On 14.01.15 10:43, Richard Earnshaw wrote:
On 13/01/15 21:08, Andreas Tobler wrote:
On 13.01.15 11:25, Ramana Radhakrishnan wrote:
On Thu, Jan 8, 2015 at 8:51 PM, Andreas Tobler <andreast-l...@fgznet.ch> wrote:
On 08.01.15 17:27, Richard Earnshaw wrote:
On 29/12/14 18:44, Andreas Tobler wrote:
All,
here is the third attempt to support ARM with FreeBSD.
In the meantime we found another issue in the unwinder where I had to
adapt some stuff.
The unwind_phase2_forced function in libgcc calls a stop_fn function.
This stop_fn is in FreeBSD's libthr implementation and is called
thread_unwind_stop. This thread_unwind_stop is a generic function used
on all FreeBSD archs.
The issue is now that this thread_unwind_stop expects a double int for
the exception_class, like on every other arch. For ARM EABI this
exception_class is an array of char which is passed in one register as
pointer vs. two registers for a double int.
To solve this issue we defined the exception_class as double integer for
FreeBSD.
My apologies for the slow response, some other work and then holidays
intervened.
Np, the only issue which made me hurry was the stage 4 entering this week.
>From my understanding of the ABI document the implementation is
currently as mandated by the ABI. Also this isn't a part of the ABI
that's available for the platform (here FreeBSD to manipulate and
change as per it's wishes). ARM EHABI is special for software, making
FreeBSD more "special" for ARM appears to be counter intuitive from my
point of view. A number of exception unwinding libraries. for e.g.
libobjc , libstdc++ all use this implementation of exception_class.
Therefore this creates a divergence for the FreeBSD port which is
different from everything else. I expect that a number of language run
time support libraries that supported the ARM EHABI would be using
such an implementation, therefore you need to fix every single
implementation of this in every unwinder that supports the ARM EHABI
which I expect to have been ported to in a number of libraries
already. (I already see this in libobjc and libstdc++ in the GCC tree)
Grr ;) I didn't want to hear this answer, but I expected it somehow.
My proposal was the least effort for me.
The other way round is going to be very hard. Maybe impossible.
It is not only FreeBSD which is affected but also llvm and friends. They
use for exception_class uint64_t.
I have to take a picture how the effort is and if it would be possible
to do such a change in FreeBSD and more important in llvm etc.
I would rather fix the thread_unwind_stop implementation in libthr for
ARM EHABI rather than make this change.
It wouldn't be a 'fix' but more a wrapper I think.
This adaptation reduced the failure count in libstdc++ by about 40 fails.
I build and test this port on a regular basis and I post the results to
the usual place.
Thanks for doing this. I'm really glad that FreeBSD is finally moving to EABI.
I agree with Ramana on this one, I feel that FreeBSD trying to plough a
slightly different furrow is just going to cause major problems for
everyone.
I don't believe a claim that LLVM can't be made to work with the
standard EHABI data structures. It can do this on Linux, so I can't
conceive of any reason why it cannot also do so on FreeBSD.
Thanks for the feedback, both! I'm busy to get a picture and I come back
as soon I have a plan.
It is not a technical problem, it is, from my point of view, a
distribution issue. Iow, we 'shipped' ABI/API X and we want/have to
change to ABI/API Y.
So it takes a while till I get the plan :)
Andreas
