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

Kostya Serebryany via llvm-dev llvm-dev at lists.llvm.org
Wed Jul 12 12:48:03 PDT 2017 

+ Chandler, Danny,

We are considering to move the libFuzzer code from llvm to compiler-rt, and
that implies a license change.
Will it be sufficient to do the following?
  * e-mail to all contributors (a short list, below) asking for their
consent
  * remove any code for which we did not get consent in, say, 1 week.

(BTW, this list is actually much shorter, I recognize many of these as
belonging to googlers or applers)

On Wed, Jul 12, 2017 at 12:41 PM, George Karpenkov <ekarpenkov at apple.com>
wrote:

>
> On Jul 12, 2017, at 11:58 AM, Kostya Serebryany <kcc at google.com> wrote:
>
>
>
> On Wed, Jul 12, 2017 at 11:54 AM, George Karpenkov <ekarpenkov at apple.com>
> wrote:
>
>>
>> On Jul 12, 2017, at 11:34 AM, Kostya Serebryany <kcc at google.com> wrote:
>>
>>
>>
>> On Wed, Jul 12, 2017 at 11:30 AM, George Karpenkov <ekarpenkov at apple.com>
>> wrote:
>>
>>>
>>> On Jul 12, 2017, at 11:01 AM, Kostya Serebryany <kcc at google.com> wrote:
>>> One question: will it make sense to *copy* the code to the new location,
>>> work on it, then delete the code from the old location,
>>> instead of doing a move in a single commit?
>>> I don't expect any dramatic changes in the code structure during a few
>>> weeks, so 'copy' might be much simpler than 'move’.
>>>
>>>
>>> I am not sure how we would handle CMake targets collision (I think we
>>> would have one: check-fuzzer vs. check-fuzzer)
>>> Of course, I can give it a different name for now,
>>>
>>
>> Yep. 'check-fuzzer-temporary' or some such.
>>
>>
>>> but that would potentially add even more confusion and complexity.
>>>
>>> Though it seems like a good idea to at least see what would happen to
>>> buildbots.
>>>
>>> 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.
>>>
>>
>> @%##%)*%
>>
>> But wait a sec, the sanitizers are ok with this license, why libFuzzer
>> isn't?
>> (Sorry, my memory has been flushed over the last month)
>>
>>
>> Apparently because the code was already contributed under a different
>> license.
>> IANAL but apparently to do the change in a fully correct way one would
>> need to chase
>> down every single contributor and ask them to agree to a license change.
>>
>
> This is a PITA, but we should do it.
> licensing issues like this should not prevent us from making our own code
> better.
>
>
>
> Should not be that hard:
>
> george@/Volumes/Transcend/code/llvm (master)≻ git log
> --pretty=format:"%ae" lib/Fuzzer | egrep -v "chromium|apple|google" | sort
> | uniq
> aaron at aaronballman.com
> ahmed.bougacha at gmail.com
> chandlerc at gmail.com
> craig.topper at gmail.com
> dan at su-root.co.uk
> eric at efcs.ca
> hans at hanshq.net
> juergen at ributzka.de
> lenny at colorado.edu
> mail at justinbogner.com
> matze at braunis.de
> mgrang at codeaurora.org
> nicholas at mxc.ca
> peter at pcc.me.uk
> rafael.espindola at gmail.com
> richard-llvm at metafoo.co.uk
> sanjoy at playingwithpointers.com
> tzuhsiang.chien at gmail.com
> vonosmas at gmail.com
> yaron.keren at gmail.com
>
> Would you know the formal process for a license change?
>
>
>
>
>
>>
>>
>>
>>>
>>> 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.
>>>
>>
>> It's totally fine for me if we *copy* the code to the new location and
>> ditch the windows support completely.
>> Then, whoever cares about windows, will reinstate it in the new location
>> once the dust settles.
>>
>>
>>
>>> All I can do is to make a commit and then try to understand the response
>>> from a bots,
>>> which is not very efficient.
