Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1105 insertions, 0 deletions

diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
new file mode 100644
index 0000000..e982532
--- /dev/null
+++ b/src/runtime/runtime2.go
@@ -0,0 +1,1105 @@
+// Copyright 2009 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 (
+	"internal/cpu"
+	"runtime/internal/atomic"
+	"runtime/internal/sys"
+	"unsafe"
+)
+
+// defined constants
+const (
+	// G status
+	//
+	// Beyond indicating the general state of a G, the G status
+	// acts like a lock on the goroutine's stack (and hence its
+	// ability to execute user code).
+	//
+	// If you add to this list, add to the list
+	// of "okay during garbage collection" status
+	// in mgcmark.go too.
+	//
+	// TODO(austin): The _Gscan bit could be much lighter-weight.
+	// For example, we could choose not to run _Gscanrunnable
+	// goroutines found in the run queue, rather than CAS-looping
+	// until they become _Grunnable. And transitions like
+	// _Gscanwaiting -> _Gscanrunnable are actually okay because
+	// they don't affect stack ownership.
+
+	// _Gidle means this goroutine was just allocated and has not
+	// yet been initialized.
+	_Gidle = iota // 0
+
+	// _Grunnable means this goroutine is on a run queue. It is
+	// not currently executing user code. The stack is not owned.
+	_Grunnable // 1
+
+	// _Grunning means this goroutine may execute user code. The
+	// stack is owned by this goroutine. It is not on a run queue.
+	// It is assigned an M and a P (g.m and g.m.p are valid).
+	_Grunning // 2
+
+	// _Gsyscall means this goroutine is executing a system call.
+	// It is not executing user code. The stack is owned by this
+	// goroutine. It is not on a run queue. It is assigned an M.
+	_Gsyscall // 3
+
+	// _Gwaiting means this goroutine is blocked in the runtime.
+	// It is not executing user code. It is not on a run queue,
+	// but should be recorded somewhere (e.g., a channel wait
+	// queue) so it can be ready()d when necessary. The stack is
+	// not owned *except* that a channel operation may read or
+	// write parts of the stack under the appropriate channel
+	// lock. Otherwise, it is not safe to access the stack after a
+	// goroutine enters _Gwaiting (e.g., it may get moved).
+	_Gwaiting // 4
+
+	// _Gmoribund_unused is currently unused, but hardcoded in gdb
+	// scripts.
+	_Gmoribund_unused // 5
+
+	// _Gdead means this goroutine is currently unused. It may be
+	// just exited, on a free list, or just being initialized. It
+	// is not executing user code. It may or may not have a stack
+	// allocated. The G and its stack (if any) are owned by the M
+	// that is exiting the G or that obtained the G from the free
+	// list.
+	_Gdead // 6
+
+	// _Genqueue_unused is currently unused.
+	_Genqueue_unused // 7
+
+	// _Gcopystack means this goroutine's stack is being moved. It
+	// is not executing user code and is not on a run queue. The
+	// stack is owned by the goroutine that put it in _Gcopystack.
+	_Gcopystack // 8
+
+	// _Gpreempted means this goroutine stopped itself for a
+	// suspendG preemption. It is like _Gwaiting, but nothing is
+	// yet responsible for ready()ing it. Some suspendG must CAS
+	// the status to _Gwaiting to take responsibility for
+	// ready()ing this G.
+	_Gpreempted // 9
+
+	// _Gscan combined with one of the above states other than
+	// _Grunning indicates that GC is scanning the stack. The
+	// goroutine is not executing user code and the stack is owned
+	// by the goroutine that set the _Gscan bit.
+	//
+	// _Gscanrunning is different: it is used to briefly block
+	// state transitions while GC signals the G to scan its own
+	// stack. This is otherwise like _Grunning.
+	//
+	// atomicstatus&~Gscan gives the state the goroutine will
+	// return to when the scan completes.
+	_Gscan          = 0x1000
+	_Gscanrunnable  = _Gscan + _Grunnable  // 0x1001
+	_Gscanrunning   = _Gscan + _Grunning   // 0x1002
+	_Gscansyscall   = _Gscan + _Gsyscall   // 0x1003
+	_Gscanwaiting   = _Gscan + _Gwaiting   // 0x1004
+	_Gscanpreempted = _Gscan + _Gpreempted // 0x1009
+)
+
+const (
+	// P status
+
+	// _Pidle means a P is not being used to run user code or the
+	// scheduler. Typically, it's on the idle P list and available
+	// to the scheduler, but it may just be transitioning between
+	// other states.
+	//
+	// The P is owned by the idle list or by whatever is
+	// transitioning its state. Its run queue is empty.
+	_Pidle = iota
+
+	// _Prunning means a P is owned by an M and is being used to
+	// run user code or the scheduler. Only the M that owns this P
+	// is allowed to change the P's status from _Prunning. The M
+	// may transition the P to _Pidle (if it has no more work to
+	// do), _Psyscall (when entering a syscall), or _Pgcstop (to
+	// halt for the GC). The M may also hand ownership of the P
+	// off directly to another M (e.g., to schedule a locked G).
+	_Prunning
+
+	// _Psyscall means a P is not running user code. It has
+	// affinity to an M in a syscall but is not owned by it and
+	// may be stolen by another M. This is similar to _Pidle but
+	// uses lightweight transitions and maintains M affinity.
