How to make shellcode

;hello.asm
[SECTION .text]

global _start


_start:

        jmp short ender

        starter:

        xor eax, eax    ;clean up the registers
        xor ebx, ebx
        xor edx, edx
        xor ecx, ecx

        mov al, 4       ;syscall write
        mov bl, 1       ;stdout is 1
        pop ecx         ;get the address of the string from the stack
        mov dl, 5       ;length of the string
        int 0x80

        xor eax, eax
        mov al, 1       ;exit the shellcode
        xor ebx,ebx
        int 0x80

        ender:
        call starter	;put the address of the string on the stack
        db 'hello'

---

$ nasm -f elf hello.asm
$ ld -o hello hello.o
$ objdump -d ./PROGRAM|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'

or
           by python

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from subprocess import Popen, PIPE import sys   def shellcode_from_objdump(obj):     res = ''     p = Popen(['objdump', '-d', obj], stdout=PIPE, stderr=PIPE)     (stdoutdata, stderrdata) = p.communicate()     if p.returncode == 0:         for line in stdoutdata.splitlines():             cols = line.split('\t')             if len(cols) > 2:                 for b in [b for b in cols[1].split(' ') if b != '']:                     res = res + ('\\x%s' % b)     else:         raise ValueError(stderrdata)       return res     if __name__ == '__main__':     if len(sys.argv) < 2:         print 'Usage: %s <obj_file>' % sys.argv[0]         sys.exit(2)     else:         print 'Shellcode for %s:' % sys.argv[1]         print shellcode_from_objdump(sys.argv[1])     sys.exit(0)