Lecture 4 - Debugging & Development Tools

Question 1

Memory stores data, but what else?

Answer 1

Program code and instructions.

Question 2

Is it possible to have a pointer to a function, if so what is it callled.

Answer 2

yes , function pointer

Question 3

What is the type of a function pointer?

Answer 3

return_type (*)(argument_types)

Question 4

When could having a function pointer be useful?

Answer 4

Having different print functions for node of a binary search tree.

Question 5

Are function names automatically converted to pointers?

Answer 5

YES

Question 6

What is a syntactical bug?

Answer 6

A grammar bug, it is something picked up by the compiler e.g. mispelling a keyword

Question 7

What is a semantic bug?

Answer 7

Error in our logic , not flagged by the compiler, but the code doesn’t do what we want it to do .

Question 8

What is a debugger?

Answer 8

A controlled enviroment in which we can run our program and investigate it’s execution.

Question 9

What is static analysis?

Answer 9

When we reason about a program’s behaviour without running it.

Question 10

What is dynamic analysis?

Answer 10

Adding instructions to program in order to be able to detect bugs at runtime.

Question 11

What are the 2 most popular debuggers for C?

Answer 11

lldb and gdb

Question 12

How to we need to compile a C program in order to be able to debug it?

Answer 12

With a g flag, this adds debug information to the binary exectuable

Question 13

After compiling with a g flag do we simply run the program normally to debug ?

Answer 13

No, we start the debugger and load the program executable

EG.
gdb –argc ./program arg1 arg2
lldb – ./program arg1 arg2

Question 14

How to exit a debugger?

Answer 14

type quit

Question 15

How to set a breakpoint in the debugger?

Answer 15

b followed by the line number

Question 16

How to execute the next line in the debugger?

Answer 16

n

Question 17

What is a seg fault?

Answer 17

An error raised by the hardware notigying the OS that our program has attempted to access a restricted area of memory
-> os immediately terminates program execution

Question 18

Common Seg Fault Causes?

Answer 18

• dangling pointers
• dereferencing a NULL pointer
• Writing to read only memory
• Buffer overflow
• stack/heap overflow

Question 19

What is a dangling pointer?

Answer 19

A pointer that doesn’t point to a valid object of an appropriate type. E.g. deallocated memory

Question 20

What does the bt command do in the debugger?

Answer 20

Shows the backtrace after an error. This shows program calls leading to error.

Question 21

Does the compiler do some static analyses every time we compile?

Answer 21

YES

Question 22

What is good practice when compiling C programs?

Answer 22

enabling -Wall -Werror

Question 23

How to we invoke the static analyzer

Answer 23

clang –analyze –ana;yzer-output html program.c

• we have a flag
• we have an output format

Question 24

What is a massive drawback of static analysis?

Answer 24

Quite expensive to perform, not worth to do in every build.

Question 25

What does the analyzer report contain?

Answer 25

Potential bugs and their explanations

Question 26

What is clang-tidy?

Answer 26

It is a linter tool, that allows us to enfodce coding guidelines and modernize source code.

Question 27

How is clang tidy turned on?

Answer 27

Including – somewhere in our command

Question 28

What are the 5 most important sanitizers?

Answer 28

• AddressSanitizer
• MemorySanitizer
• LeakSanitizer
• UndefinedBehaviourSanitizer
• ThreadSanitizer

Question 29

What is the address sanitizer?

Answer 29

A memory error detector
-> out of bounds access
-> use after free
-> double free

Question 30

What is a memory sanitizer?

Answer 30

a detector of uninitialized reads

Question 31

What is a leak sanitizer?

Answer 31

a memory leak detector

Question 32

What is a undefined behaviour sanitizer?

Answer 32

detector of undefined behaviour

Question 33

What is a thread sanitizer?

Answer 33

a data race detector

Question 34

What is undefined behaviour?

Answer 34

These are semantic bugs (fault in our logic). These are due to the fact the compiler doesn’t enforce a certain behaviour (e.g. dereferencing a NULL pointer).

e.g integer overflow

Question 35

Are C and C++ considered safe languages?

Answer 35

No

Question 36

What does it mean to be an unsafe language ?

Answer 36

executing an erroneous operation causes the entire program to be meaningless, as opposed to just the erroneous operation having an unpredictable result.