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

Ian Lepore ian at FreeBSD.org
Tue Aug 19 18:22:00 UTC 2014

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

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