[llvm-dev] moving libfuzzer to compiler-rt?

Kostya Serebryany via llvm-dev llvm-dev at lists.llvm.org
Wed Jul 12 14:16:01 PDT 2017

On Wed, Jul 12, 2017 at 2:11 PM, George Karpenkov via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> > I really like the property of libFuzzer living in its own place so that
> > it's easy to use without building the world
> But it’s not: the implementation of the coverage instrumentation
> is done in one of the sanitizers, so it’s impossible to just use libFuzzer
> without them.

Mmm. what do you mean?
libFuzzer implements it's own coverage hooks now.

> Furthermore, I would think that almost all libFuzzer users would use a
> sanitizer while fuzzing.

Although for equivalence fuzzing (aka differential fuzzing) sanitizers are
not needed.

> I can see a few more benefits of moving to compiler-rt:
> 1) It would enforce the property
> that either sanitizers and libfuzzer are both in “runtimes”, or they are
> both aren’t.
> Then we can naturally add a dependency from libFuzzer test to sanitizers
> using CMake.
> Otherwise, adding a dependency from libfuzzer tests to sanitizers requires
> hacky if/elses in CMake configuration (and we already have too many of
> those).
> 2) Orthogonally to the moving-of-source-code discussion, I would like to
> move the generated library
> to the folder where other clang libraries and sanitizers are.
> That would considerably simplify toolchain installation problem (as we
> know that sanitizers are already installed
> correctly in the toolchain) as well as simplifying driver logic for both
> Clang and Swift.
> [Diverting even further, I think it would be beneficial to build a dynamic
> library as well as an archive,
> and use that at least on Mac, where it can solve the linking issues
> discussed in https://github.com/google/sanitizers/issues/832.
> It would be also be much easier if the resulting dylib would be in the
> same folder where other sanitizers are, due to the fact
> that we already have the code for setting the expected rpath on the
> produced binary].
> This move can of course be done from any source directory, as it’s just a
> matter of setting a target property.
> Yet the logic for selecting the folder is a 20-30 lines chunk of CMake,
> which I would like to avoid copying,
> and which we could otherwise just reuse from compiler-rt.
> 3) As Chris Bieneman has previously mentioned in the beginning of this
> thread,
> adding libFuzzer to the toolchain installation might be problematic under
> the current license,
> which requires binary attribution.
> Performing the move and resolving the licensing concern would solve that.

Good! :)

> > On Jul 12, 2017, at 1:27 PM, Justin Bogner <mail at justinbogner.com>
> wrote:
> >
> > Reid Kleckner via llvm-dev <llvm-dev at lists.llvm.org> writes:
> >> On Wed, Jul 12, 2017 at 11:30 AM, George Karpenkov via llvm-dev <
> >> llvm-dev at lists.llvm.org> wrote:
> >>>
> >>> I already forgot why we decided not to move the code to compiler-rt.
> >>>
> >>> This would solve at least this problem.
> >>> Since we now have -fsanitize=fuzzer it will actually be pretty natural.
> >>>
> >>>
> >>> Licensing concerns, compiler-rt has a different license.
> >>>
> >>> BTW libFuzzer CMake has a crazy amount of hacks to work under Windows,
> >>> where logic in many parts
> >>> is entirely different, so any help on testing and fixing arising issues
> >>> would be much appreciated.
> >>> All I can do is to make a commit and then try to understand the
> response
> >>> from a bots,
> >>> which is not very efficient.
> >>>
> >>
> >> I got volunteered to help with that, I'll try your patch.
> >>
> >> There's more stuff to unpack in the rest of your email, though. I'd
> really
> >> rather go to compiler-rt instead of runtimes. runtimes seems like it's
> >> going the opposite direction from the monorepo efforts.
> >
> > I don't see how runtimes is going either for- or against- the monorepo
> > stuff. We really need a model like runtimes/ rather than a model like
> > projects/ going forward regardless of where you find the code. This is
> > necessary if we want to build cross-compiled compiler-rt libraries in
> > any sort of sane way.
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