====== MINIX 3 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 //space//d 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