Script started on Wed 28 Feb 2024 04:29:53 PM EST
[mweeks@gsuad.gsu.edu@snowball ~]$ cat ptr.asm
; Assemble:	  nasm -f elf64 ptr.asm
; Link:		  gcc ptr.o -o ptr

; This is adapted for NASM.

    extern  printf      ; We will use this external function

    section .data       ; Data section, initialized variables

mystr:    db "%x", 10, 0   ; String format to use (decimal), followed by NL
myDouble: dd 12345678h

    section .text
    global main
main:
   xor rax, rax          ; A = 0

   mov al, byte [myDouble]
   mov   rsi, rax
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

   mov al,BYTE [myDouble+1]
   mov   rsi, rax
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

   mov al,BYTE [myDouble+2]
   mov   rsi, rax
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

   mov al,BYTE [myDouble+3]
   mov   rsi, rax
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf


   mov  rax, 0
   ret
[mweeks@gsuad.gsu.edu@snowball ~]$ nasm -f elf64 ptr.asm
[mweeks@gsuad.gsu.edu@snowball ~]$ gcc ptr.o -o ptr
[mweeks@gsuad.gsu.edu@snowball ~]$ ./ptr
78
56
34
12
[mweeks@gsuad.gsu.edu@snowball ~]$ echo notice that "PTR" is *not* recgonized in nasm 
notice that PTR is *not* recgonized in nasm
[mweeks@gsuad.gsu.edu@snowball ~]$ cat ptr.c
/* 
   Example of ptr in C (see Irvine's ch 4)
   - Michael Weeks
*/

#include <stdio.h>

union myunion {
  unsigned int myint;
  char mychar[4];
};


int main (int argc, char *argv[]) {

   union myunion example;
   example.myint = 0x12345678;

   int i;

   printf("myint is %x\n", example.myint); 
   printf("mychar[0..3] are ", example.myint); 
   for (i=0; i<4; i++)
     printf("%x ", example.mychar[i]);

   printf("\n");

   return 0;
}
[mweeks@gsuad.gsu.edu@snowball ~]$ gcc ptr.c -o ptrc
[mweeks@gsuad.gsu.edu@snowball ~]$ echo different filename so it does not overwrite the assembly example
different filename so it does not overwrite the assembly example
[mweeks@gsuad.gsu.edu@snowball ~]$ ./ptrc
myint is 12345678
mychar[0..3] are 78 56 34 12 
[mweeks@gsuad.gsu.edu@snowball ~]$ exit
exit

Script done on Wed 28 Feb 2024 04:32:36 PM EST