func materializeGCProg(ptrdata uintptr, prog *byte) *mspan {
	// Each word of ptrdata needs one bit in the bitmap.
	bitmapBytes := divRoundUp(ptrdata, 8*goarch.PtrSize)
	// Compute the number of pages needed for bitmapBytes.
	pages := divRoundUp(bitmapBytes, pageSize)
	s := mheap_.allocManual(pages, spanAllocPtrScalarBits)
	runGCProg(addb(prog, 4), (*byte)(unsafe.Pointer(s.startAddr)))
	return s
}

			if hasHeader {
				size += mallocHeaderSize
			}
			var sizeclass uint8
			if size <= smallSizeMax-8 {
				sizeclass = size_to_class8[divRoundUp(size, smallSizeDiv)]
			} else {
				sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, largeSizeDiv)]
			}
			size = uintptr(class_to_size[sizeclass])
			spc := makeSpanClass(sizeclass, noscan)
			span = c.alloc[spc]