxx.test.params.DEFAULT_PARAMETERS,
     libcxx.test.features.DEFAULT_FEATURES,
     config,
     lit_config
 )

libcxx/utils/ci/buildkite-pipeline.yml

- label: "Clang-cl (Debug mode)"
       agents:
         queue: "windows"
       retry:
         automatic:
           - exit_status: -1  # Agent was lost
             limit: 2
       timeout_in_minutes: 120
 
+    - label: "Clang-cl (Static CRT)"
+      command: "bash libcxx/utils/ci/run-buildbot clang-cl-static-crt"
+      artifact_paths:
+        - "**/test-results.xml"
+        - "**/*.abilist"
+      agents:
+        queue: "windows"
+      retry:
+        automatic:
+          - exit_status: -1  # Agent was lost
+            limit: 2
+      timeout_in_minutes: 120
+
     - label: "MinGW (DLL, x86_64)"
       command: "bash libcxx/utils/ci/run-buildbot mingw-dll"
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
       agents:
         queue: "windows"
       retry:

libcxx/utils/ci/run-buildbot

 ;;
 clang-cl-debug)
     clean
     generate-cmake-libcxx-win -DLIBCXX_TEST_PARAMS="enable_experimental=False" \
                               -DCMAKE_BUILD_TYPE=Debug
     echo "+++ Running the libc++ tests"
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
 ;;
+clang-cl-static-crt)
+    clean
+    # Test linking a static libc++ with the static CRT ("MultiThreaded" denotes
+    # the static CRT, as opposed to "MultiThreadedDLL" which is the default).
+    generate-cmake-libcxx-win -DLIBCXX_ENABLE_SHARED=OFF \
+                              -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded
+    echo "+++ Running the libc++ tests"
+    ${NINJA} -vC "${BUILD_DIR}" check-cxx
+;;
 mingw-dll)
     clean
     # Explicitly specify the compiler with a triple prefix. The CI
     # environment has got two installations of Clang; the default one
     # defaults to MSVC mode, while there's an installation of llvm-mingw
     # further back in PATH. By calling the compiler with an explicit
     # triple prefix, we use the one that is bundled with a mingw sysroot.
     generate-cmake \