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runtime: move stack barrier code to its own file

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Currently the stack barrier code is mixed in with the mark and scan
code. Move all of the stack barrier related functions and variables to
a new dedicated source file. There are no code modifications.

Change-Id: I604603045465ef8573b9f88915d28ab6b5910903
Reviewed-on: https://go-review.googlesource.com/14050
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2015-08-28 23:15:41 -04:00
parent 84a8648e1d
commit 92e68c89f6
3 changed files with 184 additions and 175 deletions
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14
src/runtime/mgc.go
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@ -133,26 +133,12 @@ const (
_RootFlushCaches = 4 _RootFlushCaches = 4
_RootCount = 5 _RootCount = 5
debugStackBarrier = false
// sweepMinHeapDistance is a lower bound on the heap distance // sweepMinHeapDistance is a lower bound on the heap distance
// (in bytes) reserved for concurrent sweeping between GC // (in bytes) reserved for concurrent sweeping between GC
// cycles. This will be scaled by gcpercent/100. // cycles. This will be scaled by gcpercent/100.
sweepMinHeapDistance = 1024 * 1024 sweepMinHeapDistance = 1024 * 1024
) )
// firstStackBarrierOffset is the approximate byte offset at
// which to place the first stack barrier from the current SP.
// This is a lower bound on how much stack will have to be
// re-scanned during mark termination. Subsequent barriers are
// placed at firstStackBarrierOffset * 2^n offsets.
//
// For debugging, this can be set to 0, which will install a
// stack barrier at every frame. If you do this, you may also
// have to raise _StackMin, since the stack barrier
// bookkeeping will use a large amount of each stack.
var firstStackBarrierOffset = 1024
// heapminimum is the minimum heap size at which to trigger GC. // heapminimum is the minimum heap size at which to trigger GC.
// For small heaps, this overrides the usual GOGC*live set rule. // For small heaps, this overrides the usual GOGC*live set rule.
// //

161
src/runtime/mgcmark.go
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@ -487,167 +487,6 @@ func scanframeworker(frame *stkframe, unused unsafe.Pointer, gcw *gcWork) {
} }
} }
// gcMaxStackBarriers returns the maximum number of stack barriers
// that can be installed in a stack of stackSize bytes.
func gcMaxStackBarriers(stackSize int) (n int) {
if firstStackBarrierOffset == 0 {
// Special debugging case for inserting stack barriers
// at every frame. Steal half of the stack for the
// []stkbar. Technically, if the stack were to consist
// solely of return PCs we would need two thirds of
// the stack, but stealing that much breaks things and
// this doesn't happen in practice.
return stackSize / 2 / int(unsafe.Sizeof(stkbar{}))
}
offset := firstStackBarrierOffset
for offset < stackSize {
n++
offset *= 2
}
return n + 1
}
// gcInstallStackBarrier installs a stack barrier over the return PC of frame.
//go:nowritebarrier
func gcInstallStackBarrier(gp *g, frame *stkframe) bool {
if frame.lr == 0 {
if debugStackBarrier {
print("not installing stack barrier with no LR, goid=", gp.goid, "\n")
}
return false
}
if frame.fn.entry == cgocallback_gofuncPC {
// cgocallback_gofunc doesn't return to its LR;
// instead, its return path puts LR in g.sched.pc and
// switches back to the system stack on which
// cgocallback_gofunc was originally called. We can't
// have a stack barrier in g.sched.pc, so don't
// install one in this frame.
if debugStackBarrier {
print("not installing stack barrier over LR of cgocallback_gofunc, goid=", gp.goid, "\n")
}
return false
}
// Save the return PC and overwrite it with stackBarrier.
var lrUintptr uintptr
if usesLR {
lrUintptr = frame.sp
} else {
lrUintptr = frame.fp - regSize
}
lrPtr := (*uintreg)(unsafe.Pointer(lrUintptr))
if debugStackBarrier {
print("install stack barrier at ", hex(lrUintptr), " over ", hex(*lrPtr), ", goid=", gp.goid, "\n")
if uintptr(*lrPtr) != frame.lr {
print("frame.lr=", hex(frame.lr))
throw("frame.lr differs from stack LR")
}
}
gp.stkbar = gp.stkbar[:len(gp.stkbar)+1]
stkbar := &gp.stkbar[len(gp.stkbar)-1]
stkbar.savedLRPtr = lrUintptr
stkbar.savedLRVal = uintptr(*lrPtr)
*lrPtr = uintreg(stackBarrierPC)
return true
}
// gcRemoveStackBarriers removes all stack barriers installed in gp's stack.
//go:nowritebarrier
func gcRemoveStackBarriers(gp *g) {
if debugStackBarrier && gp.stkbarPos != 0 {
print("hit ", gp.stkbarPos, " stack barriers, goid=", gp.goid, "\n")
}
// Remove stack barriers that we didn't hit.
for _, stkbar := range gp.stkbar[gp.stkbarPos:] {
gcRemoveStackBarrier(gp, stkbar)
}
// Clear recorded stack barriers so copystack doesn't try to
// adjust them.
gp.stkbarPos = 0
gp.stkbar = gp.stkbar[:0]
}
// gcRemoveStackBarrier removes a single stack barrier. It is the
// inverse operation of gcInstallStackBarrier.
