I try write follow code, use int 0x80 to print number 5 but it don't print anything.
segment .bss
num1 resb 1
section .text
global _start
_start:
mov dword [num1],5
add [num1],byte '0'
mov ecx, dword [num1]
mov eax, 4
mov ebx, 1
mov edx, 1
int 0x80
mov eax, 1
int 0x80
System call 4 expects ecx to contain a pointer to a NUL-terminated string.
So instead of mov ecx, dword [num1] you should use mov ecx, num1.
Related
I'm a novice Assembly x86 Learner, and i want to add two numbers (5+5) and print the result on the screen.
here is my code:
global _start
section .text
_start:
mov eax, 5
mov ebx, 5
add eax, ebx
push eax
mov eax, 4 ; call the write syscall
mov ebx, 1 ; STDOUT
pop ecx ; Result
mov edx, 0x1
int 0x80
; Exit
mov eax, 0x1
xor ebx, ebx
int 0x80
Correct me please
Another approach to convert an unsigned integer to a string and write it:
section .text
global _start
_start:
mov eax, 1234567890
mov ebx, 5
add eax, ebx
; Convert EAX to ASCII and store it onto the stack
sub esp, 16 ; reserve space on the stack
mov ecx, 10
mov ebx, 16
.L1:
xor edx, edx ; Don't forget it!
div ecx ; Extract the last decimal digit
or dl, 0x30 ; Convert remainder to ASCII
sub ebx, 1
mov [esp+ebx], dl ; Store remainder on the stack (reverse order)
test eax, eax ; Until there is nothing left to divide
jnz .L1
mov eax, 4 ; SYS_WRITE
lea ecx, [esp+ebx] ; Pointer to the first ASCII digit
mov edx, 16
sub edx, ebx ; Count of digits
mov ebx, 1 ; STDOUT
int 0x80 ; Call 32-bit Linux
add esp, 16 ; Restore the stack
mov eax, 1 ; SYS_EXIT
xor ebx, ebx ; Return value
int 0x80 ; Call 32-bit Linux
When I run this program it says:
jdoodle.asm:9: error: invalid combination of opcode and operands
The problem is the AND al, ah. The rest of the code should be correct, I just need to know how to solve this problem because as it seems I can't do an AND between 2 registers.
section .text
global _start
_start:
call _input
mov al, input
mov ah, maschera
and al, ah
mov input, al
call _output
jmp _exit
_input:
mov eax, 3
mov ebx, 0
mov ecx, input
mov edx, 1
int 80h
ret
_output:
mov eax, 4
mov ebx, 1
mov ecx, input
mov edx, 1
int 80h
ret
_exit:
mov eax, 1
int 80h
section .data
maschera: db 11111111b
segment .bss
input resb 1
MASM/TASM/JWASM syntax is different from NASM. If you want to load/store data at an address you need to explicitly use square brackets. If you want to use the MOV instruction to place the address of a label in a variable you do not use square brackets. Square brackets are like a de-reference operator.
In 32-bit code you will want to ensure addresses are loaded into 32-bit registers. Any address above 255 won't fit in an 8 byte register, any address above 65535 won't fit in a 16-bit register.
The code you were probably looking for is:
section .text
global _start
_start:
call _input
mov al, [input]
mov ah, [maschera]
and al, ah
mov [input], al
call _output
jmp _exit
_input:
mov eax, 3
mov ebx, 0
mov ecx, input
mov edx, 1
int 80h
ret
_output:
mov eax, 4
mov ebx, 1
mov ecx, input
mov edx, 1
int 80h
ret
_exit:
mov eax, 1
int 80h
section .data
maschera: db 11111111b
segment .bss
input resb 1
At start I want to say that I'm a beginner in Assembly. I want to write a program which firstly adds two numbers and then divide the result by 2, so i want to get an average of two numbers. The problem is in section after dividing, but program without this section about dividing works well and prints the sum.
