Porting ZCX (not SJLJ) for GNAT ARM EABI

[Andrew Haley]

On 09/27/2010 10:36 AM, Luke A. Guest wrote:
> 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 :/

The best clue you're going to get is my work to solve the same problem in
libgcj.  Most of what you need to know is in libjava/exception.cc.  See
Revision 128098.

Andrew.