Source file src/runtime/runtime2.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"runtime/internal/atomic"
     9  	"runtime/internal/sys"
    10  	"unsafe"
    11  )
    12  
    13  // defined constants
    14  const (
    15  	// G status
    16  	//
    17  	// Beyond indicating the general state of a G, the G status
    18  	// acts like a lock on the goroutine's stack (and hence its
    19  	// ability to execute user code).
    20  	//
    21  	// If you add to this list, add to the list
    22  	// of "okay during garbage collection" status
    23  	// in mgcmark.go too.
    24  	//
    25  	// TODO(austin): The _Gscan bit could be much lighter-weight.
    26  	// For example, we could choose not to run _Gscanrunnable
    27  	// goroutines found in the run queue, rather than CAS-looping
    28  	// until they become _Grunnable. And transitions like
    29  	// _Gscanwaiting -> _Gscanrunnable are actually okay because
    30  	// they don't affect stack ownership.
    31  
    32  	// _Gidle means this goroutine was just allocated and has not
    33  	// yet been initialized.
    34  	_Gidle = iota // 0
    35  
    36  	// _Grunnable means this goroutine is on a run queue. It is
    37  	// not currently executing user code. The stack is not owned.
    38  	_Grunnable // 1
    39  
    40  	// _Grunning means this goroutine may execute user code. The
    41  	// stack is owned by this goroutine. It is not on a run queue.
    42  	// It is assigned an M and a P (g.m and g.m.p are valid).
    43  	_Grunning // 2
    44  
    45  	// _Gsyscall means this goroutine is executing a system call.
    46  	// It is not executing user code. The stack is owned by this
    47  	// goroutine. It is not on a run queue. It is assigned an M.
    48  	_Gsyscall // 3
    49  
    50  	// _Gwaiting means this goroutine is blocked in the runtime.
    51  	// It is not executing user code. It is not on a run queue,
    52  	// but should be recorded somewhere (e.g., a channel wait
    53  	// queue) so it can be ready()d when necessary. The stack is
    54  	// not owned *except* that a channel operation may read or
    55  	// write parts of the stack under the appropriate channel
    56  	// lock. Otherwise, it is not safe to access the stack after a
    57  	// goroutine enters _Gwaiting (e.g., it may get moved).
    58  	_Gwaiting // 4
    59  
    60  	// _Gmoribund_unused is currently unused, but hardcoded in gdb
    61  	// scripts.
    62  	_Gmoribund_unused // 5
    63  
    64  	// _Gdead means this goroutine is currently unused. It may be
    65  	// just exited, on a free list, or just being initialized. It
    66  	// is not executing user code. It may or may not have a stack
    67  	// allocated. The G and its stack (if any) are owned by the M
    68  	// that is exiting the G or that obtained the G from the free
    69  	// list.
    70  	_Gdead // 6
    71  
    72  	// _Genqueue_unused is currently unused.
    73  	_Genqueue_unused // 7
    74  
    75  	// _Gcopystack means this goroutine's stack is being moved. It
    76  	// is not executing user code and is not on a run queue. The
    77  	// stack is owned by the goroutine that put it in _Gcopystack.
    78  	_Gcopystack // 8
    79  
    80  	// _Gpreempted means this goroutine stopped itself for a
    81  	// suspendG preemption. It is like _Gwaiting, but nothing is
    82  	// yet responsible for ready()ing it. Some suspendG must CAS
    83  	// the status to _Gwaiting to take responsibility for
    84  	// ready()ing this G.
    85  	_Gpreempted // 9
    86  
    87  	// _Gscan combined with one of the above states other than
    88  	// _Grunning indicates that GC is scanning the stack. The
    89  	// goroutine is not executing user code and the stack is owned
    90  	// by the goroutine that set the _Gscan bit.
    91  	//
    92  	// _Gscanrunning is different: it is used to briefly block
    93  	// state transitions while GC signals the G to scan its own
    94  	// stack. This is otherwise like _Grunning.
    95  	//
    96  	// atomicstatus&~Gscan gives the state the goroutine will
    97  	// return to when the scan completes.
    98  	_Gscan          = 0x1000
    99  	_Gscanrunnable  = _Gscan + _Grunnable  // 0x1001
   100  	_Gscanrunning   = _Gscan + _Grunning   // 0x1002
   101  	_Gscansyscall   = _Gscan + _Gsyscall   // 0x1003
   102  	_Gscanwaiting   = _Gscan + _Gwaiting   // 0x1004
   103  	_Gscanpreempted = _Gscan + _Gpreempted // 0x1009
   104  )
   105  
   106  const (
   107  	// P status
   108  
   109  	// _Pidle means a P is not being used to run user code or the
   110  	// scheduler. Typically, it's on the idle P list and available
   111  	// to the scheduler, but it may just be transitioning between
   112  	// other states.
   113  	//
   114  	// The P is owned by the idle list or by whatever is
   115  	// transitioning its state. Its run queue is empty.
   116  	_Pidle = iota
   117  
   118  	// _Prunning means a P is owned by an M and is being used to
   119  	// run user code or the scheduler. Only the M that owns this P
   120  	// is allowed to change the P's status from _Prunning. The M
   121  	// may transition the P to _Pidle (if it has no more work to
   122  	// do), _Psyscall (when entering a syscall), or _Pgcstop (to
   123  	// halt for the GC). The M may also hand ownership of the P
   124  	// off directly to another M (e.g., to schedule a locked G).
   125  	_Prunning
   126  
   127  	// _Psyscall means a P is not running user code. It has
   128  	// affinity to an M in a syscall but is not owned by it and
   129  	// may be stolen by another M. This is similar to _Pidle but
   130  	// uses lightweight transitions and maintains M affinity.
   131  	//
   132  	// Leaving _Psyscall must be done with a CAS, either to steal
   133  	// or retake the P. Note that there's an ABA hazard: even if
   134  	// an M successfully CASes its original P back to _Prunning
   135  	// after a syscall, it must understand the P may have been
   136  	// used by another M in the interim.
   137  	_Psyscall
   138  
   139  	// _Pgcstop means a P is halted for STW and owned by the M
   140  	// that stopped the world. The M that stopped the world
   141  	// continues to use its P, even in _Pgcstop. Transitioning
   142  	// from _Prunning to _Pgcstop causes an M to release its P and
   143  	// park.
