Link sanitizers with libgcc on Linux, allow undefined symbols

Author: edymtt

utils/swift_build_support/swift_build_support/products/llvm.py

@@ -217,6 +217,22 @@ def should_build(self, host_target):
         # LLVM will always be built in part
         return True
 
+    @classmethod
+    def compute_cmake_args_for_runtimes(cls, host_target):
+        # Swift expects the old layout for the runtime directory
+        args_for_runtime = '-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR:BOOL=OFF'
+
+        if host_target.startswith('linux'):
+            # This preserves the behaviour we had when using
+            # LLVM_BUILD_EXTERNAL COMPILER_RT --
+            # that is, having the linker not complaing if symbols used
+            # by TSan are undefined (namely the ones for Blocks Runtime)
+            # In the long term, we want to remove this and
+            # build Blocks Runtime before LLVM
+            args_for_runtime += ';-DSANITIZER_COMMON_LINK_FLAGS:STRING=-Wl,-z,undefs'
+
+        return args_for_runtime
+
     def build(self, host_target):
         """build() -> void
 
@@ -291,7 +307,9 @@ def build(self, host_target):
         llvm_cmake_options.define('LLVM_INCLUDE_DOCS:BOOL', 'TRUE')
         llvm_cmake_options.define('LLVM_ENABLE_LTO:STRING', self.args.lto_type)
         llvm_cmake_options.define('COMPILER_RT_INTERCEPT_LIBDISPATCH', 'ON')
-        llvm_cmake_options.define('RUNTIMES_CMAKE_ARGS', '-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR:BOOL=OFF')
+        llvm_cmake_options.define(
+            'RUNTIMES_CMAKE_ARGS',
+            LLVM.compute_cmake_args_for_runtimes(host_target))
 
         if self.args.build_embedded_stdlib and system() == "Darwin":
             # Ask for Mach-O cross-compilation builtins (for Embedded Swift)
@@ -306,8 +324,6 @@ def build(self, host_target):
                 not self.is_cross_compile_target(host_target):
             llvm_enable_runtimes.append('compiler-rt')
             build_targets.append("runtimes")
-            # This is needed to build correctly TSan under Linux
-            llvm_cmake_options.define('COMPILER_RT_USE_BUILTINS_LIBRARY', 'ON')
 
         if self.args.build_clang_tools_extra:
             llvm_enable_projects.append('clang-tools-extra')