CODEWITHSUNDEEP
assemblyx86-64
sinceq
sinceq

Reputation: 924

How to make it work in x86-64 assembly?

Recently I'm learning assembly and now i have some confusion. I learned it from Professional Assembly language.

My System's arch:

#uname -m
x86_64

This is my code:

.section .data
output:
   .asciz "This is section %d\n"
.section .text
.globl _start
_start:
    pushq $1
    pushq $output
    call printf
    addq $8, %rsp
    call overhere
    pushq $3
    pushq $output
    call printf
    addq $8, %rsp
    pushq $0
    call exit
overhere:
    pushq %rbp
    movq %rsp, %rbp
    pushq $2
    pushq $output
    call printf
    addq $8, %rsp
    movq %rbp, %rsp
    popq %rbp
    ret

I assemble, link and run it like this, getting the error message shown:

#as -o calltest.o calltest.s
#ld -dynamic-linker /lib64/ld-linux-x86-64.so.2 -lc -o calltest calltest.o
#./calltest 
Segmentation fault

How do I make it work?

Upvotes: 1

Views: 1007

Answers (1)

rkhb
rkhb

Reputation: 14409

x86_64 has another kind of passing arguments, see: http://en.wikipedia.org/wiki/X86_calling_conventions#System_V_AMD64_ABI

This is how your example would work:

.section .data
output:
   .asciz "This is section %d\n"
.section .text
.globl _start
_start:
    movq $output, %rdi      # 1st argument
    movq $1, %rsi           # 2nd argument
    xorl %eax, %eax         # no floating point arguments
    call printf
    call overhere
    movq $output, %rdi      # 1st argument
    movq $3, %rsi           # 2nd argument
    xorl %eax, %eax         # no floating point arguments
    call printf
    xor %edi, %edi
    call exit
overhere:
    pushq %rbp
    movq %rsp, %rbp
    movq $output, %rdi      # 1st argument
    movq $2, %rsi           # 2nd argument
    xorl %eax, %eax         # no floating point arguments
    call printf
    movq %rbp, %rsp
    popq %rbp
    ret

Upvotes: 5

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