How to compile GDB for iOS!

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.

Darwinbuild it is! After some failed hacking last Friday (progress was great and it was near completation), I decided to try to fix the loose end today. Success was finally achieved.
This post contains almost all the information that you need to recompile GDB yourself. There is something that you will need to complete by trial & error. Let’s start the fun!

The reference post on darwinbuild usage is this one, written by yours truly. You should follow it and modify accordingly with the information provided here. My OS X version is still Snow Leopard but you should have no problems with Lion.
The image size should be 2GB, and you should use the build #10K540. When you execute the darwinxref edit command, use the following information:

environment = {
 INSTALLED_PRODUCT_ASIDES = YES;
 MACOSX_DEPLOYMENT_TARGET = 10.6;
 NEXT_ROOT = "";
 RC_ARCHS = "armv7 armv6";
 RC_JASPER = YES;
 RC_NONARCH_CFLAGS = "-pipe";
 RC_OS = macos;
 RC_PRIVATE = /private;
 RC_RELEASE = SnowLeopard;
 RC_TARGET_CONFIG = iphoneos;
 RC_XBS = YES;
 SEPARATE_STRIP = YES;
 UNAME_RELEASE = 10.0;
 UNAME_SYSNAME = Darwin;
};

Word of caution: be careful with copy & pasting this because of the “” (if you get an error while saving from darwinxref edit).

The next step is to edit the darwinbuild database. It’s located at .build/xref.db, inside the Build10K540 folder you should be located at. You need to change the GDB version to the latest one, 1708 instead of 1344. Execute the following SQL statement to verify it:

select * from properties where project="gdb" and property="version";

and then update the field:

update properties set value="1708" where project="gdb" and property="version";

Start compilation with darwinbuild -nochroot gdb. Version 1708 will be downloaded. When configuration/compilation starts, abort it with Ctrl-c.
You will need to create a link (there is probably a more elegant solution to this!). Go to the usr/lib folder inside the iOS SDK. There you need to make a link from crt1.10.6.o to crt1.o. Small example from my system:

lrwxr-xr-x  1 root  wheel     6 Apr 14 04:12 /Developer4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/usr/lib/crt1.10.6.o -> crt1.o
-rw-r–r–  1 root  wheel  2720 Aug 30  2011 /Developer4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/usr/lib/crt1.3.1.o
-rw-r–r–  1 root  wheel  4584 Aug 30  2011 /Developer4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/usr/lib/crt1.o

Next step is to modify the file BuildRoot/SourceCache/gdb/gdb-1708/src/gdb/macosx/macosx.defs. Here you need to replace the import for exc.defs. Change:

#import

to:

#import "/Developer4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/usr/include/mach/exc.defs"

(modify your path accordingly)

Last step for now is to modify the Makefile. We need to modify it so the ARM cross-compiling tools are used. It’s located at BuildRoot/SourceCache/gdb/gdb-1708/Makefile. To make it easier, you have my Makefile as a reference (all files at the end). I left the places that you need to modify tagged with FIXME. Your task is to change the paths.

Now you are ready to compile and start the trial and error process. This time, compile with darwinbuild -nochroot -nosource gdb. This will not unpack again the source package and will keep our previous changes.
The compilation process will start and hopefully you will observe lots of output, which is a good sign! Near completation, errors regarding missing includes will start to appear. Your task is to manually copy them from OS X /usr/include to the iOS SDK usr/include folder (in my case /Developer4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/usr/include/). The only modifications that you will need to do are to edit some files and change the import location to relative paths (or absolute if you prefer). Not elegant, but it works! When you reach the missing architecture includes, you can use the ones from i386. Sorry for not having a complete file list – I was hacking this without great hope that it would work heheheh.

And that’s it! After you fix the missing includes and defs, the compile should successfully finish and you have your shiny recompiled GDB. You can also apply my gdb patches (recommended!). Before starting to compile everything, just go to the SourceCache folder, apply the patch and compile.
Follow the steps from the reference post to copy the compiled binary, apply the necessary entitlements (reference), upload to your device and enjoy.

If you don’t feel adventurous enough then I include a fat binary (armv6 and armv7) with my patches. You just need to add the entitlements. Pancake (from Radare) created a package for this version. Add http://cydia.radare.org to your repo list and install it from there. Thanks to pancake for his work.

Any question or problem you run into leave a comment so everyone else can benefit from the (potential) solution.

Have fun,
fG!

Makefile.gz

gdb-arm-apple-darwin.gz

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Update: List of added/modified include files.

./_locale.h
./libproc.h
./mach/arm/machine_types.defs
./mach/exc.defs
./mach/mach_types.defs
./mach/mach_vm.h
./mach/machine/machine_types.defs
./mach/machine/thread_state.h
./mach/std_types.defs
./ncurses_dll.h
./net/route.h
./sgtty.h
./sys/dir.h
./sys/ioctl_compat.h
./sys/kern_control.h
./sys/proc_info.h
./sys/ptrace.h
./sys/ttychars.h
./sys/ttydev.h
./termcap.h