Yeditepe University
Department of Computer Engineering
ICS 232
Systems Programming and Assembly Language
Lecture Notes #4
Spring 2003
MACROPROCESSORS
A macro name is an abbreviation, which stands for some related lines of code. Macros are useful for
the following purposes:
 to simplify and reduce the amount of repetitive coding
 to reduce errors caused by repetitive coding
 to make an assembly program more readable.
Macro
definitions
expanded
source
code
Macroprocessor
Source code
with
macro calls
Assembler
Figure 1. Macro expansion on a source program.
Ex:
Macro Definition
User program
User program
(after macro expansion)
INITZ MACRO
header
MOV AX, @data
…
INITZ
…
MOV
…
MOV
MOV
…
MOV DS, AX
MOV ES, AX
ENDM
A template
(code)
trailer
prototype (macro name)
macro call
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AX, @data
DS, AX
ES, AX
Using parameters in macros:
Ex:
displaying a message. (Assume that: MES2 DB
Macro Definition
User program
PROMPT MACRO
MOV
LEA
INT
ENDM
…
MESSGE
;dummy argument
AH, 09H
DX, MESSGE
21H
;end of macro
‘Enter the data as mm/dd/yy’)
User program
(after macro expansion)
…
PROMPT MES2
…
…
MES2 DB ‘Enter the
data as mm/dd/yy’
MOV
AH, 09H
LEA
DX, MES2
INT
21H
…
MES2 DB ‘Enter the
data as mm/dd/yy’
Conditional assembly:
Only part of the macro is copied out into the code. Which part is copied out will be under the control of
the parameters in the macro call.
CONMB (condition) branch address
Ex:
Line
no.
…
8
9
…
15
…
Assembly instructions
…
CONMB
(&C>2), 15
…
…
If condition is true, skip the code up to line 15.
If condition is false, expansion continues from line 9.
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Design for a simple Macroassembler
read macro definitions into a memory buffer
more
source
code
Y
N
Assembler
get next line
N
Y
write line to the output file
macro call
call Macro Expander routine
Figure 2. A macroprocessor front end for an assembler
Find the appropriate macro definition
Build a parameter table to relate dummy and real parameters
LP = first line in the template
Examine the line
N
conditional
assembly call
Y
substitute real parameters
evaluate the Boolean expression
write it to the output file
N
LP = LP + 1
LP = LP + 1
Y
more lines
N
True
Y
LP = line number in the
statement
return
Figure 3. Macro Expander Routine
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LP: line pointer
Ex:
Source program
Macro definition
…
ALPHA A, 2, C
…
ALPHA
Parameter table
Dummy parameter
ARG1
ARG2
ARG3
MACRO ARG1, ARG2, ARG3
…
ENDM
Real parameter
A
2
C
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Macro calls within Macros
-
Use a stack to keep the order of the macro calls
Create a parameter table at each macro call
If a dummy parameter appears in the real parameter field of a called macro, search the parameter
table of the calling macro and replace it with the appropriate real parameter.
Find the appropriate macro definition
Build a parameter table to relate dummy and real parameters
Push LP onto the stack
LP = first line in the template
Examine the line
?
instruction
conditional
assembly call
substitute real parameters
macro call
macro end
evaluate the Boolean expression
write it to the output file
N
True
Find the appropriate
macro definition
Pop from stack
and set LP and
current param.
table pointer
Y
Build a parameter table
LP = LP + 1
LP = LP + 1
LP = line number in
the statement
Push LP and the pointer
to the last parameter table
onto the stack
LP = first line in the
template
Y
more lines
N
return
LP: line pointer
Figure 4. Macro Expander Routine that allows macro calls within macros
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