Clusterfuzz environment flags reused for dependencies
The build script for tor at oss-fuzz currently reuses clusterfuzz environment variables to compile dependencies. This has consequences when the dependencies themselves are upstream projects at oss-fuzz. The build environment sets the following flags to enable fuzzing of a target project:
CC=clang CXX=clang++ CFLAGS=-O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link CXXFLAGS=-O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link -stdlib=libc++
In the case of zlib: Using the environment flags above as-is results in activating oss-fuzz instrumentation. Eventually resulting in ambiguously placed
undefined symbol __sancov_lowest_stack because stack depth tracing was not instrumented properly. Which leads to a rabbit-hole of why are we fixing instrumenting fuzzers in tor's dependencies?
Now Openssl also has an upstream clusterfuzz instance and so leaving the environment flags as-is also results in instrumenting openssl for oss-fuzz.
This sounds wrong. If we're fuzzing tor then why are we also instrumenting dependencies for clusterfuzz? It looks like the dependencies should override these flags when built to avoid conflicts.
When the flags are overridden to build debug dependencies, followed by building tor's fuzzers as usual,
check_build tor passes all tests.