10.4 Debuggers

Question 1

What type of errors do debuggers / compilers catch

Answer 1

• Compiler: compile time errors
• Debugger: runtime error

Question 2

What are compiler warnings (what are they used for)

Answer 2

• Help to spot potentially problematic code (not something which is syntactically wrong which would be an error)

Question 3

What are debug symbols (and how do they relate to the compiler and debugger)

Answer 3

• Compiler adds information to file to help debuggers identify the correponsing source instructions
• Common format is DWARF (for ELF binary format)

Question 4

What are debuggers

Answer 4

• Trace and modify the program (to add breakpoints etc.)
• Needs to have access via kernel.

Question 5

What are some possible commands in the GDB (GNU debugger)

Answer 5

Question 6

How does the kernel support debuggers

Answer 6

• Debugger by nature accesses code outside its own protection boundry
• Kernel has library calls (such as ptrace) for debuggers
• Primarily software interrupts

Question 7

What is the flow diagram for a creating a breakpoint in a running piece of code (debugger)

Answer 7

Note: Code is modified / line is replaced for a breakpoint

Question 8

How do debuggers make use of software breakpoints

Answer 8

• Software interrupts are primary form of breaking

Question 9

How can debuggers make use of hardware breakpoints

Answer 9

For example: Intel trap flag for single step mode. Otherwise step mode can be done via software interrupts

Question 10

How can debuggers unwind the stack to perform a stack trace

Answer 10

• Recursively follow the return address upwards