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

[Ian Lepore]

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