shellcode error Segmentation fault (core dumped) - linux

Question

im new at shellcoding i try to write a shellcode for ( hello world ) so this is my first code with nulled bytes :
global _start
section .text
_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
and this is my second code after i remove null x00 !!
global _start
section .text
_start:
;tell linker entry point
xor edx,edx
mov dl,len ;message length
mov ecx,msg ;message to write
xor ebx,ebx
mov bl,1 ;file descriptor (stdout)
xor eax,eax
mov al,4 ;system call number (sys_write)
int 0x80 ;call kernel
xor eax,eax
mov al,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
i compile it to test by :
nasm -f elf32 -o hello-without-null.o hello-without-null.asm
ld -o hello-without-null hello-without-null.o
its work when i run it ./hello-without-null
than i used : objdump -d hello-without-null -M intel
and this is the result :
Disassembly of section .text:
08048080 <_start>:
8048080: 31 d2 xor edx,edx
8048082: b2 0e mov dl,0xe
8048084: b9 9c 90 04 08 mov ecx,0x804909c
8048089: 31 db xor ebx,ebx
804808b: b3 01 mov bl,0x1
804808d: 31 c0 xor eax,eax
804808f: b0 04 mov al,0x4
8048091: cd 80 int 0x80
8048093: 31 c0 xor eax,eax
8048095: b0 01 mov al,0x1
8048097: cd 80 int 0x80
then i convert it to shellcode by :
objdump -d ./hello-without-null|grep '[0-9a-f]:'|grep -v 'file'|cut
-f2 -d:|cut -f1-6 -d' '|tr -s ' '|tr '\t' ' '|sed 's/ $//g'|sed 's/ /\x/g'|paste -d '' -s |sed 's/^/"/'|sed 's/$/"/g'
the output is :
"\x31\xd2\xb2\x0e\xb9\x9c\x90\x04\x08\x31\xdb\xb3\x01\x31\xc0\xb0\x04\xcd\x80\x31\xc0\xb0\x01\xcd\x80"
when i test it i got this error :
Shellcode Length: 25 Segmentation fault (core dumped)
my c code for testing :
#include<stdio.h>
#include<string.h>
unsigned char code[] = \
"\x31\xd2\xb2\x0e\xb9\x9c\x90\x04\x08\x31\xdb\xb3\x01\x31\xc0\xb0\x04\xcd\x80\x31\xc0\xb0\x01\xcd\x80";
int main()
{
printf("Shellcode Length: %d\n", strlen(code));
int (*ret)() = (int(*)())code;
ret();
}
so what is the problem ?? and how i can solve it ?

Answer 1

i solve it by changing
char shellcode[]
to
const char shellcode[]
and using using the JMP/CALL/POP method