Undocumented opcodes

[inflater]

Some non-documented opcodes that I've found in my holy ASM programming e-book AThelp:

PUSH IP: db 0E8h, db 0, db 0
POP CS (only 8086): db 0Fh
LOADALL (386): db 0Fh, db 07h
db 0D6h: This will set AL to 0 when CF=0, otherwise AL = 0FFh

I didn't test them, but have fun. Also you are free to expand this article by yours, if you found any

[JamesM]

PUSH IP: db 0E8h, db 0, db 0

There's a reason this is undocumented. What does this actually expand to when it's de-microcoded? What is IP? With an architecture such as the x86 "IP" can hold one of 30-more different values depending whereabouts in the pipeline you are. At what point in the pipeline is the value of IP taken?

As I said, there's a reason it's undocumented. Expect strange behaviour.

[quirck]

afaik

Code: Select all

db 0xE8,0,0

is equivalent to

Code: Select all

call @F
@@:

So it seems to be a fully documented instruction, and there must be nothing strange in its behaviour.

[Combuster]

If you want that SALC instruction legally, just use SBB AL, AL