unwind.s :

Since I have tested the gcc, I was unable to find the way of handling
exception in C++. After some searches I discovered that the unwind
function has not been wrote for our machine. So, here it is :

When unwind is called, the stack is in this state

 +--------------------------------------------------+ 0
 |return address of the exception calling function  |
 +--------------------------------------------------+ 4
 |address of the catch routine                      |
 +--------------------------------------------------+ 8

And A5 points on the following
(the stack will go there when UNLK A5 will be performed) :
 +--------------------------------------------------+ 0
 |return address of the previous routine            |
 +--------------------------------------------------+ 4

the goal is to return from the previous function. For example :

     A() -> B() -> unwind()

the exception occurs in B() but since unwind() is called, unwind should
not return to B() but to A() which is the previous function.
Also, the return address is not the same than if B() performs normally
but the address of the catch routine in A().

when the B() function has been called the normal code is :

   link A5,count ; A5 is the previous SP and SP now points on the parameters
   ... code
   unlk A5     ; SP is restored to the A5 address
   rts


    XDEF ___unwind_function
___unwind_function:
        move.l (A7)+,A0   ; pop the B() return address into A0 (trash)
        move.l (A7)+,A1   ; pop the catch address into A1 (keep)
        unlk A5           ; restore the stack like when we entered into B()
        move.l (A7)+,A0   ; pop the A() return address into A0 (trash)
        move.l A1,-(A7)   ; push the A() catch address into the stack
        RTS               ; Go to the catch routine

To try this I have created a small project with a simple script file
named compile, use the -S option if you want to see what is going inside.
Since the GNU optimizer plays a lot with the stack, I have been unable to
make an unwind.cc file instead of unwind.s.

Author: Dominique Lorre
        Le Fabary, Bât C
        4 Allée des Peupliers
        13100  Aix-en-Provence FRANCE

Distribution: Under the GNU Library General Public License joined in the
archive. Since unwind.s is intended to be a part of G++, I have considered
that this was the correct form of distribution.

    unwind.s -- exceptions handling for g++
    Copyright © 1996 Dominique Lorre

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.