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flat assembler > Main > invalid opcode

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Ali.Z



Joined: 08 Jan 2018
Posts: 193
just wanted to say, an interesting fact about eflags:

i was messing around and generating invalid opcodes, when ever i attempt to execute that opcode resume flags is set (RF)

and im not sure why lol, anyone knows anything about the relation of RF and invalid opcode?

edit:
found something, but i did not understand it.
now how would explain it, and it feels there are more hidden things behind it.
Quote:
The RF bit in EFLAGS controls the recognition of debug faults. This permits
debug faults to be raised for a given instruction at most once, no matter
how many times the instruction is restarted.


edit edit:
now whats going on?
Quote:
Resume flag (RF) of flags register
Allows an instruction to be restarted after a debug exception without
immediately causing another debug exception due to the same condition.

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Post 23 Dec 2018, 11:52
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 16455
Location: Crab Nebula
If you are trying to restart an invalid instruction; well you can't, It will always be invalid.

If you are trying to restart a valid instruction in a protected OS, then the OS can decide to create whatever error it wants to and pass that down to the app, or simply give up and tell the user the app did something invalid.
Post 23 Dec 2018, 12:46
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Furs



Joined: 04 Mar 2016
Posts: 1388
revolution wrote:
If you are trying to restart an invalid instruction; well you can't, It will always be invalid.
I heard that if you restart it 42 times while having your monitor facing a mirror without you obstructing them, an image of Cthulhu will appear in the mirror and then... stuff happens.
Post 23 Dec 2018, 13:34
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Mikl___



Joined: 30 Dec 2014
Posts: 110
Image
Post 23 Dec 2018, 13:38
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Ali.Z



Joined: 08 Jan 2018
Posts: 193
thanks Mikl, that figure explains it well.

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Asm For Wise Humans
Post 23 Dec 2018, 22:14
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