libgo/go/runtime/lfstack_64bit.go

   1 // Copyright 2014 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // +build amd64 arm64 mips64 mips64le ppc64 ppc64le s390x
   6
   7 package runtime
   8
   9 import "unsafe"
  10
  11 const (
  12         // addrBits is the number of bits needed to represent a virtual address.
  13         //
  14         // In Linux the user address space for each architecture is limited as
  15         // follows (taken from the processor.h file for the architecture):
  16         //
  17         // Architecture  Name              Maximum Value (exclusive)
  18         // ---------------------------------------------------------------------
  19         // arm64         TASK_SIZE_64      Depends on configuration.
  20         // ppc64{,le}    TASK_SIZE_USER64  0x400000000000UL (46 bit addresses)
  21         // mips64{,le}   TASK_SIZE64       0x010000000000UL (40 bit addresses)
  22         // s390x         TASK_SIZE         0x020000000000UL (41 bit addresses)
  23         //
  24         // These values may increase over time.
  25         //
  26         // On AMD64, virtual addresses are 48-bit numbers sign extended to 64.
  27         // We shift the address left 16 to eliminate the sign extended part and make
  28         // room in the bottom for the count.
  29         addrBits = 48
  30
  31         // In addition to the 16 bits taken from the top, we can take 3 from the
  32         // bottom, because node must be pointer-aligned, giving a total of 19 bits
  33         // of count.
  34         cntBits = 64 - addrBits + 3
  35 )
  36
  37 func lfstackPack(node *lfnode, cnt uintptr) uint64 {
  38         return uint64(uintptr(unsafe.Pointer(node)))<<(64-addrBits) | uint64(cnt&(1<<cntBits-1))
  39 }
  40
  41 func lfstackUnpack(val uint64) *lfnode {
  42         if GOARCH == "amd64" {
  43                 // amd64 systems can place the stack above the VA hole, so we need to sign extend
  44                 // val before unpacking.
  45                 return (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> cntBits << 3)))
  46         }
  47         return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
  48 }