section .data
mess1 db 'Podaj pierwsza liczbe: '
len1 equ $- mess1
mess2 db 'Podaj druga liczbe: '
len2 equ $- mess2
mess3 db 'Wynik: '
len3 equ $- mess3
section .bss
zmienna1 resb 4
zmienna2 resb 4
wynik resb 8 ;result
section .text
global _start
_start:
mov eax,4
mov ebx,1
mov ecx,mess1
mov edx,len1
int 0x80
mov eax,3 ;sys_read to 3
mov ebx,0 ;stdin
mov ecx,zmienna1
mov edx,4 ;4 to rozmiar
int 0x80
mov eax,4
mov ebx,1
mov ecx,mess2
mov edx,len2
int 0x80
mov eax,3
mov ebx,0 ;sys_read i stdin
mov ecx,zmienna2
mov edx,4 ;4 rozmiar
int 0x80
mov eax,4
mov ebx,1
mov ecx,mess3
mov edx,len3
int 0x80
;Teraz wrzuc zmienna1 do eax, a zmienna2 do ebx
; odejmij ASCII-owe '0' aby przekonwertowac na dzisiejtne
mov eax,[zmienna1]
sub eax,'0'
mov ebx,[zmienna2]
sub ebx,'0'
add eax,ebx
add eax,'0' ;zamien na binarne z decymalnego
mov [wynik],eax
div wynik,'2'
add wynik,'0'
;pokaz sume
mov eax,4 ;
mov ebx,1
mov ecx,wynik
mov edx,8 ;8 to rozmiar tego wyniku z bss
int 0x80
exit:
mov eax,4
xor ebx,ebx
int 0x80
I am new have very small problem with assembly NASM in linux. I made simple program for practice that when you put in the text, it adds simple decoration in form of stars. The expected output is:
*********EXAMPLE*********
instead:
*********EXAMPLE
*********
here is the complete code of the program (long) i have use edb to check the code and check EDX register if it match the len take by the null byte check to print correct number of characters.
section .data
prompt db "Please enter a word (MAX: 10 Characters) : ", 0xa, 0xd
plen equ $ - prompt
stars times 9 db "*"
section .bss
text resb 10
section .text
global _start
_start:
mov eax, 4
mov ebx, 1
mov ecx, prompt
mov edx, plen
int 0x80
mov eax, 3
mov ebx, 0
mov ecx, text
mov edx, 11
int 0x80
xor ecx, ecx
mov esi, text
mov ecx, 0
loop1:
inc ecx
cmp byte [esi + ecx], 0x00
jne loop1
push ecx
jmp printexit
printexit:
mov eax, 4
mov ebx, 1
mov ecx, stars
mov edx, 9
int 0x80
mov eax, 4
mov ebx, 1
mov ecx, text
pop edx
int 0x80
mov eax, 4
mov ebx, 1
mov ecx, stars
mov edx, 9
int 0x80
mov eax, 1
int 0x80
Currently I'm trying to loop over every single byte in a buffer (read from a file) and compare it to see if any of them is a whitespace, and write them to STDOUT. For some reason the program compiles and runs fine, but produces zero output.
section .data
bufsize dw 1024
section .bss
buf resb 1024
section .text
global _start
_start:
; open the file provided form cli in read mode
mov edi, 0
pop ebx
pop ebx
pop ebx
mov eax, 5
mov ecx, 0
int 80h
; write the contents in to the buffer 'buf'
mov eax, 3
mov ebx, eax
mov ecx, buf
mov edx, bufsize
int 80h
; write the value at buf+edi to STDOUT
mov eax, 4
mov ebx, 1
mov ecx, [buf+edi]
mov edx, 1
int 80h
; if not equal to whitespace, jump to the loop
cmp byte [buf+edi], 0x20
jne loop
loop:
; increment the loop counter
add edi, 1
mov eax, 4
mov ebx, 1
mov ecx, [buf+edi]
int 80h
; compare the value at buf+edi with the HEX for whitespace
cmp byte [buf+edi], 0x20
jne loop
; exit the program
mov eax, 1
mov ebx, 0
int 80h
The main problem was that I didn't given the address of bufsize ([bufsize]), also the loops had some problems.
Here's the fixed version, thanks everyone for your input.
section .data
bufsize dd 1024
section .bss
buf: resb 1024
section .text
global _start
_start:
; open the file provided form cli in read mode
mov edi, 0
pop ebx
pop ebx
pop ebx
mov eax, 5
mov ecx, 0
int 80h
; write the contents in to the buffer 'buf'
mov eax, 3
mov ebx, eax
mov ecx, buf
mov edx, [bufsize]
int 80h
; write the value at buf+edi to STDOUT
; if equal to whitespace, done
loop:
cmp byte [buf+edi], 0x20
je done
mov eax, 4
mov ebx, 1
lea ecx, [buf+edi]
mov edx, 1
int 80h
; increment the loop counter
add edi, 1
jmp loop
done:
; exit the program
mov eax, 1
mov ebx, 0
int 80h