Invisible nous apporta ses lumieres en ce 2007/12/03 04:46:
> Darren New wrote:
> 
>> At the lowest lowest level, I'm pretty sure the libraries load up 
>> arguments into registers and execute an INT instruction, which is a 
>> "software interrupt", aka a trap, which causes a branch to an address 
>> loaded into a specific area of memory. I.e., just like handling an 
>> interrupt, or just like branching to a jump table in a library, except 
>> that you get privilege bits flipped around.
>>
>> I don't know of any modern multiuser OS that doesn't use that 
>> technique to get into the kernel, as it's pretty much the only way to 
>> bypass memory and execution permissions in a controlled way.
> 
> OK, that's what I wanted to know...
> 
> (PS. Is there more than one interrupt level available? Or does it decide 
> which routine to call based on some other parameter?)
If my memory is good. On the 8086, there where about 256 programable software 
interupts available to programmers. Interupts 0 to 15 are special periferals 
interupts. There where also some hardware interupts, but I don't know how many. 
The "Reset" switch triggers one of them.

-- 
Alain
-------------------------------------------------
   I'm so ugly I stuck my head out the window and got arrested for Mooning.
   	Rodney Dangerfield

Post a reply to this message