Quickpost: Machine Code Infinite Loop

Someone asked me what the byte sequence is for an infinite loop in x86 machine code (it’s something you could use while debugging, for example).

That byte sequence is just 2 bytes long: EB FE.

It’s something you can check with nasm, for example.

File jump-infinite-loop.asm:


    jmp loop1
    jmp short loop2
    jmp $
    jmp short $
    jmp short -2

nasm jump-infinite-loop.asm -l jump-infinite-loop.lst

File jump-infinite-loop.lst:

     1                                  BITS 32
     3                                  loop1:
     4 00000000 EBFE                        jmp loop1
     5                                  loop2:
     6 00000002 EBFE                        jmp short loop2
     7 00000004 EBFE                        jmp $
     8 00000006 EBFE                        jmp short $
     9 00000008 EB(FE)                      jmp short -2

Quickpost info

Article Link: Quickpost: Machine Code Infinite Loop | Didier Stevens