Re: [RFC] Teach dwarf2-frame.c about StackGhost

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

   Date: Sat, 2 Apr 2005 19:34:43 -0500
   From: Daniel Jacobowitz <drow@false.org>

   On Sun, Apr 03, 2005 at 12:18:42AM +0200, Mark Kettenis wrote:
   > One of the things that still keeps me from enabling the DWARF2
   > unwinder on SPARC is the fact that it doesn't play nice with
   > StackGhost.  Here is an attempt to make dwarf2-frame.c deal with it by
   > introducing yet another register rule.  People might object since this
   > is only sort of architecture independent code.  However it seems that
   > this is the cleanest way to solve this.

   Ewww... this isn't even vaguely architecture independent code.  It
   seems like it's in the wrong place; there's no reason StackGhost
   must be restricted to register windows.

On the contrary.  The whole idea pretty much depends on the concept of
register windows.  Now the number of register window architectures is
fairly limited: SPARC, UltraSPARC and IA-64.

   Here's an alternative that I think is cleaner (and will work... I
   hope): create a sparc-specific unwinder.  Its sniffer can call the
   dwarf2 sniffer; similarly for this_id and prev_register.  Then you can
   handle the StackGhost cookie when you are requested to unwind the PC.

The problem here is that whether you need to apply the stackghost
cookie is highly dependent on where exactly %i7 is stored.  If it is
stored in the reserved stack slot then you need to apply the cookie,
otherwise you won't.  The way you suggests makes it hard to get at
that information.

Mark