+	//
+	// Leaving _Psyscall must be done with a CAS, either to steal
+	// or retake the P. Note that there's an ABA hazard: even if
+	// an M successfully CASes its original P back to _Prunning
+	// after a syscall, it must understand the P may have been
+	// used by another M in the interim.
+	_Psyscall
+
+	// _Pgcstop means a P is halted for STW and owned by the M
+	// that stopped the world. The M that stopped the world
+	// continues to use its P, even in _Pgcstop. Transitioning
+	// from _Prunning to _Pgcstop causes an M to release its P and
+	// park.
+	//
+	// The P retains its run queue and startTheWorld will restart
+	// the scheduler on Ps with non-empty run queues.
+	_Pgcstop
+
+	// _Pdead means a P is no longer used (GOMAXPROCS shrank). We
+	// reuse Ps if GOMAXPROCS increases. A dead P is mostly
+	// stripped of its resources, though a few things remain
+	// (e.g., trace buffers).
+	_Pdead
+)
+
+// Mutual exclusion locks.  In the uncontended case,
+// as fast as spin locks (just a few user-level instructions),
+// but on the contention path they sleep in the kernel.
+// A zeroed Mutex is unlocked (no need to initialize each lock).
+// Initialization is helpful for static lock ranking, but not required.
+type mutex struct {
+	// Empty struct if lock ranking is disabled, otherwise includes the lock rank
+	lockRankStruct
+	// Futex-based impl treats it as uint32 key,
+	// while sema-based impl as M* waitm.
+	// Used to be a union, but unions break precise GC.
+	key uintptr
+}
+
+// sleep and wakeup on one-time events.
+// before any calls to notesleep or notewakeup,
+// must call noteclear to initialize the Note.
+// then, exactly one thread can call notesleep
+// and exactly one thread can call notewakeup (once).
+// once notewakeup has been called, the notesleep
+// will return.  future notesleep will return immediately.
+// subsequent noteclear must be called only after
+// previous notesleep has returned, e.g. it's disallowed
+// to call noteclear straight after notewakeup.
+//
+// notetsleep is like notesleep but wakes up after
+// a given number of nanoseconds even if the event
+// has not yet happened.  if a goroutine uses notetsleep to
+// wake up early, it must wait to call noteclear until it
+// can be sure that no other goroutine is calling
+// notewakeup.
+//
+// notesleep/notetsleep are generally called on g0,
+// notetsleepg is similar to notetsleep but is called on user g.
+type note struct {
+	// Futex-based impl treats it as uint32 key,
+	// while sema-based impl as M* waitm.
+	// Used to be a union, but unions break precise GC.
+	key uintptr
+}
+
+type funcval struct {
+	fn uintptr
+	// variable-size, fn-specific data here
+}
+
+type iface struct {
+	tab  *itab
+	data unsafe.Pointer
+}
+
+type eface struct {
+	_type *_type
+	data  unsafe.Pointer
+}
+
+func efaceOf(ep *interface{}) *eface {
+	return (*eface)(unsafe.Pointer(ep))
+}
+
+// The guintptr, muintptr, and puintptr are all used to bypass write barriers.
+// It is particularly important to avoid write barriers when the current P has
+// been released, because the GC thinks the world is stopped, and an
+// unexpected write barrier would not be synchronized with the GC,
+// which can lead to a half-executed write barrier that has marked the object
+// but not queued it. If the GC skips the object and completes before the
+// queuing can occur, it will incorrectly free the object.
+//
+// We tried using special assignment functions invoked only when not
+// holding a running P, but then some updates to a particular memory
+// word went through write barriers and some did not. This breaks the
+// write barrier shadow checking mode, and it is also scary: better to have
+// a word that is completely ignored by the GC than to have one for which
+// only a few updates are ignored.
+//
+// Gs and Ps are always reachable via true pointers in the
+// allgs and allp lists or (during allocation before they reach those lists)
+// from stack variables.
+//
+// Ms are always reachable via true pointers either from allm or
+// freem. Unlike Gs and Ps we do free Ms, so it's important that
+// nothing ever hold an muintptr across a safe point.
+
+// A guintptr holds a goroutine pointer, but typed as a uintptr
+// to bypass write barriers. It is used in the Gobuf goroutine state
+// and in scheduling lists that are manipulated without a P.
+//
+// The Gobuf.g goroutine pointer is almost always updated by assembly code.
+// In one of the few places it is updated by Go code - func save - it must be
+// treated as a uintptr to avoid a write barrier being emitted at a bad time.
+// Instead of figuring out how to emit the write barriers missing in the
+// assembly manipulation, we change the type of the field to uintptr,
+// so that it does not require write barriers at all.
+//
+// Goroutine structs are published in the allg list and never freed.
+// That will keep the goroutine structs from being collected.
+// There is never a time that Gobuf.g's contain the only references
+// to a goroutine: the publishing of the goroutine in allg comes first.
+// Goroutine pointers are also kept in non-GC-visible places like TLS,
+// so I can't see them ever moving. If we did want to start moving data
+// in the GC, we'd need to allocate the goroutine structs from an
+// alternate arena. Using guintptr doesn't make that problem any worse.
