[Openmp-dev] Using clang-offload-bundler to bundle application/executable
Jonas Hahnfeld via Openmp-dev
openmp-dev at lists.llvm.org
Mon Nov 4 08:43:05 PST 2019
Am Montag, den 04.11.2019, 17:28 +0100 schrieb Lukas Sommer:
> Hi Jonas,
> thanks for your help!
> I tried the suggested command, unfortunately it still fails:
>
>
> > clang -fopenmp
> > -fopenmp-targets=x86_64-unknown-linux-gnu app.o
>
> yields:
>
>
> > /usr/bin/ld: /tmp/app-c48732.o: relocation
> > R_X86_64_32 against `.data' can not be used when making a shared
> > object; recompile with -fPIC
> >
> > /usr/bin/ld: final link failed: nonrepresentable section on
> > output
> >
> > /usr/bin/ld: cannot find /tmp/app-23d932.out inside /
> >
> > /usr/bin/ld: cannot find /tmp/app-23d932.out inside /
> >
> > clang-9: error: linker command failed with exit code 1 (use -v
> > to see invocation)
> >
> > clang-9: error: linker command failed with exit code 1 (use -v
> > to see invocation)
>
> I also tried to generate and bundle assembly (.asm) and run that
> through clang (with openmp-flags as above), but that gave the same
> error.
Hmm, the target image is built as a shared library. To make this work, Clang adds -shared -fPIC in Generic_GCC::TranslateArgs.You're replacing this step with a manual invocation of `opt', so we need to pass some extra flags. I'm currently looking into what's needed, opt --relocation-model=pic might be a good start but I'm not sure that's all.
Jonas
>
> Lukas
>
>
> Lukas Sommer, M.Sc.TU DarmstadtEmbedded Systems and Applications Group (ESA)Hochschulstr. 10, 64289 Darmstadt, GermanyPhone: +49 6151 1622429www.esa.informatik.tu-darmstadt.de
> On 11/4/19 5:01 PM, Jonas Hahnfeld
> wrote:
>
>
>
> >
> > Hi Lukas,
> >
> >
> >
> > Am Montag, den 28.10.2019, 13:42 +0100 schrieb Lukas Sommer
> > via Openmp-dev:
> >
> > > Hello,
> > >
> > > I'm trying to use the clang-offload-bundler to merge the results of the
> > > compilation for device and host for an application using OpenMP target
> > > pragmas.
> > >
> > > My goal is to run a custom pass on the device code and then bundle an
> > > application from the modified device code and the host code. For testing
> > > purposes, I use a very simple vector addition with target offloading
> > > pragmas and the "offloading" to x86_64 (LLVM/Clang release 9.0).
> > >
> > > I use clang to generate LLVM IR from the application code. Then I use
> > > the clang-offload-bundler to unbundle the LLVM IR for device and host. I
> > > run opt and llc separately on the LLVM IR for host and device.
> > >
> > > To this end, on my application code (code.c), I run the following steps:
> > >
> > >
> > > > clang -fopenmp -fopenmp-targets=x86_64-unknown-linux-gnu -S -emit-llvm
> > > > -O3 -o bundled.ll code.c
> > > > clang-offload-bundler --inputs=bundled.ll
> > > > --outputs=host.in.ll,device.in.ll
> > > > --targets=host-x86_64-unknown-linux-gnu,openmp-x86_64-unknown-linux-gnu
> > > > --type=ll --unbundle
> > > > opt -o host.opt.ll -O3 host.in.ll
> > > > llc -o host.o -filetype=obj host.opt.ll
> > > > opt -o device.opt.ll -O3 device.in.ll (custom pass should be added
> > > > here later on)
> > > > llc -o device.o -filetype=obj device.opt.ll
> > > >
> > >
> > >
> > > Afterwards, I tried to bundle the object files for host & device:
> > >
> > >
> > > > clang-offload-bundler --inputs=host.o,device.o --outputs=app.o
> > > > --targets=host-x86_64-unknown-linux-gnu,openmp-x86_64-unknown-linux-gnu
> > > > --type=o
> > > >
> > >
> > > This command completes without any warning or error.
> > >
> > > I tried to invoke gcc on the output to generate the executable from the
> > > object file (app.o):
> > >
> > >
> > > > gcc app.o -lomp -lomptarget
> > > >
> > >
> > > However, I get the following error:
> > >
> > >
> > > > /usr/bin/ld:
> > > > app.o:(.rodata..omp_offloading.device_images[.omp_offloading.descriptor_reg.x86_64-unknown-linux-gnu]+0x10):
> > > > undefined reference to `.omp_offloading.entries_begin'
> > > > /usr/bin/ld:
> > > > app.o:(.rodata..omp_offloading.device_images[.omp_offloading.descriptor_reg.x86_64-unknown-linux-gnu]+0x18):
> > > > undefined reference to `.omp_offloading.entries_end'
> > > > /usr/bin/ld:
> > > > app.o:(.rodata..omp_offloading.descriptor[.omp_offloading.descriptor_reg.x86_64-unknown-linux-gnu]+0x10):
> > > > undefined reference to `.omp_offloading.entries_begin'
> > > > /usr/bin/ld:
> > > > app.o:(.rodata..omp_offloading.descriptor[.omp_offloading.descriptor_reg.x86_64-unknown-linux-gnu]+0x18):
> > > > undefined reference to `.omp_offloading.entries_end'
> > > >
> > >
> > > Do I need to run any additional steps before going through gcc or pass
> > > additional flags? Is there another way of accomplishing the desired
> > > behavior?
> > >
> >
> >
> >
> >
> > I think you should use clang with the full -fopenmp
> > -fopenmp-targets=x86_64-unknown-linux-gnu to build the final
> > executable, ie
> > $ clang -fopenmp -fopenmp-targets=x86_64-unknown-linux-gnu
> > app.o
> > If I remember correctly, the above symbols are provided by a
> > linker script in Clang 9.0, which gcc has no clue about.
> >
> >
> >
> > Please note that there have been recent changes in that
> > area and trunk now relies on a new tool clang-offload-wrapper
> > AFAICS (see https://github.com/llvm/llvm-project/commit/5836c356fa6e17d0e10a2f9e0e111b7236dc15fb).
> > As before this should be called transparently by clang, as
> > long as it's correctly invoked with a consistent value for
> > -fopenmp-targets.
> >
> >
> >
> > I haven't tested above command, but I hope it works. Please
> > let me know if it doesn't and I'll take a closer look!
> > Jonas
> >
> >
> >
> >
> > >
> > > Thanks a lot in advance,
> > >
> > > Best regards
> > >
> > > Lukas
> > >
> > >
> >
> >
>
>
>
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