[Ada] improve unwinding of exception through signal handles on hp-ux

[Arnaud Charlet <charlet at adacore dot com>]

Manually tested under pa-hpux, ia64-vms.
Tested on i686-linux. Committed on mainline.

The PC values the GCC unwinder sees when propagating an exception usually
are call return addresses. At each step, we are interested in checking the
EH region of the call itself, so the PC value at hand is adjusted to search
for the right region. When unwinding through a signal handler, the PC value
we get is most often the address of the faulting instruction. This is the
the instruction of interest eh-region-wise to start with, so the unwinder's
adjustment should be avoided in this case. The unwinder is not able to do
that properly, though, so it always adjusts and we need to compensate for
this. The scheme here is to tweak the PC value before the unwinder sees it,
from the signal handler as achieved for Java. We are using
__gnat_adjust_context_for_raise for that very purpose.

In addition, provide user flexibility in the choice of VMS conditions to
resignal, which used to be hardcoded and thus impossible to control.

Test program (should display 'Got exception!' 10 times):
with Ada.Text_IO; use Ada.Text_IO;
with System; use System;

procedure Simple is
   A : Integer; for A'Address use System.Null_Address;
begin
   for K in 1 .. 10 loop
      begin
         A := 1;
      exception
         when others => Put_Line ("Got exception!");
      end;
   end loop;
end Simple;


2005-03-08  Olivier Hainque  <hainque@adacore.com>

	* s-intman-posix.adb (Notify_Exception): Adjust signature, as handler
	for sigactions with SA_SIGINFO set. Call
	__gnat_adjust_context_for_raise before raising, to perform the
	potentially required adjustments to the machine context for the GCC
	unwinder.

	* raise.h (__gnat_adjust_context_for_raise): New prototype.

	* init.c (__gnat_adjust_context_for_raise) HPUX: Initial revision.
	Adjust PC by one in the provided machine context.
	(__gnat_install_handler) HPUX: Set SA_SIGINFO in the sigaction flags,
	so that the handler is passed the context structure to adjust prior to
	the raise.
	(__gnat_error_handler) HPUX: Adjust the signature to match what an
	SA_SIGINFO sigaction should look like. Call
	__gnat_adjust_context_for_raise before actually raising.
	(__gnat_adjust_context_for_raise): Default noop to help PC
	adjustments before raise from signal handlers.
	(__gnat_error_handler): Indirectly call a predicate function to
	determine if a condition should be resignaled or not.
	(__gnat_set_resignal_predicate): User interface to modify the predicate.
	(__gnat_default_resignal_p): Default GNAT predicate.

Attachment: difs.4
Description: Text document