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

George Karpenkov via llvm-dev
Wed, 12 Jul 2017 20:07:22 -0000

After additional filtering, the list is:

Author: Craig Topper <craig.topper at gmail.com>
Author: Eric Fiselier <eric at efcs.ca>
Author: Mandeep Singh Grang <mgrang at codeaurora.org>
Author: Nick Lewycky <nicholas at mxc.ca>
Author: Rafael Espindola <rafael.espindola at gmail.com>
Author: Richard Smith <richard-llvm at metafoo.co.uk>
Author: Sanjoy Das <sanjoy at playingwithpointers.com>
Author: Logan Chien <tzuhsiang.chien at gmail.com>
Author: Yaron Keren <yaron.keren at gmail.com>

Also I’ve looked at the commits, and most of them are tiny NFC’s.

> On 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
<mailto:kcc at google.com>> wrote:
>>
>>
>>
>> On Wed, Jul 12, 2017 at 11:54 AM, George Karpenkov <ekarpenkov at
apple.com <mailto:ekarpenkov at apple.com>> wrote:
>>
>>> On Jul 12, 2017, at 11:34 AM, Kostya Serebryany <kcc at
google.com <mailto:kcc at google.com>> wrote:
>>>
>>>
>>>
>>> On Wed, Jul 12, 2017 at 11:30 AM, George Karpenkov <ekarpenkov
at apple.com <mailto:ekarpenkov at apple.com>> wrote:
>>>
>>>> On Jul 12, 2017, at 11:01 AM, Kostya Serebryany <kcc at
google.com <mailto: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 <mailto:aaron at aaronballman.com>
> ahmed.bougacha at gmail.com <mailto:ahmed.bougacha at gmail.com>
> chandlerc at gmail.com <mailto:chandlerc at gmail.com>
> craig.topper at gmail.com <mailto:craig.topper at gmail.com>
> dan at su-root.co.uk <mailto:dan at su-root.co.uk>
> eric at efcs.ca <mailto:eric at efcs.ca>
> hans at hanshq.net <mailto:hans at hanshq.net>
> juergen at ributzka.de <mailto:juergen at ributzka.de>
> lenny at colorado.edu <mailto:lenny at colorado.edu>
> mail at justinbogner.com <mailto:mail at justinbogner.com>
> matze at braunis.de <mailto:matze at braunis.de>
> mgrang at codeaurora.org <mailto:mgrang at codeaurora.org>
> nicholas at mxc.ca <mailto:nicholas at mxc.ca>
> peter at pcc.me.uk <mailto:peter at pcc.me.uk>
> rafael.espindola at gmail.com <mailto:rafael.espindola at gmail.com>
> richard-llvm at metafoo.co.uk <mailto:richard-llvm at metafoo.co.uk>
> sanjoy at playingwithpointers.com <mailto:sanjoy at
playingwithpointers.com>
> tzuhsiang.chien at gmail.com <mailto:tzuhsiang.chien at gmail.com>
> vonosmas at gmail.com <mailto:vonosmas at gmail.com>
> yaron.keren at gmail.com <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>>>>>>
>>>>>>>>
>>>>>>>> On May 9, 2017, at 3:00 PM, Kostya Serebryany
<kcc at google.com <mailto: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 <mailto:cbieneman at apple.com>> wrote:
>>>>>>>>
>>>>>>>>> On May 9, 2017, at 2:19 PM, George
Karpenkov <ekarpenkov at apple.com <mailto: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 <mailto:kcc at google.com>> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Tue, May 9, 2017 at 1:56 PM, George
Karpenkov <ekarpenkov at apple.com <mailto: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 <mailto:dan at su-root.co.uk>> wrote:
>>>>>>>>>>>
>>>>>>>>>>> On 9 May 2017 at 18:55, Kostya
Serebryany <kcc at google.com <mailto:kcc at google.com>> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, May 9, 2017 at 10:23
AM, Dan Liew <dan at su-root.co.uk <mailto: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
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lists.llvm.org>
>>>>>>>
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<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>> _______________________________________________
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