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Re: [multi-arch] The frame as the global parameter (long, important)
- To: Andrew Cagney <ac131313 at cygnus dot com>, GDB Discussion <gdb at sources dot redhat dot com>
- Subject: Re: [multi-arch] The frame as the global parameter (long, important)
- From: Kevin Buettner <kevinb at cygnus dot com>
- Date: Mon, 26 Feb 2001 14:43:43 -0700
- References: <3A970102.68681EB2@cygnus.com>
On Feb 23, 7:32pm, Andrew Cagney wrote:
[Big picture snipped]
> Given all this, I'd like to propose the following structural changes to
> o The frame have an architecture
> attached to it.
> As an intermediate hack, current
> architecture and current frame would
> remain as globals.
> o All the functions that apply to
> the frame be parameterized with a
> frame argument and modified to
> use the frame's architecture.
> o (Per previous e-mail)
> The frame and its registers be more
> clearly separated from the target
> (in particular the regcache).
> Most calls that go directly to the
> regcache will instead go via the
> current frame.
> A consequence of this is that the
> current need for the RAW / PSEUDO
> / NATURAL register mess will be
> eliminated. Yessss!
> While looking simple, these changes are certainly everything but. Every
> frame / regcache / memcache access will need to be examined / modified.
> Fortunately, most of these uses can be examined independently so the
> work can be carried out incrementally.
> Clearly this change, on its own, won't be sufficient to make GDB
> multi-arch. I would argue, however, that like the initial multi-arch
> work, it is a clear step in the right direction.
> With that in mind, I'm looking for comments, questions and suggestions.
The big picture that you painted certainly looks reasonable. But even
if it didn't, I think the structural changes that your propose above
make sense even when considered on a much smaller scale...
It makes sense to associate an architecture with a frame so that we
can cleanly implement support for targets with mixed architectures
like ARM/THUMB or IA-64/IA-32.
Also, from a software engineering standpoint, I think it makes sense
to eliminate as many of the globals as possible and pass parameters
instead. Any time one or more of the parameters to a function are
passed implicitly via a global, you're just asking for trouble later