+type guintptr uintptr
+
+//go:nosplit
+func (gp guintptr) ptr() *g { return (*g)(unsafe.Pointer(gp)) }
+
+//go:nosplit
+func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) }
+
+//go:nosplit
+func (gp *guintptr) cas(old, new guintptr) bool {
+	return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
+}
+
+// setGNoWB performs *gp = new without a write barrier.
+// For times when it's impractical to use a guintptr.
+//go:nosplit
+//go:nowritebarrier
+func setGNoWB(gp **g, new *g) {
+	(*guintptr)(unsafe.Pointer(gp)).set(new)
+}
+
+type puintptr uintptr
+
+//go:nosplit
+func (pp puintptr) ptr() *p { return (*p)(unsafe.Pointer(pp)) }
+
+//go:nosplit
+func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }
+
+// muintptr is a *m that is not tracked by the garbage collector.
+//
+// Because we do free Ms, there are some additional constrains on
+// muintptrs:
+//
+// 1. Never hold an muintptr locally across a safe point.
+//
+// 2. Any muintptr in the heap must be owned by the M itself so it can
+//    ensure it is not in use when the last true *m is released.
+type muintptr uintptr
+
+//go:nosplit
+func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) }
+
+//go:nosplit
+func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }
+
+// setMNoWB performs *mp = new without a write barrier.
+// For times when it's impractical to use an muintptr.
+//go:nosplit
+//go:nowritebarrier
+func setMNoWB(mp **m, new *m) {
+	(*muintptr)(unsafe.Pointer(mp)).set(new)
+}
+
+type gobuf struct {
+	// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
+	//
+	// ctxt is unusual with respect to GC: it may be a
+	// heap-allocated funcval, so GC needs to track it, but it
+	// needs to be set and cleared from assembly, where it's
+	// difficult to have write barriers. However, ctxt is really a
+	// saved, live register, and we only ever exchange it between
+	// the real register and the gobuf. Hence, we treat it as a
+	// root during stack scanning, which means assembly that saves
+	// and restores it doesn't need write barriers. It's still
+	// typed as a pointer so that any other writes from Go get
+	// write barriers.
+	sp   uintptr
+	pc   uintptr
+	g    guintptr
+	ctxt unsafe.Pointer
+	ret  sys.Uintreg
+	lr   uintptr
+	bp   uintptr // for framepointer-enabled architectures
+}
+
+// sudog represents a g in a wait list, such as for sending/receiving
+// on a channel.
+//
+// sudog is necessary because the g ↔ synchronization object relation
+// is many-to-many. A g can be on many wait lists, so there may be
+// many sudogs for one g; and many gs may be waiting on the same
+// synchronization object, so there may be many sudogs for one object.
+//
+// sudogs are allocated from a special pool. Use acquireSudog and
+// releaseSudog to allocate and free them.
+type sudog struct {
+	// The following fields are protected by the hchan.lock of the
+	// channel this sudog is blocking on. shrinkstack depends on
+	// this for sudogs involved in channel ops.
+
+	g *g
+
+	next *sudog
+	prev *sudog
+	elem unsafe.Pointer // data element (may point to stack)
+
+	// The following fields are never accessed concurrently.
+	// For channels, waitlink is only accessed by g.
+	// For semaphores, all fields (including the ones above)
+	// are only accessed when holding a semaRoot lock.
+
+	acquiretime int64
+	releasetime int64
+	ticket      uint32
+
+	// isSelect indicates g is participating in a select, so
+	// g.selectDone must be CAS'd to win the wake-up race.
+	isSelect bool
+
+	// success indicates whether communication over channel c
+	// succeeded. It is true if the goroutine was awoken because a
+	// value was delivered over channel c, and false if awoken
+	// because c was closed.
+	success bool
+
+	parent   *sudog // semaRoot binary tree
+	waitlink *sudog // g.waiting list or semaRoot
+	waittail *sudog // semaRoot
+	c        *hchan // channel
+}
+
+type libcall struct {
+	fn   uintptr
+	n    uintptr // number of parameters
+	args uintptr // parameters
+	r1   uintptr // return values
+	r2   uintptr
+	err  uintptr // error number
+}
+
+// Stack describes a Go execution stack.
+// The bounds of the stack are exactly [lo, hi),
+// with no implicit data structures on either side.
+type stack struct {
+	lo uintptr
+	hi uintptr
+}
+
+// heldLockInfo gives info on a held lock and the rank of that lock
+type heldLockInfo struct {
+	lockAddr uintptr
+	rank     lockRank
+}
+
+type g struct {
+	// Stack parameters.
+	// stack describes the actual stack memory: [stack.lo, stack.hi).
+	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
+	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
+	// stackguard1 is the stack pointer compared in the C stack growth prologue.
+	// It is stack.lo+StackGuard on g0 and gsignal stacks.
+	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
+	stack       stack   // offset known to runtime/cgo
+	stackguard0 uintptr // offset known to liblink
+	stackguard1 uintptr // offset known to liblink
+
+	_panic       *_panic // innermost panic - offset known to liblink
+	_defer       *_defer // innermost defer
+	m            *m      // current m; offset known to arm liblink
+	sched        gobuf
+	syscallsp    uintptr        // if status==Gsyscall, syscallsp = sched.sp to use during gc
+	syscallpc    uintptr        // if status==Gsyscall, syscallpc = sched.pc to use during gc
+	stktopsp     uintptr        // expected sp at top of stack, to check in traceback
+	param        unsafe.Pointer // passed parameter on wakeup
+	atomicstatus uint32
+	stackLock    uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
+	goid         int64
+	schedlink    guintptr
+	waitsince    int64      // approx time when the g become blocked
+	waitreason   waitReason // if status==Gwaiting
+
+	preempt       bool // preemption signal, duplicates stackguard0 = stackpreempt
+	preemptStop   bool // transition to _Gpreempted on preemption; otherwise, just deschedule
+	preemptShrink bool // shrink stack at synchronous safe point
+
+	// asyncSafePoint is set if g is stopped at an asynchronous
+	// safe point. This means there are frames on the stack
+	// without precise pointer information.
