runtime: merge 64bit lfstack impls

Merge all the 64bit lfstack impls into one file, adjust build tags to
match.

Merge all the comments on the various lfstack implementations for
posterity.

lfstack_amd64.go can probably be merged, but it is slightly different so
that will happen in a followup.

Change-Id: I5362d5e127daa81c9cb9d4fa8a0cc5c5e5c2707c
Reviewed-on: https://go-review.googlesource.com/21591
Run-TryBot: Dave Cheney <dave@cheney.net>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/src/runtime/lfstack_64bit.go b/src/runtime/lfstack_64bit.go
new file mode 100644
index 0000000000..27a058c763
--- /dev/null
+++ b/src/runtime/lfstack_64bit.go
@@ -0,0 +1,35 @@
+// 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) (node *lfnode, cnt uintptr) {
+	node = (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
+	cnt = uintptr(val & (1<<cntBits - 1))
+	return
+}