CODEWITHSUNDEEP
c++segmentation-faultnasm
Aleksander Monk
Aleksander Monk

Reputation: 2907

nasm 64, segmentation fault

I'm trying to copy array A to array B. Here's my cpp file.

#include <stdio.h>

using namespace std;

void copy(int * to, int * from, unsigned int n); //_Z6copyPiS_j

int main(){
  int * a = new int [4];
  int * b = new int [4];
  for (int i=0;i<4;++i)
  {
    a[i] = i+1;
  }
  kopiuj(b,a,4);
  for (int i=0;i<4;++i)
  {
    printf("%d - ", b[i]);
  }
  delete(a);
  delete(b);
  return 0;
}

and here is my asm file with copy function implementation

BITS 64
section .text

global _Z6kopiujPiS_j

_Z6kopiujPiS_j:                  

push rbp
mov rbp, rsp
cld
mov edi,  dword [rbp+8] ; destination
mov esi,  dword [rbp+12] ; source
mov ecx,  dword [rbp+16] ; size

rep movsd; repeat ecx times


mov rsp, rbp
pop rbp
ret

here is how I compile it. Unfortunately it has to be 64 bit.(exercise requirement)

// nasm -felf64 82.asm -o 82.o
// g++ -m64 -o 82m.o -c 82m.cpp
// g++ -m64 82m.o 82.o -o 82

and at rep movsd I get segmentation fault. What I'm doing wrong ?

Upvotes: 0

Views: 110

Answers (1)

Alan Stokes
Alan Stokes

Reputation: 18972

You seem to be assuming the parameters are passed on the stack. The common calling conventions for x64 use registers for the first few parameters. See Why does Windows64 use a different calling convention from all other OSes on x86-64?. (Or look at the generated assembly for the call to see how the parameters are passed.)

Upvotes: 3

Related Questions