Assm_example
asw 2 March 2000

I was recently asked a question about Minix assembly language syntax,
and I realized that, although there are lots of examples of Minix
assembly language in the source code, and there are a few files with
information about the assembly language in ftp://minix1/pub/info,
there are very few, if any, examples of how to write a standalone
program in assembly.  Now, why would anyone want to do that? Well,
some of us create web pages with vi or emacs.

Several years ago I was teaching an OS course using Minix 1.5, and was
also teaching assembly language using MASM to the same group of students. 
As a demonstration I put together a few files to show how to write a
Minix program in assembly language. My main program shows how to use 
a few of the directives, and looked like this:

| hola.s
| version ensamblador de hello.c
| para ensamblador asld de Minix
| asw 28.5.93 

.globl _main
.text
_main:  push bp
        mov bp,sp
        mov ax,#msg
        push ax

        call _printf

        pop bx
        xor ax,ax
        push ax
        call _exit

.data
msg:    .ascii  "Hola, mundo\n"

To make a standalone program this must be linked with Minix library
routines. The Makefile handles all of this. my Makefile for the above
program looks like this: 

hola:
        asld crtso.s hola.s /usr/lib/libc.a end.s
        mv a.out hola

Crtso.s is the C Run Time Start Off routine, and is linked with all
programs compiled under Minix. It takes care of setting up arguments (if
any) and environment variables to be passed by the operating system to 
a program. End.s similarly handles passing return codes back to the OS.

Note that this Makefile assumes that copies of crtso.s and end.s are
in the same directory with the hola.s source code. A useful Makefile 
should include the paths to the standard locations of these files.

Also note that Minix 2.0.x does not have an asld command. In Minix 2.0
you just call the C compiler (cc) and it invokes the assembler when it
sees that the source files are written in assembler. I haven't tested
this, and some compiler flags may be needed.  The above assembler code
is for 16 bit Minix and the Minix systems I have available now are
32-bit Minix. Also, it is possible that the code above, written for
use with Minix 1.5, may not work correctly with Minix 2.0.

If someone will update this so it really works under Minix 2.0 I'd
love to have a copy to post on my site. Even better, send me examples
for both 16-bit and 32-bit Minix. A complete example requires both 
an assembly language main program and a Makefile, including paths to
additional files needed to compile a complete working program.

+----------------------------------+
| Albert S. Woodhull               |
| Hampshire College, Amherst, MA   |
| awoodhull@hampshire.edu          |
| http://minix1.hampshire.edu/asw/ |
+----------------------------------+