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Full Discussion: x86 Interrupts and system calls
Top Forums UNIX for Dummies Questions & Answers x86 Interrupts and system calls Post 302609293 by shamrock on Monday 19th of March 2012 03:32:29 PM
Old 03-19-2012
Quote:
Originally Posted by ab_tall
@Shamrock

Yes infact, I believe I was getting confused between system calls and interrupts.

More specifically, where system call handling and exception handling meet, that is what portion of the system call handling is managed by exceptions and so on.
System call handling is the second step of exception handling.
Quote:
Originally Posted by ab_tall
Could you tell me if the following diagram seems correct to you?

Linux system call È£Ãâ °úÁ¤ :: ³×À̹ö ºí·Î±×
Which book did you get this from...it is awesome and it shows exactly how system call handling occurs...and thanks for posting it.
Quote:
Originally Posted by ab_tall
This diagram concurs with my current understanding, but from the prev. posts in this thread seem to suggest that there isn't a separate dispatch table from the interrupt vector table...so what am I missing here?
That depends on the type of interrupt...if the kernel gets the divide_by_zero interrupt it will get the address of its exception handler and jump to the location where it is located...system call handling is done differently due to the numerous handlers associated with it. Also the linux kernel may implement it differently from the legacy unix kernels like aix solaris hpux.
Quote:
Originally Posted by ab_tall
Btw I was concerned about the system call no. as the total system call count exceeds the no. of interrupts provided by the x86 architecture so I was wondering how we indexed into the vector table (300 odd v/s 255 s/w interrupts)... Please feel free to correct me if I'm wrong.
System call handling is multiplexed due to the numerous ISRs...the read syscall will have a separate ISR from write so that is why after the int 0x80 instruction the kernel gets the base address of the interrupt vector table from the IDT and then uses the system call no to index into the IVT to get the address of the ISR to execute...and if my explanation is confusing the picture you posted is perfect for an explanation and you can totally ignore my blah blah blah Smilie
 

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