Previously, the {Basic,}TestingSetup for fuzzers were set up in many ways:
1. Calling InitializeFuzzingContext, which implicitly constructs a static
const BasicTestingSetup
2. Directly constructing a static const BasicTestingSetup in the initialize_*
function
3. Directly constructing a static TestingSetup and reproducing the
initialization arguments (I'm assuming because
InitializeFuzzingContext only initializes a BasicTestingSetup)
The new, relatively-simple MakeFuzzingContext function allows us to
consolidate these methods of initialization by being flexible enough to
be used in all situations. It:
1. Is templated so that we can choose to initialize any of
the *TestingSetup classes
2. Has sane defaults which are often used in fuzzers but are also
easily overridable
3. Returns a unique_ptr, explicitly transferring ownership to the caller
to deal with according to its situation
fa13e1b0c5 build: Add option --enable-danger-fuzz-link-all (MarcoFalke)
44444ba759 fuzz: Link all targets once (MarcoFalke)
Pull request description:
Currently the linker is invoked more than 150 times when compiling with `--enable-fuzz`. This is problematic for several reasons:
* It wastes disk space north of 20 GB, as all libraries and sanitizers are linked more than 150 times
* It wastes CPU time, as the link step can practically not be cached (similar to ccache for object files)
* It makes it a blocker to compile the fuzz tests by default for non-fuzz builds #19388, for the aforementioned reasons
* The build file is several thousand lines of code, without doing anything meaningful except listing each fuzz target in a highly verbose manner
* It makes writing new fuzz tests unnecessarily hard, as build system knowledge is required; Compare that to boost unit tests, which can be added by simply editing an existing cpp file
* It encourages fuzz tests that re-use the `buffer` or assume the `buffer` to be concatenations of seeds, which increases complexity of seeds and complexity for the fuzz engine to explore; Thus reducing the effectiveness of the affected fuzz targets
Fixes #20088
ACKs for top commit:
practicalswift:
Tested ACK fa13e1b0c5
sipa:
ACK fa13e1b0c5. Reviewed the code changes, and tested the 3 different test_runner.py modes (run once, merge, generate). I also tested building with the new --enable-danger-fuzz-link-all
Tree-SHA512: 962ab33269ebd51810924c51266ecc62edd6ddf2fcd9a8c359ed906766f58c3f73c223f8d3cc49f2c60f0053f65e8bdd86ce9c19e673f8c2b3cd676e913f2642
