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

[Daniel Berlin via llvm-dev]

On Mon, Jul 17, 2017 at 2:18 PM, George Karpenkov <ekarpenkov at apple.com>
wrote:

>
>
> On Jul 17, 2017, at 2:06 PM, Daniel Berlin <dannyb at google.com> wrote:
>
> This process works legally, but i can't speak to whether the foundation
> would be okay with it, as it may result in bad press, etc, if you rip code
> out.
>
>
> Thank you for your reply!
> I have two additional questions:
>
> 1) Why is it ripping the code out if compiler-rt is still part of LLVM?
>

Because we won't change the license of the existing code that others have
contributed without their consent.
If they do not consent, your only choice is to rip it out.


> 2) Does it mean that we should reach out to board at llvm.org to okay the
> issue?
>
> IMHO, yes.


> Thanks,
> George
>
>
>
>>
>> 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-inf
>>>>>> rastructure
>>>>>> 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.com> 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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