I wanted to recompile GDB so I can modify its source and add some custom patches to enhance its output… Easier said than done! There’s not much information around about this and my first attempt was by downloading GDB source package from Apple and trying to compile it. Didn’t compile out of the box so I had to fix here and there and finally it compiled, but then it didn’t work....

I forgot to mention this previously but there is a mailing list available at http://0x90.org/mailman/listinfo/xso and an IRC channel at irc.freenode.net, #osxre. It’s still a small community but more people are showing up and IRC is always a good communication tool. I’m not administrator of both, but YOU are invited to join 😄. fG!

End of the year is slow and I was a bit inspired so I decided to hack around another features I was missing from gdbinit! First one is about conditional jump display. Original gdbinit doesn’t tell you what will be the decision that will be taken on a conditional jump. You must look at the flags and check that! Well… I can’t memorize this kind of stuff (in reality I can but it’s useless so I refuse to) and computers were created to automate tasks!...

While I was messing with gdbinit three weeks ago, I added a small feature that displays the messages being sent to objc_msgSend. Usually I follow the otool or IDA dump and see what’s being sent, but that it’s not very practical! So I made a dirty hack with gdbinit so that information appears automatically into GDB window. It’s not very pretty, but gdbinit is very limited 😦. Example: gdb$ 0x00002bc5 in main () --------------------------------------------------------------------------[regs] EAX: 9FF43924 EBX: 00002B9D ECX: 9FF37B64 EDX: 00403250 o d I t S z a P c ESI: BFFFF8F4 EDI: BFFFF898 EBP: BFFFF838 ESP: BFFFF7F0 EIP: 00002BC5 CS: 0017 DS: 001F ES: 001F FS: 0000 GS: 0037 SS: 001F [001F:BFFFF7F0]----------------------------------------------------------[stack] BFFFF840 : 01 00 00 00 98 F8 FF BF - A0 F8 FF BF F4 F8 FF BF ....

I was trying to add some features to gdbinit and I needed global variables. I already knew that feature wasn’t working on Mac OS X GDB and I was puzzled why it didn’t work. Some quick tests on a Linux box couldn’t reproduce the same behaviour so something is wrong with Apple’s GDB version. I finally found how it happens ! A very simple .gdbinit to test things would be:...