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 =E2=80=A2 Clang=E2=80=99s 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. =E2=80=A2 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++=E2=80=99s 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++=E2=80=99s headers together may lead to = ODR violations and ABI issues. END QUOTE =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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