1. GNU DEBUGGER TOOL

2. What is the GDB ? GNU Debugger It Works for several languages – including C/C++ [Assembly, Fortran,Go,Objective-C,Pascal]

3. Not Every Exe Debugging Friendly 1. The executable has to carry debugging symbols The symbols tell GDB where to look in the source To include symbols, use the – g flag for gcc – E.g. :gcc Hello.c –g –o Hello 2. The source tree needs to remain the same. It was when the program was compiled

4. Starting GDB gdb --help - Display all available options gdb - - silent prog - invoking gdb in silent mode, to stop printing the front material, which describes gdb. Let GDB be able to read all the information line by line from the symbol table, - we need to compile it a bit differently. Normally we compile our programs Ex: gcc Hello.cc -o Hello - Instead of doing this, we need to compile with the -g flag. Ex : gcc -g hello.cc -o hello

5. Quitting GDB To exit GDB - Type quit(abbreviated q) at the GDB prompt.

6. GDB COMMANDS Most of the commands in GDB can be issued by simply giving the starting letter For ex : ‘b’ can be used instead of ‘break’. A blank line as input to GDB means to repeat the previous command.

7. Running the program run (r) to start program under GDB. run arg1 arg2 to run with command line args run > outfile.txt diverting output to the file 'outfile.txt'

8. Breakpoints(1/3) Breakpoints stops the program when certain point is reached. - break (b) command is used to set break points. Setting break points : break fun_name ex: break main or b main - Sets a break point at entry to function name break lineumber ex : b 3 - Set a break point at line line num in current sourcefile

9. Breakpoints(2/3) break filename:linenum ex:- b value.c : 2 - Set a break point at the linenum in source file filename break filename:linenum ex:- b value.c : fun - Set a breakpoint at entry to function function found in file filename. break - When called without any arguments, break sets a breakpoint at the next instruction to be executed.

10. Breakpoints(3/3) info breakpoints ex: info b - Prints a table of all breakpoints. clear - Delete any breakpoints at the next instruction to be executed c lear function - Delete any breakpoints set at entry to the function. Clear linennum -Delete any breakpoints at the particular linenum delete -Delete all breakpoints.

11. Continuing & Stepping(1/2) Continuing means resuming program execution until your program completes normally. Stepping means executing just one line of source code, or one machine instruction. continue (c) - After resume program execution. Next (n) - Executes next instruction & stops. Stop (s) - Executes next instruction & stops.

12. Continuing & Stepping(2/2) step [count] & next [count] ex: next 5 - We can execute count no of instructions by giving a count. Diff b/w next & step is that,if there is a function call it proceeds until the function returns in case of step.

13. Printing Source lines print linenum - prints lines centered around linenum in the current source file. Print function - prints lines centered around beginning of the function l ist show listsize set listsize count

14. Examining Data print expr - value of expr is printed. print variable print file :: variable print function :: variable - Ex :- p func::z To display automatically use display - Ex:- display expr or variable.

15. Jump It helps to go to a specific line of instruction jump func:line - jumps to a particular line in function func. jump linenum - jumps to a specific line.

16. logging set logging on - Enable logging set logging off - Disable logging set logging file out.txt - Change the name of the current logfile, default is gdb.txt help - displays a short list of classes of commands

17. Backtraces backtrace is a summary of how your program got where it is. It shows one line per frame, for many frames.The backtrace (or where ) command prints information about the call stack. backtrace (bt) - bt Print a backtrace of the entire stack: one line per frame for all frames in the stack. backtrace n (bt n) - Similar, but print only the innermost n frames. backtrace full (bt full) - Print the values of the local variables also. n specifies the number of frames to print.

18. References https://www.tecmint.com/debug-source-code-in- linux-using-gdb/ https://www.eecs.umich.edu/courses/eecs373/reading s/Debugger.pdf

19. THANK Q ANY QUERIES ?