llvm dev - Oct 2020 - LLVM Developers Meeting JIT BoF -- Request for Topics of Interest

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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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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Hi Geoff,

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.

Was the static library compiled with large code model too?

I think this is probably a RuntimeDyld bug: It's not great at error
reporting. A few people in the community are working on an ELF/x86-64
implementation of JITLink at the moment -- Once we have that you should get
small code model support and better error handling.

-- Lang.

On Fri, Oct 2, 2020 at 4:03 AM Geoff Levner <glevner at gmail.com> wrote:
> 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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