//
// This is nosplit to ensure gp's stack does not move.
//
//go:nowritebarrier
//go:nosplit
func gcRemoveStackBarrier(gp *g, stkbar stkbar) {
if debugStackBarrier {
print("remove stack barrier at ", hex(stkbar.savedLRPtr), " with ", hex(stkbar.savedLRVal), ", goid=", gp.goid, "\n")
}
lrPtr := (*uintreg)(unsafe.Pointer(stkbar.savedLRPtr))
if val := *lrPtr; val != uintreg(stackBarrierPC) {
printlock()
print("at *", hex(stkbar.savedLRPtr), " expected stack barrier PC ", hex(stackBarrierPC), ", found ", hex(val), ", goid=", gp.goid, "\n")
print("gp.stkbar=")
gcPrintStkbars(gp.stkbar)
print(", gp.stkbarPos=", gp.stkbarPos, ", gp.stack=[", hex(gp.stack.lo), ",", hex(gp.stack.hi), ")\n")
throw("stack barrier lost")
}
*lrPtr = uintreg(stkbar.savedLRVal)
}
// gcPrintStkbars prints a []stkbar for debugging.
func gcPrintStkbars(stkbar []stkbar) {
print("[")
for i, s := range stkbar {
if i > 0 {
print(" ")
}
print("*", hex(s.savedLRPtr), "=", hex(s.savedLRVal))
}
print("]")
}
// gcUnwindBarriers marks all stack barriers up the frame containing
// sp as hit and removes them. This is used during stack unwinding for
// panic/recover and by heapBitsBulkBarrier to force stack re-scanning
// when its destination is on the stack.
//
// This is nosplit to ensure gp's stack does not move.
//
//go:nosplit
func gcUnwindBarriers(gp *g, sp uintptr) {
// On LR machines, if there is a stack barrier on the return
// from the frame containing sp, this will mark it as hit even
// though it isn't, but it's okay to be conservative.
before := gp.stkbarPos
for int(gp.stkbarPos) < len(gp.stkbar) && gp.stkbar[gp.stkbarPos].savedLRPtr < sp {
gcRemoveStackBarrier(gp, gp.stkbar[gp.stkbarPos])
gp.stkbarPos++
}
if debugStackBarrier && gp.stkbarPos != before {
print("skip barriers below ", hex(sp), " in goid=", gp.goid, ": ")
gcPrintStkbars(gp.stkbar[before:gp.stkbarPos])
print("\n")
}
}
// nextBarrierPC returns the original return PC of the next stack barrier.
// Used by getcallerpc, so it must be nosplit.
//go:nosplit
func nextBarrierPC() uintptr {
gp := getg()
return gp.stkbar[gp.stkbarPos].savedLRVal
}
// setNextBarrierPC sets the return PC of the next stack barrier.
// Used by setcallerpc, so it must be nosplit.
//go:nosplit
func setNextBarrierPC(pc uintptr) {
gp := getg()
gp.stkbar[gp.stkbarPos].savedLRVal = pc
}
// TODO(austin): Can we consolidate the gcDrain* functions? // TODO(austin): Can we consolidate the gcDrain* functions?
// gcDrain scans objects in work buffers, blackening grey // gcDrain scans objects in work buffers, blackening grey

184
src/runtime/mstkbar.go Normal file
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@ -0,0 +1,184 @@
// Copyright 2015 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.
// Garbage collector: stack barriers
package runtime
import "unsafe"
const debugStackBarrier = false
// firstStackBarrierOffset is the approximate byte offset at
// which to place the first stack barrier from the current SP.
// This is a lower bound on how much stack will have to be
// re-scanned during mark termination. Subsequent barriers are
// placed at firstStackBarrierOffset * 2^n offsets.
//
// For debugging, this can be set to 0, which will install a
// stack barrier at every frame. If you do this, you may also
// have to raise _StackMin, since the stack barrier
// bookkeeping will use a large amount of each stack.
var firstStackBarrierOffset = 1024
// gcMaxStackBarriers returns the maximum number of stack barriers
// that can be installed in a stack of stackSize bytes.
func gcMaxStackBarriers(stackSize int) (n int) {
if firstStackBarrierOffset == 0 {
// Special debugging case for inserting stack barriers
// at every frame. Steal half of the stack for the
// []stkbar. Technically, if the stack were to consist
// solely of return PCs we would need two thirds of
// the stack, but stealing that much breaks things and
// this doesn't happen in practice.
return stackSize / 2 / int(unsafe.Sizeof(stkbar{}))
}
offset := firstStackBarrierOffset
for offset < stackSize {
n++
offset *= 2
}
return n + 1
}
// gcInstallStackBarrier installs a stack barrier over the return PC of frame.
