CODEWITHSUNDEEP
assemblyx86nasm
Eli Zatlawy
Eli Zatlawy

Reputation: 1012

Understanding some Assembly "Hello World" code: equ $ - msg1 prints both messages?

I have the following Assembly code:

section .text
      global _start
_start:
       mov edx,len2
       mov ecx,msg1
       mov ebx,1
       mov eax,4
       int 0x80     ; write(1, msg1, len2)
       mov eax,1  ;system call number (sys_exit) 
       int 0x80   ;call kernel

section  .data

   msg1 db   'Hello '
   len1 equ  $ - msg1
   msg2 db   'world!',0xa
   len2 equ  $ - msg1

I have been told that this code should print "Hello World!" but I can't understand why?

When I first looked at it I was sure it supposed to print just "Hello ". Can someone please help me to understand this, please?

Upvotes: 1

Views: 431

Answers (1)

Eli Zatlawy
Eli Zatlawy

Reputation: 1012

as @Jester said in the comment the reason is that len2 is defined as $ - msg1 not as $ - msg2 so it includes the length of the Hello as well.

Upvotes: 4

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