gfortran/OpenMP/declare target link issue

Ioannis E. Venetis venetis@ceid.upatras.gr
Sat Sep 5 14:35:41 GMT 2020


Any comment on this? Are global variables defined in a module and used 
in subroutines in the target region supported through the declare target 
link mechanism currently on gcc? If so, am I doing something wrong on 
how to use that mechanism? If not, is there any other approach I could 
follow without too many changes in the code? In the real code I have 
about 20 such variables and the call tree in the target region goes up 
to 3 subroutines deep.

Ioannis E. Venetis

On 3/9/2020 9:36 μ.μ., Ioannis E. Venetis wrote:
> Hello everyone,
>
> I have a larger program that I am trying to convert so that the 
> computationally intensive part will run on an NVidia GPU using OpenMP. 
> However, I am running into trouble when compiling the program. The 
> part of the program to run on the GPU contains calls to subroutines, 
> where variables declared in a separate module are used. This seems to 
> be creating issues. I have reduced the problem to the attached files.
>
> I compile as follows:
>
> gfortran test_link.f90 common_vars.f90 parameters.f90 -O0 -fopenmp 
> -Wall -Wextra -o test_link
>
> With the file test_link.f90 as attached, the program compiles and runs 
> without a problem.
>
> If I remove the comments for the subroutine TEST() and comment out 
> line 31 in test_link.f90 (the line "I = NR") the compilation gives the 
> following error:
>
> ptxas /tmp/ccw3FqJD.o, line 52; error   : Illegal operand type to 
> instruction 'ld'
> ptxas /tmp/ccw3FqJD.o, line 52; error   : Unknown symbol 
> '__common_vars_MOD_nr$linkptr'
> ptxas fatal   : Ptx assembly aborted due to errors
> nvptx-as: ptxas returned 255 exit status
> mkoffload: fatal error: 
> /home/myself/apps/gcc-10.2.0/bin/x86_64-pc-linux-gnu-accel-nvptx-none-gcc 
> returned 1 exit status
> compilation terminated.
> lto-wrapper: fatal error: 
> /home/myself/apps/gcc-10.2.0/libexec/gcc/x86_64-pc-linux-gnu/10.2.0//accel/nvptx-none/mkoffload 
> returned 1 exit status
> compilation terminated.
> /usr/bin/ld: error: lto-wrapper failed
> collect2: error: ld returned 1 exit status
>
> Is this a bug in gfortran or have I misunderstood how DECLARE TARGET 
> LINK works in combination with using subroutines?
>
> And a last point: If I use -O3 during compilation the program compiles 
> and runs fine in both cases. I assume that TEST() is inlined in this 
> case and the error disappears?
>
> Any help to overcome this issue is more than welcome.
>
> Best regards,
>
> Ioannis E. Venetis
>
> PS1: The problem happens with gcc 10.2 that I compiled myself:
>
> $ ~/apps/gcc-10.2.0/bin/gfortran -v
> Using built-in specs.
> COLLECT_GCC=/home/myself/apps/gcc-10.2.0/bin/gfortran
> COLLECT_LTO_WRAPPER=/home/myself/apps/gcc-10.2.0/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper 
>
> OFFLOAD_TARGET_NAMES=nvptx-none
> Target: x86_64-pc-linux-gnu
> Configured with: ../gcc-10.2.0/configure 
> --enable-offload-targets=nvptx-none 
> --with-cuda-driver-include=/usr/local/cuda/include 
> --with-cuda-driver-lib=/usr/local/cuda/lib64 --disable-bootstrap 
> --disable-multilib --enable-languages=c,c++,fortran,lto 
> --prefix=/home/myself/apps/gcc-10.2.0
> Thread model: posix
> Supported LTO compression algorithms: zlib
> gcc version 10.2.0 (GCC)
>
>
> PS2: Same problem also happens with gcc 9.3 as installed on Ubuntu 
> 16.04 from apt:
>
> $ gfortran -v
> Using built-in specs.
> COLLECT_GCC=gfortran
> COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
> OFFLOAD_TARGET_NAMES=nvptx-none:hsa
> OFFLOAD_TARGET_DEFAULT=1
> Target: x86_64-linux-gnu
> Configured with: ../src/configure -v --with-pkgversion='Ubuntu 
> 9.3.0-10ubuntu2~16.04' 
> --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs 
> --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 
> --prefix=/usr --with-gcc-major-version-only --program-suffix=-9 
> --program-prefix=x86_64-linux-gnu- --enable-shared 
> --enable-linker-build-id --libexecdir=/usr/lib 
> --without-included-gettext --enable-threads=posix --libdir=/usr/lib 
> --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug 
> --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new 
> --enable-gnu-unique-object --disable-vtable-verify --enable-plugin 
> --with-system-zlib --with-target-system-zlib=auto 
> --enable-objc-gc=auto --enable-multiarch --disable-werror 
> --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 
> --enable-multilib --with-tune=generic 
> --enable-offload-targets=nvptx-none,hsa --without-cuda-driver 
> --enable-checking=release --build=x86_64-linux-gnu 
> --host=x86_64-linux-gnu --target=x86_64-linux-gnu
> Thread model: posix
> gcc version 9.3.0 (Ubuntu 9.3.0-10ubuntu2~16.04)
>


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