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ackassemblylanguage

This page describes the assembly language(s) used in MINIX 1.6, MINIX 2.0 and MINIX 3.1. It is not relevant to recent (after 2010) releases of MINIX.

MINIX ACK Assembly Language

What do the pseudo-ops in Minix assembly code mean?

An ACK assembly file can have a number of sections. Things declared in the same section are collected together by the loader in the order they are found in an assembly file and in the order the object files are loaded together. Sections get meaning once they are put in a Minix binary. Section 0 (usually named .text) contains program code and is put in the code segment, section 1 (.rom) is read-only data and is put in the data segment, and so are section 2 (.data) for read-write data and section 3 (.bss) for read-write data initialized to zero. The ACK binary to Minix binary converter (cv) will complain if there are nonzero objects in the .bss section, but it doesn't care if there's code in .rom, .data, or data in .text. With .define a label is turned into a global variable that other files can use, otherwise it stays local to the assembly file it is in. With .extern one can import a global label, but the assembler seems to do that automatically anyway. With .comm (or .lcomm) you can put a label on a bunch of zeros. This is useful in the .bss section. The difference between “.comm junk, 10” and “junk: .space 10” only appears when the label is made global: multiple common declarations are merged at link-time, while multiple spaced variables will conflict. With .align you can insert the number of zeros needed to align . (the address where stuff is put) to a given multiple. Objects bigger than a byte should be aligned to multiples of 2 or 4 bytes. Otherwise it will be slow on 386 descendants, and may cause alignment fault messages on a 486+. With .data[124] you can assemble 1, 2 or 4 byte sized numbers. With .ascii “xyz”, and .asciz “xyz” you can do the same as with .data1 120, 121, 122 and .data1 120, 121, 122, 0.

In the code there are lines starting with ".sect". What do they mean?

At the beginning of the code there is a line: “.sect .text; .sect .rom; .sect .data; .sect .bss”, or there is “.sect .text begtext:”. In the code “.sect .text” shows up again. What do these mean? What is the explanation of the segments in Minix assembly code?

A new section name opens up a new section. By naming all sections in the first line you can be sure that the names are tied to the proper section numbers.

How are comments indicated?

The comment character is !. The C preprocessor is run on an assembly file if the very first character is a #. If so, then the /*… */ comment characters also work, because the C preprocessor removes C comments. The quote characters (', “) are a bit of a problem, because the preprocessor wants them to match. This is why you see '' (backquote) used in comments sometimes where one would normally use a ' (single quote).

Inconsistency in syntax

From: drminix@naver.com (Sam)
Subject: assembly syntax inconsistency in MINIX.
Date: 31 May 2004 19:42:42 -0700

I was reading two different MINIX assembly files, masterboot.s and
mpx386.s. I then came across some differences between the assembly
syntax used in each files.

In mpx386.s, each section starts with .sect followed by the section
name. For example, a text section starts with .sect .text

However in masterboot.s, a text section starts with just .text 

MASTERBOOT.S  |     MPX386.s
---------------------------------------
.text         |   .sect .text
.data         |   .sect .data

And also, the pound sign(#) is used to indicate an immediate data in
masterboot.s whereas using a pound sign(#) in mpx386.s gives you an
error.

I guess minix compiler understands both syntax. Can anyone tell me why
there are two different ways to start a section?
From: kjb=733616@cs.vu.nl (Kees J Bot)
Subject: Re: assembly syntax inconsistency in MINIX.
Date: Tue, 1 Jun 2004 12:18:58 +0200

There's that, and there's this:

mov ax, #10         |     mov ax, 10
mov ax, variable    |     mov ax, (variable)

The syntax for the 16-bit assembler under the 16-bit version was changed
to be like Xenix or something.  I have no idea why.

The 32-bit assembler uses the syntax on the right, both with 8086 and
386 input.  I had to make an assembly syntax converter to allow this
assembler to process the Xenix syntax.  The -Was-ncc option tells the
compiler driver that the assembly input is the "new cc" syntax.  (Yes,
there's also an "old cc" syntax.  Luckily we buried that.)

Kees J. Bot
Modified 12 March 2003
ackassemblylanguage.txt · Last modified: 2015/01/03 07:05 by antoineleca