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me239



Joined: 06 Jan 2011
Posts: 200
me239
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?
Post 16 Jun 2011, 06:23
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typedef



Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000
typedef
or it ?

idk, wait for the os gurus who know about fat12
Post 16 Jun 2011, 07:02
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JohnFound



Joined: 16 Jun 2003
Posts: 3500
Location: Bulgaria
JohnFound
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.
Post 16 Jun 2011, 07:37
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me239



Joined: 06 Jan 2011
Posts: 200
me239
JohnFound wrote:
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.
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.
Post 16 Jun 2011, 07:52
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
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
    
Post 16 Jun 2011, 17:17
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