Question

What are the available commands for gdb in Xcode 4 which I can use to debug my app?

(Although a relatively seasoned developer, I’m looking to expand my skills with this question.)

Answer 1

You can start from here http://darkdust.net/files/GDB%20Cheat%20Sheet.pdf, come is very handy.

Points worth mentioning

• You can attach gdb to an already running process, there by start
  debugging
• Enter on gdb command line will execute last instruction, comes in
  very handy

• You can do some amount of scripting with GDB, use -x falg to point to
  your script suppose you want to connect to a target over ip (remote
  debugging), and you dont want to remember its ip / kepp entering it
  every time. Starting from gdb 7.1 Python scripts are also supported
  so much more powerful now

  echo “target remote 192.168.XX.XX:1234” > gscript
  gdb -x gscript application

Ok some niche stuffs –

(gdb)start
(gdb)layout split               // list the assembly and c
(gdb)ni                         // exec next instruction in assembly
(gdb)print $pc                  // prints the contents of register PC(use $)

you can try doing some unit testing on the go

(gdb)start
(gdb)call factorial(5)

Suppose you dont want to disturb the the application timing (reatime behaviour) but still want to view some variable updates, you can try following

(gdb)start
(gdb)break <func>:<line>
(gdb)commands 1                  // '1' is the break number
> silent
> printf "var1 = %d\t var2 =%d\n",var1,var2
> continue
> end

data break points, conditional breakpoints can be very useful when debugging memory corruptions

(gdb)start
(gdb)watch var
(gdb)watch 0x80001212

debugging threads

(gdb)info threads
(gdb)thread 2                      // switch to thread '2'