   144  	//
   145  	// The P retains its run queue and startTheWorld will restart
   146  	// the scheduler on Ps with non-empty run queues.
   147  	_Pgcstop
   148  
   149  	// _Pdead means a P is no longer used (GOMAXPROCS shrank). We
   150  	// reuse Ps if GOMAXPROCS increases. A dead P is mostly
   151  	// stripped of its resources, though a few things remain
   152  	// (e.g., trace buffers).
   153  	_Pdead
   154  )
   155  
   156  // Mutual exclusion locks.  In the uncontended case,
   157  // as fast as spin locks (just a few user-level instructions),
   158  // but on the contention path they sleep in the kernel.
   159  // A zeroed Mutex is unlocked (no need to initialize each lock).
   160  // Initialization is helpful for static lock ranking, but not required.
   161  type mutex struct {
   162  	// Empty struct if lock ranking is disabled, otherwise includes the lock rank
   163  	lockRankStruct
   164  	// Futex-based impl treats it as uint32 key,
   165  	// while sema-based impl as M* waitm.
   166  	// Used to be a union, but unions break precise GC.
   167  	key uintptr
   168  }
   169  
   170  // sleep and wakeup on one-time events.
   171  // before any calls to notesleep or notewakeup,
   172  // must call noteclear to initialize the Note.
   173  // then, exactly one thread can call notesleep
   174  // and exactly one thread can call notewakeup (once).
   175  // once notewakeup has been called, the notesleep
   176  // will return.  future notesleep will return immediately.
   177  // subsequent noteclear must be called only after
   178  // previous notesleep has returned, e.g. it's disallowed
   179  // to call noteclear straight after notewakeup.
   180  //
   181  // notetsleep is like notesleep but wakes up after
   182  // a given number of nanoseconds even if the event
   183  // has not yet happened.  if a goroutine uses notetsleep to
   184  // wake up early, it must wait to call noteclear until it
   185  // can be sure that no other goroutine is calling
   186  // notewakeup.
   187  //
   188  // notesleep/notetsleep are generally called on g0,
   189  // notetsleepg is similar to notetsleep but is called on user g.
   190  type note struct {
   191  	// Futex-based impl treats it as uint32 key,
   192  	// while sema-based impl as M* waitm.
   193  	// Used to be a union, but unions break precise GC.
   194  	key uintptr
   195  }
   196  
   197  type funcval struct {
   198  	fn uintptr
   199  	// variable-size, fn-specific data here
   200  }
   201  
   202  type iface struct {
   203  	tab  *itab
   204  	data unsafe.Pointer
   205  }
   206  
   207  type eface struct {
   208  	_type *_type
   209  	data  unsafe.Pointer
   210  }
   211  
   212  func efaceOf(ep *interface{}) *eface {
   213  	return (*eface)(unsafe.Pointer(ep))
   214  }
   215  
   216  // The guintptr, muintptr, and puintptr are all used to bypass write barriers.
   217  // It is particularly important to avoid write barriers when the current P has
   218  // been released, because the GC thinks the world is stopped, and an
   219  // unexpected write barrier would not be synchronized with the GC,
   220  // which can lead to a half-executed write barrier that has marked the object
   221  // but not queued it. If the GC skips the object and completes before the
   222  // queuing can occur, it will incorrectly free the object.
   223  //
   224  // We tried using special assignment functions invoked only when not
   225  // holding a running P, but then some updates to a particular memory
   226  // word went through write barriers and some did not. This breaks the
   227  // write barrier shadow checking mode, and it is also scary: better to have
   228  // a word that is completely ignored by the GC than to have one for which
   229  // only a few updates are ignored.
   230  //
   231  // Gs and Ps are always reachable via true pointers in the
   232  // allgs and allp lists or (during allocation before they reach those lists)
   233  // from stack variables.
   234  //
   235  // Ms are always reachable via true pointers either from allm or
   236  // freem. Unlike Gs and Ps we do free Ms, so it's important that
   237  // nothing ever hold an muintptr across a safe point.
   238  
   239  // A guintptr holds a goroutine pointer, but typed as a uintptr
   240  // to bypass write barriers. It is used in the Gobuf goroutine state
   241  // and in scheduling lists that are manipulated without a P.
   242  //
   243  // The Gobuf.g goroutine pointer is almost always updated by assembly code.
   244  // In one of the few places it is updated by Go code - func save - it must be
   245  // treated as a uintptr to avoid a write barrier being emitted at a bad time.
   246  // Instead of figuring out how to emit the write barriers missing in the
   247  // assembly manipulation, we change the type of the field to uintptr,
   248  // so that it does not require write barriers at all.
   249  //
   250  // Goroutine structs are published in the allg list and never freed.
   251  // That will keep the goroutine structs from being collected.
   252  // There is never a time that Gobuf.g's contain the only references
   253  // to a goroutine: the publishing of the goroutine in allg comes first.
   254  // Goroutine pointers are also kept in non-GC-visible places like TLS,
   255  // so I can't see them ever moving. If we did want to start moving data
   256  // in the GC, we'd need to allocate the goroutine structs from an
   257  // alternate arena. Using guintptr doesn't make that problem any worse.
   258  type guintptr uintptr
   259  
   260  //go:nosplit
   261  func (gp guintptr) ptr() *g { return (*g)(unsafe.Pointer(gp)) }
   262  
   263  //go:nosplit
   264  func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) }
   265  
   266  //go:nosplit
   267  func (gp *guintptr) cas(old, new guintptr) bool {
   268  	return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
   269  }
   270  
   271  // setGNoWB performs *gp = new without a write barrier.
   272  // For times when it's impractical to use a guintptr.
   273  //go:nosplit
   274  //go:nowritebarrier
   275  func setGNoWB(gp **g, new *g) {
   276  	(*guintptr)(unsafe.Pointer(gp)).set(new)
   277  }
   278  
   279  type puintptr uintptr
   280  
   281  //go:nosplit
   282  func (pp puintptr) ptr() *p { return (*p)(unsafe.Pointer(pp)) }
   283  
   284  //go:nosplit
   285  func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }
   286  
   287  // muintptr is a *m that is not tracked by the garbage collector.
