Transcript Debug and Assembler - National Institute of Technology

Debug and Assembler
By,
B.R.Chandavarkar
Lect. COMP Department
NITK, Surathkal.
Debug
• Debugging is a methodical process of finding and
reducing the number of bugs, or defects, in a
computer program, thus making it behave as
expected.
• It is program which allows the programmer to
write , execute and debug assembly language
programs, and to examine the content of
registers and memory. It can also be used to run
a program one instruction at a time.
• To start DEBUG its name is typed after DOS
prompt. i.e. c:\> DEBUG
Debug Commands
• It has a number of commands to facilitate users
to write, execute and debug programs.
• A DEBUG command is represented by a one-letter
symbol.
• DEBUG commands are not case-sensitive.
• A – Assemble Command.: It allows user to enter assembly
language program and converts it into machine codes.
Syntax: A [offset-address]
• U – Unassemble Command : It disassembles machine codes
of specified memory addresses and gives corresponding
mnemonics.
Syntax: U [address-range]
• R – Register Command : Used to display the contents of
one or more registers. It also display the status of the
flags.
Syntax: R [register name]
• G – Go Command : It is used to execute a program.
Syntax: G [= address]
• T – Trace Command : It is used to run a program in
single-step mode.
Syntax: T = address [step]
• D – Display or Dump Command : It is used to
display the contents of specified memory
locations.
Syntax: D address-range or D address
• E – Enter Command : It is used to enter the
data or machine code. Its default register is
the DS.
Syntax: E address
• F – Fill Command : It is used to fill the
specified range of locations with the values
given in a list.
Syntax: F address-range values
• M – Move Command : It copies the block of data
from one memory area to another.
Syntax: M range address
• S – Search Command :It is used to search the
specified memory range for the specified list of
bytes. The default register is the DS.
Syntax: S range list
• N – Save Command : It is used to save a file.
Syntax: N filename.com
• W – Write Command
• L – Load Command
• Q – Quit Command
Assembler
• An assembler is a computer program for
translating assembly language — essentially, a
mnemonic representation of machine language —
into object code
• It is program which allows the programmer to
write , execute and debug assembly language
programs, and to examine the content of
registers and memory. It can also be used to run
a program one instruction at a time.
• It is more powerful and provides more facilities
as compared to DEBUG.
• Self-Assembler or Resident-Assembler : It runs
on a computer for which it produces object
codes.
• Cross-Assembler : It runs on a computer other
than that for which it produces object codes.
• Macro-Assembler : Which allows the user to
define sequence of instructions as macro.
• Meta-Assembler : Which can handle different
instruction sets.
• Disassembler : Which generates assembly Language
Program corresponding to an object program.
• One-Pass Assembler : Which goes through an ALP
only once and produces its object codes.
• Two-Pass Assembler : Which goes through an ALP
only twice and produces its object codes.
• An ALP contains two types of statements :
Instructions : These are translated into machine
codes.
Directives : These are not translated into
machine codes. It gives the direction to the
assembler to perform the task of assembly
process. The assembler supports directives for
data definition, segment organization,
procedures, macro definition, etc.
• Examples : MASM(Microsoft ASseMbler), TASM(Turbo
ASseMbler), FASM(FlatASseMbler), NASM(Netwide
ASseMbler), etc.
• Symbols, Variables and Constants :
* The following characters are used for
symbols: A to Z, a to z, 0 to 9, _, @, $, ?
* The following characters are used for
variables: A to Z, a to z, 0 to 9, _, @. The
digits are not used as a first character of a
variable name. Maximum Length of a variable is
up to 32 characters. The letters B, D and H are
written at the end of a binary, decimal and
hexadecimal number respectively.
Directives
• DB – Define Byte : It defines a byte type
variable. It direct the assembler to reserve one
byte of memory and initialize that byte with the
specified value. It can define single or
multiple variables.
Examples:
Temperature DB 10
Temperature DB ?
Temperature DB 10. 20. 30. 40. 50
Temperature DB ?. ?. ?. ?. ?
Temperature DB 100 DUP(?)
Temperature DB 10. 5 dup(55). 20
Temperature DB 4 DUP( 3 DUP(5))
Temperature DB “ABCD”
• DW – Define Word : It defines a word type
variable. It direct the assembler to reserve two
byte of memory and initialize those bytes with
the specified value. It can define single or
multiple variables.
Examples :
Temperature DW 1234H
Temperature DW 1234. 5678. 1456
Temperature DW 2 DUP(0)
• DD – Define Double Word : It defines a double
word(4 bytes) type variable. It direct the
assembler to reserve four byte of memory and
initialize those bytes with the specified value.
It can define single or multiple variables.
Examples :
Temperature DD 12345678
Temperature DD 5 DUP(0)
• DQ – Define Quad Word : It defines a quad
word(8 bytes) type variable. It direct the
assembler to reserve eight byte of memory and
initialize those bytes with the specified value.
It can define single or multiple variables.
Examples :
Temperature DQ 12345678
Temperature DQ 5 DUP(0)
• DT – Define Ten Bytes
• EXTRN – External : It tells the assembler that
names or labels following the directive are in
some other assembly module.
Examples:
EXTERN Temperature : word
EXTERN Temperature : far
• PUBLIC : It informs the assembler that the
defined name or label can be accessed from other
program modules.
Examples:
PUBLIC Temperature1, Temperature2
• GLOBAL :
• SEGMENT : It indicate the beginning of a logical
segment.
Syntax: segment name SEGMENT [word/public]
• ENDS : It informs the assembler the end of the
segment.
Syntax: segment name ENDS
• ENDP : It indicate the end of procedure.
Syntax: procedure name ENDP
• END : It indicate the end of the program.
• ASSUME : This tells the assembler the name of a
logical segment, which is to be used for a
specified segment.
Examples: ASSUME CS:code; DS:data
• EQU : It assign name to some value.
Examples: Temp EQU 04H
• ORG : It tells the assembler to assign addresses
to data items or instruction in a program.
Examples:
•
•
•
•
•
ORG 0100H
ORG $
current value of address
ORG $ + 30
SRUCT or STRUC :It is used to define the start
of a data structure.
PTR : It is an operator. It points the type of
memory access.
Examples: mov byte ptr [bx], 58h
LENGTH : It tells the assembler to determine the
number of elements in a specified variable.
Examples: mov cx, length arry1
SIZE : It gives the number of byte allocated to
data item.
OFFSET : It determines the offset.
MASM(Microsoft
Macro Assembler)
• The Microsoft Macro Assembler (abbreviated MASM)
is an assembler for the x86 family of
microprocessors. It was originally produced by
Microsoft for development work on their MS-DOS
operating system, and was for some time the most
popular assembler available for that operating
system.
• Steps to work on MASM:
* c:\masm> edit [filename.asm]
* Save file with filename.asm
* c:\masm> masm filename.asm
* c:\masm> link filename + io
* c:\masm> filename
TASM(Turbo
ASseMbler)
• The Turbo Assembler (TASM) mainly PC-targeted
assembler package.
• TASM worked well with Borland's high-level
language compilers for the PC, such as Turbo C
and Turbo Pascal.
• Steps to work on TASM:
* c:\tasm> edit [filename.asm]
* Save file with filename.asm
* c:\tasm> tasm filename.asm
* c:\tasm> tlink filename + io
* c:\tasm> td filename