From banz@umbc.edu  Mon Sep 21 22:13:07 1998
Date: Mon, 21 Sep 1998 22:13:05 -0400
From: Robert Banz <banz@umbc.edu>
To: squire@gl.umbc.edu
Subject: Re: [Req #17906] c89 why different?

On Mon, 21 Sep 1998 squire@gl.umbc.edu wrote:

> My students are thinking I am more crazy than I actually am.
> 
> On gl=umbc8      c89 -g3 -O4 xxx.c    works
> On gl=umbc9      c89 -g3 -O4 xxx.c  does not work, says -O4 is ilegal
> 
> besides that, in gdb a.out  the addresses are different
> for   x/200xw 0x10000aa0     umbc9  vs   x/200xw 0x400980  umbc 8
> 
> How can you expect us to teach how to use debugger when we can
> not give examples that work on all the gl machines ???


The compilers on umbc8 & umbc9 are the same version, however, the
OS's are different.  We can't do anything about it, unfortunatly, because
Irix 6.2 won't run on umbc9 & Irix 6.4 won't run on anything but umbc9.
With the OS rev change, SGI made the default object file format
"-n32" on the 6.4 machines, but it's "-o32" on the others.  You can have
them always commpile with either off those options, and they'll get the
same compilers.

BTW, the optimization levels are handled differently with the newer
compilers, when ran in -n32 mode which umbc9 does by default, which is
why you're getting the -O4 message.

The basic difference between the object file formats are

	-o32		32bit ptrs	32bit ints
	-n32		32bit ptrs	64bit ints
	-n64		64bit ptrs	64bit ints

(hint: don't use -n64 anyhwere, it won't work on the workstations --
they're only 32 bit machines :) )

-n32 is the good one to use.  The backend compilers for it are *really
good* -- the backend that generates the -o32 code and does the
optimizations hadn't been developed on for a couple years by SGI.

rob