   288  //
   289  // Because we do free Ms, there are some additional constrains on
   290  // muintptrs:
   291  //
   292  // 1. Never hold an muintptr locally across a safe point.
   293  //
   294  // 2. Any muintptr in the heap must be owned by the M itself so it can
   295  //    ensure it is not in use when the last true *m is released.
   296  type muintptr uintptr
   297  
   298  //go:nosplit
   299  func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) }
   300  
   301  //go:nosplit
   302  func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }
   303  
   304  // setMNoWB performs *mp = new without a write barrier.
   305  // For times when it's impractical to use an muintptr.
   306  //go:nosplit
   307  //go:nowritebarrier
   308  func setMNoWB(mp **m, new *m) {
   309  	(*muintptr)(unsafe.Pointer(mp)).set(new)
   310  }
   311  
   312  type gobuf struct {
   313  	// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
   314  	//
   315  	// ctxt is unusual with respect to GC: it may be a
   316  	// heap-allocated funcval, so GC needs to track it, but it
   317  	// needs to be set and cleared from assembly, where it's
   318  	// difficult to have write barriers. However, ctxt is really a
   319  	// saved, live register, and we only ever exchange it between
   320  	// the real register and the gobuf. Hence, we treat it as a
   321  	// root during stack scanning, which means assembly that saves
   322  	// and restores it doesn't need write barriers. It's still
   323  	// typed as a pointer so that any other writes from Go get
   324  	// write barriers.
   325  	sp   uintptr
   326  	pc   uintptr
   327  	g    guintptr
   328  	ctxt unsafe.Pointer
   329  	ret  uintptr
   330  	lr   uintptr
   331  	bp   uintptr // for framepointer-enabled architectures
   332  }
   333  
   334  // sudog represents a g in a wait list, such as for sending/receiving
   335  // on a channel.
   336  //
   337  // sudog is necessary because the g ↔ synchronization object relation
   338  // is many-to-many. A g can be on many wait lists, so there may be
   339  // many sudogs for one g; and many gs may be waiting on the same
   340  // synchronization object, so there may be many sudogs for one object.
   341  //
   342  // sudogs are allocated from a special pool. Use acquireSudog and
   343  // releaseSudog to allocate and free them.
   344  type sudog struct {
   345  	// The following fields are protected by the hchan.lock of the
   346  	// channel this sudog is blocking on. shrinkstack depends on
   347  	// this for sudogs involved in channel ops.
   348  
   349  	g *g
   350  
   351  	next *sudog
   352  	prev *sudog
   353  	elem unsafe.Pointer // data element (may point to stack)
   354  
   355  	// The following fields are never accessed concurrently.
   356  	// For channels, waitlink is only accessed by g.
   357  	// For semaphores, all fields (including the ones above)
   358  	// are only accessed when holding a semaRoot lock.
   359  
   360  	acquiretime int64
   361  	releasetime int64
   362  	ticket      uint32
   363  
   364  	// isSelect indicates g is participating in a select, so
   365  	// g.selectDone must be CAS'd to win the wake-up race.
   366  	isSelect bool
   367  
   368  	// success indicates whether communication over channel c
   369  	// succeeded. It is true if the goroutine was awoken because a
   370  	// value was delivered over channel c, and false if awoken
   371  	// because c was closed.
   372  	success bool
   373  
   374  	parent   *sudog // semaRoot binary tree
   375  	waitlink *sudog // g.waiting list or semaRoot
   376  	waittail *sudog // semaRoot
   377  	c        *hchan // channel
   378  }
   379  
   380  type libcall struct {
   381  	fn   uintptr
   382  	n    uintptr // number of parameters
   383  	args uintptr // parameters
   384  	r1   uintptr // return values
   385  	r2   uintptr
   386  	err  uintptr // error number
   387  }
   388  
   389  // Stack describes a Go execution stack.
   390  // The bounds of the stack are exactly [lo, hi),
   391  // with no implicit data structures on either side.
   392  type stack struct {
   393  	lo uintptr
   394  	hi uintptr
   395  }
   396  
   397  // heldLockInfo gives info on a held lock and the rank of that lock
   398  type heldLockInfo struct {
   399  	lockAddr uintptr
   400  	rank     lockRank
   401  }
   402  
   403  type g struct {
   404  	// Stack parameters.
   405  	// stack describes the actual stack memory: [stack.lo, stack.hi).
   406  	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
   407  	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
   408  	// stackguard1 is the stack pointer compared in the C stack growth prologue.
   409  	// It is stack.lo+StackGuard on g0 and gsignal stacks.
   410  	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
   411  	stack       stack   // offset known to runtime/cgo
   412  	stackguard0 uintptr // offset known to liblink
   413  	stackguard1 uintptr // offset known to liblink
   414  
   415  	_panic    *_panic // innermost panic - offset known to liblink
   416  	_defer    *_defer // innermost defer
   417  	m         *m      // current m; offset known to arm liblink
   418  	sched     gobuf
   419  	syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc
   420  	syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc
   421  	stktopsp  uintptr // expected sp at top of stack, to check in traceback
   422  	// param is a generic pointer parameter field used to pass
   423  	// values in particular contexts where other storage for the
   424  	// parameter would be difficult to find. It is currently used
   425  	// in three ways:
   426  	// 1. When a channel operation wakes up a blocked goroutine, it sets param to
   427  	//    point to the sudog of the completed blocking operation.
   428  	// 2. By gcAssistAlloc1 to signal back to its caller that the goroutine completed
   429  	//    the GC cycle. It is unsafe to do so in any other way, because the goroutine's
   430  	//    stack may have moved in the meantime.
   431  	// 3. By debugCallWrap to pass parameters to a new goroutine because allocating a
   432  	//    closure in the runtime is forbidden.
   433  	param        unsafe.Pointer
   434  	atomicstatus uint32
   435  	stackLock    uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
   436  	goid         int64
   437  	schedlink    guintptr
   438  	waitsince    int64      // approx time when the g become blocked
   439  	waitreason   waitReason // if status==Gwaiting
   440  
   441  	preempt       bool // preemption signal, duplicates stackguard0 = stackpreempt
   442  	preemptStop   bool // transition to _Gpreempted on preemption; otherwise, just deschedule
   443  	preemptShrink bool // shrink stack at synchronous safe point
   444  
   445  	// asyncSafePoint is set if g is stopped at an asynchronous
   446  	// safe point. This means there are frames on the stack
   447  	// without precise pointer information.
