Working with the Unix OS

Processes I
The Context of a Process
The register context consists of:
- program counter processor status
- register stack pointer
- general purpose registers
The system-level context consists of:
- process table entry
- the u area
- pregion entries
- kernel stack
- dynamic part - set of layer
Figure 11. Components of Context of a Process
Saving the Context of a Process
! Interrupts and Exceptions
Kernel sequence to handle interrupts:
1. save current register context, push a new context layer
2. determine source of interrupt, type of interrupt, interrupt number
Figure 12. Sample Interrupt Vector
Interrupt Interrupt
Number Handler
0 c1ockintr
1 diskintr
2 ttyintr
3 devintr
4 softintr
5 otherintr
3. invoke interrupt handler
4. restore register context and kernel stack of previous context layer
algorithm inthand /* handle interrupts */
input: none
output: none
{
save (push) current context layer; determine interrupt source;
find interrupt vector;
call interrupt handler;
restore (pop) previous context layer;
}
Figure 13. Handling Interrupts
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