[compiler-rt] [test] Fix using toolchains that rely on Clang default configs

compiler-rt/CMakeLists.txt

@@ -44,6 +44,22 @@ include(CompilerRTUtils)
 include(CMakeDependentOption)
 include(GetDarwinLinkerVersion)
 
+include(CheckCXXCompilerFlag)
+
+# Check if we can compile with --no-default-config, or if that omits a config
+# file that is essential for the toolchain to work properly.
+#
+# Using CMAKE_REQUIRED_FLAGS to make sure the flag is used both for compilation
+# and for linking.
+#
+# Doing this test early on, to see if the flag works on the toolchain
+# out of the box. Later on, we end up adding -nostdlib and similar flags
+# to all test compiles, which easily can give false positives on this test.
+set(OLD_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
+set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --no-default-config")
+check_cxx_compiler_flag("" COMPILER_RT_HAS_NO_DEFAULT_CONFIG_FLAG)
+set(CMAKE_REQUIRED_FLAGS "${OLD_CMAKE_REQUIRED_FLAGS}")
+
 option(COMPILER_RT_BUILD_BUILTINS "Build builtins" ON)
 mark_as_advanced(COMPILER_RT_BUILD_BUILTINS)
 option(COMPILER_RT_DISABLE_AARCH64_FMV "Disable AArch64 Function Multi Versioning support" OFF)

compiler-rt/test/CMakeLists.txt

@@ -12,6 +12,8 @@ pythonize_bool(COMPILER_RT_ENABLE_INTERNAL_SYMBOLIZER)
 
 pythonize_bool(COMPILER_RT_HAS_AARCH64_SME)
 
+pythonize_bool(COMPILER_RT_HAS_NO_DEFAULT_CONFIG_FLAG)
+
 configure_compiler_rt_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.common.configured.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.common.configured)

compiler-rt/test/lit.common.cfg.py

@@ -993,7 +993,11 @@ def is_windows_lto_supported():
 # default configs for the test runs. In particular, anything hardening
 # related is likely to cause issues with sanitizer tests, because it may
 # preempt something we're looking to trap (e.g. _FORTIFY_SOURCE vs our ASAN).
-config.environment["CLANG_NO_DEFAULT_CONFIG"] = "1"
+#
+# Only set this if we know we can still build for the target while disabling
+# default configs.
+if config.has_no_default_config_flag:
+    config.environment["CLANG_NO_DEFAULT_CONFIG"] = "1"
 
 if config.has_compiler_rt_libatomic:
   base_lib = os.path.join(config.compiler_rt_libdir, "libclang_rt.atomic%s.so"

compiler-rt/test/lit.common.configured.in

@@ -53,6 +53,7 @@ set_default("test_standalone_build_libs", @COMPILER_RT_TEST_STANDALONE_BUILD_LIB
 set_default("has_compiler_rt_libatomic", @COMPILER_RT_BUILD_STANDALONE_LIBATOMIC_PYBOOL@)
 set_default("aarch64_sme", @COMPILER_RT_HAS_AARCH64_SME_PYBOOL@)
 set_default("darwin_linker_version", "@COMPILER_RT_DARWIN_LINKER_VERSION@")
+set_default("has_no_default_config_flag", @COMPILER_RT_HAS_NO_DEFAULT_CONFIG_FLAG_PYBOOL@)
 # True iff the test suite supports ignoring the test compiler's runtime library path
 # and using `config.compiler_rt_libdir` instead. This only matters when the runtime
 # library paths differ.