Bug 862420 – =llvm-runtimes/libcxxabi-14.0.6 fails to compile with < GCC 11 (incomplete C++20 support) with: ../include/c++/v1/__bit/bit_cast.h:31:38: error: expected primary-expression before ‘,’ token

• Status: RESOLVED WONTFIX
• Product: Gentoo Linux

[Description tt_1 2022-07-31 05:38:29 UTC]

Created attachment 795940 [details]
compressed build log

emerge -pv libcxx

[ebuild  N     ] sys-libs/libcxxabi-14.0.6::gentoo  USE="libunwind -static-libs -test -verify-sig" 0 KiB
[ebuild  N     ] sys-libs/libcxx-14.0.6::gentoo  USE="(libcxxabi) libunwind -static-libs -test -verify-sig" 0 KiB



from the build log:

FAILED: libcxxabi/src/CMakeFiles/cxxabi_shared.dir/cxa_default_handlers.cpp.o 
/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
In file included from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__compare/strong_order.h:12,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__compare/weak_order.h:14,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__compare/partial_order.h:14,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__compare/compare_partial_order_fallback.h:13,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/compare:144,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/utility:236,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/__functional_base:26,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/runtimes_build-.arm64/include/c++/v1/memory:808,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/libcxxabi/../libcxx/src/include/atomic_support.h:13,
                 from /var/tmp/portage/sys-libs/libcxxabi-14.0.6/work/libcxxabi/src/cxa_default_handlers.cpp:19:
/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);
      |                                      ^


the full and compressed build.log is attached

[Comment 1 tt_1 2022-07-31 05:39:15 UTC]

Created attachment 795943 [details]
output of emerge --info

[Comment 2 Sam James 2022-07-31 05:40:26 UTC]

Did it work for you before?

[Comment 3 Sam James 2022-07-31 05:43:53 UTC]

My complete guess is incomplete C++20 support in GCC 10. Does 11 or 12 work?

[Comment 4 tt_1 2022-07-31 06:26:06 UTC]

indeed, it compiles with gcc-11

best course of action is to upstream the bug then?

[Comment 5 Sam James 2022-07-31 06:28:40 UTC]

(In reply to tt_1 from comment #4)
> indeed, it compiles with gcc-11
> 
> best course of action is to upstream the bug then?

Yes please!

[Comment 6 Sam James 2025-02-17 21:05:16 UTC]

Upstream WONTFIX'd it and < GCC 11 is masked (and EOL).