[MacPorts] #62330: clang-5.0 - clang-11: add emulated_tls functionality to compiler_rt

[MacPorts]

#62330: clang-5.0 - clang-11: add emulated_tls functionality to compiler_rt
-------------------------+-------------------------------------------------
 Reporter:  kencu        |      Owner:  (none)
     Type:  defect       |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:               |       Port:  libcxx clang-5.0 clang-6.0
                         |  clang-7.0 clang-8.0 clang-9.0 clang-10 clang-11
                         |  clang-devel
-------------------------+-------------------------------------------------
 To support {{{thread_local_storage}}} in c++ software, I added the
 required emulated_tls bits directly into {{{libc++abi.dylib}}}.
 {{{libc++abi.dylib}}} uses these emulated_tls functions, and copying it
 into {{{libc++abi.dylib}}} and leaving it there worked nicely to fill that
 need.

 That also allowed all c++ software to find the needed emulated_tls
 symbols, as they all link against libc++abi.dylib automatically.

 However, this does not allow "C" software to find the emulated_tls symbols
 anywhere, as "C" software does not automatically link against
 {{{libc++abi.dylib}}}.

 There have been very rare build failures for this reason, and I have until
 now worked around them in other ways.

 Upstream clang embeds the emulated_tls functions in compiler_rt.a, and
 they are therefore linked into all builds automatically. The emulated_tls
 functions are not automatically added to {{{compiler_rt.a}}} on Darwin,
 because Darwin >= 10.7 uses a different TLS system (tlv_*).

 To support "C" software that uses TLS on < 10.7, you can force it to link
 against {{{libc++abi.dylib}}} (abomination, but works to find the
 symblols), or I can rewrite the compiler_rt cmake build scripts to add the
 emulated_tls symbols to compiler_rt.a on < 10.7.

 The latter is no doubt the better thing, and it is exactly what upstream
 does on all the other systems without system TLS functionality, or without
 emulated_tls functionality in libc.

 I'm not (at the moment) certain how that might or might affect what I've
 already done in {{{libc++abi.dylib}}}. The reason the symbol was added to
 {{{libc++abi.dylib}}} directly is that the build was not using it when it
 was added to compiler_rt, but the last time I tried this was about 2016.

-- 
Ticket URL: <https://trac.macports.org/ticket/62330>
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