[llvm-dev] Inclusion of the ORC runtime in compiler-rt.

[Lang Hames via llvm-dev]

>
> From this it sounds like "convenient reusing of the build system" rather
> than "should be included in compiler-rt as a library"? If that's the case
> maybe making it clear or lifting the common build system support out might
> be maintainable without the "this is a runtime library for the system" sort
> of thing?


Yeah. It sounds like in an ideal world we'd lift out the common build
system support, then have a new set of sub-projects that re-use that
generic build system.

Do you have any sense of how difficult it would be to lift out that common
build system code? If that's relatively easy then maybe the right approach
is to do that first, then land the ORC runtime. Otherwise the ORC runtime
could go in to compiler-rt for now, then be split out with the rest of
compiler-rt when it's broken up -- it doesn't require any meaningful
changes to existing compiler-rt code, so it should be very easy to break
back out again later.

-- Lang.


On Mon, Apr 12, 2021 at 3:51 PM Eric Christopher <echristo at gmail.com> wrote:

>
>
> On Mon, Apr 12, 2021 at 6:36 PM Lang Hames <lhames at gmail.com> wrote:
>
>> Hi Petr,
>>
>> I'd like to better understand the structure of the ORC runtime and its
>>> dependencies (both build and runtime). Does it use the C or C++ standard
>>> library? Does it depend on other parts of LLVM? Do you plan on reusing some
>>> of the existing compiler-rt libraries like sanitizer_common?
>>
>>
>> The ORC runtime currently uses the C++ standard library.
>> Since the ORC runtime needs to communicate with the LLVM ORC library it
>> also currently uses some header-only includes from LLVM. It does not depend
>> on any LLVM libraries. We could duplicate this code, but I'd prefer to
>> share it if possible.
>> I have not used sanitizer_common, but some parts of it look like they may
>> be useful.
>>
>> I gravitated towards implementing the ORC runtime in compiler-rt because
>> I need to be able to write parts of it in platform-specific assembly (which
>> compiler-rt supports), and because the runtime should be build for all
>> targets, not just the host (which seems to be the standard way that
>> compiler-rt is configured).
>>
>>
> From this it sounds like "convenient reusing of the build system" rather
> than "should be included in compiler-rt as a library"? If that's the case
> maybe making it clear or lifting the common build system support out might
> be maintainable without the "this is a runtime library for the system" sort
> of thing?
>
> -eric
>
>
>> To give a bit more background on why I'm interested, compiler-rt has
>>> grown fairly organically this has been making the maintenance more and more
>>> difficult, at least from the build perspective. There are some runtimes
>>> that only use C, some that use C++, some that use C++ standard library.
>>> When building compiler-rt together with other runtimes like libc or libc++,
>>> it's difficult to pick up the right order which is why we have several
>>> entry points into compiler-rt's build system to build different subsets and
>>> that's been a maintenance headache.
>>
>>
>>> I've been thinking about this quite a bit recently and I repeatedly came
>>> to the conclusion that compiler-rt would ideally be broken up into several
>>> subprojects, but that should probably be discussed as a separate topic.
>>> However, understanding the build and runtimes dependencies of the ORC
>>> runtime could help us decide whether it should be a part of compiler-rt or
>>> be a separate subproject.
>>
>>
>> That makes sense to me. I think of the ORC runtime as a compiler-rt-style
>> runtime with a libc++ dependency. In that sense I think it's similar to
>> libFuzzer, and whatever solution we come up with for libFuzzer would
>> probably also be applicable to the ORC runtime too.
>>
>> -- Lang.
>>
>> On Mon, Apr 12, 2021 at 2:36 PM Petr Hosek <phosek at google.com> wrote:
>>
>>> I'd like to better understand the structure of the ORC runtime and its
>>> dependencies (both build and runtime). Does it use the C or C++ standard
>>> library? Does it depend on other parts of LLVM? Do you plan on reusing some
>>> of the existing compiler-rt libraries like sanitizer_common?
>>>
>>> To give a bit more background on why I'm interested, compiler-rt has
>>> grown fairly organically this has been making the maintenance more and more
>>> difficult, at least from the build perspective. There are some runtimes
>>> that only use C, some that use C++, some that use C++ standard library.
>>> When building compiler-rt together with other runtimes like libc or libc++,
>>> it's difficult to pick up the right order which is why we have several
>>> entry points into compiler-rt's build system to build different subsets and
>>> that's been a maintenance headache.
>>>
>>> I've been thinking about this quite a bit recently and I repeatedly came
>>> to the conclusion that compiler-rt would ideally be broken up into several
>>> subprojects, but that should probably be discussed as a separate topic.
>>> However, understanding the build and runtimes dependencies of the ORC
>>> runtime could help us decide whether it should be a part of compiler-rt or
>>> be a separate subproject.
>>>
>>> On Mon, Apr 12, 2021 at 12:26 PM Lang Hames <lhames at gmail.com> wrote:
>>>
>>>> Hi All,
>>>>
>>>> I'd like to add the ORC runtime library (preview available at
>>>> https://github.com/lhames/llvm-project/tree/orc-runtime-preview) to
>>>> compiler-rt.
>>>>
>>>> Background:
>>>>
>>>> ORC, like MCJIT, can link JIT'd code either into the current process
>>>> ("in-process" mode) or into a remote executor process ("cross-process"
>>>> mode). Some JIT features require support code in the executor process, but
>>>> the existing ORC libraries are only linked into the JIT process. This has
>>>> made cross-process mode support for those features (which include static
>>>> initializers, thread local variables, exception handling, and others)
>>>> awkward or impractical to implement. The ORC runtime library aims to
>>>> provide the necessary support code in a form that is loadable by the JIT
>>>> itself, which should allow these features to work uniformly in both modes.
>>>>
>>>> My prototype branch of the ORC runtime (available at
>>>> https://github.com/lhames/llvm-project/tree/orc-runtime-preview) has
>>>> advanced to the point where it can provide uniform support for static
>>>> initializers, destructors, exceptions, thread locals, and language
>>>> registration for Objective C and Swift code. This support is all
>>>> MachO/Darwin only so far, but should be easily adaptable for ELF/Linux/BSD
>>>> support.
>>>>
>>>> Proposal:
>>>>
>>>> The proof of concept implementation has been very successful, so I
>>>> would like to move future development to the LLVM main branch so that
>>>> others can benefit from this.
>>>>
>>>> Before I start posting patches, though:
>>>>
>>>> Does anyone see any problems with including this in compiler-rt?
>>>>
>>>> Does anyone think that there is a more reasonable home for the ORC
>>>> runtime within the llvm-project? I considered LLVM itself, or a new
>>>> top-level project, but neither seemed as natural a fit as compiler-rt.
>>>>
>>>> Finally, if everyone is happy for it to be included in principle, are
>>>> there any volunteers to review ORC runtime patches?
>>>>
>>>> Regards,
>>>> Lang.
>>>>
>>>
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