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:::\_____\:::::::::::................................ASSEMBLY.TECHNIQUES
80x86 Register Equates
by te987
te987@hotmail.com
Have you ever had to debug a program where most of the data was
contained in registers? (As it should be in a good assembly program.)
Have you gone crazy trying to trace register usage? (Yeah, I know that
being crazy helps when writing assembly programs!) The following
technique makes tracing register usage easy...
Simply create an equate for each register. Place the equates in an
include file and "include register.inc" at the top of every file.
Now, assemble your program using the following Turbo Assembler
command line:
tasm /l/c somefile
The /l switch instructs TASM to generate a listing, and the /c says
to create a cross reference.
(An aside: I also use MASM 6.xx, but have never been able to find
the correct switch(es) in either MASM.EXE or ML.EXE to make it
generate a cross reference. "masm /l/c somefile" generates a symbol
table, but it doesn't give the LINE NUMBERS where the symbol is used.
Most useless... If anyone knows how to do so, I would appreciate
hearing from you...)
The following three files show how to use register equates. First,
the include file:
;====== start of register.inc ================================
| CODE | ;============================================================================
; File: REGISTER.INC
;
; Description: Register symbolic constants.
;============================================================================
ifndef __INCLUDE_REGISTER__
__INCLUDE_REGISTER__ equ 1
_ax equ <ax>
_bx equ <bx>
_cx equ <cx>
_dx equ <dx>
_ah equ <ah>
_bh equ <bh>
_ch equ <ch>
_dh equ <dh>
_al equ <al>
_bl equ <bl>
_cl equ <cl>
_dl equ <dl>
_si equ <si>
_di equ <di>
_sp equ <sp>
_bp equ <bp>
_cs equ <cs>
_ds equ <ds>
_es equ <es>
_ss equ <ss>
_eax equ <eax>
_ebx equ <ebx>
_ecx equ <ecx>
_edx equ <edx>
_esi equ <esi>
_edi equ <edi>
_esp equ <esp>
_ebp equ <ebp>
_fs equ <fs>
_gs equ <gs>
endif;ifndef __INCLUDE_REGISTER__ |
;====== end of register.inc ================================
Next, a "Hello, world!" program showing equated registers. The first
four lines are TASM directives controlling how the listing is created.
I normally run the == line (and comments) out to column 96. This
prints the full page width in portrait when using 16.67 characters per
inch.
;====== start of hello.asm =================================
| CODE | %TITLE "Everyone's first program---""Hello, world!"""
%NOINCL
%CREFREF
%TRUNC
;==================================================
; Description: Display "Hello, world!".
; Sample program showing register equates.
;==================================================
.model small
.stack 100h
include register.inc
;==================================================
.data
hello db "Hello, world!",0Dh,0Ah,'$'
;==================================================
.code
main proc
mov _ax,@data ;initialize segment registers
mov _ds,_ax
mov _es,_ax
mov _ah,9 ;DOS display string
mov _dx,OFFSET hello
int 21h
mov _ax,4C00h ;exit program with errorlevel 0
int 21h
main endp
end main |
;====== end of hello.asm =================================
Finally, the (edited) listing file. Editing consisted of deleting
extra blank lines, form feeds, and narrowing column widths so that the
listing was 72 columns wide (in particular, comments were truncated).
Notice in the symbol table that registers are cross referenced,
with, for example, register _ax being defined at line 10 (in the include
file) and used at lines 20, 21, 22, and 28. Imagine how useful a cross
reference would be if a register was used 200 times!
;====== start of hello.lst ==================================
| CODE | Turbo Assembler Version 4.0 99/99/99 99:99:99 Page 1
HELLO.ASM
Everyone's first program---"Hello, world!"
1 ;==========================================
2 ; Description: Display "Hello, world!".
3 ; Sample program showing register equat
4 ;==========================================
5
6 0000 .model small
7 0000 .stack 100h
8
9 include register.inc
10
11 ;==========================================
12 0000 .data
13
14 0000 48 65 6C+ hello db "Hello, world!",0Dh,0Ah,'$'
15
16 ;==========================================
17 0010 .code
18
19 0000 main proc
20 0000 B8 0000s mov _ax,@data ;initialize s
21 0003 8E D8 mov _ds,_ax
22 0005 8E C0 mov _es,_ax
23
24 0007 B4 09 mov _ah,9 ;DOS display
25 0009 BA 0000r mov _dx,OFFSET hello
26 000C CD 21 int 21h
27
28 000E B8 4C00 mov _ax,4C00h ;exit program
29 0011 CD 21 int 21h
30 0013 main endp
31 end main
Turbo Assembler Version 4.0 99/99/99 99:99:99 Page 2
Symbol Table
Everyone's first program---"Hello, world!"
Symbol Name Type Value Cref (defined at #)
@CODE Text _TEXT #6 #6 #17
@CURSEG Text _TEXT #12 #17
@DATA Text DGROUP #6 20
@WORDSIZE Text 2 #12 #17
HELLO Byte DGROUP:0000 #14 25
MAIN Near _TEXT:0000 #19 31
_AH Text ah #10 24
_AX Text ax #10 20 21 22 28
_DS Text ds #10 21
_DX Text dx #10 25
_ES Text es #10 22
Groups & Segments Bit Size Align Combine Class Cref (defined at #)
DGROUP Group #6 6 20
STACK 16 0100 Para Stack STACK #7
_DATA 16 0010 Word Public DATA #6 #12
_TEXT 16 0013 Word Public CODE #6 6 #17 17 |
;====== end of hello.lst ==================================
I hope this technique helps. I've been using it for years, having
first learned it in an IBM 360 mainframe environment in college.
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