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me239

Joined: 06 Jan 2011
Posts: 200

me239 16 Jun 2011, 06:23

Hello everyone! I just got directory support and file execution on my OS and now I want to add some form of protection from running the kernel again. I want to make it so that hidden files can neither be run or seen. I know that the attribute byte on fat12 is at 11d and that bit 2 is hidden. My question is how do I find whether bit 2 is enabled or not?

16 Jun 2011, 06:23

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 16 Jun 2011, 07:02

or it ?

idk, wait for the os gurus who know about fat12

16 Jun 2011, 07:02

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 16 Jun 2011, 07:37

It is strange you write your own OS, but miss so basic knowledge as testing bits... Shocked

Anyway, read "bt" instruction and "test" instruction reference.

16 Jun 2011, 07:37

me239

Joined: 06 Jan 2011
Posts: 200

me239 16 Jun 2011, 07:52

JohnFound wrote:

It is strange you write your own OS, but miss so basic knowledge as testing bits...
Anyway, read "bt" instruction and "test" instruction reference.

LOL, I know how to test for things like odd numbers. I think I figured it out now. I and it with 2 and test for a zero. Is this correct?
P.S it's 4am where I live and am very tired so I'm probably not thinking too well.

16 Jun 2011, 07:52

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 16 Jun 2011, 17:17

Code:

BIT_TO_TEST = 2 ; Change at will
test byte[mem], 1 shl BIT_TO_TEST
jnz .itIsSet

; If you want to create a BOOL in AL
mov al, [mem]
shr al, BIT_TO_TEST
and al, 1
; Now AL is either zero or one

;Alternate method (386+):
test byte[mem], 1 shl BIT_TO_TEST
setnz al

16 Jun 2011, 17:17

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