   448  	asyncSafePoint bool
   449  
   450  	paniconfault bool // panic (instead of crash) on unexpected fault address
   451  	gcscandone   bool // g has scanned stack; protected by _Gscan bit in status
   452  	throwsplit   bool // must not split stack
   453  	// activeStackChans indicates that there are unlocked channels
   454  	// pointing into this goroutine's stack. If true, stack
   455  	// copying needs to acquire channel locks to protect these
   456  	// areas of the stack.
   457  	activeStackChans bool
   458  	// parkingOnChan indicates that the goroutine is about to
   459  	// park on a chansend or chanrecv. Used to signal an unsafe point
   460  	// for stack shrinking. It's a boolean value, but is updated atomically.
   461  	parkingOnChan uint8
   462  
   463  	raceignore     int8     // ignore race detection events
   464  	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine
   465  	tracking       bool     // whether we're tracking this G for sched latency statistics
   466  	trackingSeq    uint8    // used to decide whether to track this G
   467  	runnableStamp  int64    // timestamp of when the G last became runnable, only used when tracking
   468  	runnableTime   int64    // the amount of time spent runnable, cleared when running, only used when tracking
   469  	sysexitticks   int64    // cputicks when syscall has returned (for tracing)
   470  	traceseq       uint64   // trace event sequencer
   471  	tracelastp     puintptr // last P emitted an event for this goroutine
   472  	lockedm        muintptr
   473  	sig            uint32
   474  	writebuf       []byte
   475  	sigcode0       uintptr
   476  	sigcode1       uintptr
   477  	sigpc          uintptr
   478  	gopc           uintptr         // pc of go statement that created this goroutine
   479  	ancestors      *[]ancestorInfo // ancestor information goroutine(s) that created this goroutine (only used if debug.tracebackancestors)
   480  	startpc        uintptr         // pc of goroutine function
   481  	racectx        uintptr
   482  	waiting        *sudog         // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
   483  	cgoCtxt        []uintptr      // cgo traceback context
   484  	labels         unsafe.Pointer // profiler labels
   485  	timer          *timer         // cached timer for time.Sleep
   486  	selectDone     uint32         // are we participating in a select and did someone win the race?
   487  
   488  	// Per-G GC state
   489  
   490  	// gcAssistBytes is this G's GC assist credit in terms of
   491  	// bytes allocated. If this is positive, then the G has credit
   492  	// to allocate gcAssistBytes bytes without assisting. If this
   493  	// is negative, then the G must correct this by performing
   494  	// scan work. We track this in bytes to make it fast to update
   495  	// and check for debt in the malloc hot path. The assist ratio
   496  	// determines how this corresponds to scan work debt.
   497  	gcAssistBytes int64
   498  }
   499  
   500  // gTrackingPeriod is the number of transitions out of _Grunning between
   501  // latency tracking runs.
   502  const gTrackingPeriod = 8
   503  
   504  const (
   505  	// tlsSlots is the number of pointer-sized slots reserved for TLS on some platforms,
   506  	// like Windows.
   507  	tlsSlots = 6
   508  	tlsSize  = tlsSlots * sys.PtrSize
   509  )
   510  
   511  type m struct {
   512  	g0      *g     // goroutine with scheduling stack
   513  	morebuf gobuf  // gobuf arg to morestack
   514  	divmod  uint32 // div/mod denominator for arm - known to liblink
   515  
   516  	// Fields not known to debuggers.
   517  	procid        uint64            // for debuggers, but offset not hard-coded
   518  	gsignal       *g                // signal-handling g
   519  	goSigStack    gsignalStack      // Go-allocated signal handling stack
   520  	sigmask       sigset            // storage for saved signal mask
   521  	tls           [tlsSlots]uintptr // thread-local storage (for x86 extern register)
   522  	mstartfn      func()
   523  	curg          *g       // current running goroutine
   524  	caughtsig     guintptr // goroutine running during fatal signal
   525  	p             puintptr // attached p for executing go code (nil if not executing go code)
   526  	nextp         puintptr
   527  	oldp          puintptr // the p that was attached before executing a syscall
   528  	id            int64
   529  	mallocing     int32
   530  	throwing      int32
   531  	preemptoff    string // if != "", keep curg running on this m
   532  	locks         int32
   533  	dying         int32
   534  	profilehz     int32
   535  	spinning      bool // m is out of work and is actively looking for work
   536  	blocked       bool // m is blocked on a note
   537  	newSigstack   bool // minit on C thread called sigaltstack
   538  	printlock     int8
   539  	incgo         bool   // m is executing a cgo call
   540  	freeWait      uint32 // if == 0, safe to free g0 and delete m (atomic)
   541  	fastrand      [2]uint32
   542  	needextram    bool
   543  	traceback     uint8
   544  	ncgocall      uint64      // number of cgo calls in total
   545  	ncgo          int32       // number of cgo calls currently in progress
   546  	cgoCallersUse uint32      // if non-zero, cgoCallers in use temporarily
   547  	cgoCallers    *cgoCallers // cgo traceback if crashing in cgo call
   548  	doesPark      bool        // non-P running threads: sysmon and newmHandoff never use .park
   549  	park          note
   550  	alllink       *m // on allm
   551  	schedlink     muintptr
   552  	lockedg       guintptr
   553  	createstack   [32]uintptr // stack that created this thread.
   554  	lockedExt     uint32      // tracking for external LockOSThread
   555  	lockedInt     uint32      // tracking for internal lockOSThread
   556  	nextwaitm     muintptr    // next m waiting for lock
   557  	waitunlockf   func(*g, unsafe.Pointer) bool
   558  	waitlock      unsafe.Pointer
   559  	waittraceev   byte
   560  	waittraceskip int
   561  	startingtrace bool
   562  	syscalltick   uint32
   563  	freelink      *m // on sched.freem
   564  
   565  	// mFixup is used to synchronize OS related m state
   566  	// (credentials etc) use mutex to access. To avoid deadlocks
   567  	// an atomic.Load() of used being zero in mDoFixupFn()
   568  	// guarantees fn is nil.
