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[Flang-RT] Fix GCC 15.1 Fortran Runtime libstdc++ Undefined Symbols (#157385)

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Define the _GLIBCXX_THROW_OR_ABORT macro to not use its _EXC argument. _EXC may contain an expression constructing an std::exception object which is non-inline and therefore require a link dependency on the libstdc++ runtime. In -fno-exceptions builds it is typically optimized away when appearing in unreachable code, but is still present when compiling with -O0 when compiling with Clang.

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Co-authored-by: Michael Kruse <github@meinersbur.de>
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Patrick Simmons 2025-10-16 11:24:06 -05:00 committed by GitHub
parent 8fa4a1029c
commit be3aa41ecc
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21
flang-rt/cmake/modules/AddFlangRT.cmake
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@ -231,6 +231,27 @@ function (add_flangrt_library name)
target_compile_options(${tgtname} PRIVATE
$<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions -fno-rtti -funwind-tables -fno-asynchronous-unwind-tables>
)
# We define our own _GLIBCXX_THROW_OR_ABORT here because, as of
# GCC 15.1, the libstdc++ header file <bits/c++config> uses
# (void)_EXC in its definition of _GLIBCXX_THROW_OR_ABORT to
# silence a warning.
#
# This is a problem for us because some compilers, specifically
# clang, do not always optimize away that (void)_EXC even though
# it is unreachable since it occurs after a call to
# _builtin_abort(). Because _EXC is typically an object derived
# from std::exception, (void)_EXC, when not optimized away,
# calls std::exception methods defined in the libstdc++ shared
# library. We shouldn't link against that library since our
# build version may conflict with the version used by a hybrid
# Fortran/C++ application.
#
# Redefining _GLIBCXX_THROW_OR_ABORT in this manner is not
# supported by the maintainers of libstdc++, so future changes
# to libstdc++ may require future changes to this build script
# and/or future changes to the Fortran runtime source code.
target_compile_options(${tgtname} PUBLIC "-D_GLIBCXX_THROW_OR_ABORT(_EXC)=(__builtin_abort())")
elseif (MSVC)
target_compile_options(${tgtname} PRIVATE
$<$<COMPILE_LANGUAGE:CXX>:/EHs-c- /GR->