Source: checkptr.go in package runtime


package runtime

import "unsafe"

Check that (*[n]elem)(p) is appropriately aligned. Note that we allow unaligned pointers if the types they point to contain no pointers themselves. See issue 37298. TODO(mdempsky): What about fieldAlign?

	if elem.ptrdata != 0 && uintptr(p)&(uintptr(elem.align)-1) != 0 {
		throw("checkptr: misaligned pointer conversion")
	}

Check that (*[n]elem)(p) doesn't straddle multiple heap objects.

	if size := n * elem.size; size > 1 && checkptrBase(p) != checkptrBase(add(p, size-1)) {
		throw("checkptr: converted pointer straddles multiple allocations")
	}
}

func checkptrArithmetic(p unsafe.Pointer, originals []unsafe.Pointer) {
	if 0 < uintptr(p) && uintptr(p) < minLegalPointer {
		throw("checkptr: pointer arithmetic computed bad pointer value")
	}

Check that if the computed pointer p points into a heap object, then one of the original pointers must have pointed into the same object.

	base := checkptrBase(p)
	if base == 0 {
		return
	}

	for _, original := range originals {
		if base == checkptrBase(original) {
			return
		}
	}

	throw("checkptr: pointer arithmetic result points to invalid allocation")
}

checkptrBase returns the base address for the allocation containing the address p. Importantly, if p1 and p2 point into the same variable, then checkptrBase(p1) == checkptrBase(p2). However, the converse/inverse is not necessarily true as allocations can have trailing padding, and multiple variables may be packed into a single allocation.

stack

TODO(mdempsky): Walk the stack to identify the specific stack frame or even stack object that p points into. In the mean time, use "1" as a pseudo-address to represent the stack. This is an invalid address on all platforms, so it's guaranteed to be distinct from any of the addresses we might return below.

		return 1
	}

heap (must check after stack because of #35068)

	if base, _, _ := findObject(uintptr(p), 0, 0); base != 0 {
		return base
	}

data or bss

	for _, datap := range activeModules() {
		if datap.data <= uintptr(p) && uintptr(p) < datap.edata {
			return datap.data
		}
		if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss {
			return datap.bss
		}
	}

	return 0