   569  	mFixup struct {
   570  		lock mutex
   571  		used uint32
   572  		fn   func(bool) bool
   573  	}
   574  
   575  	// these are here because they are too large to be on the stack
   576  	// of low-level NOSPLIT functions.
   577  	libcall   libcall
   578  	libcallpc uintptr // for cpu profiler
   579  	libcallsp uintptr
   580  	libcallg  guintptr
   581  	syscall   libcall // stores syscall parameters on windows
   582  
   583  	vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call)
   584  	vdsoPC uintptr // PC for traceback while in VDSO call
   585  
   586  	// preemptGen counts the number of completed preemption
   587  	// signals. This is used to detect when a preemption is
   588  	// requested, but fails. Accessed atomically.
   589  	preemptGen uint32
   590  
   591  	// Whether this is a pending preemption signal on this M.
   592  	// Accessed atomically.
   593  	signalPending uint32
   594  
   595  	dlogPerM
   596  
   597  	mOS
   598  
   599  	// Up to 10 locks held by this m, maintained by the lock ranking code.
   600  	locksHeldLen int
   601  	locksHeld    [10]heldLockInfo
   602  }
   603  
   604  type p struct {
   605  	id          int32
   606  	status      uint32 // one of pidle/prunning/...
   607  	link        puintptr
   608  	schedtick   uint32     // incremented on every scheduler call
   609  	syscalltick uint32     // incremented on every system call
   610  	sysmontick  sysmontick // last tick observed by sysmon
   611  	m           muintptr   // back-link to associated m (nil if idle)
   612  	mcache      *mcache
   613  	pcache      pageCache
   614  	raceprocctx uintptr
   615  
   616  	deferpool    [5][]*_defer // pool of available defer structs of different sizes (see panic.go)
   617  	deferpoolbuf [5][32]*_defer
   618  
   619  	// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
   620  	goidcache    uint64
   621  	goidcacheend uint64
   622  
   623  	// Queue of runnable goroutines. Accessed without lock.
   624  	runqhead uint32
   625  	runqtail uint32
   626  	runq     [256]guintptr
   627  	// runnext, if non-nil, is a runnable G that was ready'd by
   628  	// the current G and should be run next instead of what's in
   629  	// runq if there's time remaining in the running G's time
   630  	// slice. It will inherit the time left in the current time
   631  	// slice. If a set of goroutines is locked in a
   632  	// communicate-and-wait pattern, this schedules that set as a
   633  	// unit and eliminates the (potentially large) scheduling
   634  	// latency that otherwise arises from adding the ready'd
   635  	// goroutines to the end of the run queue.
   636  	//
   637  	// Note that while other P's may atomically CAS this to zero,
   638  	// only the owner P can CAS it to a valid G.
   639  	runnext guintptr
   640  
   641  	// Available G's (status == Gdead)
   642  	gFree struct {
   643  		gList
   644  		n int32
   645  	}
   646  
   647  	sudogcache []*sudog
   648  	sudogbuf   [128]*sudog
   649  
   650  	// Cache of mspan objects from the heap.
   651  	mspancache struct {
   652  		// We need an explicit length here because this field is used
   653  		// in allocation codepaths where write barriers are not allowed,
   654  		// and eliminating the write barrier/keeping it eliminated from
   655  		// slice updates is tricky, moreso than just managing the length
   656  		// ourselves.
   657  		len int
   658  		buf [128]*mspan
   659  	}
   660  
   661  	tracebuf traceBufPtr
   662  
   663  	// traceSweep indicates the sweep events should be traced.
   664  	// This is used to defer the sweep start event until a span
   665  	// has actually been swept.
   666  	traceSweep bool
   667  	// traceSwept and traceReclaimed track the number of bytes
   668  	// swept and reclaimed by sweeping in the current sweep loop.
   669  	traceSwept, traceReclaimed uintptr
   670  
   671  	palloc persistentAlloc // per-P to avoid mutex
   672  
   673  	_ uint32 // Alignment for atomic fields below
   674  
   675  	// The when field of the first entry on the timer heap.
   676  	// This is updated using atomic functions.
   677  	// This is 0 if the timer heap is empty.
   678  	timer0When uint64
   679  
   680  	// The earliest known nextwhen field of a timer with
   681  	// timerModifiedEarlier status. Because the timer may have been
   682  	// modified again, there need not be any timer with this value.
   683  	// This is updated using atomic functions.
   684  	// This is 0 if there are no timerModifiedEarlier timers.
   685  	timerModifiedEarliest uint64
   686  
   687  	// Per-P GC state
   688  	gcAssistTime         int64 // Nanoseconds in assistAlloc
   689  	gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic)
   690  
   691  	// gcMarkWorkerMode is the mode for the next mark worker to run in.
   692  	// That is, this is used to communicate with the worker goroutine
   693  	// selected for immediate execution by
   694  	// gcController.findRunnableGCWorker. When scheduling other goroutines,
   695  	// this field must be set to gcMarkWorkerNotWorker.
   696  	gcMarkWorkerMode gcMarkWorkerMode
   697  	// gcMarkWorkerStartTime is the nanotime() at which the most recent
   698  	// mark worker started.
   699  	gcMarkWorkerStartTime int64
   700  
   701  	// gcw is this P's GC work buffer cache. The work buffer is
   702  	// filled by write barriers, drained by mutator assists, and
   703  	// disposed on certain GC state transitions.
   704  	gcw gcWork
   705  
   706  	// wbBuf is this P's GC write barrier buffer.
   707  	//
   708  	// TODO: Consider caching this in the running G.
   709  	wbBuf wbBuf
   710  
   711  	runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point
   712  
   713  	// statsSeq is a counter indicating whether this P is currently
   714  	// writing any stats. Its value is even when not, odd when it is.
   715  	statsSeq uint32
   716  
   717  	// Lock for timers. We normally access the timers while running
   718  	// on this P, but the scheduler can also do it from a different P.
   719  	timersLock mutex
   720  
   721  	// Actions to take at some time. This is used to implement the
   722  	// standard library's time package.
   723  	// Must hold timersLock to access.
   724  	timers []*timer
   725  
   726  	// Number of timers in P's heap.
   727  	// Modified using atomic instructions.
