1. Memory & Storage Architecture Lab. @ Seoul National University GDB commands Hyeon-gyu Lee(hglee@archi.snu.ac.kr) School of Computer Science and Engineering Seoul National University

2. Memory & Storage Architecture Lab. @ Seoul National University To Use GDB in Your Program  Additional compile option  gcc –g –o prog prog.c  Execute gdb  gdb prog 2

3. Memory & Storage Architecture Lab. @ Seoul National University Looking the Program Source  List instruction  (gdb) list Abbreviated to the letter ‘l’ Shows your code of your program 3

4. Memory & Storage Architecture Lab. @ Seoul National University Looking the Program Source  List instruction options  (gdb) list Shows the code of  (gdb) list : Shows the code of in the  (gdb) list Shows the code from  (gdb) list : Shows the code from in the  (gdb) list - Shows the code right before your current position  Current unit lines of printing: 10  (gdb) set listsize 20 Set the unit lines of printing to 20 4

5. Memory & Storage Architecture Lab. @ Seoul National University Running the program  Run the program  (gdb) run Abbreviated to the letter ‘r’ Run your code continuously -If confronts breakpoint, gdb stops there. -If there are no breakpoints, gdb runs until the program terminates. Useful when your program has errors  (gdb) run arg1 arg2 … Run your code continuously with arguments 5

6. Memory & Storage Architecture Lab. @ Seoul National University Breakpoints  Make points to stop  (gdb) break Abbreviated to the letter ‘b’ Without any option, breakpoint is made at your current position 6

7. Memory & Storage Architecture Lab. @ Seoul National University Making Breakpoints  Breakpoint options  (gdb) break Breakpoint at the start of the function  (gdb) break : Breakpoint at the start of the function in the file  (gdb) break Breakpoint at the designated line  (gdb) break Breakpoint at the current-position-relatively designated line  (gdb) break Breakpoint at the instruction that pointed by the memory address Used at assembly debugging  Above all options can be done with conditions e.g. (gdb) break 10 if var==0 7

8. Memory & Storage Architecture Lab. @ Seoul National University Manipulating Breakpoints  Breakpoint information  (gdb) info break Shows the information about your breakpoints Valid until the gdb terminates  Deleting breakpoint  (gdb) clear Abbreviated to ‘cl’ Clear breakpoints that you made Should be used with options  (gdb) clear Delete breakpoint at that line number 8

9. Memory & Storage Architecture Lab. @ Seoul National University Manipulating Breakpoints  Deleting breakpoint options  (gdb) clear Delete breakpoint at that line number  (gdb) clear Delete breakpoint at the start of the function  (gdb) clear : Delete breakpoint at the start of the function in the file  (gdb) d Delete all breakpoints  (gdb) disable/enable br Disable/enable all breakpoints  (gdb) disable/enable br 1 3 Disable/enable breakpoints with number 1, 3. 9

10. Memory & Storage Architecture Lab. @ Seoul National University Single-stepping  Single stepping  (gdb) step Abbreviated to the letter ‘s’ When a function is called at the point, it goes into the function  (gdb) step Repeat ‘step’ with times of the number.  (gdb) next Abbreviated to the letter ‘n’ When a function is called at the point, it executes the whole function continuously  (gdb) next Repeat ‘next’ with times of the number. 10

11. Memory & Storage Architecture Lab. @ Seoul National University Single-stepping  Other instructions  (gdb) continue Abbreviated to the letter ‘c’ Continuously execute from your current position  (gdb) advance Continuously execute from your current position to the line number  (gdb) until Continuously execute until current repetition finish point When the current position is not in a repetition, it operates like ‘next’ 11

12. Memory & Storage Architecture Lab. @ Seoul National University Single-stepping  Other instructions  (gdb) finish Continuously execute from your current position until current function finish point  (gdb) return Return without executing the remaining part of the function When needed, you can manually designate a return value  (gdb) set var = Change the content of the variable to the given value 12

13. Memory & Storage Architecture Lab. @ Seoul National University Watchpoints  Stop when a variable is set to a specific value  (gdb) watch Break when a value is written in the variable  (gdb) rwatch Break when the value is read in the variable  (gdb) awatch Break when a value is read/written in the variable 13

14. Memory & Storage Architecture Lab. @ Seoul National University Displaying Values  See values in your program  (gdb) info locals Shows values of local variables that you can access from your current position  (gdb) info variables Shows values of global variables that you can access from your current position  (gdb) print Shows value of the variable When the variable is a pointer, dereferencing is possible with an asterisk.  (gdb) print Shows address of the function 14

15. Memory & Storage Architecture Lab. @ Seoul National University Displaying Values  See values in your program  (gdb) print $ Shows value of the register.  (gdb) print ‘ ’:: Shows value of the variable in the file.  (gdb) print :: Shows value of the variable in the function  (gdb) whatis Shows type of the variable  (gdb) display Shows value of the variable automatically with progress of the program Enabling/disabling is possible  (gdb) undisplay Delete display 15

16. Memory & Storage Architecture Lab. @ Seoul National University Examining the Stack  Backtracing the stack  (gdb) backtrace Abbreviated to the ‘bt’ Shows stack trace of your current position 16

17. Memory & Storage Architecture Lab. @ Seoul National University Killing the Executing Program in the GDB  Kill instruction  (gdb) kill Kill the executing program forcefully 17

18. Memory & Storage Architecture Lab. @ Seoul National University Quitting the GDB  Quit and exit to the Linux  (gdb) quit Abbreviated to the letter ‘q’ 18

19. Memory & Storage Architecture Lab. @ Seoul National University References  References  http://kwanseob.blogspot.kr/2012/03/gdb.html, retrieved on May 20, 2015. http://kwanseob.blogspot.kr/2012/03/gdb.html  http://darkdust.net/files/GDB%20Cheat%20Sheet.pdf, retrieved on May 20, 2015. http://darkdust.net/files/GDB%20Cheat%20Sheet.pdf  https://kldp.org/node/71806, retrieved on May 20, 2015. https://kldp.org/node/71806 19