Date: Thu, 20 Sep 2018 12:02:46 -0700 From: Mark Millard <marklmi@yahoo.com> To: FreeBSD Toolchain <freebsd-toolchain@freebsd.org> Subject: Re: svn commit: r480180 - in head/devel: . xtoolchain-llvm70 [FYI: 2 ABI changes compared to older clangs] Message-ID: <4B81760C-251A-4DCA-B322-495E3A535A38@yahoo.com>
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When I looked at http://releases.llvm.org/7.0.0/tools/clang/docs/ReleaseNotes.html I found notes about 2 ABI breakages compared to clang 6 and before: QUOTE • Clang’s handling of the GCC packed class attribute in C++ has been fixed to apply only to non-static data members and not to base classes. This fixes an ABI difference between Clang and GCC, but creates an ABI difference between Clang 7 and earlier versions. The old behavior can be restored by setting -fclang-abi-compat to 6 or lower. • Clang implements the proposed resolution of LWG issue 2358, along with the corresponding change to the Itanium C++ ABI, which make classes containing only unnamed non-zero-length bit-fields be considered non-empty. This is an ABI break compared to prior Clang releases, but makes Clang generate code that is ABI-compatible with other compilers. The old behavior can be restored by setting -fclang-abi-compat to 6 or lower. END QUOTE Also it reports: QUOTE libc++ Changes Users that wish to link together translation units built with different versions of libc++’s headers into the same final linked image should define the _LIBCPP_HIDE_FROM_ABI_PER_TU macro to 1 when building those translation units. In a future release, not defining _LIBCPP_HIDE_FROM_ABI_PER_TU to 1 and linking translation units built with different versions of libc++’s headers together may lead to ODR violations and ABI issues. END QUOTE === Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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