On 2016-Nov-29, at 2:56 PM, Ed Maste <emaste at freebsd.org> wrote:
> On 29 November 2016 at 16:46, Mark Millard <markmi at dsl-only.net> wrote:
>>
>>
>> Summary: Does using clang 3.9.0 as the system compiler imply one should or
>> must (eventually?) use WITH_LLVM_LIBUNWIND to have C++ exceptions work?
>>
>> Do WITH_LLVM_LIBUNWIND and WITHOUT_LLVM_LIBUNWIND have the same criteria
>> for what dwarfdump should show for the exception information (if the
>> information to be shown is to be correct/sufficient for libunwind)?
>
> It does not. It should be possible to build a functional system both
> WITH_ and WITHOUT_LLVM_LIBUNWIND. The compiler is unaware of the
> _LLVM_LIBUNWIND setting. Both unwind libraries use the same unwind
> data.
>
> Eventually new features may show up in Clang and LLVM's libunwind (and
> new versions of GNU's unwinder) that won't work with the old unwinder.
>
>> Your answer's detail might indicate that I've misdirected the llvm folks
>> in submittals like https://llvm.org/bugs/show_bug.cgi?id=26844 .
>>
>> There is also the question of if/when llvm's libunwind is ready to be used
>> for powerpc64 or powerpc (or . . .) if there are architecture specifics
>> involved. That answer might determine when C++ exceptions work (and so
>> when devel/kyua might have a chance to work) and is sort of separate from
>> the main question here but is still of interest overall.
>>
>> Should powerpc64 and powerpc clang 3.9.0 testing be using
>> WITH_LLVM_LIBUNWIND ? WITHOUT_LLVM_LIBUNWIND ? Both?
>
> For testing I think WITH_LLVM_LIBUNWIND is the interesting case. My
> eventual goal is to have a functioning Clang, LLD, LLDB, libunwind,
> and ELF Tool Chain on all of our supported architectures.
I tried adding WITH_LLVM_LIBUNWIND= to the SRC_CONF_ENV file that I
use on powerpc64 for TARGET_ARCH=powerpc64 for (a minor variation of)
head -r309179 based on clang 3.9.0. It failed to complete buildworld:
A) An assert failed in libunwind/src/UnwindCursor.hpp .
B) Two .S files got massive numbers of error messages
( libgcc_eh/UnwindRegisterRestore.S and
libgcc_eh/UnwindRegisterSave.S )
And those points stopped the build.
See: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=215039
Note: using WITHOUT_LLVM_LIBUNWIND= (implicit) I've done
buildworld using WITH_LIB32= just fine and rebooted with
it installed and then did more buildworld experiments. The
above started from a working environment for such things.
Unfortunately for gcc's libunwind clang's code generation
is broken (counting .eh dwarf information as code). C++
exceptions are one area that does not even do simple
things correctly for powerpc64 (or for powerpc): I have
to avoid using programs that depend on C++ exceptions
happening.
===
Mark Millard
markmi at dsl-only.net
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