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Source file src/runtime/lfstack_64bit.go

Documentation: runtime

  // Copyright 2014 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  // +build amd64 arm64 mips64 mips64le ppc64 ppc64le s390x wasm
  package runtime
  import "unsafe"
  const (
  	// addrBits is the number of bits needed to represent a virtual address.
  	// See heapAddrBits for a table of address space sizes on
  	// various architectures. 48 bits is enough for all
  	// architectures except s390x.
  	// On AMD64, virtual addresses are 48-bit (or 57-bit) numbers sign extended to 64.
  	// We shift the address left 16 to eliminate the sign extended part and make
  	// room in the bottom for the count.
  	// On s390x, virtual addresses are 64-bit. There's not much we
  	// can do about this, so we just hope that the kernel doesn't
  	// get to really high addresses and panic if it does.
  	addrBits = 48
  	// In addition to the 16 bits taken from the top, we can take 3 from the
  	// bottom, because node must be pointer-aligned, giving a total of 19 bits
  	// of count.
  	cntBits = 64 - addrBits + 3
  func lfstackPack(node *lfnode, cnt uintptr) uint64 {
  	return uint64(uintptr(unsafe.Pointer(node)))<<(64-addrBits) | uint64(cnt&(1<<cntBits-1))
  func lfstackUnpack(val uint64) *lfnode {
  	if GOARCH == "amd64" {
  		// amd64 systems can place the stack above the VA hole, so we need to sign extend
  		// val before unpacking.
  		return (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> cntBits << 3)))
  	return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))

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