Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
docs/devel/fuzzing.txt | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/docs/devel/fuzzing.txt b/docs/devel/fuzzing.txt
index 324d2cd92b..3458763e53 100644
--- a/docs/devel/fuzzing.txt
+++ b/docs/devel/fuzzing.txt
@@ -45,6 +45,39 @@ Information about these is available by passing -help=1
Now the only thing left to do is wait for the fuzzer to trigger potential
crashes.
+== Useful libFuzzer flags ==
+
+As mentioned above, libFuzzer accepts some arguments. Passing -help=1 will list
+the available arguments. In particular, these arguments might be helpful:
+
+$CORPUS_DIR/ : Specify a directory as the last argument to libFuzzer. libFuzzer
+stores each "interesting" input in this corpus directory. The next time you run
+libFuzzer, it will read all of the inputs from the corpus, and continue fuzzing
+from there.
+
+-max_len=4096 : specify the maximum byte-length of the inputs libFuzzer will
+generate.
+
+-close_fd_mask={1,2,3} : close, stderr, or both. Useful for targets that
+trigger many debug/error messages, or create output on the serial console.
+
+-jobs=4 -workers=4 : These arguments configure libFuzzer to run 4 fuzzers in
+parallel. Replace 4 with a number appropriate for your machine. Make sure to
+specify a $CORPUS_DIR, which will allow the parallel fuzzers to share
+information about the interesting inputs they find.
+
+-use_value_profile=1 : For each comparison operation, libFuzzer computes
+(caller_pc&4095) | (popcnt(Arg1 ^ Arg2) << 12) and places this in the coverage
+table. Useful for targets with "magic" constants. If Arg1 came from the fuzzer's
+input and Arg2 is a magic constant, then each time the hamming distance
+between Arg1 and Arg2 decreases, libFuzzer adds the input to the corpus.
+
+-shrink=1 : Tries to make elements of the corpus "smaller". Might lead to
+better coverage performance, depending on the target.
+
+Note that libFuzzer's exact behavior will depend on the version of
+clang and libFuzzer used to build the device fuzzers.
+
== Adding a new fuzzer ==
Coverage over virtual devices can be improved by adding additional fuzzers.
Fuzzers are kept in tests/qtest/fuzz/ and should be added to
--
2.26.2
On 5/24/20 4:37 PM, Alexander Bulekov wrote: > Signed-off-by: Alexander Bulekov <alxndr@bu.edu> > --- > docs/devel/fuzzing.txt | 33 +++++++++++++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > > diff --git a/docs/devel/fuzzing.txt b/docs/devel/fuzzing.txt > index 324d2cd92b..3458763e53 100644 > --- a/docs/devel/fuzzing.txt > +++ b/docs/devel/fuzzing.txt > @@ -45,6 +45,39 @@ Information about these is available by passing -help=1 > Now the only thing left to do is wait for the fuzzer to trigger potential > crashes. > > +== Useful libFuzzer flags == > + > +As mentioned above, libFuzzer accepts some arguments. Passing -help=1 will list > +the available arguments. In particular, these arguments might be helpful: > + > +$CORPUS_DIR/ : Specify a directory as the last argument to libFuzzer. libFuzzer > +stores each "interesting" input in this corpus directory. The next time you run > +libFuzzer, it will read all of the inputs from the corpus, and continue fuzzing > +from there. Maybe describe we can use multiple directories, the first one is where new inputs are written. > + > +-max_len=4096 : specify the maximum byte-length of the inputs libFuzzer will > +generate. > + > +-close_fd_mask={1,2,3} : close, stderr, or both. Useful for targets that > +trigger many debug/error messages, or create output on the serial console. > + > +-jobs=4 -workers=4 : These arguments configure libFuzzer to run 4 fuzzers in > +parallel. The difference between job/worker is not clear... > Replace 4 with a number appropriate for your machine. Make sure to > +specify a $CORPUS_DIR, which will allow the parallel fuzzers to share > +information about the interesting inputs they find. > + > +-use_value_profile=1 : For each comparison operation, libFuzzer computes > +(caller_pc&4095) | (popcnt(Arg1 ^ Arg2) << 12) and places this in the coverage > +table. Useful for targets with "magic" constants. If Arg1 came from the fuzzer's > +input and Arg2 is a magic constant, then each time the hamming distance "Hamming" (lastname). Thanks! > +between Arg1 and Arg2 decreases, libFuzzer adds the input to the corpus. > + > +-shrink=1 : Tries to make elements of the corpus "smaller". Might lead to > +better coverage performance, depending on the target. > + > +Note that libFuzzer's exact behavior will depend on the version of > +clang and libFuzzer used to build the device fuzzers. > + > == Adding a new fuzzer == > Coverage over virtual devices can be improved by adding additional fuzzers. > Fuzzers are kept in tests/qtest/fuzz/ and should be added to >
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