+	asyncSafePoint bool
+
+	paniconfault bool // panic (instead of crash) on unexpected fault address
+	gcscandone   bool // g has scanned stack; protected by _Gscan bit in status
+	throwsplit   bool // must not split stack
+	// activeStackChans indicates that there are unlocked channels
+	// pointing into this goroutine's stack. If true, stack
+	// copying needs to acquire channel locks to protect these
+	// areas of the stack.
+	activeStackChans bool
+	// parkingOnChan indicates that the goroutine is about to
+	// park on a chansend or chanrecv. Used to signal an unsafe point
+	// for stack shrinking. It's a boolean value, but is updated atomically.
+	parkingOnChan uint8
+
+	raceignore     int8     // ignore race detection events
+	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine
+	sysexitticks   int64    // cputicks when syscall has returned (for tracing)
+	traceseq       uint64   // trace event sequencer
+	tracelastp     puintptr // last P emitted an event for this goroutine
+	lockedm        muintptr
+	sig            uint32
+	writebuf       []byte
+	sigcode0       uintptr
+	sigcode1       uintptr
+	sigpc          uintptr
+	gopc           uintptr         // pc of go statement that created this goroutine
+	ancestors      *[]ancestorInfo // ancestor information goroutine(s) that created this goroutine (only used if debug.tracebackancestors)
+	startpc        uintptr         // pc of goroutine function
+	racectx        uintptr
+	waiting        *sudog         // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
+	cgoCtxt        []uintptr      // cgo traceback context
+	labels         unsafe.Pointer // profiler labels
+	timer          *timer         // cached timer for time.Sleep
+	selectDone     uint32         // are we participating in a select and did someone win the race?
+
+	// Per-G GC state
+
+	// gcAssistBytes is this G's GC assist credit in terms of
+	// bytes allocated. If this is positive, then the G has credit
+	// to allocate gcAssistBytes bytes without assisting. If this
+	// is negative, then the G must correct this by performing
+	// scan work. We track this in bytes to make it fast to update
+	// and check for debt in the malloc hot path. The assist ratio
+	// determines how this corresponds to scan work debt.
+	gcAssistBytes int64
+}
+
+type m struct {
+	g0      *g     // goroutine with scheduling stack
+	morebuf gobuf  // gobuf arg to morestack
+	divmod  uint32 // div/mod denominator for arm - known to liblink
+
+	// Fields not known to debuggers.
+	procid        uint64       // for debuggers, but offset not hard-coded
+	gsignal       *g           // signal-handling g
+	goSigStack    gsignalStack // Go-allocated signal handling stack
+	sigmask       sigset       // storage for saved signal mask
+	tls           [6]uintptr   // thread-local storage (for x86 extern register)
+	mstartfn      func()
+	curg          *g       // current running goroutine
+	caughtsig     guintptr // goroutine running during fatal signal
+	p             puintptr // attached p for executing go code (nil if not executing go code)
+	nextp         puintptr
+	oldp          puintptr // the p that was attached before executing a syscall
+	id            int64
+	mallocing     int32
+	throwing      int32
+	preemptoff    string // if != "", keep curg running on this m
+	locks         int32
+	dying         int32
+	profilehz     int32
+	spinning      bool // m is out of work and is actively looking for work
+	blocked       bool // m is blocked on a note
+	newSigstack   bool // minit on C thread called sigaltstack
+	printlock     int8
+	incgo         bool   // m is executing a cgo call
+	freeWait      uint32 // if == 0, safe to free g0 and delete m (atomic)
+	fastrand      [2]uint32
+	needextram    bool
+	traceback     uint8
+	ncgocall      uint64      // number of cgo calls in total
+	ncgo          int32       // number of cgo calls currently in progress
+	cgoCallersUse uint32      // if non-zero, cgoCallers in use temporarily
+	cgoCallers    *cgoCallers // cgo traceback if crashing in cgo call
+	doesPark      bool        // non-P running threads: sysmon and newmHandoff never use .park
+	park          note
+	alllink       *m // on allm
+	schedlink     muintptr
+	lockedg       guintptr
+	createstack   [32]uintptr // stack that created this thread.
+	lockedExt     uint32      // tracking for external LockOSThread
+	lockedInt     uint32      // tracking for internal lockOSThread
+	nextwaitm     muintptr    // next m waiting for lock
+	waitunlockf   func(*g, unsafe.Pointer) bool
+	waitlock      unsafe.Pointer
+	waittraceev   byte
+	waittraceskip int
+	startingtrace bool
+	syscalltick   uint32
+	freelink      *m // on sched.freem
+
+	// mFixup is used to synchronize OS related m state
+	// (credentials etc) use mutex to access. To avoid deadlocks
+	// an atomic.Load() of used being zero in mDoFixupFn()
+	// guarantees fn is nil.
