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runtime: merge lfstack{Pack,Unpack} into one file

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Merge the remaining lfstack{Pack,Unpack} implemetations into one file.

unsafe.Sizeof(uintptr(0)) == 4 is a constant comparison so this branch
folds away at compile time.

Dmitry confirmed that the upper 17 bits of an address will be zero for a
user mode pointer, so there is no need to sign extend on amd64 during
unpack, so we can reuse the same implementation as all othe 64 bit
archs.

Change-Id: I99f589416d8b181ccde5364c9c2e78e4a5efc7f1
Reviewed-on: https://go-review.googlesource.com/21597
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
This commit is contained in:
Dave Cheney 2016-04-07 07:29:22 +10:00
parent 438ce713a1
commit 3b02c5b1b6
4 changed files with 35 additions and 74 deletions
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35
src/runtime/lfstack.go
View File

@ -41,3 +41,38 @@ func lfstackpop(head *uint64) unsafe.Pointer {
}
}
}
const (
addrBits = 48
cntBits = 64 - addrBits + 3
)
func lfstackPack(node *lfnode, cnt uintptr) uint64 {
if unsafe.Sizeof(uintptr(0)) == 4 {
// On 32-bit systems, the stored uint64 has a 32-bit pointer and 32-bit count.
return uint64(uintptr(unsafe.Pointer(node)))<<32 | uint64(cnt)
}
// On ppc64, Linux limits the user address space to 46 bits (see
// TASK_SIZE_USER64 in the Linux kernel). This has grown over time,
// so here we allow 48 bit addresses.
//
// On mips64, Linux limits the user address space to 40 bits (see
// TASK_SIZE64 in the Linux kernel). This has grown over time,
// so here we allow 48 bit addresses.
//
// On AMD64, virtual addresses are 48-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.
//
// 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.
return uint64(uintptr(unsafe.Pointer(node)))<<(64-addrBits) | uint64(cnt&(1<<cntBits-1))
}
func lfstackUnpack(val uint64) *lfnode {
if unsafe.Sizeof(uintptr(0)) == 4 {
return (*lfnode)(unsafe.Pointer(uintptr(val >> 32)))
}
return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
}

19
src/runtime/lfstack_32bit.go
View File

@ -1,19 +0,0 @@
// 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 386 arm nacl
package runtime
import "unsafe"
// On 32-bit systems, the stored uint64 has a 32-bit pointer and 32-bit count.
func lfstackPack(node *lfnode, cnt uintptr) uint64 {
return uint64(uintptr(unsafe.Pointer(node)))<<32 | uint64(cnt)
}
func lfstackUnpack(val uint64) *lfnode {
return (*lfnode)(unsafe.Pointer(uintptr(val >> 32)))
}

33
src/runtime/lfstack_64bit.go
View File

@ -1,33 +0,0 @@
// 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 arm64 mips64 mips64le ppc64 ppc64le
package runtime
import "unsafe"
// On ppc64, Linux limits the user address space to 46 bits (see
// TASK_SIZE_USER64 in the Linux kernel). This has grown over time,
// so here we allow 48 bit addresses.
//
// On mips64, Linux limits the user address space to 40 bits (see
// TASK_SIZE64 in the Linux kernel). This has grown over time,
// so here we allow 48 bit addresses.
//
// 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.
const (
addrBits = 48
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 {
return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
}

22
src/runtime/lfstack_amd64.go
View File

@ -1,22 +0,0 @@
// 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.
package runtime
import "unsafe"
// On AMD64, virtual addresses are 48-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.
// 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.
func lfstackPack(node *lfnode, cnt uintptr) uint64 {
return uint64(uintptr(unsafe.Pointer(node)))<<16 | uint64(cnt&(1<<19-1))
}
func lfstackUnpack(val uint64) *lfnode {
return (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> 19 << 3)))
}