>>>
>>>
>>>
>>>>
>>>> 3) CMake files in LLVM root repository do a rather large amount of
>>>> trickery:
>>>> more warning flags are introduced, default linking commands for
>>>> different platforms are changed,
>>>> etc.
>>>> None of this is picked up when running from the “runtimes” directory,
>>>> which is often undesirable,
>>>> as the runtime would be built very differently from the rest of LLVM,
>>>> missing those desired warnings/optimizations.
>>>>
>>>> Additionally, working with “runtimes” introduces some inherent
>>>> restrictions.
>>>> Namely:
>>>>
>>>> 4) Extra arguments to CMake will not be propagated.
>>>> E.g. invoking `cmake … -DLLVM_USE_SANITIZE_COVERAGE=1` will not have
>>>> any effect on the compilation of any project
>>>> in “runtimes”.
>>>> It’s not clear how those flags can be explicitly propagated.
>>>>
>>>> 5) In a similar vein to (4), additional flags to `ninja` will not be
>>>> propagated.
>>>> E.g. running “ninja -v check-blah” will actually not show the commands
>>>> required to execute the tests,
>>>> as it goes through a CMake invocation.
>>>> This issue has a workaround: ninja can be launched directly from
>>>> “runtimes/runtime-bins”, but that is counterintuitive.
>>>>
>>>> 6) Recursive invocation required for “runtimes” breaks
>>>> `compile_commands.json` construction, which is used
>>>> by many editors and tools (e.g. Vim+Ale or rtags) for go-to-defintion
>>>> and error highlight functionality.
>>>> There is a workaround: a separate `compile_commands.json` is generated
>>>> for the `runtimes` directory,
>>>> and it might be possible to write some magic to inject it back into the
>>>> parent one, but that would be yet-another-piece-of-build-infrastructure
>>>> which would have to be maintained.
>>>>
>>>> 7) Similarly to (6), recursive invocation breaks XCode tooling: in a
>>>> generated XCode project,
>>>> no libfuzzer files are accessible. I would assume same would hold for
>>>> other IDEs.
>>>>
>>>> Any thoughts or comments on these?
>>>> While (1) is not really a problem, and I can probably find a workaround
>>>> for (2), the issues
>>>> listed in (3)-(7) seem inherent to recursive CMake invocation.
>>>> I can think of a number of alternative suggestions, which would solve
>>>> the problem of requiring a 2-stage build:
>>>>
>>>> a) We can move the compilation commands for libFuzzer tests from CMake
>>>> into lit.
>>>> This would have an added benefit of each lit test being self-contained:
>>>> it would be sufficient to just run
>>>> “lit” to reproduce everything, and it would pick up all changes to
>>>> compiler/coverage instrumentation/sanitizers/etc.
>>>> The first run would generate the tested binaries, and further tinkering
>>>> could be done with binaries directly if desired.
>>>>
>>>> b) We can use the “tools” directory instead.
>>>>
>>>>
>>>> Thanks,
>>>> George
>>>>
>>>> On May 11, 2017, at 10:31 AM, Kostya Serebryany <kcc at google.com> wrote:
>>>>
>>>>
>>>>
>>>> On Wed, May 10, 2017 at 6:09 PM, Chris Bieneman via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>>>
>>>>> On May 10, 2017, at 4:43 PM, George Karpenkov via llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>> Actually, there’s another problem we have missed: libraries under
>>>>> `build/lib` are not installed into toolchain
>>>>> on mac os (and neither on linux, I would suppose).
>>>>>
>>>>>
>>>>> Actually that isn't accurate. By default we don't install the LLVM
>>>>> libraries, but that is completely configurable in the build system. It
>>>>> doesn't work for libFuzzer because the CMake build for libFuzzer is not
>>>>> built using any of the LLVM CMake modules or following any of LLVM's
>>>>> conventions.
>>>>>
>>>>> Thus installations of Clang would not contain libLLVMFuzzer, but we
>>>>> would like them to, so that users would not have
>>>>> to compile anything, and could just call `clang -fsanitize=fuzzer`.
