[runtimes] Properly handle the sysroot/triple/gcc-toolchain

[ldionne]

Summary

In 395271a, I simplified how we handled the target triple for the
runtimes. However, in doing so, we stopped considering the default
in CMAKE_CXX_COMPILER_TARGET, so we'd use the LLVM_DEFAULT_TARGET_TRIPLE
(which is the host triple) even if CMAKE_CXX_COMPILER_TARGET was specified.
This commit fixes that problem and also refactors the code so that it's
easy to see what the default value is.

The fact that nobody seems to have been broken by this makes me think
that perhaps nobody is using CMAKE_CXX_COMPILER_TARGET to specify the
triple -- but it should still work.

[ldionne]

Gentle ping @phosek , this is pretty bad actually, since we currently don't honour building for the target requested by the user. I'd like to fix this ASAP and even merge the fix to release/13.x.

[phosek]

I wonder if we can deprecate LIBCXX_TARGET_TRIPLE, LIBCXX_SYSROOT, and LIBCXX_GCC_TOOLCHAIN (and their libc++abi and libunwind counterparts), and switch to the CMake variables instead? Do those custom variables give us anything?

libcxx/CMakeLists.txt

281–283

This changes the semantics slightly. Previously the values of LIBCXX_TARGET_TRIPLE, LIBCXX_SYSROOT, and LIBCXX_GCC_TOOLCHAIN wouldn't be cached, so if you changed CMAKE_CXX_COMPILER_TARGET, CMAKE_SYSROOT, or CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN those changes would be immediately picked. Now, you'll have to modify LIBCXX_TARGET_TRIPLE, LIBCXX_SYSROOT, and LIBCXX_GCC_TOOLCHAIN instead because any subsequent changes to CMAKE_CXX_COMPILER_TARGET, CMAKE_SYSROOT, or CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN would be ignored.

[ldionne]

In D111672#3071246, @phosek wrote:

I wonder if we can deprecate LIBCXX_TARGET_TRIPLE, LIBCXX_SYSROOT, and LIBCXX_GCC_TOOLCHAIN (and their libc++abi and libunwind counterparts), and switch to the CMake variables instead? Do those custom variables give us anything?

I thought you added those variables for the Bootstrapping build? I'm more than happy to remove them if you don't need them.

libcxx/CMakeLists.txt

281–283

Oh, that's right. It does seem to be more consistent with that we do for other per-project setting, though.

[phosek]

LGTM

[phosek]

In D111672#3073648, @ldionne wrote:

In D111672#3071246, @phosek wrote:

I wonder if we can deprecate LIBCXX_TARGET_TRIPLE, LIBCXX_SYSROOT, and LIBCXX_GCC_TOOLCHAIN (and their libc++abi and libunwind counterparts), and switch to the CMake variables instead? Do those custom variables give us anything?

I thought you added those variables for the Bootstrapping build? I'm more than happy to remove them if you don't need them.

I don't think they should be needed anymore, but it's possible that other parts of the build depend on them. In any case, this can be addressed in a follow up change.

[ldionne]

Cherry-picked to release/13.x as 30c05f43b662ae0365715449a05a5429ed3562d9.

libcxx/CMakeLists.txt

option(LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS
    instead. If you define them in libc++, make sure they are NOT defined in
    libc++abi. Doing otherwise is an ODR violation." OFF)
 # Build libc++abi with libunwind. We need this option to determine whether to
 # link with libunwind or libgcc_s while running the test cases.
 option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
 
 # Target options --------------------------------------------------------------
 option(LIBCXX_BUILD_32_BITS "Build 32 bit libc++." ${LLVM_BUILD_32_BITS})
-set(LIBCXX_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Use alternate target triple.")
-set(LIBCXX_SYSROOT "" CACHE STRING "Use alternate sysroot.")
-set(LIBCXX_GCC_TOOLCHAIN "" CACHE STRING "Use alternate GCC toolchain.")
+
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBCXX_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBCXX_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBCXX_TARGET_TRIPLE "${LIBCXX_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Use alternate target triple.")
+set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}" CACHE STRING "Use alternate sysroot.")
+set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE STRING "Use alternate GCC toolchain.")
 
