ci: add MemorySanitizer CI job

Add build_msan_toolchain.sh to produce a tarball containing an
MSan-instrumented libc++/libc++abi/libunwind toolchain, and add an msan
CI job that downloads the tarball and runs the test suite under MSan.

Also add USE_MSAN CMake option that disables conflicting sanitizers,
switches to lld, and propagates -fsanitize=memory to the shared library
and fuzz_driver targets.

CMakeLists.txt

@@ -49,6 +49,18 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
         ${LLVM_OBJCOPY}
         CACHE FILEPATH "path to objcopy binary" FORCE)
   endif()
+  if(USE_MSAN)
+    find_program(LLD_LINKER lld)
+    if(LLD_LINKER)
+      set(CMAKE_LINKER_TYPE
+          "LLD"
+          CACHE STRING "Use LLD linker" FORCE)
+      set(CMAKE_LINKER
+          ${LLD_LINKER}
+          CACHE FILEPATH "path to linker binary" FORCE)
+      add_link_options("-fuse-ld=lld")
+    endif()
+  endif()
 endif()
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
@@ -103,6 +115,8 @@ option(USE_SIMD_FALLBACK
 
 option(DISABLE_TSAN "Disable TSAN" OFF)
 
+option(USE_MSAN "Build with MemorySanitizer (disables ASan/UBSan)" OFF)
+
 # This is encouraged according to
 # https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq
 include_directories(SYSTEM ${CMAKE_CURRENT_SOURCE_DIR}/third_party/valgrind)
@@ -232,8 +246,10 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   target_compile_definitions(conflict_set_main PRIVATE ENABLE_MAIN)
   target_link_libraries(conflict_set_main PRIVATE nanobench)
 
-  if(NOT APPLE)
-    # libfuzzer target, to generate/manage corpus
+  if(NOT APPLE AND NOT USE_MSAN)
+    # libfuzzer target, to generate/manage corpus. MSan requires an instrumented
+    # libfuzzer runtime, which is not shipped with the compiler, so skip this
+    # target when building with MSan.
     set(FUZZ_FLAGS "-fsanitize=fuzzer-no-link,address,undefined")
     include(CheckCXXCompilerFlag)
     cmake_push_check_state()
@@ -257,8 +273,13 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   add_executable(fuzz_driver ConflictSet.cpp FuzzTestDriver.cpp)
   target_compile_options(fuzz_driver PRIVATE ${TEST_FLAGS})
   if(NOT CMAKE_CROSSCOMPILING)
-    target_compile_options(fuzz_driver PRIVATE -fsanitize=address,undefined)
-    target_link_options(fuzz_driver PRIVATE -fsanitize=address,undefined)
+    if(USE_MSAN)
+      target_compile_options(fuzz_driver PRIVATE -fsanitize=memory)
+      target_link_options(fuzz_driver PRIVATE -fsanitize=memory)
+    else()
+      target_compile_options(fuzz_driver PRIVATE -fsanitize=address,undefined)
+      target_link_options(fuzz_driver PRIVATE -fsanitize=address,undefined)
+    endif()
   endif()
   target_compile_definitions(fuzz_driver PRIVATE ENABLE_FUZZ)
   target_include_directories(fuzz_driver
@@ -269,7 +290,9 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   endforeach()
 
   # tsan tests
-  if(NOT CMAKE_CROSSCOMPILING AND NOT DISABLE_TSAN)
+  if(NOT CMAKE_CROSSCOMPILING
+     AND NOT DISABLE_TSAN
+     AND NOT USE_MSAN)
     add_executable(tsan_driver ConflictSet.cpp FuzzTestDriver.cpp)
     target_compile_options(tsan_driver PRIVATE ${TEST_FLAGS} -fsanitize=thread)
     target_link_options(tsan_driver PRIVATE -fsanitize=thread)
@@ -491,6 +514,11 @@ target_include_directories(
   PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
          $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}>)
 
+if(USE_MSAN)
+  target_compile_options(${PROJECT_NAME} PUBLIC -fsanitize=memory)
+  target_link_options(${PROJECT_NAME} PUBLIC -fsanitize=memory)
+endif()
+
 set_target_properties(
   ${PROJECT_NAME} PROPERTIES VERSION ${PROJECT_VERSION}
                              SOVERSION ${PROJECT_VERSION_MAJOR})