//go:nowritebarrier
func gcInstallStackBarrier(gp *g, frame *stkframe) bool {
if frame.lr == 0 {
if debugStackBarrier {
print("not installing stack barrier with no LR, goid=", gp.goid, "\n")
}
return false
}
if frame.fn.entry == cgocallback_gofuncPC {
// cgocallback_gofunc doesn't return to its LR;
// instead, its return path puts LR in g.sched.pc and
// switches back to the system stack on which
// cgocallback_gofunc was originally called. We can't
// have a stack barrier in g.sched.pc, so don't
// install one in this frame.
if debugStackBarrier {
print("not installing stack barrier over LR of cgocallback_gofunc, goid=", gp.goid, "\n")
}
return false
}
// Save the return PC and overwrite it with stackBarrier.
var lrUintptr uintptr
if usesLR {
lrUintptr = frame.sp
} else {
lrUintptr = frame.fp - regSize
}
lrPtr := (*uintreg)(unsafe.Pointer(lrUintptr))
if debugStackBarrier {
print("install stack barrier at ", hex(lrUintptr), " over ", hex(*lrPtr), ", goid=", gp.goid, "\n")
if uintptr(*lrPtr) != frame.lr {
print("frame.lr=", hex(frame.lr))
throw("frame.lr differs from stack LR")
}
}
gp.stkbar = gp.stkbar[:len(gp.stkbar)+1]
stkbar := &gp.stkbar[len(gp.stkbar)-1]
stkbar.savedLRPtr = lrUintptr
stkbar.savedLRVal = uintptr(*lrPtr)
*lrPtr = uintreg(stackBarrierPC)
return true
}
// gcRemoveStackBarriers removes all stack barriers installed in gp's stack.
//go:nowritebarrier
func gcRemoveStackBarriers(gp *g) {
if debugStackBarrier && gp.stkbarPos != 0 {
print("hit ", gp.stkbarPos, " stack barriers, goid=", gp.goid, "\n")
}
// Remove stack barriers that we didn't hit.
for _, stkbar := range gp.stkbar[gp.stkbarPos:] {
gcRemoveStackBarrier(gp, stkbar)
}
// Clear recorded stack barriers so copystack doesn't try to
// adjust them.
gp.stkbarPos = 0
gp.stkbar = gp.stkbar[:0]
}
// gcRemoveStackBarrier removes a single stack barrier. It is the
// inverse operation of gcInstallStackBarrier.
//
// This is nosplit to ensure gp's stack does not move.
//
//go:nowritebarrier
//go:nosplit
func gcRemoveStackBarrier(gp *g, stkbar stkbar) {
if debugStackBarrier {
print("remove stack barrier at ", hex(stkbar.savedLRPtr), " with ", hex(stkbar.savedLRVal), ", goid=", gp.goid, "\n")
}
lrPtr := (*uintreg)(unsafe.Pointer(stkbar.savedLRPtr))
if val := *lrPtr; val != uintreg(stackBarrierPC) {
printlock()
print("at *", hex(stkbar.savedLRPtr), " expected stack barrier PC ", hex(stackBarrierPC), ", found ", hex(val), ", goid=", gp.goid, "\n")
print("gp.stkbar=")
gcPrintStkbars(gp.stkbar)
print(", gp.stkbarPos=", gp.stkbarPos, ", gp.stack=[", hex(gp.stack.lo), ",", hex(gp.stack.hi), ")\n")
throw("stack barrier lost")
}
*lrPtr = uintreg(stkbar.savedLRVal)
}
// gcPrintStkbars prints a []stkbar for debugging.
func gcPrintStkbars(stkbar []stkbar) {
print("[")
for i, s := range stkbar {
if i > 0 {
print(" ")
}
print("*", hex(s.savedLRPtr), "=", hex(s.savedLRVal))
}
print("]")
}
// gcUnwindBarriers marks all stack barriers up the frame containing
// sp as hit and removes them. This is used during stack unwinding for
// panic/recover and by heapBitsBulkBarrier to force stack re-scanning
// when its destination is on the stack.
//
// This is nosplit to ensure gp's stack does not move.
//
//go:nosplit
func gcUnwindBarriers(gp *g, sp uintptr) {
// On LR machines, if there is a stack barrier on the return
// from the frame containing sp, this will mark it as hit even
// though it isn't, but it's okay to be conservative.
before := gp.stkbarPos
for int(gp.stkbarPos) < len(gp.stkbar) && gp.stkbar[gp.stkbarPos].savedLRPtr < sp {
gcRemoveStackBarrier(gp, gp.stkbar[gp.stkbarPos])
gp.stkbarPos++
}
if debugStackBarrier && gp.stkbarPos != before {
print("skip barriers below ", hex(sp), " in goid=", gp.goid, ": ")
gcPrintStkbars(gp.stkbar[before:gp.stkbarPos])
print("\n")
}
}
// nextBarrierPC returns the original return PC of the next stack barrier.
// Used by getcallerpc, so it must be nosplit.
//go:nosplit
func nextBarrierPC() uintptr {
gp := getg()
return gp.stkbar[gp.stkbarPos].savedLRVal
}
// setNextBarrierPC sets the return PC of the next stack barrier.
// Used by setcallerpc, so it must be nosplit.
//go:nosplit
func setNextBarrierPC(pc uintptr) {
gp := getg()
gp.stkbar[gp.stkbarPos].savedLRVal = pc
}