+	mFixup struct {
+		lock mutex
+		used uint32
+		fn   func(bool) bool
+	}
+
+	// these are here because they are too large to be on the stack
+	// of low-level NOSPLIT functions.
+	libcall   libcall
+	libcallpc uintptr // for cpu profiler
+	libcallsp uintptr
+	libcallg  guintptr
+	syscall   libcall // stores syscall parameters on windows
+
+	vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call)
+	vdsoPC uintptr // PC for traceback while in VDSO call
+
+	// preemptGen counts the number of completed preemption
+	// signals. This is used to detect when a preemption is
+	// requested, but fails. Accessed atomically.
+	preemptGen uint32
+
+	// Whether this is a pending preemption signal on this M.
+	// Accessed atomically.
+	signalPending uint32
+
+	dlogPerM
+
+	mOS
+
+	// Up to 10 locks held by this m, maintained by the lock ranking code.
+	locksHeldLen int
+	locksHeld    [10]heldLockInfo
+}
+
+type p struct {
+	id          int32
+	status      uint32 // one of pidle/prunning/...
+	link        puintptr
+	schedtick   uint32     // incremented on every scheduler call
+	syscalltick uint32     // incremented on every system call
+	sysmontick  sysmontick // last tick observed by sysmon
+	m           muintptr   // back-link to associated m (nil if idle)
+	mcache      *mcache
+	pcache      pageCache
+	raceprocctx uintptr
+
+	deferpool    [5][]*_defer // pool of available defer structs of different sizes (see panic.go)
+	deferpoolbuf [5][32]*_defer
+
+	// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
+	goidcache    uint64
+	goidcacheend uint64
+
+	// Queue of runnable goroutines. Accessed without lock.
+	runqhead uint32
+	runqtail uint32
+	runq     [256]guintptr
+	// runnext, if non-nil, is a runnable G that was ready'd by
+	// the current G and should be run next instead of what's in
+	// runq if there's time remaining in the running G's time
+	// slice. It will inherit the time left in the current time
+	// slice. If a set of goroutines is locked in a
+	// communicate-and-wait pattern, this schedules that set as a
+	// unit and eliminates the (potentially large) scheduling
+	// latency that otherwise arises from adding the ready'd
+	// goroutines to the end of the run queue.
+	runnext guintptr
+
+	// Available G's (status == Gdead)
+	gFree struct {
+		gList
+		n int32
+	}
+
+	sudogcache []*sudog
+	sudogbuf   [128]*sudog
+
+	// Cache of mspan objects from the heap.
+	mspancache struct {
+		// We need an explicit length here because this field is used
+		// in allocation codepaths where write barriers are not allowed,
+		// and eliminating the write barrier/keeping it eliminated from
+		// slice updates is tricky, moreso than just managing the length
+		// ourselves.
+		len int
+		buf [128]*mspan
+	}
+
+	tracebuf traceBufPtr
+
+	// traceSweep indicates the sweep events should be traced.
+	// This is used to defer the sweep start event until a span
+	// has actually been swept.
+	traceSweep bool
+	// traceSwept and traceReclaimed track the number of bytes
+	// swept and reclaimed by sweeping in the current sweep loop.
+	traceSwept, traceReclaimed uintptr
+
+	palloc persistentAlloc // per-P to avoid mutex
+
+	_ uint32 // Alignment for atomic fields below
+
+	// The when field of the first entry on the timer heap.
+	// This is updated using atomic functions.
+	// This is 0 if the timer heap is empty.
+	timer0When uint64
+
+	// The earliest known nextwhen field of a timer with
+	// timerModifiedEarlier status. Because the timer may have been
+	// modified again, there need not be any timer with this value.
+	// This is updated using atomic functions.
+	// This is 0 if there are no timerModifiedEarlier timers.
+	timerModifiedEarliest uint64
+
+	// Per-P GC state
+	gcAssistTime         int64 // Nanoseconds in assistAlloc
+	gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic)
+
+	// gcMarkWorkerMode is the mode for the next mark worker to run in.
+	// That is, this is used to communicate with the worker goroutine
+	// selected for immediate execution by
+	// gcController.findRunnableGCWorker. When scheduling other goroutines,
+	// this field must be set to gcMarkWorkerNotWorker.
+	gcMarkWorkerMode gcMarkWorkerMode
+	// gcMarkWorkerStartTime is the nanotime() at which the most recent
+	// mark worker started.
+	gcMarkWorkerStartTime int64
+
+	// gcw is this P's GC work buffer cache. The work buffer is
+	// filled by write barriers, drained by mutator assists, and
+	// disposed on certain GC state transitions.
+	gcw gcWork
+
+	// wbBuf is this P's GC write barrier buffer.
+	//
+	// TODO: Consider caching this in the running G.
+	wbBuf wbBuf
+
+	runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point
+
+	// statsSeq is a counter indicating whether this P is currently
+	// writing any stats. Its value is even when not, odd when it is.
+	statsSeq uint32
+
+	// Lock for timers. We normally access the timers while running
+	// on this P, but the scheduler can also do it from a different P.
+	timersLock mutex
+
+	// Actions to take at some time. This is used to implement the
+	// standard library's time package.
+	// Must hold timersLock to access.
