gdb

Many years ago I had to use gdb for the first time and I absolutely hated it. At the time I was reversing (cof cof cof) Windows apps so SoftIce and friends were my favorite tools. Compared to these gdb was a complete trash, mostly because the naked gdb lacks a nice context display. I like to know what the hell is going around each time I step in the debugger, without having to type a bunch of commands for it. Then I discovered the original gdbinit by +mammon and life with gdb was a bit easier. ...

This is an up-to-date version of the old original post about recompiling GDB and other open source packages available at opensource.apple.com. I’m doing it mostly because code signing is now mandatory for GDB and there’s a stupid old bug that Apple still didn’t fixed since Snow Leopard. I forgot about it on my latest reinstall and lost an afternoon. This way you and me will not make the same mistake....

One obstacle that I faced long time ago and came again into spotlight is how to recompile GDB for iOS. It is not useful to fix the ARM disassembler and then not be able to compile. As far as I know there isn’t any documentation available or an easy method to accomplish this – Saurik’s build environment is not public (?) and Apple sources do not compile directly. Darwinbuild project works great for OS X but it’s a question mark for iOS....

Here it is, a merge between the x86 and ARM versions of gdbinit. The only inconvenience is that you need to manually change the target, using the 32bits and 64bits commands for x86/x86_64 architectures, and arm for ARM. That’s a small price to pay for. This version features a lot of cosmetic fixes (indentation mostly) but also some fixes to the ARM related code, and a new command – dumpmacho. This command will dump the Mach-O header to a file....

I developed this funny trick while trying to find a solution for a problem in a project. It is pretty easy to implement and fun. The trick consists in abusing the offset field in the dylib_command and pointing it to somewhere else. From the Mach-O File Format Reference document, the command structures are: struct dylib_command { uint_32 cmd; uint_32 cmdsize; struct dylib dylib; } struct dylib { union lc_str name; uint_32 timestamp; uint_32 current_version; uint_32 compatibility_version; } union lc_str { uint32_t offset; #ifndef __LP64__ char *ptr; #endif } The definition of the offset field is:...