libcxxabi-14.0.6 fails to compile with: ../include/c++/v1/__bit/bit_cast.h:31:38: error: expected primary-expression before ‘,’ token

[stefson]

hey everyone,

I ran into a compile error when compiling libcxxabi:

[545/563] /usr/bin/aarch64-unknown-linux-gnu-g++ -DHAVE___CXA_THREAD_ATEXIT_IMPL -DLIBCXXABI_USE_LLVM_UNWINDER -D_LIBCPP_BUILDING_LIBRARY -D_LIBCPP_DISABLE_EXTERN_TEMPLATE -D_LIBCXXABI_BUILDING_LIBRARY -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/libcxxabi/include -I/usr/include -I/var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/libcxxabi/../libcxx/src  -O2 -pipe -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wimplicit-fallthrough -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wmisleading-indentation -fdiagnostics-color -fdata-sections  -fPIC -nostdinc++ -Werror=return-type -W -Wall -Wchar-subscripts -Wconversion -Wmismatched-tags -Wmissing-braces -Wunused-function -Wshadow -Wsign-compare -Wsign-conversion -Wstrict-aliasing=2 -Wstrict-overflow=4 -Wunused-parameter -Wunused-variable -Wwrite-strings -Wundef -Wno-suggest-override -Wno-error -pedantic -fstrict-aliasing -D_DEBUG -I/var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1 -std=c++2a -MD -MT libcxxabi/src/CMakeFiles/cxxabi_shared.dir/cxa_default_handlers.cpp.o -MF libcxxabi/src/CMakeFiles/cxxabi_shared.dir/cxa_default_handlers.cpp.o.d -o libcxxabi/src/CMakeFiles/cxxabi_shared.dir/cxa_default_handlers.cpp.o -c /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/libcxxabi/src/cxa_default_handlers.cpp
FAILED: libcxxabi/src/CMakeFiles/cxxabi_shared.dir/cxa_default_handlers.cpp.o 
/var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__bit/bit_cast.h: In function ‘constexpr _ToType std::__1::bit_cast(const _FromType&)’:
/var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__bit/bit_cast.h:31:38: error: expected primary-expression before ‘,’ token
   31 |     return __builtin_bit_cast(_ToType, __from);
      |   

compressed build.log: build.log.gz

[thesamesam]

Originally reported downstream in Gentoo by OP at #56828.

The bug is for w/ GCC 10, 11 is fine.

[stefson]

the issue was first detected on aarch64, but happens as well on amd64 hardware.

my toolchain is gcc-10 based, and it seems this is an issue here for unknown reasons. libcxxabi does compile if using a gcc-11 based toolchain.

[mrjoel]

I'm running into this as well, using default GCC 10 from Debian. In some quick tag checking, I get build failures starting with llvmorg-14.0.0-rc1, but llvmorg-13.0.1 builds correctly