CODEWITHSUNDEEP
linuxassemblyx86system-callscalling-convention
bhuvanesh arasu
bhuvanesh arasu

Reputation: 5

Difference between EAX,1 and EBX,1 in assembly?

section     .text
global      _start                              ;must be declared for linker (ld)

_start:                                         ;tell linker entry point

    mov     edx,len                             ;message length
    mov     ecx,msg                             ;message to write
    mov     ebx,1                               ;file descriptor (stdout)
    mov     eax,4                               ;system call number (sys_write)
    int     0x80                                ;call kernel

    mov     eax,1                               ;system call number (sys_exit)
    int     0x80                                ;call kernel

section     .data

msg     db  'Hello, world!',0xa                 ;our dear string
len     equ $ - msg                             ;length of our dear string

Kernel source references:

How does the system know that it has to exit when it read EAX,1 and not EBX,1 ? Since 1 means Sys_Exit.

Upvotes: 0

Views: 7270

Answers (1)

Pierre
Pierre

Reputation: 1174

This comportement is defined in what we call ABI (application binary interface). This should help : What is Application Binary Interface (ABI)?

Upvotes: 1

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