Porting ZCX (not SJLJ) for GNAT ARM EABI

[Luke A. Guest]

On Mon, 2010-09-27 at 11:12 +0200, Olivier Hainque wrote:
> Hello Luke,
> 
> Luke A. Guest wrote:
> > I'm having a look into getting DWARF2 exceptions (ZCX) working on ARM.
> 
>  Thanks :-)

Well, I'm reading as much as I can regarding this, but finding it hard
to work some things out. I've been reading through:
http://gcc.gnu.org/ml/gcc/2004-03/msg01779.html and trying some example
code in C++ and Ada, but it doesn't seem to match up in some places,
i.e. no calls into __register_frame_info() yet the libgcc_eh.so contains
the function.

> > Any pointers would be gratefully received. I'm fairly sure I know where
> > to start. 
> 
>  A few general points, jic.
> 
>  The first thing will be to adjust your target system.ads to
>  have GCC_ZCX_Support := True, then use the gnatlib-zcx Makefile
>  target, with essentially two effects: adjust your target system.ads
>  further to switch the GCC_ZCX_Support to True as well, and arrange
>  to build/link with the "-gcc" variants of a-exexpr.adb and raise.c.

Yup, aware of this so far.

>  The system.ads changes control the compiler to declare eh regions, produce
>  dwarf eh info etc.

Yup.

>  The use of -gcc variants is for the runtime library, switching to the
>  libgcc services for exception propagations.
> 
>  raise-gcc.c hosts the Ada personality routine, where a number of changes
>  will be needed I believe.

Also, I think tracebak.c is where the ARM specific routine(s) will need
to go, included from another file tb-armlinux.c? I think this will be
required as (if I'm right), different ARM CPU's have differing number of
registers, and I think I read in the ARM docs that float regs won't need
to be saved if they're not used. I could be wrong about this though.

>  There, please, I'd rather have the ARM specializations abstracted as
>  much as possible, e.g. with new functions and alternate implementations,
>  instead of provided as #ifdefs blocks spread within existing functions.

Well, I think that's possible to a point, obviously some things will
have to go into ifdef's unfortunately (it's not Ada :D).

Hopefully, I can rely on some help from you AdaCore guys? This is my
first foray into GCC internals :/

Thanks,
Luke.