GDB Info (original) (raw)

Breakpoints:

Setting and removing single breakpoints:

• break (some function)
• break (line number)
• break *(some memory address)
• delete (breakpoint number)

Removing all breakpoints:

• clear [clears current break point]
• clear (some function)
• clear (some line number)
• clear *(some memory address)

Running:

• run arg1 arg2 ... starts or restarts the program with the given arguments
• run starts or restarts the program at full speed. If restarting, uses the same arguments used last time.
• s or step steps by one line of source code, going into function calls. This only works after the program is running, so you usually need to set a breakpoint somewhere so that you can get to where you want to start stepping.
• n or next steps by one line of source code, not going into function calls
• stepi steps by one instruction, going into function calls
• nexti steps by one instruction, not going into function calls
• c or continue goes at full speed after a breakpoint
• kill end the running program
• enter do the same command again.
• finish step out of the current function.

Stack:

• bt or backtrace shows the current stack.
• frame N goes to the _N_th stack frame.
• info locals prints all local variables.
• info args prints all of the arguments to the current function as they are now (as opposed to as they were at the top of the function).
• call function calls function. Arguments can be provided. Note: this works by pushing arguments on the stack, resetting %eip to point the the function, and letting the program run. In some circumstances, this can fail
• whatis something prints the type of_something_

Command Line:

• set args (stuff) passes_stuff_ as command line arguments to the program the next time run is used.
• file stuff sets stuff as the program to be run and debugged.

Lazy Typing:

• Enter (the key) at an empty command prompt repeats the last command. This is especially handy for step and next commands
• Ambigious abreviations will resolve to the last command with that abbreviation

Lazy Math:

• print/d 0xsome hex number will convert it to decimal
• print/x some decimal number will convert it to hex
• print complicated expression will evaluate the expression and print the result in decimal or hex. You can use standard C notation, variables of your program, and register names ($eax, etc.)

Useful Tricks:

• info b will tell you how many times a breakpoint has been hit.
• continue n (or c n) will continue past a breakpoint n times. For example, if the fourth call to a function is the one that fails, you can use "c 3" to skip the first three calls.
• You can combine the two above tricks to deal with a function that crashes after many calls. Set a breakpoint in the function, run the program, and type "c 9999999". When it crashes, use info b to find out how many times the function was called. Then rerun the program and usecontinue n-1 to get to the invocation that crashes.

© 2007, Geoff Kuenning

This page is maintained by Geoff Kuenning.