How to use the split utility
The split utility operates on a LLVM bitcode file and it splits all of the
functions in it into separate (.bc
) files.
Obtaining the final "fat" LLVM bitcode file can, theoretically, be done in multiple ways. The recommended way is to use CapableVMs fork of "Go Whole Program LLVM", gllvm. For example, to get the bitcode from a generic Makefile project:
-
Install gllvm: go get github.com/capablevms/gllvm/cmd/...
-
Build with GLLVM:
GCLANG=$HOME/go/bin/gclang
export GET_BC=$HOME/go/bin/get-bc
CC=$GCLANG LLVM_COMPILER_PATH=path/to/llvm/bin make
# or CC=$GCLANG ./configure if you are feeling lucky
- Extract the bitcode:
Finally, the split utility can be launched with:
./split-llvm-extract path/to/binary.bc -o outdir
To run the version of the binary just split, it is necessary to join the parts
(in outdir
) together as shared libraries. A "joiner" Makefile can be found
here.
Steps specific to CHERI cross-compilation can be found in .buildbot.sh.
Other (old and not maintained) variants
There are 2 other utilities that reside in this repository. The
firstone shows how splitting can be done using the llvm API
instead of using llvm-extract
. The other utility
focuses on finding functions which are not public and should be. It also tries
to find ways to split the bitcode files while preserving the linkage of the
functions. The 2 previously presented splitters are not meant for general
purpose use, and are kept as a showcase of what is possible.