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Merge pull request #4360 from mattaereal/doc_patches-1

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Docs: Adding AFL's alternative configuration with clang.
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Alex Beregszaszi 2018-06-27 17:56:51 +02:00 committed by GitHub
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docs/contributing.rst
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@ -184,7 +184,8 @@ does not fail if e.g. the code contains an error. This way, internal problems in
can be found by fuzzing tools.
We mainly use `AFL <http://lcamtuf.coredump.cx/afl/>`_ for fuzzing. You need to download and
build AFL manually. Next, build Solidity (or just the ``solfuzzer`` binary) with AFL as your compiler:
install AFL packages from your repos (afl, afl-clang) or build them manually.
Next, build Solidity (or just the ``solfuzzer`` binary) with AFL as your compiler:
::
@ -194,6 +195,47 @@ build AFL manually. Next, build Solidity (or just the ``solfuzzer`` binary) with
cmake .. -DCMAKE_C_COMPILER=path/to/afl-gcc -DCMAKE_CXX_COMPILER=path/to/afl-g++
make solfuzzer
At this stage you should be able to see a message similar to the following:
::
Scanning dependencies of target solfuzzer
[ 98%] Building CXX object test/tools/CMakeFiles/solfuzzer.dir/fuzzer.cpp.o
afl-cc 2.52b by <lcamtuf@google.com>
afl-as 2.52b by <lcamtuf@google.com>
[+] Instrumented 1949 locations (64-bit, non-hardened mode, ratio 100%).
[100%] Linking CXX executable solfuzzer
If the instrumentation messages did not appear, try switching the cmake flags pointing to AFL's clang binaries:
::
# if previously failed
make clean
cmake .. -DCMAKE_C_COMPILER=path/to/afl-clang -DCMAKE_CXX_COMPILER=path/to/afl-clang++
make solfuzzer
Othwerise, upon execution the fuzzer will halt with an error saying binary is not instrumented:
::
afl-fuzz 2.52b by <lcamtuf@google.com>
... (truncated messages)
[*] Validating target binary...
[-] Looks like the target binary is not instrumented! The fuzzer depends on
compile-time instrumentation to isolate interesting test cases while
mutating the input data. For more information, and for tips on how to
instrument binaries, please see /usr/share/doc/afl-doc/docs/README.
When source code is not available, you may be able to leverage QEMU
mode support. Consult the README for tips on how to enable this.
(It is also possible to use afl-fuzz as a traditional, "dumb" fuzzer.
For that, you can use the -n option - but expect much worse results.)
[-] PROGRAM ABORT : No instrumentation detected
Location : check_binary(), afl-fuzz.c:6920
Next, you need some example source files. This will make it much easer for the fuzzer
to find errors. You can either copy some files from the syntax tests or extract test files
from the documentation or the other tests: