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Ali.Z



Joined: 08 Jan 2018
Posts: 510
Ali.Z
I know for the fact that fasm use the shortest form available to encode instructions, so this not a bug report or whatsoever; but it would be nice to somehow be able to disable this optimization feature.

Code:
use32
; pseudo NOP instructions that are valid in 32-bit mode
; from 2 bytes, up to 9 bytes of pseudo NOP instructions

nop2:
; can assemble .......... YES
; assembled correctly ... YES
; expected bytes ....... 66 90
; assembled bytes ....... 66 90
db 66h
nop



nop3:
; can assemble .......... YES
; assembled correctly ... YES
; expected bytes ....... 0f 1f 00
; assembled bytes ....... 0f 1f 00
nop dword [eax]



nop4:
; can assemble .......... YES
; assembled correctly ... NO
; expected bytes ....... 0f 1f 40 00
; assembled bytes ....... 0f 1f 00
nop dword [eax+00h]



nop5:
; can assemble .......... YES
; assembled correctly ... NO
; expected bytes ....... 0f 1f 44 00 00
; assembled bytes ....... 0f 1f 04 00
nop dword [eax+eax*1+00h]



nop6:
; can assemble .......... YES
; assembled correctly ... NO
; expected bytes ....... 66 0f 1f 44 00 00
; assembled bytes ....... 66 0f 1f 04 00
db 66h
nop dword [eax+eax*1+00h]



nop7:
; can assemble .......... YES
; assembled correctly ... NO
; expected bytes ....... 0f 1f 80 00 00 00 00
; assembled bytes ....... 0f 1f 00
nop dword [eax+00000000h]



nop8:
; can assemble .......... YES
; assembled correctly ... NO
; expected bytes ....... 0f 1f 84 00 00 00 00 00
; assembled bytes ....... 0f 1f 04 00
nop dword [eax+eax*1+00000000h]



nop9:
; can assemble .......... YES
; assembled correctly ... NO
; expected bytes ....... 66 0f 1f 84 00 00 00 00 00
; assembled bytes ....... 66 0f 1f 04 00
db 66h
nop dword [eax+eax*1+00000000h]    

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Asm For Wise Humans
Post 23 Jan 2022, 10:09
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 18449
Location: In your JS exploiting you and your system
revolution
The usual method is to create a macro or equ for what you need.
Code:
macro nop2 { db 0x66, 0x90 }    
Post 23 Jan 2022, 11:01
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Ali.Z



Joined: 08 Jan 2018
Posts: 510
Ali.Z
this should be sufficient for my tests, thanks.

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Asm For Wise Humans
Post 24 Jan 2022, 13:09
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