A signature file contains patterns of standard runtime functions. With their help, IDA is able to recognize the standard functions and names them accordingly. IDA attempts to detect the necessary signature files automatically but unfortunately, this is not always possible. This command adds the specified signature file into the planned signature files queue. Signature files reside in the subdirectories of the SIG directory. Each processor has its own subdirectory. The name of the subdirectory is equivalent to the name of the processor module file.

IDA Ported On iPhone6

Download iPhone IDA Pro Signature Files:

Open terminal and type these commands:
wget /scripts/iPhone-Baseband-IDA-Pro-Signatures.zip
unzip iPhone-Baseband-IDA-Pro-Signatures
You can also use our GitHub repo as the alternative download source (more tools included). They are made up of signatures for ARM's RealView Compiler Tools (RVCT) runtime libraries:
  • RVCT RTL 2.2
  • RVCT RTL 3.1
  • RVCT RTL 4.4
  • ThreadX sig for iPhone 4 - however this only picks up a couple of functions, not sure how Apple compiled threadx, with which compiler, optimizations.
As you might know the ARM RVCT Compiler's code density is higher and performance is much better than in binaries which are produced with other leading tools. As the size of binary file has a significant meaning for the finishing cost of phone's hardware, phone manufacturers use RealView Compiler Tools to compile ROM dedicated binaries. The listed here signature files are presented with following toolchains that can support iPhone Basebands and their platforms (chipsets):
  • 2.2
  • 3.1
  • 4.4
Supported by iPhone, iPhone 3g, iPhone 3gs basebands.
  • ThreadX sigs
Files on iPhone 4 firmware can pickup up to 800 functions when all the sigs applied. Happy baseband reversing!!!
Source: theiphonewiki