06 - Process attributes

Class: CSCE-313

Notes:

Outline:

• Process attributes
• Process context switching as a way of virtualizing the CPU
• Process states and some early thoughts on process schedulers

The story so far

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Notes:

• We write a program in some high-level language
• The compiler turns it into an executable stored into a specially formatted file (linking format)
• In that file there are sections that define where the code and data segment is
  • It also takes care of libraries, becoming part of the executable
• Every time you want some service from the OS you go from privilege 3 to 0 and execute code in the kernel
  • There is a dispatching mechanism that allows you to redirect to entry points

Program execution flow

1. Load code and data segments from executable file into memory
2. Create stack and heap
3. Transfer control to program's entry point
4. Provide services to it (network, file connections IO, etc.)

Notes:

• Heap is created on-demand, the OS gives you 1 or two pages extra into your virtual address space
• You jump into the entry point of your program (which is not your main function)
  • This will build a stack frame for your main function
• As you do system calls you get more services from your OS

Program execution flow

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Notes:

• Context switching is saving all of this info into some block of memory and restoring the state from another process
• The moment you assign the instruction pointer, it will be that other processes instruction
• Is really nothing more than switching memory blocks