CPU Modes and Memory

Question 1

What are the 3 IA-32 CPU Modes?

Answer 1

• Real mode
• Protected mode
• System management mode

Question 2

Which mode is the mode discussed in this course?

Answer 2

• Protected mode

Question 3

System Management Mode

Answer 3

• used for power management tasks

Question 4

Real Mode

Answer 4

• at power up or rest
• can only access 1 MB memory
• no memory protection
• privilege levels (kernel vs. user space) not possible

Question 5

Protected Mode

Answer 5

• Up to 4GB memory
• Memory protection
• Privilege level
• Multi-task
• Supports Virtual-8086 mode
• • Used to operate outdated software

Question 6

Memory Models

Answer 6

• Flat memory model
• Segmented model
• Real-address mode model

Question 7

What model is this course primarily concerned with?

Answer 7

• flat memory model

Question 8

32-bit Linux CPU Model and Model

Answer 8

• Protected mode
• Flat memory model
• 4GB addressable space => 2^32
• Memory protection
• Privilege levels of code
• Segment registers point to segment descriptor tables

Question 9

What are the three types of Segment Descriptor Tables?

Answer 9

• Global Descriptor Table (GDT)
• Local Descriptor Table (LDT)
• Interrupt Descriptor Table (IDT)

Question 10

What are the levels of the Virtual Memory Model

Answer 10

1. Kernel Space
   - ——– USER SPACE (2-7) ——–
2. Stack: funtion args and local vars
3. Shared libs and mappings
4. Heap: dynamic memory
5. BSS: uninitialized data
6. Data: initialized data
7. Text: program code

Question 11

How can you view process organization starting with ‘ps’?

Answer 11

• ps
• Get the PID
• cat /proc//maps

Question 12

How can you map a process with GDB?

Answer 12

• gdb /bin/bash
• break main
• run
• info proc mappings