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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/113216] New: [OpenMP] Improve omp_target_is_accessible
Date: Wed, 03 Jan 2024 12:00:18 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: libgomp
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: openmp
X-Bugzilla-Severity: normal
X-Bugzilla-Who: burnus at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113216

            Bug ID: 113216
           Summary: [OpenMP] Improve omp_target_is_accessible
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: openmp
          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: ---

For omp_target_is_accessible + unified address:

* it is not 100% correct to assume that any address is accessible on the ho=
st,
  it might be a device-only address

(For handling NULL, see also PR 113213)

Likewise for the nonhost device:

* memory might be accessible even if only unified address

* * *

The host case is a bit trickier as no generic documentation seems to be
available albeit some ranges like 0x7F...... seem to denote device addresse=
s +
a superset has to be formed.

* * *

For the device side, an API function might be available to check for it.

* *=20

In case of nvptx / CUDA, the following function seems to be suitable:

CUresult cuMemGetAccess ( unsigned long long* flags,
                          const CUmemLocation* location, CUdeviceptr ptr )

checking for flags =3D=3D CU_MEM_ACCESS_FLAGS_PROT_READWRITE, if I understa=
nd it
correctly.

typedef enum CUmemAccess_flags_enum {
 CU_MEM_ACCESS_FLAGS_PROT_NONE   =3D 0x0,  /**< Default, make the address r=
ange
not accessible */
  CU_MEM_ACCESS_FLAGS_PROT_READ  =3D 0x1,  /**< Make the address range read
accessible */
  CU_MEM_ACCESS_FLAGS_PROT_READWRITE =3D 0x3,  /**< Make the address range
read-write accessible */
  CU_MEM_ACCESS_FLAGS_PROT_MAX   =3D 0x7FFFFFFF
} CUmemAccess_flags;

* *

In case of HSA/ROCm, I bet there is also some function.

For instance, hipPointerGetAttribute{,s} + hipDrvPointerGetAttributes permi=
t to
query some pointer data.=