CODEWITHSUNDEEP
cassemblyprintfnasm
user902691
user902691

Reputation: 1159

Linux assembly and printf

i try write simple assemble program with printf function. I compile it nasm -f elf 64 and link using gcc. After run i see segmentation fault. What is wrong?

[Bits 32]

extern printf
global main

section .data 

hello:
db "Hello", 0xa, 0 

section .text

main:

push hello
call [printf]

add esp, 4

mov eax, 1
mov ebx, 0
int 80h

Upvotes: 6

Views: 8598

Answers (2)

olivecoder
olivecoder

Reputation: 2914

If you really want to get a 32 bit binary as your code header shows then you just need to fix the line:

call [printf]

changing it to:

call printf

When you do call [printf] you are not calling printf but the address pointed by first printf code bytes, that construction ([address]) is called an effective address.

Upvotes: 3

user1157391
user1157391

Reputation:

Linux on ia32 doesn't use the same calling convention as on amd64. As your code uses the former you must assemble it as 32 bits and link with a 32 bits libc. On debian you'll need the libc6-dev-i386 package.

You must also replace 'call [printf]' with 'call printf', that's a mistake.

Note also that as you are using the main interface you should return from main instead of performing an exit system call to allow the C runtime shutdown code to run.

Hello World example for x86-32 with build instructions.

If you are working on amd64, you might want to learn how to write 64 bits assembly instead.

Hello World example for x86-64 with build instructions.

Upvotes: 8

Related Questions