>>>>>
>>>>> That could probably be done with another CMake change, but I have no
>>>>> idea how to do that.
>>>>>
>>>>>
>>>>> Yea, libFuzzer's CMake really needs a big overhaul, and probably an
>>>>> almost complete rewrite.
>>>>>
>>>>
>>>> no objections.
>>>>
>>>>
>>>>>
>>>>> -Chris
>>>>>
>>>>>
>>>>> On May 9, 2017, at 4:04 PM, George Karpenkov via llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>>
>>>>> On May 9, 2017, at 3:00 PM, Kostya Serebryany <kcc at google.com> wrote:
>>>>>
>>>>> Thanks for the explanations! (it was worth asking)
>>>>>
>>>>> I do want to build libFuzzer itself (and its tests) using the just-built
>>>>> clang. So, llvm/runtimes then.
>>>>> I'd name the directory llvm/runtimes/libFuzzer, if possible (the old
>>>>> path was lib/Fuzzer which is how the tool got it's name, actually)
>>>>> George, would you like to send the change for review?
>>>>>
>>>>> OK
>>>>>
>>>>>
>>>>> --kcc
>>>>>
>>>>>
>>>>>
>>>>> On Tue, May 9, 2017 at 2:37 PM, Chris Bieneman <cbieneman at apple.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>> On May 9, 2017, at 2:19 PM, George Karpenkov <ekarpenkov at apple.com>
>>>>>> wrote:
>>>>>>
>>>>>> +Chris.
>>>>>>
>>>>>> My understanding was that it is technically impossible for things in
>>>>>> “lib”, as they are built first, and there’s no way to tell them to do that
>>>>>> before “clang”.
>>>>>> I’m not a CMake expert, and I might be wrong.
>>>>>>
>>>>>>
>>>>>> It is not impossible, it would just involve excessive hacks. Since it
>>>>>> seems like this isn't a short-term solution we're talking about I am very
>>>>>> opposed to throwing hacks into the build system. I'd rather we actually fix
>>>>>> the problem(s). More below.
>>>>>>
>>>>>>
>>>>>> On May 9, 2017, at 2:15 PM, Kostya Serebryany <kcc at google.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Tue, May 9, 2017 at 1:56 PM, George Karpenkov <ekarpenkov at apple.co
>>>>>> m> wrote:
>>>>>>
>>>>>>> Again, after offline conversation with Chris Bieneman:
>>>>>>>
>>>>>>>  - move to compiler-rt would be too complicated due to change in
>>>>>>> licenses
>>>>>>>  - it would make much more sense to move to “tools” folder instead,
>>>>>>> for the following reasons:
>>>>>>>     * conceptually, it’s a tool, not a library
>>>>>>>     * all other projects in “lib” depend on LLVM and can not build
>>>>>>> without LLVM, libFuzzer does not
>>>>>>>     * practically speaking, CMake has no way of knowing whether
>>>>>>> Clang is being built when
>>>>>>>       “lib” is compiled, yet it does know for projects in tools.
>>>>>>>
>>>>>>> Using a freshly built clang for projects in “tools” is
>>>>>>> embarrassingly easy and only requires a couple of lines
>>>>>>> of configuration change.
>>>>>>>
>>>>>>> Kostya, what about moving to “tools” then?
>>>>>>>
>>>>>>
>>>>>> Well, ok, this sounds cool.
>>>>>> But can we make one more step and try to preserve the code where it
>>>>>> is, for the sake of compatibility?
>>>>>>
>>>>>>
>>>>>> Please no. This code doesn't actually belong in lib, it has never fit
>>>>>> the model of an LLVM library, we really need to pull it out of there.
>>>>>>
>>>>>> E.g. can we have the CMake in tools while still keeping the code in
>>>>>> lib?
>>>>>>
>>>>>>
>>>>>> Could we contrive a hack in the build system to do it? Yes, but I
>>>>>> will fight violently against allowing that change into the build system
>>>>>> because the right answer here is to move the code.
