By default we enable the Kernel Undefined Behavior Sanitizer, which
checks for undefined behavior at runtime. However, sometimes a developer
might want to turn that off, so now there is a easy way to do that.
This option sets -fprofile-instr-generate -fcoverage-mapping for Clang
builds only on almost all of Userland. Loader and LibTimeZone are
exempt. This can be used for generating code coverage reports, or even
PGO in the future.
This commit adds support for building the SerenityOS userland with the
new [mold linker].
This is not enabled by default yet; to link using mold, run the
`Toolchain/BuildMold.sh` script to build the latest release of mold, and
set the `ENABLE_MOLD_LINKER` CMake variable to ON. This option relies on
toolchain support that has been added just recently, so you might need
to rebuild your toolchain for mold to work.
[mold linker]: https://github.com/rui314/mold
We used to build with -Os in order to fit within a certain size, but
there isn't really a good reason for that kind of restriction.
Switching to -O2 yields a significant improvement in throughput,
for example `test-js` is roughly 20% faster on my machine. :^)
GCC and Clang allow us to inject a call to a function named
__sanitizer_cov_trace_pc on every edge. This function has to be defined
by us. By noting down the caller in that function we can trace the code
we have encountered during execution. Such information is used by
coverage guided fuzzers like AFL and LibFuzzer to determine if a new
input resulted in a new code path. This makes fuzzing much more
effective.
Additionally this adds a basic KCOV implementation. KCOV is an API that
allows user space to request the kernel to start collecting coverage
information for a given user space thread. Furthermore KCOV then exposes
the collected program counters to user space via a BlockDevice which can
be mmaped from user space.
This work is required to add effective support for fuzzing SerenityOS to
the Syzkaller syscall fuzzer. :^) :^)
The WASM spec tests caused a stack overflow when generated with wat2wasm
version 1.0.23, which ships with homebrew. To give feature parity,
manually download the same version from GitHub packages for Ubuntu.
Document the dependencies of the WASM spec tests option, as well.
