clakerbu

Tool to get cumulative LLVM bitcode files for kernel drivers for architectures arm32 and aarch64.

This tool helps you get cumulative bitcode files for each of the kernel drivers. This is helpful for any instrumentation tasks based on LLVM. For instance, You can use this tool to build the bitcode file for a driver, perform instrumentation, convert it back to object file, and then use the make to create the kernel with the instrumented driver.

Note

For the kernels built using gcc this tool only works for arm32 or aarch64 architectures.

Dependencies

• Install Bear
• Install clang and llvm

How to use:

Build your kernel.

Run make using the following command:

bear make

The above command will create compile_commands.json in the current directory.

Running

usage: clakerbu.py [-h] -l LLVM_BC_OUT -k KERNEL_SRC_DIR -m COMPILE_JSON -n
                   ARCH_NUM [-isclang] [-clangp CLANG_PATH]
                   [-llvmlinkp LLVMLINK_PATH]
optional arguments:
  -h, --help            show this help message and exit
  -l LLVM_BC_OUT        Destination directory where all the generated bitcode
                        files should be stored.
  -k KERNEL_SRC_DIR     Base directory of the kernel sources.
  -m COMPILE_JSON       Path to the json file generated by Bear.
  -n ARCH_NUM           Destination architecture, 32 bit (1) or 64 bit (2).
  -isclang              flag to indicate that clang was used to built the
                        kernel
  -clangp CLANG_PATH    Absolute path to the clang binary (if not provided,
                        the one available in the path will be used)
  -llvmlinkp LLVMLINK_PATH
                        Absolute path to the llvm-link binary (if not
                        provided, the one available in the path will be used)

Example for aarch64 (if built using gcc):

cd clakerbu/
python clakerbu.py -l /llvm_bitcode_out -k <PATH_WHERE_YOU_RAN_MAKE> -m <PATH_TO_THE_COMPILE_COMMANDS_JSON_CREATED_ABOVE> -n 2

If your kernel was originally built with clang+llvm, then you should specify the flag -isclang, path to the clang that was used to build the kernel (this is usually what you would have provided for REAL_CC) and path to the llvm-link.

Example for aarch64 (if built using clang):

cd clakerbu/
python clakerbu.py -l /llvm_bitcode_out -k <PATH_WHERE_YOU_RAN_MAKE> -m <PATH_TO_THE_COMPILE_COMMANDS_JSON_CREATED_ABOVE> -n 2 -isclang -clangp <PATH_TO_CLANG_THAT_WAS_USED_TO_BUILT_THE_KERNEL> -llvmlinkp <PATH_TO_THE_LLVM_LINK (usually in the same folder as the clang)>

The driver bitcode files will be present in the folder <LLVM_BC_OUT> with extension final.linked.bc along with other intermediate files.

The kernel modules end with ..final.linked.bc i.e., if you find iproc-rng200..final.linked.bc, that means it is the bitcode file for iproc-rng200.ko from the kernel build.

Shoutouts

• rizsotto for the amazing Bear tool.