>>>>>>
>>>>>> Or a link of some kind?
>>>>>>
>>>>>>
>>>>>> Links are incredibly fragile on Windows, and they trip up a lot of
>>>>>> SCM tools. We have one in LLDB's repo that causes me nothing but problems,
>>>>>> so I am also strongly opposed to that.
>>>>>>
>>>>>>
>>>>>> My worry is that there are already quite a few places that know where
>>>>>> libFuzzer code is,
>>>>>> and I don't control all of them.
>>>>>>
>>>>>>
>>>>>> Downstream clients will have to update. That is kinda how these
>>>>>> things work, I can't imagine re-pointing an SCM checkout being a huge
>>>>>> burden.
>>>>>>
>>>>>>
>>>>>> And, finally, I really don't get why we can do something in tools and
>>>>>> can't do the same in lib.
>>>>>> Or we simply don't want to do it to keep things simple?
>>>>>>
>>>>>>
>>>>>> Not all functionality in CMake is order-independent. Specifically the
>>>>>> detection of targets is not. In order to support what you're trying to do
>>>>>> you are going to change behavior based on the presence of the clang target.
>>>>>> Which means the clang target must be added before your CMake is processed.
>>>>>>
>>>>>> To support this our build system has strict ordering requirements
>>>>>> such that things in lib cannot depend on things in tools. If you need to
>>>>>> depend on clang, you need to not be in lib.
>>>>>>
>>>>>> Also, generally speaking Fuzzer is a library under lib that also has
>>>>>> nested tests, which is *not* how the lib directory is supposed to be
>>>>>> structured. It never should have been allowed to be structured like that.
>>>>>> If you want the tests next to the library, it is a tool or a runtime, but
>>>>>> not a lib.
>>>>>>
>>>>>> As I see there are two options to move forward with, and it really
>>>>>> depends on how you intend to use the just-built clang.
>>>>>>
>>>>>> (1) If you want to use just-built clang to build libFuzzer and its
>>>>>> tests, it should be a runtime.
>>>>>> (2) If you want to use just-built clang to only build libFuzzer's
>>>>>> tests, it should be a tool.
>>>>>>
>>>>>> I think that since it is a runtime library, it should be a runtime,
>>>>>> and I expect it would mostly work to just copy the Fuzzer directory into
>>>>>> llvm/runtimes.
>>>>>>
>>>>>> -Chris
>>>>>>
>>>>>>
>>>>>> --kcc
>>>>>>
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> On May 9, 2017, at 11:07 AM, Dan Liew <dan at su-root.co.uk> wrote:
>>>>>>>
>>>>>>> On 9 May 2017 at 18:55, Kostya Serebryany <kcc at google.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Tue, May 9, 2017 at 10:23 AM, Dan Liew <dan at su-root.co.uk> wrote:
>>>>>>>
>>>>>>>
>>>>>>> Does anyone see good reasons why libFuzzer should remain in llvm repo
>>>>>>> (as
>>>>>>> opposed to moving it to compiler-rt)?
>>>>>>>
>>>>>>>
>>>>>>> Does moving LibFuzzer to compiler-rt imply that it is compiled as
>>>>>>> part
>>>>>>> of compiler-rt and shipped with it?
>>>>>>>
>>>>>>> How does that fit with LibFuzzer's model of allowing the user to
>>>>>>> provide their own `main()`.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> libFuzzer doesn't allow users to use their own main (not any more).
>>>>>>> Although I am not sure how that's related to moving libFuzzer
>>>>>>> somewhere.
>>>>>>>
>>>>>>>
>>>>>>> Oops. That shows how long it's been since I looked at the source
>>>>>>> code.
>>>>>>>
>>>>>>> It was related in that if LibFuzzer was shipped as part of
>>>>>>> compiler-rt
>>>>>>> I presumed we would need to supply both libraries to end users.
>>>>>>> Given that this feature was removed it is a non-issue.
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>>
>>>
>>
>>
>
>
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