CODEWITHSUNDEEP
assemblyx86nasm
ocket8888
ocket8888

Reputation: 1140

Can't output to stdout twice in nasm x86

I'm learning basic NASM x86 assembly, and I'm having issues printing to stdout twice in the same binary. My code is:

section .data
    pokelst:                dw  'Bulbasaur',0xa,'Charmander',0xa,'Squirtle',0
    pokelstLen:             equ $-pokelst
    endl:                   db      '\n'
    smiley:                 db  '\u23a',0xa
    smileyLen:              equ $-smiley

section .text
    global _start
    _start:
            mov ebx,1
            mov ecx,smiley
            mov eax,4
            mov edx,smileyLen
            int 80h
            int 80h
            mov eax,1       ;syscall code 1 is exit
            mov ebx,0       ;ebx contains exit code (canonically, 0 means no errors)
            int 80h         ;int 80h=syscall

The output was:

\u23a
 ocket8888@ParanoidLinux  ~ 

Ignoring the fact that it's not resolving uni-code, it seems to me that if I use int 80h twice, it should print twice. But, it very clearly is not.

What am I doing wrong?

Upvotes: 1

Views: 421

Answers (1)

SirPython
SirPython

Reputation: 647

Reading the RETURN section or write(2)...

On success, the number of bytes written is returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately.

After this call finishes, a value is returned to EAX. That means, when you try to run the interrupt again, you are going to be running a different interrupt.

Upvotes: 4

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