Class layout accross multiple architectures.

[Ben Scherrey <scherrey at gte dot net>]

To all compiler hackers, 

	My company is investigating porting an existing commercial software
system to Linux. Part of the functionality of this software requires
that it process C++ source code to generate code that deals directly
with the physical layout of the object instances (data, methods,
vtables, etc...). Obviously this makes supporting each platform/compiler
a significant development effort. The software currently runs on several
UNIX workstations but only supports the compiler developed by the
manufacturer. While this might be an understandable marketing decision,
we all know that these compilers are often the last to implement
standardized features correctly (if at all).

	The compiler of choice that we want to support is whatever the latest
stable release of egcs is (hopefully we can keep up along the way). My
desire is to take this one step further. Just about every REAL UNIX
development shop I've worked in uses the GNU compiler (or egcs now) as
their primary or backup development environment. I want to allow this
software product to use egcs under the current operating systems it
already supports in addition to Linux. This would be beneficial to
existing users of the product as well as the new ones who want a Linux
version.

	Which leads (eventually) to my question. Just how large a difference is
there between the object layouts of various hardware/OS implementations
of egcs? I guess the first platforms we'd like to support are probably
Linux/Intel, Solaris/SPARC, and HP/Ux on
whatever-processor-is-in-the-9000. I suspect that some areas should be
pretty consistent but that others will be entirely platform dependent.
Is it possible to effectively abstract out these layouts? Yes, this will
be a significant development effort but, fortunately, I will have the
budget to do this right with good hardware support and the ability to
bring on additional staff specifically for this task (résumé's
anybody?!?!?).

	Thanx for any and all advise in this matter,

		Ben Scherrey
		scherrey@proteus-tech.com