GDB BASICS
GDB Basics - GNU Debugger
Compile each course code file using -g. Without the -g flag, the compiled binary may have insufficient information to assist GDB in debugging the progrma. Older documents from the department may recommend the -gstabs+ flag but this is no longer standard.
A SAMPLE GDB SESSION
- Run the executable
a.outthrough the debugger:gdb a.out - Setting a breakpoint follows the format
break <POINT>, where<POINT>is a named function, or label in your code. Examples:- Set a break point in the program, such as at
main()execute:break main - Set a break point in the calculate method of
Timeclass:break 'Time::calculate'(hit TAB to view choices). - Set a break point in the copy constructor of the List template class:
break List<int>::List(const List<int> &). - Set a break point at line 7:
break 7 - Break on line 7 if condition met:
break 7 if (num == 1) - Assuming, before compiling, you created an arbitrary breakpoint in your C-code not associated with a fuction:
int main() { ... _apples: i++; ...break _apples
- Set a break point in the program, such as at
- Generally, after setting a breakpoint the next step is to run the program:
run - However, if you intended to provide command line arguments, they are executed with
runas:run arg1 arg2 - When the program has stopped at a breakpoint, you have several options:
- Execute the next source line without stepping into called functions:
next - Force return from current function:
return - List code starting at 5 lines before and after line 20:
list 20 - List code from line 20 to line 30:
list 20,30 - Continue until current function returns:
finish - Display value of variables:
print i - Display the value of a dereferenced pointer:
print *ptr - Examine memory at address 0xF087A:
x/d 0xF087A - Get help on examine command:
help x - Assign variables:
print num = 3 - Step through your program line by line:
step - Step through your program 5 lines:
step 5 - View the type of a variable or class object:
whatis i - View current breakpoints:
info breakpoints - View stack trace of current active functions:
info stack,btorbacktrace - Continue with execution:
continue - Delete the first break point set:
delete 1 - Exit gdb:
quit
- Execute the next source line without stepping into called functions:
NOTE: Commands can be shortened to their smallest set of unique characters; e.g. print can be replaced by p; step can be replaced by s.