From 3b02c5b1b66df9cdb23d5a3243bb37b2c312ea1b Mon Sep 17 00:00:00 2001 From: Dave Cheney Date: Thu, 7 Apr 2016 07:29:22 +1000 Subject: runtime: merge lfstack{Pack,Unpack} into one file 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 TryBot-Result: Gobot Gobot Reviewed-by: Minux Ma --- src/runtime/lfstack.go | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) (limited to 'src/runtime/lfstack.go') diff --git a/src/runtime/lfstack.go b/src/runtime/lfstack.go index 1261f54d97..8a2d519402 100644 --- a/src/runtime/lfstack.go +++ b/src/runtime/lfstack.go @@ -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<> 32))) + } + return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3))) +} -- cgit v1.3