[BUG]: `StridedMemoryView.from_dlpack` ignores `DLTensor.byte_offset`

[fedonman]

Type of Bug

Silent Failure

Component

cuda.core

Describe the bug

The DLPack specification places a tensor's first element at data + byte_offset. StridedMemoryView.from_dlpack sets ptr from data alone, so a producer that reports an allocation base in data and expresses a slice in byte_offset yields a view whose ptr is short by exactly byte_offset bytes. Nothing raises, and every consumer built on ptr reads the wrong memory, including the __dlpack__ re-export, which writes ptr back out as data with byte_offset = 0 and so loses the offset permanently. from_any_interface is affected too, since it delegates to from_dlpack for a DLPack producer. The capsule-consuming helper in the same module, _smv_from_dlpack_capsule, does add byte_offset.

How to Reproduce

This producer describes src[8:] the way the spec allows, with the allocation base in data and the slice in byte_offset. It exits 0 when ptr is correct and 1 when it is not.

import ctypes

import numpy as np
from cuda.core.utils import StridedMemoryView

i64p = ctypes.POINTER(ctypes.c_int64)


class DLTensor(ctypes.Structure):
    _fields_ = [("data", ctypes.c_void_p), ("device_type", ctypes.c_int32), ("device_id", ctypes.c_int32),
                ("ndim", ctypes.c_int32), ("code", ctypes.c_uint8), ("bits", ctypes.c_uint8),
                ("lanes", ctypes.c_uint16), ("shape", i64p), ("strides", i64p), ("byte_offset", ctypes.c_uint64)]


class DLManagedTensorVersioned(ctypes.Structure):
    _fields_ = [("major", ctypes.c_uint32), ("minor", ctypes.c_uint32), ("manager_ctx", ctypes.c_void_p),
                ("deleter", ctypes.c_void_p), ("flags", ctypes.c_uint64), ("dl_tensor", DLTensor)]


ctypes.pythonapi.PyCapsule_New.argtypes = (ctypes.c_void_p, ctypes.c_char_p, ctypes.c_void_p)
ctypes.pythonapi.PyCapsule_New.restype = ctypes.py_object

src = np.arange(16, dtype=np.int32)
offset = 8 * src.itemsize
shape, strides = (ctypes.c_int64 * 1)(8), (ctypes.c_int64 * 1)(1)
t = DLManagedTensorVersioned(major=1, minor=0)
# Describe src[8:] the way the DLPack spec allows: allocation base in `data`,
# the slice expressed as `byte_offset`. First element is at data + byte_offset.
t.dl_tensor = DLTensor(data=src.ctypes.data, device_type=1, device_id=0, ndim=1, code=0, bits=32,
                       lanes=1, shape=shape, strides=strides, byte_offset=offset)


class Producer:
    def __dlpack_device__(self):
        return (1, 0)  # kDLCPU

    def __dlpack__(self, stream=None, max_version=None):
        return ctypes.pythonapi.PyCapsule_New(ctypes.addressof(t), b"dltensor_versioned", None)


view = StridedMemoryView.from_dlpack(Producer(), stream_ptr=-1)
print("expected ptr :", src.ctypes.data + offset)
print("view.ptr     :", view.ptr)
print("expected data:", src[8:])
print("view data    :", np.from_dlpack(view))
raise SystemExit(0 if view.ptr == src.ctypes.data + offset else 1)

Output:

expected ptr : 387455296
view.ptr     : 387455264
expected data: [ 8  9 10 11 12 13 14 15]
view data    : [0 1 2 3 4 5 6 7]

The process exits 1. Reproduced against a build of main at commit 757731a.

Expected behavior

ptr should be data + byte_offset, so the view begins at the tensor's first element, and the reproducer prints the producer's data and exits 0.

[aryanputta]

I would like to prepare a focused fix for this. The import path in cuda_core/cuda/core/_memoryview.pyx currently sets buf.ptr from dl_tensor.data but omits dl_tensor.byte_offset; the capsule helper path already includes the offset. I have a minimal regression test using a versioned CPU DLPack capsule with a nonzero offset. Please confirm this is the intended fix before I open a PR.