svn commit: r480180 - in head/devel: . xtoolchain-llvm70 [FYI: 2 ABI changes compared to older clangs]

[Mark Millard]

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)