   728  	numTimers uint32
   729  
   730  	// Number of timerDeleted timers in P's heap.
   731  	// Modified using atomic instructions.
   732  	deletedTimers uint32
   733  
   734  	// Race context used while executing timer functions.
   735  	timerRaceCtx uintptr
   736  
   737  	// preempt is set to indicate that this P should be enter the
   738  	// scheduler ASAP (regardless of what G is running on it).
   739  	preempt bool
   740  
   741  	// Padding is no longer needed. False sharing is now not a worry because p is large enough
   742  	// that its size class is an integer multiple of the cache line size (for any of our architectures).
   743  }
   744  
   745  type schedt struct {
   746  	// accessed atomically. keep at top to ensure alignment on 32-bit systems.
   747  	goidgen   uint64
   748  	lastpoll  uint64 // time of last network poll, 0 if currently polling
   749  	pollUntil uint64 // time to which current poll is sleeping
   750  
   751  	lock mutex
   752  
   753  	// When increasing nmidle, nmidlelocked, nmsys, or nmfreed, be
   754  	// sure to call checkdead().
   755  
   756  	midle        muintptr // idle m's waiting for work
   757  	nmidle       int32    // number of idle m's waiting for work
   758  	nmidlelocked int32    // number of locked m's waiting for work
   759  	mnext        int64    // number of m's that have been created and next M ID
   760  	maxmcount    int32    // maximum number of m's allowed (or die)
   761  	nmsys        int32    // number of system m's not counted for deadlock
   762  	nmfreed      int64    // cumulative number of freed m's
   763  
   764  	ngsys uint32 // number of system goroutines; updated atomically
   765  
   766  	pidle      puintptr // idle p's
   767  	npidle     uint32
   768  	nmspinning uint32 // See "Worker thread parking/unparking" comment in proc.go.
   769  
   770  	// Global runnable queue.
   771  	runq     gQueue
   772  	runqsize int32
   773  
   774  	// disable controls selective disabling of the scheduler.
   775  	//
   776  	// Use schedEnableUser to control this.
   777  	//
   778  	// disable is protected by sched.lock.
   779  	disable struct {
   780  		// user disables scheduling of user goroutines.
   781  		user     bool
   782  		runnable gQueue // pending runnable Gs
   783  		n        int32  // length of runnable
   784  	}
   785  
   786  	// Global cache of dead G's.
   787  	gFree struct {
   788  		lock    mutex
   789  		stack   gList // Gs with stacks
   790  		noStack gList // Gs without stacks
   791  		n       int32
   792  	}
   793  
   794  	// Central cache of sudog structs.
   795  	sudoglock  mutex
   796  	sudogcache *sudog
   797  
   798  	// Central pool of available defer structs of different sizes.
   799  	deferlock mutex
   800  	deferpool [5]*_defer
   801  
   802  	// freem is the list of m's waiting to be freed when their
   803  	// m.exited is set. Linked through m.freelink.
   804  	freem *m
   805  
   806  	gcwaiting  uint32 // gc is waiting to run
   807  	stopwait   int32
   808  	stopnote   note
   809  	sysmonwait uint32
   810  	sysmonnote note
   811  
   812  	// While true, sysmon not ready for mFixup calls.
   813  	// Accessed atomically.
   814  	sysmonStarting uint32
   815  
   816  	// safepointFn should be called on each P at the next GC
   817  	// safepoint if p.runSafePointFn is set.
   818  	safePointFn   func(*p)
   819  	safePointWait int32
   820  	safePointNote note
   821  
   822  	profilehz int32 // cpu profiling rate
   823  
   824  	procresizetime int64 // nanotime() of last change to gomaxprocs
   825  	totaltime      int64 // ∫gomaxprocs dt up to procresizetime
   826  
   827  	// sysmonlock protects sysmon's actions on the runtime.
   828  	//
   829  	// Acquire and hold this mutex to block sysmon from interacting
   830  	// with the rest of the runtime.
   831  	sysmonlock mutex
   832  
   833  	_ uint32 // ensure timeToRun has 8-byte alignment
   834  
   835  	// timeToRun is a distribution of scheduling latencies, defined
   836  	// as the sum of time a G spends in the _Grunnable state before
   837  	// it transitions to _Grunning.
   838  	//
   839  	// timeToRun is protected by sched.lock.
   840  	timeToRun timeHistogram
   841  }
   842  
   843  // Values for the flags field of a sigTabT.
   844  const (
   845  	_SigNotify   = 1 << iota // let signal.Notify have signal, even if from kernel
   846  	_SigKill                 // if signal.Notify doesn't take it, exit quietly
   847  	_SigThrow                // if signal.Notify doesn't take it, exit loudly
   848  	_SigPanic                // if the signal is from the kernel, panic
   849  	_SigDefault              // if the signal isn't explicitly requested, don't monitor it
   850  	_SigGoExit               // cause all runtime procs to exit (only used on Plan 9).
   851  	_SigSetStack             // add SA_ONSTACK to libc handler
   852  	_SigUnblock              // always unblock; see blockableSig
   853  	_SigIgn                  // _SIG_DFL action is to ignore the signal
   854  )
   855  
   856  // Layout of in-memory per-function information prepared by linker
   857  // See https://golang.org/s/go12symtab.
   858  // Keep in sync with linker (../cmd/link/internal/ld/pcln.go:/pclntab)
   859  // and with package debug/gosym and with symtab.go in package runtime.
   860  type _func struct {
   861  	entry   uintptr // start pc
   862  	nameoff int32   // function name
   863  
   864  	args        int32  // in/out args size
   865  	deferreturn uint32 // offset of start of a deferreturn call instruction from entry, if any.
   866  
   867  	pcsp      uint32
   868  	pcfile    uint32
   869  	pcln      uint32
   870  	npcdata   uint32
   871  	cuOffset  uint32 // runtime.cutab offset of this function's CU
   872  	funcID    funcID // set for certain special runtime functions
   873  	flag      funcFlag
   874  	_         [1]byte // pad
   875  	nfuncdata uint8   // must be last, must end on a uint32-aligned boundary
   876  }
   877  
   878  // Pseudo-Func that is returned for PCs that occur in inlined code.
