Undocumented instruction \ VOGONS

Undocumented instruction

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First post, by kekko

Posted on 2004-06-27, 19:42

kekko Offline

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some days ago I tried to run norton sysinfo on emulated
system and discovered that the program calls instruction
ffh 07h (two-byte opcode in group 5)
that is officially unsupported by intel.
of course the program crashes!
Does anyone knows which instruction is it?
Is there a way to understand and implement it
studying the execution of the opcode on a true cpu?
thanks!

Reply 1 of 3, by Harekiet

Posted on 2004-06-28, 08:36

Harekiet Offline

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Check http://www.sandpile.org/

Reply 2 of 3, by kekko

Posted on 2004-06-28, 11:02

kekko Offline

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Already done: nothing.
somewhere I saw that using softice with the program
on a true cpu i can obtain the behavior of the instruction
but I don't know how

Reply 3 of 3, by wd

Posted on 2004-06-28, 20:07

wd Offline

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> that is officially unsupported by intel
Where did you get that from? It's a standard INC,
just look at the address harekiet mentioned.

I guess you are mislead by the dosbox output
GRP5:Illegal Call 7 which is not 0xff 0x07.
It occurs when the program flow gets wrong, in
this case a zero pointer from int21/65 i think.

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