+	timers []*timer
+
+	// Number of timers in P's heap.
+	// Modified using atomic instructions.
+	numTimers uint32
+
+	// Number of timerDeleted timers in P's heap.
+	// Modified using atomic instructions.
+	deletedTimers uint32
+
+	// Race context used while executing timer functions.
+	timerRaceCtx uintptr
+
+	// preempt is set to indicate that this P should be enter the
+	// scheduler ASAP (regardless of what G is running on it).
+	preempt bool
+
+	pad cpu.CacheLinePad
+}
+
+type schedt struct {
+	// accessed atomically. keep at top to ensure alignment on 32-bit systems.
+	goidgen   uint64
+	lastpoll  uint64 // time of last network poll, 0 if currently polling
+	pollUntil uint64 // time to which current poll is sleeping
+
+	lock mutex
+
+	// When increasing nmidle, nmidlelocked, nmsys, or nmfreed, be
+	// sure to call checkdead().
+
+	midle        muintptr // idle m's waiting for work
+	nmidle       int32    // number of idle m's waiting for work
+	nmidlelocked int32    // number of locked m's waiting for work
+	mnext        int64    // number of m's that have been created and next M ID
+	maxmcount    int32    // maximum number of m's allowed (or die)
+	nmsys        int32    // number of system m's not counted for deadlock
+	nmfreed      int64    // cumulative number of freed m's
+
+	ngsys uint32 // number of system goroutines; updated atomically
+
+	pidle      puintptr // idle p's
+	npidle     uint32
+	nmspinning uint32 // See "Worker thread parking/unparking" comment in proc.go.
+
+	// Global runnable queue.
+	runq     gQueue
+	runqsize int32
+
+	// disable controls selective disabling of the scheduler.
+	//
+	// Use schedEnableUser to control this.
+	//
+	// disable is protected by sched.lock.
+	disable struct {
+		// user disables scheduling of user goroutines.
+		user     bool
+		runnable gQueue // pending runnable Gs
+		n        int32  // length of runnable
+	}
+
+	// Global cache of dead G's.
+	gFree struct {
+		lock    mutex
+		stack   gList // Gs with stacks
+		noStack gList // Gs without stacks
+		n       int32
+	}
+
+	// Central cache of sudog structs.
+	sudoglock  mutex
+	sudogcache *sudog
+
+	// Central pool of available defer structs of different sizes.
+	deferlock mutex
+	deferpool [5]*_defer
+
+	// freem is the list of m's waiting to be freed when their
+	// m.exited is set. Linked through m.freelink.
+	freem *m
+
+	gcwaiting  uint32 // gc is waiting to run
+	stopwait   int32
+	stopnote   note
+	sysmonwait uint32
+	sysmonnote note
+
+	// While true, sysmon not ready for mFixup calls.
+	// Accessed atomically.
+	sysmonStarting uint32
+
+	// safepointFn should be called on each P at the next GC
+	// safepoint if p.runSafePointFn is set.
+	safePointFn   func(*p)
+	safePointWait int32
+	safePointNote note
+
+	profilehz int32 // cpu profiling rate
+
+	procresizetime int64 // nanotime() of last change to gomaxprocs
+	totaltime      int64 // ∫gomaxprocs dt up to procresizetime
+
+	// sysmonlock protects sysmon's actions on the runtime.
+	//
+	// Acquire and hold this mutex to block sysmon from interacting
+	// with the rest of the runtime.
+	sysmonlock mutex
+}
+
+// Values for the flags field of a sigTabT.
+const (
+	_SigNotify   = 1 << iota // let signal.Notify have signal, even if from kernel
+	_SigKill                 // if signal.Notify doesn't take it, exit quietly
+	_SigThrow                // if signal.Notify doesn't take it, exit loudly
+	_SigPanic                // if the signal is from the kernel, panic
+	_SigDefault              // if the signal isn't explicitly requested, don't monitor it
+	_SigGoExit               // cause all runtime procs to exit (only used on Plan 9).
+	_SigSetStack             // add SA_ONSTACK to libc handler
+	_SigUnblock              // always unblock; see blockableSig
+	_SigIgn                  // _SIG_DFL action is to ignore the signal
+)
+
+// Layout of in-memory per-function information prepared by linker
+// See https://golang.org/s/go12symtab.
+// Keep in sync with linker (../cmd/link/internal/ld/pcln.go:/pclntab)
+// and with package debug/gosym and with symtab.go in package runtime.
+type _func struct {
+	entry   uintptr // start pc
+	nameoff int32   // function name
+
+	args        int32  // in/out args size
+	deferreturn uint32 // offset of start of a deferreturn call instruction from entry, if any.
+
+	pcsp      uint32
+	pcfile    uint32
+	pcln      uint32
+	npcdata   uint32
+	cuOffset  uint32  // runtime.cutab offset of this function's CU
+	funcID    funcID  // set for certain special runtime functions
+	_         [2]byte // pad
+	nfuncdata uint8   // must be last
+}
+
+// Pseudo-Func that is returned for PCs that occur in inlined code.
+// A *Func can be either a *_func or a *funcinl, and they are distinguished
+// by the first uintptr.
+type funcinl struct {
+	zero  uintptr // set to 0 to distinguish from _func
+	entry uintptr // entry of the real (the "outermost") frame.
