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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libgomp/109837] New: [OpenMP] despite 'requires
 unified_address' there is segfault when 'is_device_ptr' is not used
Date: Fri, 12 May 2023 23:08:02 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: libgomp
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109837

            Bug ID: 109837
           Summary: [OpenMP] despite 'requires unified_address' there is
                    segfault when 'is_device_ptr' is not used
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

Cf. https://github.com/SOLLVE/sollve_vv/pull/734 for a testcase.

For nvptx, we currently have:

GOMP_OFFLOAD_get_num_devices (unsigned int omp_requires_mask)
...
      && ((omp_requires_mask
           & ~(GOMP_REQUIRES_UNIFIED_ADDRESS
               | GOMP_REQUIRES_REVERSE_OFFLOAD)) !=3D 0))

That is: we accept for nvptx

  omp requires unfied_address

However, while the address space is the same, the following is not handled:

> the is_device_ptr clause is not necessary to obtain device addresses from=
 device pointers for use inside target regions.

Expected:
(A) Mapping related: is_device_ptr can be left out.
(B) omp_target_is_accessible - will properly work for such pointers.


For nvptx, the check can be done via cudaPointerGetAttributes
if I understand
https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__UNIFIED.html
correctly.

 * * *

NOTE: Something similar is needed for GCN, except that its
GOMP_OFFLOAD_get_num_devices currently returns -1 when
GOMP_REQUIRES_UNIFIED_ADDRESS has been requested.

It seems as if hsa_amd_pointer_info is the function to be used,
cf.
https://github.com/RadeonOpenCompute/ROCR-Runtime/blob/master/src/inc/hsa_e=
xt_amd.h=