golang lfstack_64bit 代码
文件路径：/src/runtime/lfstack_64bit.go
/ 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.
/go:build amd64 || arm64 || loong64 || mips64 || mips64le || ppc64 || ppc64le || riscv64 || 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
/ On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit
/ offset in segment. Segment numbers in the range 0x0A0000000-0x0AFFFFFFF(LSA)
/ are available for mmap.
/ We assume all lfnode addresses are from memory allocated with mmap.
/ We use one bit to distinguish between the two ranges.
aixAddrBits = 57
aixCntBits = 64 - aixAddrBits + 3
)
func lfstackPack(node *lfnode, cnt uintptr) uint64 {
if GOARCH == "ppc64" && GOOS == "aix" {
return uint64(uintptr(unsafe.Pointer(node)))<<(64-aixAddrBits) | uint64(cnt&(1<<aixCntBits-1))
}
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)))
}
if GOARCH == "ppc64" && GOOS == "aix" {
return (*lfnode)(unsafe.Pointer(uintptr((val >> aixCntBits << 3) | 0xa<<56)))
}
return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
}