+	name  string
+	file  string
+	line  int
+}
+
+// layout of Itab known to compilers
+// allocated in non-garbage-collected memory
+// Needs to be in sync with
+// ../cmd/compile/internal/gc/reflect.go:/^func.dumptabs.
+type itab struct {
+	inter *interfacetype
+	_type *_type
+	hash  uint32 // copy of _type.hash. Used for type switches.
+	_     [4]byte
+	fun   [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
+}
+
+// Lock-free stack node.
+// Also known to export_test.go.
+type lfnode struct {
+	next    uint64
+	pushcnt uintptr
+}
+
+type forcegcstate struct {
+	lock mutex
+	g    *g
+	idle uint32
+}
+
+// extendRandom extends the random numbers in r[:n] to the whole slice r.
+// Treats n<0 as n==0.
+func extendRandom(r []byte, n int) {
+	if n < 0 {
+		n = 0
+	}
+	for n < len(r) {
+		// Extend random bits using hash function & time seed
+		w := n
+		if w > 16 {
+			w = 16
+		}
+		h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
+		for i := 0; i < sys.PtrSize && n < len(r); i++ {
+			r[n] = byte(h)
+			n++
+			h >>= 8
+		}
+	}
+}
+
+// A _defer holds an entry on the list of deferred calls.
+// If you add a field here, add code to clear it in freedefer and deferProcStack
+// This struct must match the code in cmd/compile/internal/gc/reflect.go:deferstruct
+// and cmd/compile/internal/gc/ssa.go:(*state).call.
+// Some defers will be allocated on the stack and some on the heap.
+// All defers are logically part of the stack, so write barriers to
+// initialize them are not required. All defers must be manually scanned,
+// and for heap defers, marked.
+type _defer struct {
+	siz     int32 // includes both arguments and results
+	started bool
+	heap    bool
+	// openDefer indicates that this _defer is for a frame with open-coded
+	// defers. We have only one defer record for the entire frame (which may
+	// currently have 0, 1, or more defers active).
+	openDefer bool
+	sp        uintptr  // sp at time of defer
+	pc        uintptr  // pc at time of defer
+	fn        *funcval // can be nil for open-coded defers
+	_panic    *_panic  // panic that is running defer
+	link      *_defer
+
+	// If openDefer is true, the fields below record values about the stack
+	// frame and associated function that has the open-coded defer(s). sp
+	// above will be the sp for the frame, and pc will be address of the
+	// deferreturn call in the function.
+	fd   unsafe.Pointer // funcdata for the function associated with the frame
+	varp uintptr        // value of varp for the stack frame
+	// framepc is the current pc associated with the stack frame. Together,
+	// with sp above (which is the sp associated with the stack frame),
+	// framepc/sp can be used as pc/sp pair to continue a stack trace via
+	// gentraceback().
+	framepc uintptr
+}
+
+// A _panic holds information about an active panic.
+//
+// A _panic value must only ever live on the stack.
+//
+// The argp and link fields are stack pointers, but don't need special
+// handling during stack growth: because they are pointer-typed and
+// _panic values only live on the stack, regular stack pointer
+// adjustment takes care of them.
+type _panic struct {
+	argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
+	arg       interface{}    // argument to panic
+	link      *_panic        // link to earlier panic
+	pc        uintptr        // where to return to in runtime if this panic is bypassed
+	sp        unsafe.Pointer // where to return to in runtime if this panic is bypassed
+	recovered bool           // whether this panic is over
+	aborted   bool           // the panic was aborted
+	goexit    bool
+}
+
+// stack traces
+type stkframe struct {
+	fn       funcInfo   // function being run
+	pc       uintptr    // program counter within fn
+	continpc uintptr    // program counter where execution can continue, or 0 if not
+	lr       uintptr    // program counter at caller aka link register
+	sp       uintptr    // stack pointer at pc
+	fp       uintptr    // stack pointer at caller aka frame pointer
+	varp     uintptr    // top of local variables
+	argp     uintptr    // pointer to function arguments
+	arglen   uintptr    // number of bytes at argp
+	argmap   *bitvector // force use of this argmap
+}
+
+// ancestorInfo records details of where a goroutine was started.
+type ancestorInfo struct {
+	pcs  []uintptr // pcs from the stack of this goroutine
+	goid int64     // goroutine id of this goroutine; original goroutine possibly dead
+	gopc uintptr   // pc of go statement that created this goroutine
+}
+
+const (
+	_TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
+	_TraceTrap                      // the initial PC, SP are from a trap, not a return PC from a call
+	_TraceJumpStack                 // if traceback is on a systemstack, resume trace at g that called into it
+)
+
+// The maximum number of frames we print for a traceback
+const _TracebackMaxFrames = 100
+
+// A waitReason explains why a goroutine has been stopped.
+// See gopark. Do not re-use waitReasons, add new ones.
