I try to print b, but it prints nothing. Also I wanted to find length of b to hardcode it (because dws have the same length), but it printed nothing too (that's why I created lenlen — len of blen, so that I can print blen). Don't pay attention to k and a, they are not used yet.
global _main:
section .data
b: dw 10
blen: equ $-b
lenlen: equ $-blen
k: dw 6
section .bss
a: resw 1
section .text
_main:
mov rax, 0x2000004
mov rdi, 1
mov rsi, b
mov rdx, blen
syscall
mov rax, 0x2000001
mov rdi, 0
syscall
Related
In nasm assembly on mac with the processor architecture x86_64, I am struggling to compare input to a string or character. When comparing input (stdin) to a character, it's not being true when it should be. I am new to assembly.
Here is my code.
global start
section .bss
input resb 10
section .text
start:
;getting the input
mov rax, 0x2000003 ;meaning read
mov rdi, 0
mov rsi, input
mov rdx, 10
syscall ;special
;here is where I do the comparing
mov rax, r
mov rbx, input
cmp rax, rbx
je right
;jumping to the return function
jmp ret
right:
mov rax, 0x2000004 ;meaning write
mov rdi, 1
mov rsi, right_way
mov rdx, right_len
syscall ;special
ret:
mov rax, 0x2000001 ;return 0
xor rdi, rdi ;which means to make rdi = 0 could be replaced with mov rdi, 0 but xor is faster
syscall
section .data
right_way: db "You are correct!", 10, 0
right_len: equ $-right_way
r: db "r", 10
At the "je right" line, it should jump to the right function but it does not. Do I need to convert the input to something else?
Help would be appreciated. Thanks!
I am trying to write a program that accepts 2 digits as user input, and then outputs their sum. I keep getting segmentation error when trying to run program(I am able to input 2 digits, but then the program crashes). I already check answers to similar questions and many of them pointed out to clear the registers, which I did, but I am still getting a segmentation fault.
section .text
global _main ;must be declared for linker (ld)
default rel
_main: ;tells linker entry point
call _readData
call _readData1
call _addData
call _displayData
mov RAX, 0x02000001 ;system call number (sys_exit)
syscall
_addData:
mov byte [sum], 0 ; init sum with 0
lea EAX, [buffer] ; load value from buffer to register
lea EBX, [buffer1] ; load value from buffer1 to register
sub byte [EAX], '0' ; transfrom to digit
sub byte [EBX], '0' ; transform to digit
add [sum], EAX ; increment value of sum by value from register
add [sum], EBX ; increment value of sum by value from 2nd register
add byte [sum], '0' ; convert to ASCI
xor EAX, EAX ; clear registers
xor EBX, EBX ; clear registers
ret
_readData:
mov RAX, 0x02000003
mov RDI, 2
mov RSI, buffer
mov RDX, SIZE
syscall
ret
_readData1:
mov RAX, 0x02000003
mov RDI, 2
mov RSI, buffer1
mov RDX, SIZE
syscall
ret
_displayData:
mov RAX, 0x02000004
mov RDI, 1
mov RSI, sum
mov RDX, SIZE
syscall
ret
section .bss
SIZE equ 4
buffer: resb SIZE
buffer1: resb SIZE
sum: resb SIZE
I see that, unlike other languages I learned, it is quite difficult to find a good source /tutorial about programming assembly using nasm on x86_64 architecture. Is there any kind of walkthrough for beginners(so I do not need to ask on SO everytime I am stuck :D)
So I have this code here were I'm trying to add two numbers in it but I can't seem to get the output from this code that I've been trying do for a while. :
section .text
global _start ;must be declared for using gcc
_start: ;tell linker entry point
mov edx, '6'
sub edx,'0'
mov ecx ,'7'
sub ecx,'0'
add edx,ecx
mov [math_sum], edx
mov eax,msg
mov ebx, len
mov ecx,1
mov edx,4
int 0x80
mov eax,math_sum
mov ebx,1
mov ecx,1
mov edx,4
int 0x80
mov edx,1
int 0x80
section .data
msg db "Sum of 6 and 7 is:"
len equ $ - msg
segment .bss
math_sum resb 2
I'm getting Segmentation fault but I don't know how to fix it.
