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From: rbj@icst-cmr.arpa (Root Boy Jim)
Newsgroups: comp.unix.questions
Subject: Teaching Assembler on VAX (BSD 4.3)
Message-ID: <7449@brl-adm.ARPA>
Date: Tue, 19-May-87 10:51:17 EDT
Article-I.D.: brl-adm.7449
Posted: Tue May 19 10:51:17 1987
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   >I did look at m4, but it is really geared to C

   It is?  Why, then, is someone I know experimenting with using it as
   a front end to the Sun assembler?  (Well, then again, he has some some
   other pretty dumb things :-) .)

I don't have the original article, but maybe he meant "is it" rather
then "it is". I don't see m4 as being particularly tailored for or
against C or assembly or anything else for that matter. Fortran maybe?

   >and did not really address the problem of sophomore students learning
   >a very user-unfriendly assembler.

   Okay, here is the *real* question:

   What makes an assembler friendly or unfriendly?

I'm surprised you had to ask, Chris, or was that a rhetorical question?

   I have used:

	   EDTASM (Z80);
	   two homegrown assemblers (Z80);
	   Microsoft's M80 (Z80);
	   a rather weird assembler written in FORTRAN (IBM 370);
	   4BSD `as' (Vax);
	   Sun `as' (680x0);
	   GENIX `as' (NS320xx);
	   Microsoft's MASM (80x86).

   Only M80 and MASM had extensive built-in macro facilities, but I
   never really missed these with the others.

I think this is a major requirement for serious asm hacking. As a litmus
test, I would say the ability to write a set of macros which implemented
if-then-else, while, and the like (in short, a mini compiler), is a
pretty good assembler. Two such beasts are the VMS assembler, basically
a descendent of MACRO-11 (um, maybe it's *still* called that), and
@ASM or @MASM over on the UNI{VAC,SYS} 1108 (or whatever model). Walk on
over to ZBEN's office sometime and ask to see a copy of STRUC$.

   In the case of the Vax
   and Sun assemblers, I use the C preprocessor, since the assemblers
   will accept semicolon-separated statements:

	   movl $0,r7; 1: addl2 r9,r7; ashl $1,r9,r9; bbc $12,r9,1b

   (/lib/cpp eats newlines in macros, hence something like this is
   required.  m4 does not eat newlines.)

In fact, I would rather use cpp for assembly as well. But perhaps m4
can generate multi-line text?

   So what is /bin/as missing, or what does it do wrong, that makes it
   user-unfriendly?

Of course, the UNIX `as' is not supposed to be friendly, because you're
not encouraged to use it. I think any UNIX `as' is probably not very
good for teaching purposes. It's main purpose and design is as a back
end for compilers.

On the other hand, perhaps it is very well suited for teaching,
because there are no frills to be distracted by.

   In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
   Domain:	chris@mimsy.umd.edu	Path:	seismo!mimsy!chris

	(Root Boy) Jim "Just Say Yes" Cottrell	<rbj@icst-cmr.arpa>
	Yow!  I want to mail a bronzed artichoke to Nicaragua!