[llvm-dev] LLVM Developers Meeting JIT BoF -- Request for Topics of Interest

[Geoff Levner via llvm-dev]

StaticLibraryDefinitionGenerator works as promised on ELF archives!

I have only encountered one problem. If a static library has not been
compiled with -fPIC and uses symbols from a shared library, LLJIT does not
complain, but the code may crash without warning when it is executed.

Geoff

On Mon, Sep 28, 2020 at 11:58 PM Lang Hames <lhames at gmail.com> wrote:

> Hi Geoff,
>
> We use LLJIT. Do addObjectFile() and StaticLibraryDefinitionGenerator work
>> for ELF objects?
>
>
> They do. :)
>
> I've not tested StaticLibraryDefinitionGenerator extensively on Linux. but
> we have a regression test checking basic usage. If you run into any trouble
> at all please file a bug and assign it to me.
>
> -- Lang.
>
>
>
> On Mon, Sep 28, 2020 at 2:05 PM Geoff Levner <glevner at gmail.com> wrote:
>
>> We use LLJIT. Do addObjectFile() and StaticLibraryDefinitionGenerator
>> work for ELF objects?
>>
>> On Mon, Sep 28, 2020 at 10:57 PM Lang Hames <lhames at gmail.com> wrote:
>> >
>> > Hi Geoff,
>> >
>> >> Importing symbols into the JIT from an object file or static
>> library...?
>> >
>> >
>> > Sure! Are you interested in doing this with the C API, LLJIT, or raw
>> OrcV2 components?
>> >
>> > The high-level answer here (which we can dig into further in the BoF)
>> is:
>> >
>> > For object files:
>> > - For raw OrcV2 components you'll want to create an
>> RTDyldObjectLinkingLayer or ObjectLinkingLayer and use the 'add' method.
>> > - For an LLJIT instance you can just call the 'addObjectFile' method.
>> > - For the OrcV2 C API you can call the 'LLVMOrcLLJITAddObjectFile'
>> function.
>> >
>> > For static libraries:
>> > - For raw OrcV2 components or an LLJIT instance you can attach a
>> StaticLibraryDefinitionGenerator [1] to the JITDylib that you would like to
>> load the library into. See [2] for an example.
>> > - For the OrcV2 C API we will just need to add a method to wrap the
>> operation above. We already have
>> 'LLVMOrcCreateDynamicLibrarySearchGeneratorForProcess'. We should add
>> counterparts to that to load dynamic and static libraries from paths.
>> >
>> > -- Lang.
>> >
>> > [1]
>> https://github.com/llvm/llvm-project/blob/5aa56b242951ab0f0181386ea58509f19b09206e/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h#L361
>> > [2]
>> https://github.com/llvm/llvm-project/blob/e7549dafcd33ced4280a81ca1d1ee4cc78ed253f/llvm/tools/lli/lli.cpp#L968
>> >
>> >
>> > On Mon, Sep 28, 2020 at 7:18 AM Geoff Levner <glevner at gmail.com> wrote:
>> >>
>> >> Importing symbols into the JIT from an object file or static
>> library...?
>> >>
>> >> On Mon, Sep 28, 2020 at 5:29 AM Lang Hames <lhames at gmail.com> wrote:
>> >>>
>> >>> Hi Andres,
>> >>>
>> >>>> A topic that I'd find interesting is what it'd take to make it
>> easier to
>> >>>> use profile guided optimization in the context of JIT.  A few years
>> back
>> >>>> I crudely hacked this together, but it was fairly ugly. It'd be nice
>> to
>> >>>> make that easier.  Possibly too complicated for that type of session?
>> >>>
>> >>>
>> >>> We couldn't go into detail, but we could kick off a discussion and
>> identify who is interested in working on this. My pitch: We should solve
>> this by investing in JITLink and implementing profiling (and debugger
>> support) via ObjectLinkingLayer::Plugins. Maybe a brief overview of /
>> discussion on how these work would be useful?
>> >>>
>> >>> -- Lang.
>> >>>
>> >>>
>> >>> On Fri, Sep 25, 2020 at 7:19 PM Andres Freund <andres at anarazel.de>
>> wrote:
>> >>>>
>> >>>> Hi,
>> >>>>
>> >>>> On 2020-09-25 19:05:42 -0700, Lang Hames wrote:
>> >>>> > The 2020 Virtual LLVM Developer's Meeting is coming up the week
>> after next.
>> >>>> > I'll be hosting a JIT Birds-of-a-Feather session on Thursday the
>> 8th at
>> >>>> > 10:55am PDT (See http://llvm.org/devmtg/2020-09/schedule/). I'm
>> planning to
>> >>>> > run this more like a Round Table: Minimal introduction, plenty of
>> time for
>> >>>> > discussion.
>> >>>> >
>> >>>> > Does anyone have any LLVM JIT related topics that they would
>> particularly
>> >>>> > like to discuss at this session? Any questions that they think
>> could be
>> >>>> > best answered by a round-table style discussion? I'll aim to rope
>> in the
>> >>>> > right people and prepare answers to make sure we get the most out
>> of the
>> >>>> > session.
>> >>>>
>> >>>> A topic that I'd find interesting is what it'd take to make it
>> easier to
>> >>>> use profile guided optimization in the context of JIT.  A few years
>> back
>> >>>> I crudely hacked this together, but it was fairly ugly. It'd be nice
>> to
>> >>>> make that easier.  Possibly too complicated for that type of session?
>> >>>>
>> >>>> I dimly recall that the main issue was that there is no good way to
>> >>>> extract the profile information without going through files /
>> applying
>> >>>> the profile data without going through files.
>> >>>>
>> >>>> Greetings,
>> >>>>
>> >>>> Andres Freund
>>
>
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