   879  // A *Func can be either a *_func or a *funcinl, and they are distinguished
   880  // by the first uintptr.
   881  type funcinl struct {
   882  	zero  uintptr // set to 0 to distinguish from _func
   883  	entry uintptr // entry of the real (the "outermost") frame.
   884  	name  string
   885  	file  string
   886  	line  int
   887  }
   888  
   889  // layout of Itab known to compilers
   890  // allocated in non-garbage-collected memory
   891  // Needs to be in sync with
   892  // ../cmd/compile/internal/reflectdata/reflect.go:/^func.WriteTabs.
   893  type itab struct {
   894  	inter *interfacetype
   895  	_type *_type
   896  	hash  uint32 // copy of _type.hash. Used for type switches.
   897  	_     [4]byte
   898  	fun   [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
   899  }
   900  
   901  // Lock-free stack node.
   902  // Also known to export_test.go.
   903  type lfnode struct {
   904  	next    uint64
   905  	pushcnt uintptr
   906  }
   907  
   908  type forcegcstate struct {
   909  	lock mutex
   910  	g    *g
   911  	idle uint32
   912  }
   913  
   914  // extendRandom extends the random numbers in r[:n] to the whole slice r.
   915  // Treats n<0 as n==0.
   916  func extendRandom(r []byte, n int) {
   917  	if n < 0 {
   918  		n = 0
   919  	}
   920  	for n < len(r) {
   921  		// Extend random bits using hash function & time seed
   922  		w := n
   923  		if w > 16 {
   924  			w = 16
   925  		}
   926  		h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
   927  		for i := 0; i < sys.PtrSize && n < len(r); i++ {
   928  			r[n] = byte(h)
   929  			n++
   930  			h >>= 8
   931  		}
   932  	}
   933  }
   934  
   935  // A _defer holds an entry on the list of deferred calls.
   936  // If you add a field here, add code to clear it in freedefer and deferProcStack
   937  // This struct must match the code in cmd/compile/internal/reflectdata/reflect.go:deferstruct
   938  // and cmd/compile/internal/gc/ssa.go:(*state).call.
   939  // Some defers will be allocated on the stack and some on the heap.
   940  // All defers are logically part of the stack, so write barriers to
   941  // initialize them are not required. All defers must be manually scanned,
   942  // and for heap defers, marked.
   943  type _defer struct {
   944  	siz     int32 // includes both arguments and results
   945  	started bool
   946  	heap    bool
   947  	// openDefer indicates that this _defer is for a frame with open-coded
   948  	// defers. We have only one defer record for the entire frame (which may
   949  	// currently have 0, 1, or more defers active).
   950  	openDefer bool
   951  	sp        uintptr  // sp at time of defer
   952  	pc        uintptr  // pc at time of defer
   953  	fn        *funcval // can be nil for open-coded defers
   954  	_panic    *_panic  // panic that is running defer
   955  	link      *_defer
   956  
   957  	// If openDefer is true, the fields below record values about the stack
   958  	// frame and associated function that has the open-coded defer(s). sp
   959  	// above will be the sp for the frame, and pc will be address of the
   960  	// deferreturn call in the function.
   961  	fd   unsafe.Pointer // funcdata for the function associated with the frame
   962  	varp uintptr        // value of varp for the stack frame
   963  	// framepc is the current pc associated with the stack frame. Together,
   964  	// with sp above (which is the sp associated with the stack frame),
   965  	// framepc/sp can be used as pc/sp pair to continue a stack trace via
   966  	// gentraceback().
   967  	framepc uintptr
   968  }
   969  
   970  // A _panic holds information about an active panic.
   971  //
   972  // A _panic value must only ever live on the stack.
   973  //
   974  // The argp and link fields are stack pointers, but don't need special
   975  // handling during stack growth: because they are pointer-typed and
   976  // _panic values only live on the stack, regular stack pointer
   977  // adjustment takes care of them.
   978  type _panic struct {
   979  	argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
   980  	arg       interface{}    // argument to panic
   981  	link      *_panic        // link to earlier panic
   982  	pc        uintptr        // where to return to in runtime if this panic is bypassed
   983  	sp        unsafe.Pointer // where to return to in runtime if this panic is bypassed
   984  	recovered bool           // whether this panic is over
   985  	aborted   bool           // the panic was aborted
   986  	goexit    bool
   987  }
   988  
   989  // stack traces
   990  type stkframe struct {
   991  	fn       funcInfo   // function being run
   992  	pc       uintptr    // program counter within fn
   993  	continpc uintptr    // program counter where execution can continue, or 0 if not
   994  	lr       uintptr    // program counter at caller aka link register
   995  	sp       uintptr    // stack pointer at pc
   996  	fp       uintptr    // stack pointer at caller aka frame pointer
   997  	varp     uintptr    // top of local variables
   998  	argp     uintptr    // pointer to function arguments
   999  	arglen   uintptr    // number of bytes at argp
  1000  	argmap   *bitvector // force use of this argmap
  1001  }
  1002  
  1003  // ancestorInfo records details of where a goroutine was started.
  1004  type ancestorInfo struct {
  1005  	pcs  []uintptr // pcs from the stack of this goroutine
  1006  	goid int64     // goroutine id of this goroutine; original goroutine possibly dead
  1007  	gopc uintptr   // pc of go statement that created this goroutine
  1008  }
  1009  
  1010  const (
  1011  	_TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
  1012  	_TraceTrap                      // the initial PC, SP are from a trap, not a return PC from a call
  1013  	_TraceJumpStack                 // if traceback is on a systemstack, resume trace at g that called into it
  1014  )
  1015  
  1016  // The maximum number of frames we print for a traceback
  1017  const _TracebackMaxFrames = 100
  1018  
  1019  // A waitReason explains why a goroutine has been stopped.
  1020  // See gopark. Do not re-use waitReasons, add new ones.
