libpsl/fuzz/README.md

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# Fuzzers
These are fuzzers designed for use with `libFuzzer` or `afl`. They can
be used to run on Google's OSS-Fuzz (https://github.com/google/oss-fuzz/).
The convention used here is that the initial values for each parser fuzzer
are taken from the $NAME.in directory.
Crash reproducers from OSS-Fuzz are put into $NAME.repro directory for
regression testing with top dir 'make check' or 'make check-valgrind'.
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The ./configure runs below are for libidn2.
To test libicu replace 'libidn2' with 'libicu', to test with
libidn replace 'libidn2' by 'libidn'.
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# Running a fuzzer using clang
Use the following commands on top dir:
```
export CC=clang-5.0
export CXX=clang++-5.0
export CFLAGS="-O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize-coverage=trace-pc-guard,trace-cmp"
export CXXFLAGS="-O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize-coverage=trace-pc-guard,trace-cmp -stdlib=libc++"
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./configure --enable-static --disable-gtk-doc --enable-runtime=libidn2 --enable-builtin=libidn2
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make clean
make -j$(nproc)
cd fuzz
# build and run libpsl_fuzzer
./run-clang.sh libpsl_fuzzer
```
# Running a fuzzer using AFL
Use the following commands on top dir:
```
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$ CC=afl-clang-fast ./configure --disable-gtk-doc --enable-runtime=libidn2 --enable-builtin=libidn2
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$ make -j$(nproc) clean all
$ cd fuzz
$ ./run-afl.sh libpsl_fuzzer
```
# Fuzz code coverage using the corpus directories *.in/
Code coverage reports currently work best with gcc+lcov+genhtml.
In the top directory:
```
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CC=gcc CFLAGS="-O0 -g" ./configure --disable-gtk-doc --enable-runtime=libidn2 --enable-builtin=libidn2
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make fuzz-coverage
xdg-open lcov/index.html
```
Each fuzzer target has it's own functions to cover, e.g.
`libpsl_fuzzer` covers psl_is_public_suffix.
To work on corpora for better coverage, `cd fuzz` and use e.g.
`./view-coverage.sh libpsl_fuzzer`.
# Enhancing the testsuite for issues found
Each reproducer file should be dropped into the appropriate *.repro/
directory.