from LLVM's libunwind, which end up in libgcc_eh.a and libgcc_s.so.
This is because the unwinder needs the unwinder data for its own
functions.
However, for the C++ sources in libunwind, -fexceptions is already the
default, and this can have the side effect of generating a reference to
__gxx_personality_v0, the so-called personality function, which is
normally provided by the C++ ABI library (libcxxrt or libsupc++).
If the reference ends up in the eventual libgcc_s.so, linking any
non-C++ programs against it will fail with "undefined reference to
`__gxx_personality_v0'".
Note that at high optimization levels, the reference is usually
optimized away, which is why we have never noticed this problem before.
With clang 7.0.0 though, higher optimization levels don't help anymore,
since the addition of address-significance tables [1] in
<https://reviews.llvm.org/rL337339>. Effectively, this always causes a
reference to __gxx_personality_v0.
After discussion with the upstream author of that change, it turns out
that we should compile libunwind sources with the -fno-exceptions
-funwind-tables flags instead. This ensures unwind tables are
generated, but no references to any personality functions are emitted.
[1] https://lists.llvm.org/pipermail/llvm-dev/2018-May/123514.html
Reported by: jbeich
PR: 230399
MFC after: 1 week
33c39ab688