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Diffstat (limited to 'instrumentation/README.lto.md')
| -rw-r--r-- | instrumentation/README.lto.md | 36 |
1 files changed, 32 insertions, 4 deletions
diff --git a/instrumentation/README.lto.md b/instrumentation/README.lto.md index 626bc9cb..6174cdc0 100644 --- a/instrumentation/README.lto.md +++ b/instrumentation/README.lto.md @@ -60,12 +60,12 @@ AUTODICTIONARY: 11 strings found ## Getting llvm 11+ -### Installing llvm version 11 +### Installing llvm version 11 or 12 -llvm 11 should be available in all current Linux repositories. +llvm 11 or even 12 should be available in all current Linux repositories. If you use an outdated Linux distribution read the next section. -### Installing llvm from the llvm repository (version 12) +### Installing llvm from the llvm repository (version 12+) Installing the llvm snapshot builds is easy and mostly painless: @@ -85,7 +85,7 @@ apt-get install -y clang-12 clang-tools-12 libc++1-12 libc++-12-dev \ libomp5-12 lld-12 lldb-12 llvm-12 llvm-12-dev llvm-12-runtime llvm-12-tools ``` -### Building llvm yourself (version 12) +### Building llvm yourself (version 12+) Building llvm from github takes quite some long time and is not painless: ```sh @@ -138,6 +138,34 @@ make NOTE: some targets also need to set the linker, try both `afl-clang-lto` and `afl-ld-lto` for `LD=` before `configure`. +## Instrumenting shared libraries + +Note: this is highly discouraged! Try to compile to static libraries with +afl-clang-lto instead of shared libraries! + +To make instrumented shared libraries work with afl-clang-lto you have to do +quite some extra steps. + +Every shared library you want to instrument has to be individually compiled. +The environment variable `AFL_LLVM_LTO_DONTWRITEID=1` has to be set during +compilation. +Additionally the environment variable `AFL_LLVM_LTO_STARTID` has to be set to +the added edge count values of all previous compiled instrumented shared +libraries for that target. +E.g. for the first shared library this would be `AFL_LLVM_LTO_STARTID=0` and +afl-clang-lto will then report how many edges have been instrumented (let's say +it reported 1000 instrumented edges). +The second shared library then has to be set to that value +(`AFL_LLVM_LTO_STARTID=1000` in our example), for the third to all previous +counts added, etc. + +The final program compilation step then may *not* have `AFL_LLVM_LTO_DONTWRITEID` +set, and `AFL_LLVM_LTO_STARTID` must be set to all edge counts added of all shared +libraries it will be linked to. + +This is quite some hands-on work, so better stay away from instrumenting +shared libraries :-) + ## AUTODICTIONARY feature While compiling, a dictionary based on string comparisons is automatically |