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int 21 causes an access violation

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Join Date: Jan 2007

Posts: 13

Reputation: blerina12 is an unknown quantity at this point

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blerina12

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Newbie Poster

int 21 causes an access violation

-1

Sep 26th, 2009

Hello guys. I am having a problem with the following code. When I try to run the program the instruction int 21 causes an access violation. Can someone tell me how to fix this problem?

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
.386
.model flat
 
.stack 100h
 
.data
 
message db 'Hello World', 13, 10, '$'
 
.code
 
_start: 
 
lea dx, message 
 
mov ah, 9h ; string output
 
int 21h ; display string
 
mov ax, 4c00h
 
int 21h
 
mov ah, 1h 
 
int 21h ; read character into al
 
mov dl, al 
 
mov ah, 2h 
 
int 21h ; display character in dl
 
mov ax, 4c00h 
 
int 21h
 
end _start
.386
.model flat

.stack 100h

.data

message db 'Hello World', 13, 10, '$'

.code

_start: 

lea dx, message 

mov ah, 9h ; string output

int 21h ; display string

mov ax, 4c00h

int 21h

mov ah, 1h 

int 21h ; read character into al

mov dl, al 

mov ah, 2h 

int 21h ; display character in dl

mov ax, 4c00h 

int 21h

end _start

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Join Date: Oct 2008

Posts: 137

Reputation: NotNull is an unknown quantity at this point

Solved Threads: 14

NotNull

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Junior Poster

Re: int 21 causes an access violation

Sep 26th, 2009

Access violation is caused when a program attempts to
access memory reserved for the operating system.
I thought this could only happen in a windows program?

I assume your using MASM:

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
mov ax, seg message ; initialize the DS register so
mov ds, ax                  ; you can access variable 'message'
lea dx, message
mov ax, seg message ; initialize the DS register so
mov ds, ax                  ; you can access variable 'message'
lea dx, message

Program flow stops before line 23, because you terminated
with 21/4C.

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Join Date: Jan 2007

Posts: 13

Reputation: blerina12 is an unknown quantity at this point

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blerina12

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Newbie Poster

Re: int 21 causes an access violation

Sep 27th, 2009

•

Originally Posted by NotNull

Access violation is caused when a program attempts to
access memory reserved for the operating system.
I thought this could only happen in a windows program?

I assume your using MASM:
Help with Code Tags

Assembly Syntax (Toggle Plain Text)
mov ax, seg message ; initialize the DS register so
mov ds, ax                  ; you can access variable 'message'
lea dx, message
mov ax, seg message ; initialize the DS register so mov ds, ax ; you can access variable 'message' lea dx, message
Program flow stops before line 23, because you terminated
with 21/4C.