  1021  type waitReason uint8
  1022  
  1023  const (
  1024  	waitReasonZero                  waitReason = iota // ""
  1025  	waitReasonGCAssistMarking                         // "GC assist marking"
  1026  	waitReasonIOWait                                  // "IO wait"
  1027  	waitReasonChanReceiveNilChan                      // "chan receive (nil chan)"
  1028  	waitReasonChanSendNilChan                         // "chan send (nil chan)"
  1029  	waitReasonDumpingHeap                             // "dumping heap"
  1030  	waitReasonGarbageCollection                       // "garbage collection"
  1031  	waitReasonGarbageCollectionScan                   // "garbage collection scan"
  1032  	waitReasonPanicWait                               // "panicwait"
  1033  	waitReasonSelect                                  // "select"
  1034  	waitReasonSelectNoCases                           // "select (no cases)"
  1035  	waitReasonGCAssistWait                            // "GC assist wait"
  1036  	waitReasonGCSweepWait                             // "GC sweep wait"
  1037  	waitReasonGCScavengeWait                          // "GC scavenge wait"
  1038  	waitReasonChanReceive                             // "chan receive"
  1039  	waitReasonChanSend                                // "chan send"
  1040  	waitReasonFinalizerWait                           // "finalizer wait"
  1041  	waitReasonForceGCIdle                             // "force gc (idle)"
  1042  	waitReasonSemacquire                              // "semacquire"
  1043  	waitReasonSleep                                   // "sleep"
  1044  	waitReasonSyncCondWait                            // "sync.Cond.Wait"
  1045  	waitReasonTimerGoroutineIdle                      // "timer goroutine (idle)"
  1046  	waitReasonTraceReaderBlocked                      // "trace reader (blocked)"
  1047  	waitReasonWaitForGCCycle                          // "wait for GC cycle"
  1048  	waitReasonGCWorkerIdle                            // "GC worker (idle)"
  1049  	waitReasonPreempted                               // "preempted"
  1050  	waitReasonDebugCall                               // "debug call"
  1051  )
  1052  
  1053  var waitReasonStrings = [...]string{
  1054  	waitReasonZero:                  "",
  1055  	waitReasonGCAssistMarking:       "GC assist marking",
  1056  	waitReasonIOWait:                "IO wait",
  1057  	waitReasonChanReceiveNilChan:    "chan receive (nil chan)",
  1058  	waitReasonChanSendNilChan:       "chan send (nil chan)",
  1059  	waitReasonDumpingHeap:           "dumping heap",
  1060  	waitReasonGarbageCollection:     "garbage collection",
  1061  	waitReasonGarbageCollectionScan: "garbage collection scan",
  1062  	waitReasonPanicWait:             "panicwait",
  1063  	waitReasonSelect:                "select",
  1064  	waitReasonSelectNoCases:         "select (no cases)",
  1065  	waitReasonGCAssistWait:          "GC assist wait",
  1066  	waitReasonGCSweepWait:           "GC sweep wait",
  1067  	waitReasonGCScavengeWait:        "GC scavenge wait",
  1068  	waitReasonChanReceive:           "chan receive",
  1069  	waitReasonChanSend:              "chan send",
  1070  	waitReasonFinalizerWait:         "finalizer wait",
  1071  	waitReasonForceGCIdle:           "force gc (idle)",
  1072  	waitReasonSemacquire:            "semacquire",
  1073  	waitReasonSleep:                 "sleep",
  1074  	waitReasonSyncCondWait:          "sync.Cond.Wait",
  1075  	waitReasonTimerGoroutineIdle:    "timer goroutine (idle)",
  1076  	waitReasonTraceReaderBlocked:    "trace reader (blocked)",
  1077  	waitReasonWaitForGCCycle:        "wait for GC cycle",
  1078  	waitReasonGCWorkerIdle:          "GC worker (idle)",
  1079  	waitReasonPreempted:             "preempted",
  1080  	waitReasonDebugCall:             "debug call",
  1081  }
  1082  
  1083  func (w waitReason) String() string {
  1084  	if w < 0 || w >= waitReason(len(waitReasonStrings)) {
  1085  		return "unknown wait reason"
  1086  	}
  1087  	return waitReasonStrings[w]
  1088  }
  1089  
  1090  var (
  1091  	allm       *m
  1092  	gomaxprocs int32
  1093  	ncpu       int32
  1094  	forcegc    forcegcstate
  1095  	sched      schedt
  1096  	newprocs   int32
  1097  
  1098  	// allpLock protects P-less reads and size changes of allp, idlepMask,
  1099  	// and timerpMask, and all writes to allp.
  1100  	allpLock mutex
  1101  	// len(allp) == gomaxprocs; may change at safe points, otherwise
  1102  	// immutable.
  1103  	allp []*p
  1104  	// Bitmask of Ps in _Pidle list, one bit per P. Reads and writes must
  1105  	// be atomic. Length may change at safe points.
  1106  	//
  1107  	// Each P must update only its own bit. In order to maintain
  1108  	// consistency, a P going idle must the idle mask simultaneously with
  1109  	// updates to the idle P list under the sched.lock, otherwise a racing
  1110  	// pidleget may clear the mask before pidleput sets the mask,
  1111  	// corrupting the bitmap.
  1112  	//
  1113  	// N.B., procresize takes ownership of all Ps in stopTheWorldWithSema.
  1114  	idlepMask pMask
  1115  	// Bitmask of Ps that may have a timer, one bit per P. Reads and writes
  1116  	// must be atomic. Length may change at safe points.
  1117  	timerpMask pMask
  1118  
  1119  	// Pool of GC parked background workers. Entries are type
  1120  	// *gcBgMarkWorkerNode.
  1121  	gcBgMarkWorkerPool lfstack
  1122  
  1123  	// Total number of gcBgMarkWorker goroutines. Protected by worldsema.
  1124  	gcBgMarkWorkerCount int32
  1125  
  1126  	// Information about what cpu features are available.
  1127  	// Packages outside the runtime should not use these
  1128  	// as they are not an external api.
  1129  	// Set on startup in asm_{386,amd64}.s
  1130  	processorVersionInfo uint32
  1131  	isIntel              bool
  1132  	lfenceBeforeRdtsc    bool
  1133  
  1134  	goarm uint8 // set by cmd/link on arm systems
  1135  )
  1136  
  1137  // Set by the linker so the runtime can determine the buildmode.
  1138  var (
  1139  	islibrary bool // -buildmode=c-shared
  1140  	isarchive bool // -buildmode=c-archive
  1141  )
  1142  
  1143  // Must agree with internal/buildcfg.Experiment.FramePointer.
  1144  const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64"
  1145  

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