 # Feature options -------------------------------------------------------------
 option(LIBCXX_ENABLE_EXCEPTIONS "Use exceptions." ON)
 option(LIBCXX_ENABLE_RTTI "Use run time type information." ON)
 option(LIBCXX_ENABLE_THREADS "Build libc++ with support for threads." ON)
 option(LIBCXX_ENABLE_MONOTONIC_CLOCK
   "Build libc++ with support for a monotonic clock.
    This option may only be set to OFF when LIBCXX_ENABLE_THREADS=OFF." ON)

 # Include macros for adding and removing libc++ flags.
 include(HandleLibcxxFlags)
 
 # Target flags ================================================================
 # These flags get added to CMAKE_CXX_FLAGS and CMAKE_C_FLAGS so that
 # 'config-ix' use them during feature checks. It also adds them to both
 # 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'
 add_target_flags_if(LIBCXX_BUILD_32_BITS "-m32")
-
 if(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_if_supported("--sysroot=${LIBCXX_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 if(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()
 
 # Configure compiler.
 include(config-ix)
 
 # Configure coverage options.
 if (LIBCXX_GENERATE_COVERAGE)
   include(CodeCoverage)

libcxxabi/CMakeLists.txt

option(LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS
   "Build libc++abi with definitions for operator new/delete. These are normally
    defined in libc++abi, but it is also possible to define them in libc++, in
    which case the definition in libc++abi should be turned off." ON)
 option(LIBCXXABI_BUILD_32_BITS "Build 32 bit libc++abi." ${LLVM_BUILD_32_BITS})
 option(LIBCXXABI_INCLUDE_TESTS "Generate build targets for the libc++abi unit tests." ${LLVM_INCLUDE_TESTS})
 set(LIBCXXABI_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXXABI_INSTALL_LIBRARY "Install the libc++abi library." ON)
-set(LIBCXXABI_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
-set(LIBCXXABI_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
-set(LIBCXXABI_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
+
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBCXXABI_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBCXXABI_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBCXXABI_TARGET_TRIPLE "${LIBCXXABI_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
+set(LIBCXXABI_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE PATH "GCC toolchain for cross compiling.")
+set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}" CACHE PATH "Sysroot for cross compiling.")
+
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 set(LIBCXXABI_LIBRARY_VERSION "1.0" CACHE STRING
 "Version of libc++abi. This will be reflected in the name of the shared \
 library produced. For example, -DLIBCXXABI_LIBRARY_VERSION=x.y will \
 result in the library being named libc++abi.x.y.dylib, along with the \
 usual symlinks pointing to that.")
 
 # Default to building a shared library so that the default options still test

 # Setup Compiler Flags
 #===============================================================================
 
 # Configure target flags
 add_target_flags_if(LIBCXXABI_BUILD_32_BITS "-m32")
 
 if(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)
+if(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_if_supported("--sysroot=${LIBCXXABI_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 
 # Configure compiler. Must happen after setting the target flags.
 include(config-ix)
 
 if (LIBCXXABI_HAS_NOSTDINCXX_FLAG)
   list(APPEND LIBCXXABI_COMPILE_FLAGS -nostdinc++)
   # cmake 3.14 and above remove system include paths that are explicitly

libunwind/CMakeLists.txt

set(LIBUNWIND_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBUNWIND_INSTALL_LIBRARY "Install the libunwind library." ON)
 cmake_dependent_option(LIBUNWIND_INSTALL_STATIC_LIBRARY
   "Install the static libunwind library." ON
   "LIBUNWIND_ENABLE_STATIC;LIBUNWIND_INSTALL_LIBRARY" OFF)
 cmake_dependent_option(LIBUNWIND_INSTALL_SHARED_LIBRARY
   "Install the shared libunwind library." ON
   "LIBUNWIND_ENABLE_SHARED;LIBUNWIND_INSTALL_LIBRARY" OFF)
-set(LIBUNWIND_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
-set(LIBUNWIND_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
-set(LIBUNWIND_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBUNWIND_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBUNWIND_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBUNWIND_TARGET_TRIPLE "${LIBUNWIND_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
+set(LIBUNWIND_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE PATH "GCC toolchain for cross compiling.")
+set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}" CACHE PATH "Sysroot for cross compiling.")
 set(LIBUNWIND_TEST_LINKER_FLAGS "" CACHE STRING
     "Additional linker flags for test programs.")
 set(LIBUNWIND_TEST_COMPILER_FLAGS "" CACHE STRING
     "Additional compiler flags for test programs.")
 set(LIBUNWIND_TEST_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/test/lit.site.cfg.in" CACHE STRING
   "The path to the Lit testing configuration to use when running the tests.
    If a relative path is provided, it is assumed to be relative to '<monorepo>/libunwind/test/configs'.")
 if (NOT IS_ABSOLUTE "${LIBUNWIND_TEST_CONFIG}")

 # Setup Compiler Flags
 #===============================================================================
 
 # Get required flags.
 add_target_flags_if(LIBUNWIND_BUILD_32_BITS "-m32")
 
 if(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_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_if_supported("--sysroot=${LIBUNWIND_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 
 # Configure compiler.
 include(config-ix)
 
 if (LIBUNWIND_USE_COMPILER_RT AND NOT LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
   list(APPEND LIBUNWIND_LINK_FLAGS "-rtlib=compiler-rt")
 endif()