[Openmp-dev] [RFC] Clarify the absence of API stability for the *device runtime* (aka. libomptarget-nvptx-sm_XX.bc)

[Michael Kruse via Openmp-dev]

Correct.

I inferred from your response that we have no such guarantee yet, we just
haven't broken it yet.

However, I think that change will break ABI of libomptarget-nvptx.a

Just want to clarify what ABI stability guarantees we have.

Michael


Le jeu. 9 juil. 2020 à 17:08, Hal Finkel <hfinkel at anl.gov> a écrit :

>
> On 7/9/20 3:39 PM, Michael Kruse wrote:
> > Am Do., 9. Juli 2020 um 14:08 Uhr schrieb Hal Finkel <hfinkel at anl.gov>:
> >> Also, if we wanted to change clang so that it linked version-locked
> >> versions of these libraries, -lomptarget-11 or whatever, that, in my
> >> opinion, would also be a reasonable choice to discuss.
> >>
> >> One thing worth capturing is the extent to which these things are
> >> connected. There is a relationship between libomptarget and its plugins,
> >> and the plugins and the device-side runtimes. There is an ABI boundary
> >> there somewhere. If we change nothing else, we might need to consider
> >> ABI stability of this part of the device-side interface.
> > The official distribution apt.llvm.org contains libomptarget.so for
> > LLVM 7 to 10, but each into separate directories under
> > /usr/lib/llvm-<version>/libomptarget.so. The prebuilt binaries under
> > https://releases.llvm.org/download.html puts it directly under
> > <prefix>/libomptarget.so. If libomptarget is version-locked, users
> > need to be careful about pointing to the right LD_LIBRARY_PATH.
> > However, I could not find target device plugins in the distributions
> > (such as lib/libomptarget-nvptx-sm_60.bc when built on a machine with
> > CUDA). The official ubuntu repository doesn't contain libomptarget at
> > all. Arch Linux contains at least the x86_64 rtl
> > (https://www.archlinux.org/packages/extra/x86_64/openmp/files/)
> > without any versioning resolution.
> >
> > Should make it explicit what the compatibility guarantees for
> > libomptarget are, maybe even discourage OS distributions to
> > pre-package libomptarget into ldconfig default paths? At least on Arch
> > Linux updating the openmp package will break previously
> > compiled-with-offloading binaries.
>
>
> You mean that it will break them *if* we make an ABI-breaking change in
> libomptarget. Changing the device-side runtime doesn't necessarily imply
> that. Nevertheless, certainly good to know.
>
>   -Hal
>
>
> >
> > Michael
>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>
>
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