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docs/fuzz: add instructions for generating a coverage report 

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20200706195534.14962-5-alxndr@bu.edu>
[thuth: Replaced --enable-sanitizers with --enable-fuzzing]
Signed-off-by: Thomas Huth <thuth@redhat.com>
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Alexander Bulekov 2020-07-06 15:55:34 -04:00 committed by Thomas Huth
parent 19a91e4af8
commit 09a14f586c
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docs/devel/fuzzing.txt
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@ -85,6 +85,25 @@ 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.
== Generating Coverage Reports ==
Code coverage is a crucial metric for evaluating a fuzzer's performance.
libFuzzer's output provides a "cov: " column that provides a total number of
unique blocks/edges covered. To examine coverage on a line-by-line basis we
can use Clang coverage:
1. Configure libFuzzer to store a corpus of all interesting inputs (see
CORPUS_DIR above)
2. ./configure the QEMU build with:
--enable-fuzzing \
--extra-cflags="-fprofile-instr-generate -fcoverage-mapping"
3. Re-run the fuzzer. Specify $CORPUS_DIR/* as an argument, telling libfuzzer
to execute all of the inputs in $CORPUS_DIR and exit. Once the process
exits, you should find a file, "default.profraw" in the working directory.
4. Execute these commands to generate a detailed HTML coverage-report:
llvm-profdata merge -output=default.profdata default.profraw
llvm-cov show ./path/to/qemu-fuzz-i386 -instr-profile=default.profdata \
--format html -output-dir=/path/to/output/report
== 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