[runtimes] Don't try passing --target flags to GCC

When a target triple is specified in CMake via XXX_TARGET_TRIPLE, we tried passing the --target=<...> flag to the compiler. However, not all compilers support that flag (e.g. GCC, which is not a cross-compiler). As a result, setting e.g. LIBCXX_TARGET_TRIPLE=<host-triple> would end up trying to pass --target=<host-triple> to GCC, which breaks everything because the flag isn't even supported. This commit only adds `--target=<...>` & friends to the flags if it is supported by the compiler. One could argue that it's confusing to pass LIBCXX_TARGET_TRIPLE=<...> and have it be ignored. That's correct, and one possibility would be to assert that the requested triple is the same as the host triple when we know the compiler is unable to cross-compile. However, note that this is a pre-existing issue (setting the TARGET_TRIPLE variable never had an influence on the flags passed to the compiler), and also fixing that is starting to look like reimplementing a lot of CMake logic that is already handled with CMAKE_CXX_COMPILER_TARGET. Differential Revision: https://reviews.llvm.org/D106082
intel · Jul 15, 2021 · a59165b · a59165b
1 parent 6596778
commit a59165b
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Showing 6 changed files with 42 additions and 9 deletions.
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
@@ -465,17 +465,17 @@ include(HandleLibcxxFlags)
 add_target_flags_if(LIBCXX_BUILD_32_BITS "-m32")
 
 if(LIBCXX_TARGET_TRIPLE)
-  add_target_flags("--target=${LIBCXX_TARGET_TRIPLE}")
+  add_target_flags_if_supported("--target=${LIBCXX_TARGET_TRIPLE}")
 elseif(CMAKE_CXX_COMPILER_TARGET)
   set(LIBCXX_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBCXX_SYSROOT)
-  add_target_flags("--sysroot=${LIBCXX_SYSROOT}")
+  add_target_flags_if_supported("--sysroot=${LIBCXX_SYSROOT}")
 elseif(CMAKE_SYSROOT)
   set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 if(LIBCXX_GCC_TOOLCHAIN)
-  add_target_flags("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
+  add_target_flags_if_supported("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
 elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
   set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()

diff --git a/libcxx/cmake/Modules/HandleLibcxxFlags.cmake b/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
@@ -121,6 +121,17 @@ macro(add_target_flags_if condition)
   endif()
 endmacro()
 
+# Add all the flags supported by the compiler to all of
+# 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBCXX_COMPILE_FLAGS'
+# and 'LIBCXX_LINK_FLAGS'.
+macro(add_target_flags_if_supported)
+  foreach(flag ${ARGN})
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBCXX_SUPPORTS_${flagname}_FLAG")
+    add_target_flags_if(LIBCXX_SUPPORTS_${flagname}_FLAG ${flag})
+  endforeach()
+endmacro()
+
 # Add a specified list of flags to both 'LIBCXX_COMPILE_FLAGS' and
 # 'LIBCXX_LINK_FLAGS'.
 macro(add_flags)

diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
@@ -258,17 +258,17 @@ include(HandleLibcxxabiFlags)
 add_target_flags_if(LIBCXXABI_BUILD_32_BITS "-m32")
 
 if(LIBCXXABI_TARGET_TRIPLE)
-  add_target_flags("--target=${LIBCXXABI_TARGET_TRIPLE}")
+  add_target_flags_if_supported("--target=${LIBCXXABI_TARGET_TRIPLE}")
 elseif(CMAKE_CXX_COMPILER_TARGET)
   set(LIBCXXABI_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBCXX_GCC_TOOLCHAIN)
-  add_target_flags("--gcc-toolchain=${LIBCXXABI_GCC_TOOLCHAIN}")
+  add_target_flags_if_supported("--gcc-toolchain=${LIBCXXABI_GCC_TOOLCHAIN}")
 elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
   set(LIBCXXABI_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 if(LIBCXXABI_SYSROOT)
-  add_target_flags("--sysroot=${LIBCXXABI_SYSROOT}")
+  add_target_flags_if_supported("--sysroot=${LIBCXXABI_SYSROOT}")
 elseif(CMAKE_SYSROOT)
   set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}")
 endif()

diff --git a/libcxxabi/cmake/Modules/HandleLibcxxabiFlags.cmake b/libcxxabi/cmake/Modules/HandleLibcxxabiFlags.cmake
@@ -123,6 +123,17 @@ macro(add_target_flags_if condition)
   endif()
 endmacro()
 
+# Add all the flags supported by the compiler to all of
+# 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBCXXABI_COMPILE_FLAGS'
+# and 'LIBCXXABI_LINK_FLAGS'.
+macro(add_target_flags_if_supported)
+  foreach(flag ${ARGN})
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBCXXABI_SUPPORTS_${flagname}_FLAG")
+    add_target_flags_if(LIBCXXABI_SUPPORTS_${flagname}_FLAG ${flag})
+  endforeach()
+endmacro()
+
 # Add a specified list of flags to both 'LIBCXXABI_COMPILE_FLAGS' and
 # 'LIBCXXABI_LINK_FLAGS'.
 macro(add_flags)

diff --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
@@ -152,17 +152,17 @@ include(HandleLibunwindFlags)
 add_target_flags_if(LIBUNWIND_BUILD_32_BITS "-m32")
 
 if(LIBUNWIND_TARGET_TRIPLE)
-  add_target_flags("--target=${LIBUNWIND_TARGET_TRIPLE}")
+  add_target_flags_if_supported("--target=${LIBUNWIND_TARGET_TRIPLE}")
 elseif(CMAKE_CXX_COMPILER_TARGET)
   set(LIBUNWIND_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBUNWIND_GCC_TOOLCHAIN)
-  add_target_flags("--gcc-toolchain=${LIBUNWIND_GCC_TOOLCHAIN}")
+  add_target_flags_if_supported("--gcc-toolchain=${LIBUNWIND_GCC_TOOLCHAIN}")
 elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
   set(LIBUNWIND_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 if(LIBUNWIND_SYSROOT)
-  add_target_flags("--sysroot=${LIBUNWIND_SYSROOT}")
+  add_target_flags_if_supported("--sysroot=${LIBUNWIND_SYSROOT}")
 elseif(CMAKE_SYSROOT)
   set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}")
 endif()

diff --git a/libunwind/cmake/Modules/HandleLibunwindFlags.cmake b/libunwind/cmake/Modules/HandleLibunwindFlags.cmake
@@ -124,6 +124,17 @@ macro(add_target_flags_if condition)
   endif()
 endmacro()
 
+# Add all the flags supported by the compiler to all of
+# 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBUNWIND_COMPILE_FLAGS'
+# and 'LIBUNWIND_LINK_FLAGS'.
+macro(add_target_flags_if_supported)
+  foreach(flag ${ARGN})
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBUNWIND_SUPPORTS_${flagname}_FLAG")
+    add_target_flags_if(LIBUNWIND_SUPPORTS_${flagname}_FLAG ${flag})
+  endforeach()
+endmacro()
+
 # Add a specified list of flags to both 'LIBUNWIND_COMPILE_FLAGS' and
 # 'LIBUNWIND_LINK_FLAGS'.
 macro(add_flags)