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Diffstat (limited to 'instrumentation/README.neverzero.md')
| -rw-r--r-- | instrumentation/README.neverzero.md | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/instrumentation/README.neverzero.md b/instrumentation/README.neverzero.md index 49104e00..9bcae324 100644 --- a/instrumentation/README.neverzero.md +++ b/instrumentation/README.neverzero.md @@ -16,11 +16,12 @@ at a very little cost (one instruction per edge). (The alternative of saturated counters has been tested also and proved to be inferior in terms of path discovery.) -This is implemented in afl-gcc and afl-gcc-fast, however for llvm_mode this is optional if -the llvm version is below 9 - as there is a perfomance bug that is only fixed -in version 9 and onwards. +This is implemented in afl-gcc and afl-gcc-fast, however for llvm_mode this is +optional if multithread safe counters are selected or the llvm version is below +9 - as there are severe performance costs in these cases. -If you want to enable this for llvm versions below 9 then set +If you want to enable this for llvm versions below 9 or thread safe counters +then set ``` export AFL_LLVM_NOT_ZERO=1 @@ -33,3 +34,8 @@ AFL_LLVM_SKIP_NEVERZERO=1 ``` If the target does not have extensive loops or functions that are called a lot then this can give a small performance boost. + +Please note that the default counter implementations are not thread safe! + +Support for thread safe counters in mode LLVM CLASSIC can be activated with setting +`AFL_LLVM_THREADSAFE_INST=1`. \ No newline at end of file |