+type waitReason uint8
+
+const (
+	waitReasonZero                  waitReason = iota // ""
+	waitReasonGCAssistMarking                         // "GC assist marking"
+	waitReasonIOWait                                  // "IO wait"
+	waitReasonChanReceiveNilChan                      // "chan receive (nil chan)"
+	waitReasonChanSendNilChan                         // "chan send (nil chan)"
+	waitReasonDumpingHeap                             // "dumping heap"
+	waitReasonGarbageCollection                       // "garbage collection"
+	waitReasonGarbageCollectionScan                   // "garbage collection scan"
+	waitReasonPanicWait                               // "panicwait"
+	waitReasonSelect                                  // "select"
+	waitReasonSelectNoCases                           // "select (no cases)"
+	waitReasonGCAssistWait                            // "GC assist wait"
+	waitReasonGCSweepWait                             // "GC sweep wait"
+	waitReasonGCScavengeWait                          // "GC scavenge wait"
+	waitReasonChanReceive                             // "chan receive"
+	waitReasonChanSend                                // "chan send"
+	waitReasonFinalizerWait                           // "finalizer wait"
+	waitReasonForceGCIdle                             // "force gc (idle)"
+	waitReasonSemacquire                              // "semacquire"
+	waitReasonSleep                                   // "sleep"
+	waitReasonSyncCondWait                            // "sync.Cond.Wait"
+	waitReasonTimerGoroutineIdle                      // "timer goroutine (idle)"
+	waitReasonTraceReaderBlocked                      // "trace reader (blocked)"
+	waitReasonWaitForGCCycle                          // "wait for GC cycle"
+	waitReasonGCWorkerIdle                            // "GC worker (idle)"
+	waitReasonPreempted                               // "preempted"
+	waitReasonDebugCall                               // "debug call"
+)
+
+var waitReasonStrings = [...]string{
+	waitReasonZero:                  "",
+	waitReasonGCAssistMarking:       "GC assist marking",
+	waitReasonIOWait:                "IO wait",
+	waitReasonChanReceiveNilChan:    "chan receive (nil chan)",
+	waitReasonChanSendNilChan:       "chan send (nil chan)",
+	waitReasonDumpingHeap:           "dumping heap",
+	waitReasonGarbageCollection:     "garbage collection",
+	waitReasonGarbageCollectionScan: "garbage collection scan",
+	waitReasonPanicWait:             "panicwait",
+	waitReasonSelect:                "select",
+	waitReasonSelectNoCases:         "select (no cases)",
+	waitReasonGCAssistWait:          "GC assist wait",
+	waitReasonGCSweepWait:           "GC sweep wait",
+	waitReasonGCScavengeWait:        "GC scavenge wait",
+	waitReasonChanReceive:           "chan receive",
+	waitReasonChanSend:              "chan send",
+	waitReasonFinalizerWait:         "finalizer wait",
+	waitReasonForceGCIdle:           "force gc (idle)",
+	waitReasonSemacquire:            "semacquire",
+	waitReasonSleep:                 "sleep",
+	waitReasonSyncCondWait:          "sync.Cond.Wait",
+	waitReasonTimerGoroutineIdle:    "timer goroutine (idle)",
+	waitReasonTraceReaderBlocked:    "trace reader (blocked)",
+	waitReasonWaitForGCCycle:        "wait for GC cycle",
+	waitReasonGCWorkerIdle:          "GC worker (idle)",
+	waitReasonPreempted:             "preempted",
+	waitReasonDebugCall:             "debug call",
+}
+
+func (w waitReason) String() string {
+	if w < 0 || w >= waitReason(len(waitReasonStrings)) {
+		return "unknown wait reason"
+	}
+	return waitReasonStrings[w]
+}
+
+var (
+	allm       *m
+	gomaxprocs int32
+	ncpu       int32
+	forcegc    forcegcstate
+	sched      schedt
+	newprocs   int32
+
+	// allpLock protects P-less reads and size changes of allp, idlepMask,
+	// and timerpMask, and all writes to allp.
+	allpLock mutex
+	// len(allp) == gomaxprocs; may change at safe points, otherwise
+	// immutable.
+	allp []*p
+	// Bitmask of Ps in _Pidle list, one bit per P. Reads and writes must
+	// be atomic. Length may change at safe points.
+	//
+	// Each P must update only its own bit. In order to maintain
+	// consistency, a P going idle must the idle mask simultaneously with
+	// updates to the idle P list under the sched.lock, otherwise a racing
+	// pidleget may clear the mask before pidleput sets the mask,
+	// corrupting the bitmap.
+	//
+	// N.B., procresize takes ownership of all Ps in stopTheWorldWithSema.
+	idlepMask pMask
+	// Bitmask of Ps that may have a timer, one bit per P. Reads and writes
+	// must be atomic. Length may change at safe points.
+	timerpMask pMask
+
+	// Pool of GC parked background workers. Entries are type
+	// *gcBgMarkWorkerNode.
+	gcBgMarkWorkerPool lfstack
+
+	// Total number of gcBgMarkWorker goroutines. Protected by worldsema.
+	gcBgMarkWorkerCount int32
+
+	// Information about what cpu features are available.
+	// Packages outside the runtime should not use these
+	// as they are not an external api.
+	// Set on startup in asm_{386,amd64}.s
+	processorVersionInfo uint32
+	isIntel              bool
+	lfenceBeforeRdtsc    bool
+
+	goarm uint8 // set by cmd/link on arm systems
+)
+
+// Set by the linker so the runtime can determine the buildmode.
+var (
+	islibrary bool // -buildmode=c-shared
+	isarchive bool // -buildmode=c-archive
+)
+
+// Must agree with cmd/internal/objabi.Framepointer_enabled.
+const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64" && (GOOS == "linux" || GOOS == "darwin" || GOOS == "ios")