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Quickpost: Machine Code Infinite Loop

published on 2022-04-30 08:04:25 UTC by Didier Stevens
Content:

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:

BITS 32

loop1:
    jmp loop1
loop2:
    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
     2                                  
     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: Quickpost: Machine Code Infinite Loop - published over 2 years ago.

https://blog.didierstevens.com/2022/04/30/quickpost-machine-code-infinite-loop/
Published: 2022 04 30 08:04:25
Received: 2022 04 30 08:05:57
Feed: Didier Stevens
Source: Didier Stevens
Category: Cyber Security
Topic: Cyber Security
Views: 2