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webgpu : avoid crash when offset is not multiple of 4 in WebGPU ggml_backend_tensor_get() implementation #28045

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Merged
fairydreaming merged 3 commits into from
Aug 31, 2026
Merged

webgpu : avoid crash when offset is not multiple of 4 in WebGPU ggml_backend_tensor_get() implementation #28045

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0a7424d
webgpu : avoid crash when offset is not multiple of 4 in WebGPU ggml_…
sszymczy Aug 30, 2026
b74c0f6
chore : improve code readability
fairydreaming Aug 31, 2026
272a70d
Merge branch 'ggml-org:master' into webgpu-buffer-get-offset
fairydreaming Aug 31, 2026
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15 changes: 11 additions & 4 deletions ggml/src/ggml-webgpu/ggml-webgpu.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3713,11 +3713,18 @@ static void ggml_backend_webgpu_buffer_get_tensor(ggml_backend_buffer_t buffer,

size_t total_offset = ggml_webgpu_tensor_offset(tensor) + offset;

size_t final_size = size;
if (size % 4 != 0) {
size_t local_offset = total_offset % 4;
if (local_offset != 0) {
// If offset is not a multiple of 4, we need to round it down to the previous
// multiple of 4
total_offset -= local_offset;
}

size_t final_size = size + local_offset;
if (final_size % 4 != 0) {
// If size is not a multiple of 4, we need to round it up to the next
// multiple of 4
final_size = size + (4 - (size % 4));
final_size += 4 - (final_size % 4);
}

std::lock_guard<std::recursive_mutex> lock(buf_ctx->global_ctx->mutex);
Expand Down Expand Up @@ -3748,7 +3755,7 @@ static void ggml_backend_webgpu_buffer_get_tensor(ggml_backend_buffer_t buffer,
const void * mapped_range = buf_ctx->global_ctx->get_tensor_staging_buf.GetConstMappedRange(0, final_size);

// Copy the data from the mapped range to the output buffer
std::memcpy(data, mapped_range, size);
std::memcpy(data, (const void *) ((const char *) mapped_range + local_offset), size);
buf_ctx->global_ctx->get_tensor_staging_buf.Unmap();
WEBGPU_CPU_PROFILE_TOTAL_END(get_tensor, buf_ctx->global_ctx);
}
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