[Ada] Add missing tb-gcc.c file

[Arnaud Charlet <charlet at gcc dot gnu dot org>]

This file is needed to implement the System.Traceback functionality under
some systems, in particular mips-irix.

Committed on mainline.

2004-11-25  Olivier Hainque  <hainque@adacore.com>

        * tb-gcc.c: GCC infrastructure based implementation of
        __gnat_backtrace.
--
*** /dev/null	2002-08-31 01:31:37.000000000 +0200
--- tb-gcc.c	2004-11-25 14:10:35.000000000 +0100
***************
*** 0 ****
--- 1,102 ----
+ /****************************************************************************
+  *                                                                          *
+  *                         GNAT COMPILER COMPONENTS                         *
+  *                                                                          *
+  *                   T R A C E B A C K - G C C t a b l e s                  *
+  *                                                                          *
+  *                          C Implementation File                           *
+  *                                                                          *
+  *              Copyright (C) 2004 Ada Core Technologies, Inc               *
+  *                                                                          *
+  * GNAT is free software;  you can  redistribute it  and/or modify it under *
+  * terms of the  GNU General Public License as published  by the Free Soft- *
+  * ware  Foundation;  either version 2,  or (at your option) any later ver- *
+  * sion.  GNAT is distributed in the hope that it will be useful, but WITH- *
+  * OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY *
+  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License *
+  * for  more details.  You should have  received  a copy of the GNU General *
+  * Public License  distributed with GNAT;  see file COPYING.  If not, write *
+  * to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, *
+  * MA 02111-1307, USA.                                                      *
+  *                                                                          *
+  * As a  special  exception,  if you  link  this file  with other  files to *
+  * produce an executable,  this file does not by itself cause the resulting *
+  * executable to be covered by the GNU General Public License. This except- *
+  * ion does not  however invalidate  any other reasons  why the  executable *
+  * file might be covered by the  GNU Public License.                        *
+  *                                                                          *
+  * GNAT was originally developed  by the GNAT team at  New York University. *
+  * Extensive contributions were provided by Ada Core Technologies Inc.      *
+  *                                                                          *
+  ****************************************************************************/
+ 
+ /* This is an implementation of the __gnat_backtrace routine using the
+    underlying GCC unwinding support associated with the exception handling
+    infrastructure.  This will only work for ZCX based applications.  */
+ 
+ #include <unwind.h>
+ 
+ /* The implementation boils down to a call to _Unwind_Backtrace with a
+    tailored callback and carried-on datastructure to keep track of the
+    input parameters we got as well as of the basic processing state.  */
+ 
+ typedef struct {
+   void ** traceback;
+   int max_len;
+   void * exclude_min;
+   void * exclude_max;
+   int  n_frames_to_skip;
+   int  n_frames_skipped;
+   int  n_entries_filled;
+ } uw_data_t;
+ 
+ /******************
+  * trace_callback *
+  ******************/
+ 
+ static _Unwind_Reason_Code
+ trace_callback (struct _Unwind_Context * uw_context, uw_data_t * uw_data)
+ {
+   void * pc = (void *) _Unwind_GetIP (uw_context);
+ 
+   if (uw_data->n_frames_skipped < uw_data->n_frames_to_skip)
+     {
+       uw_data->n_frames_skipped ++;
+       return _URC_NO_REASON;
+     }
+ 
+   if (uw_data->n_entries_filled >= uw_data->max_len)
+     return _URC_NORMAL_STOP;
+ 
+   if (pc < uw_data->exclude_min || pc > uw_data->exclude_max)
+     uw_data->traceback [uw_data->n_entries_filled ++] = pc + PC_ADJUST;
+ 
+   return _URC_NO_REASON;
+ }
+ 
+ /********************
+  * __gnat_backtrace *
+  ********************/
+ 
+ int
+ __gnat_backtrace (void ** traceback, int max_len,
+ 		  void * exclude_min, void * exclude_max,
+ 		  int  skip_frames)
+ {
+   uw_data_t uw_data;
+   /* State carried over during the whole unwinding process.  */
+ 
+   uw_data.traceback   = traceback;
+   uw_data.max_len     = max_len;
+   uw_data.exclude_min = exclude_min;
+   uw_data.exclude_max = exclude_max;
+ 
+   uw_data.n_frames_to_skip = skip_frames;
+ 
+   uw_data.n_frames_skipped = 0;
+   uw_data.n_entries_filled = 0;
+ 
+   _Unwind_Backtrace ((_Unwind_Trace_Fn)trace_callback, &uw_data);
+ 
+   return uw_data.n_entries_filled;
+ }