Linux - GNU Debugger (GDB)

GDB is the world famous GNU debugger, which is very powerful. In this article, its elementary usages can be listed as follows.

• b(reak) LINE_IDX: set breakpoint in line LINE_IDX.
• b(reak) FUN_NAME: set breakpoint at the begin of function FUN_NAME.
• b(reak) ... if ...: set conditional breakpoint.
• delete breakpoints BP_IDX: delete breakpoint BP_IDX (if BP_IDX is omitted, all the breakpoints will be deleted).
• disable breakpoints BP_IDX: disable breakpoint BP_IDX (if BP_IDX is omitted, all the breakpoints will be disabled).
• enable breakpoints BP_IDX: enable breakpoint BP_IDX (if BP_IDX is omitted, all the breakpoints will be enabled).
• display VAR_NAME: track varable VAR_NAME, every time the program stops, its value will be displayed.
• undisplay VAR_NAME: cancel tracking of variable VAR_NAME.
• start: start to excute the program and stop at the first statement of main.
• r(un): excute the program from beginning continuously.
• c(ontinue): excute the program from current position contiously.
• s(tep): excute the program by one step and enter the function if available.
• n(ext): excute the program by one step and don’t enter any function.
• backtrace(or bt): view the function call of all the levels and their parameters.
• f(rame) FRM_IDX: select the stack frame of index FRM_IDX.
• watch: set observation point.
• i(nfo) locals: view the values of local variables in current stack frame.
• i(nfo) b(reakpoints): view current breakpoints.
• i(nfo) watchpoints: view current observation points.
• l(ist): list 10 lines of source code, continuing the last.
• l(ist) LINE_IDX: list the source code around line LINE_IDX.
• l(ist) FUN_NAME: list the source code of function FUN_NAME.
• x: print part content of register from some position. All the contents are treated as bytes without consideration that which bytes correspond to which variable. For example, x/7b p will print the content of size 7 bytes after point variable p.
• p(rint) expr: print the value of expr. This functionality can be used to change the values of variables or provoke a function.
• finish: excute the current function until return, and then stop.