C++ exceptions in freebsd-arm doesn't seem to work

Fri Aug 29 16:34:06 UTC 2014

On 25 Aug 2014, at 20:48 , Ian Lepore <ian at FreeBSD.org> wrote:

> On Thu, 2014-08-21 at 18:54 +0200, Olavi Kumpulainen wrote:
>> On 20 Aug 2014, at 21:19 , Ian Lepore <ian at FreeBSD.org> wrote:
>> 
>>> On Wed, 2014-08-20 at 19:19 +0200, Olavi Kumpulainen wrote:
>>>> On 19 Aug 2014, at 20:21 , Ian Lepore <ian at FreeBSD.org> wrote:
>>>> 
>>>>> On Tue, 2014-08-19 at 19:40 +0200, Olavi Kumpulainen wrote:
>>>>>> On 25 Jul 2014, at 23:44 , Andreas Tobler <andreast-list at fgznet.ch> wrote:
>>>>>> 
>>>>>>> On 22.07.14 23:11, Ian Lepore wrote:
>>>>>>>> On Sat, 2014-07-19 at 16:35 -0600, Ian Lepore wrote:
>>>>>>>>> On Sat, 2014-06-07 at 14:12 +0200, Olavi Kumpulainen wrote:
>>>>>>>>>> [c++ exceptions don't work and related discussion]
>>>>>>>>> 
>>>>>>>>> I checked in a partial fix for c++ exception handling in r268893.  It
>>>>>>>>> fixes the specific problem you detailed above, which was essentially
>>>>>>>>> that the __gnu_Unwind_Find_exidx() function was not available in any
>>>>>>>>> shared library, making the unwinder fall back to using the __exidx_start
>>>>>>>>> and end symbols, which are only valid in a statically-linked app.
>>>>>>>>> 
>>>>>>>>> With the new function in place, exceptions are closer to working with
>>>>>>>>> gcc 4.2.1, but still don't work with clang.  With gcc, some things work
>>>>>>>>> and some things don't.  For example if you throw an exception and in the
>>>>>>>>> same function have a catch with the right specific type it segfaults,
>>>>>>>>> but a catch(...) will catch it without problems.  But you can catch an
>>>>>>>>> exception by type if the catch is in a function higher up the call chain
>>>>>>>>> from the place it was thrown.
>>>>>>>>> 
>>>>>>>>> We're continuing to debug this at $work, and welcome any input if anyone
>>>>>>>>> else makes progress with it.  Right now we still don't know whether the
>>>>>>>>> segfaults are because of bad unwinder library code or bad unwind data
>>>>>>>>> emitted by gcc.  (I sure hope it's the library, because that's easier to
>>>>>>>>> fix.)
>>>>>>>>> 
>>>>>>>>> On the clang front, it has been said that c++ exceptions work in clang
>>>>>>>>> 3.5, so we tried the clang-devel port, and it didn't just work.  But it
>>>>>>>>> turns out that port hasn't been updated for quite a while, so we may not
>>>>>>>>> have tested the code that's supposed to work right.  While trying that I
>>>>>>>>> discovered that clang 3.5 isn't scheduled for release for about another
>>>>>>>>> year, so that really isn't a viable solution for anyone with near-term
>>>>>>>>> needs, unless the required changes can be cherry-picked and brought into
>>>>>>>>> our version of 3.4.
>>>>>>>>> 
>>>>>>>>> -- Ian
>>>>>>>> 
>>>>>>>> Another update to this... today I committed r268993 and r268994, and now
>>>>>>>> I believe arm eabi c++ exceptions are fully working with gcc.  I haven't
>>>>>>>> run an extensive test suite, but all the test cases we've been using at
>>>>>>>> $work to debug this now work correctly.
>>>>>>> 
>>>>>>> Thank you! Confirmed. My test cases which are working with gcc-4.10 are now also working with the system gcc, 4.2.1.
>>>>>>> I totally forgot about this change. I have it in my local gcc tree since a while but I forgot about.....
>>>>>>> 
>>>>>>> Andreas
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>>>> Please excuse my late reply. I’ve been away from keyboard for a while.
>>>>>> 
>>>>>> I back-ported r268893,  r268993 and r268994 to stable/10 for beaglebone. C++ exceptions works for static builds, but not for binaries linked to shared libs.
>>>>>> 
>>>>>> Since this seems to work ok in HEAD, I’m obviously missing something. Do any of you guys have any ideas?
>>>>>> 
>>>>>> Cheers
>>>>>> 
>>>>> 
>>>>> I'm not sure what you mean by "backported to stable/10", I merged all
>>>>> the necessary changes to stable-10 as r269792 on Aug 10.  Are you
>>>>> working with a checkout from earlier than that?  If so, just updating
>>>>> should fix it for you.
>>>>> 
>>>>> -- Ian
>>>>> 
>>>>> 
>>>> 
>>>> 
>>>> Updating to stable-10 as of today didn’t help. I’m running a clean checkout except for a couple of drivers in the kernel.
>>>> This makes me think I have a bad src.conf - How shall I configure the build for this to work?
>>>> 
>>>> /Olavi
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>>> You need to use GCC, not clang, as the compiler.  Exceptions are just
>>> broken on clang 3.4, so we're waiting for 3.5 (should be released any
>>> time now I think).
>>> 
>>> To compile with gcc, put this in your /etc/make.conf:
>>> 
>>> WITH_GCC=yes
>>> WITH_GNUCXX=yes
>>> WITH_GCC_BOOTSTRAP=yes
>>> WITHOUT_CLANG=yes
>>> WITHOUT_CLANG_IS_CC=yes
>>> WITHOUT_CLANG_BOOTSTRAP=yes
>>> 
>>> -- Ian
>>> 
>>> 
>> 
>> 
>> Thank you. It turned out that I already used these with the exception of WITHOUT_CLANG_BOOTSTRAP.
>> 
>> However, c++ exceptions in stable/10 is still defunct when I build it. 
>> 
>> So instead I pulled master, built and installed that instead. And voila - Exceptions do work! 
>> 
>> Therefore it seems my build method, flags and environment is ok after all. I glanced the commit logs in master but didn’t find anything obvious, but still; something related seems missing in stable/10 if you ask me.
>> 
>> /Olavi
>> 
>> 
>> 
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>> 
> 
> I chased this down today to a missing MFC.  One of my merges claimed to
> include a change that wasn't really included.  I fixed it today with
> r270606, and this time I actually tested that I could throw and catch an
> exception using freebsd built from stable-10 at this rev. :)
> 
> Thanks for testing this, and sorry for claiming it was fixed when it
> wasn't quite complete.
> 
> -- Ian
> 
> 

I’m a little late again, but I still want to confirm that stable/10 works for me too. It catches c++ exceptions like a real champ!

Thanks a million -

/Olavi