Monday, February 17, 2014

Colorizing GDB backtrace

Being in a startup, we get to see a lot of core dumps, every day ;-). With too many stack frames and long file+function names, I hate the output!. In fact the visual clutter is so much, that it takes me long time to compare two tracebacks! I was thinking what can be done about it - hit upon gdb hooks in a SO post. Put together with my all time fav - Perl, to color the output, got some nice colorful tracebacks! ;-). The following is what I put in my ~/.gdbinit
shell mkfifo /tmp/colorPipe.gdb
# no pause/automore 
set height 0
# dont break line
set width 0
define hook-backtrace
        shell cat /tmp/colorPipe.gdb |  ~/ &
        set logging redirect on
        set logging on /tmp/colorPipe.gdb
define hookpost-backtrace
        set logging off
        set logging redirect off
        shell sleep 0.1
define hook-quit
        shell rm /tmp/colorPipe.gdb
define re
   echo \033[0m

And the Perl script ( to do the highlight:

Try it!, at least identifying the culprit will be much quicker, if not fixing the issue! ;-)

Tuesday, February 04, 2014

Using API docs as a test aid

I wrote about my custom documentation using Lua embedded in my C source. With the complete description of the function - its arguments [and their type], return type etc, can we do more with it?
I wanted some test stubs for the Lua APIs (that I am defining from my C back-end) and all I had to do, was re-define the mydoc function which will consume the same data, but instead of generating documentation, generate some Lua code to test the APIs.
i.e, if I have a function that takes a number and returns a string (on success) and nil on failure, I generate:
function Stub.test (n)
  assert(type(n) == 'number', 'n should be a number)
  if g_nil_path then return nil end
  return 'rand-str'

With this, I can see and get a feel of the Lua APIs that my C functions are exposing, also I can invoke the user scripts just to check the argument types for correctness, and I can exercise the success path as well as the failure path by setting the global g_nil_path. And of course for more randomness, I use 
 when I return a number and
string.rep(string.char(math.random(65,90)), math.random(1,10)) 
when returning strings.