I've searched around and I haven't found anything.
The code is as follows:
hello_world db "Hello World!",10
.hellolen equ $ - hello_world
get_input db "Enter a number: ",10
.getlen equ $ - get_input
input times 10 db 0
.len equ $ - input
section .text
global start
; Arguments go in the registers
;RDI, RSI, RDX, R10, R8, and R9, in order.
;System call number goes into RAX.
start:
call printHello
call askInput
call takeInput
call printInput
call exit
ret
printHello:
mov rax, 0x2000004
mov rdi, 1
mov rsi, hello_world
mov rdx, hello_world.hellolen
syscall
askInput:
mov rax, 0x2000004 ; System call write = 4
mov rdi, 1 ; Write to standard out = 1
mov rsi, get_input ; The address of enter string
mov rdx, get_input.getlen ; The size to write
syscall
takeInput:
mov rax, 0x2000003 ; System call read = 3
mov rdi, 2 ;
mov rsi, input ; buffer that we are reading to
mov rdx, input.len ;to create buffer overflow
;we can input more than
;input.len
syscall
printInput:
mov rax, 0x2000004 ; System call write = 4
mov rdi, 1 ; Write to standard out = 1
mov rsi, input ; The address of enter string
mov rdx, input.len ; The size to write
syscall
exit:
mov rax, 0x2000001 ; System call number for exit = 1
mov rdi, 0 ; Exit success = 0
syscall ; Invoke the kernel
And the output:
Hello World!
Enter a number:
r: <- weird random r:
test <- input by me
test <- correct value returned
Is there a way to view this with GDB so that I may figure out what is causing this problem? I'm not sure how to approach this from a troubleshooting perspective. Thank you!
I edited the code according to commentary and I am still getting the same odd r: in the output.
I need help. I'm trying to run the program (NASM) below in SASM.
SYS_EXIT equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1
segment .data
msg1 db "Enter a digit ", 0xA,0xD
len1 equ $- msg1
msg2 db "Please enter a second digit", 0xA,0xD
len2 equ $- msg2
msg3 db "The sum is: "
len3 equ $- msg3
segment .bss
num1 resb 2
num2 resb 2
res resb 1
section .text
global _start ;must be declared for using gcc
_start: ;tell linker entry point
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num1
mov edx, 2
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg2
mov edx, len2
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num2
mov edx, 2
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80
; moving the first number to eax register and second number to ebx
; and subtracting ascii '0' to convert it into a decimal number
mov eax, [num1]
sub eax, '0'
mov ebx, [num2]
sub ebx, '0'
; add eax and ebx
add eax, ebx
; add '0' to to convert the sum from decimal to ASCII
add eax, '0'
; storing the sum in memory location res
mov [res], eax
; print the sum
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res
mov edx, 1
int 0x80
exit:
mov eax, SYS_EXIT
xor ebx, ebx
int 0x80
I had this error:
[20:53:11] Warning! Errors have occurred in the build:
c:/program files (x86)/sasm/mingw/bin/../lib/gcc/mingw32/4.6.2/../../../libmingw32.a(main.o): In function 'main':
C:\MinGW\msys\1.0\src\mingwrt/../mingw/main.c:73: undefined reference to `WinMain#16'
Also, how do I limit users input up to 4 digits only?
global _start should change to global main and Linux system calls should be replaced by Windows API function calls and declared as external. Modern versions of Windows doesn't approve use of system calls due to malware or badware risks, so deprecated (permanent) system call codes. Every modern version of Windows has different system call number codes, though you can find them on internet, you shouldn't rely on them unless you want to revise your assembly code for each version of Windows thus reducing portability and increasing workload. There are significant differences between Linux/Mac and Windows in the way of handling registers, stack and function names.