Source file src/runtime/stack.go

     1  // Copyright 2013 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  	"internal/abi"
     9  	"internal/cpu"
    10  	"internal/goarch"
    11  	"internal/goexperiment"
    12  	"internal/goos"
    13  	"internal/runtime/atomic"
    14  	"internal/runtime/gc"
    15  	"internal/runtime/sys"
    16  	"math/bits"
    17  	"unsafe"
    18  )
    19  
    20  /*
    21  Stack layout parameters.
    22  Included both by runtime (compiled via 6c) and linkers (compiled via gcc).
    23  
    24  The per-goroutine g->stackguard is set to point StackGuard bytes
    25  above the bottom of the stack.  Each function compares its stack
    26  pointer against g->stackguard to check for overflow.  To cut one
    27  instruction from the check sequence for functions with tiny frames,
    28  the stack is allowed to protrude StackSmall bytes below the stack
    29  guard.  Functions with large frames don't bother with the check and
    30  always call morestack.  The sequences are (for amd64, others are
    31  similar):
    32  
    33  	guard = g->stackguard
    34  	frame = function's stack frame size
    35  	argsize = size of function arguments (call + return)
    36  
    37  	stack frame size <= StackSmall:
    38  		CMPQ guard, SP
    39  		JHI 3(PC)
    40  		MOVQ m->morearg, $(argsize << 32)
    41  		CALL morestack(SB)
    42  
    43  	stack frame size > StackSmall but < StackBig
    44  		LEAQ (frame-StackSmall)(SP), R0
    45  		CMPQ guard, R0
    46  		JHI 3(PC)
    47  		MOVQ m->morearg, $(argsize << 32)
    48  		CALL morestack(SB)
    49  
    50  	stack frame size >= StackBig:
    51  		MOVQ m->morearg, $((argsize << 32) | frame)
    52  		CALL morestack(SB)
    53  
    54  The bottom StackGuard - StackSmall bytes are important: there has
    55  to be enough room to execute functions that refuse to check for
    56  stack overflow, either because they need to be adjacent to the
    57  actual caller's frame (deferproc) or because they handle the imminent
    58  stack overflow (morestack).
    59  
    60  For example, deferproc might call malloc, which does one of the
    61  above checks (without allocating a full frame), which might trigger
    62  a call to morestack.  This sequence needs to fit in the bottom
    63  section of the stack.  On amd64, morestack's frame is 40 bytes, and
    64  deferproc's frame is 56 bytes.  That fits well within the
    65  StackGuard - StackSmall bytes at the bottom.
    66  The linkers explore all possible call traces involving non-splitting
    67  functions to make sure that this limit cannot be violated.
    68  */
    69  
    70  const (
    71  	// stackSystem is a number of additional bytes to add
    72  	// to each stack below the usual guard area for OS-specific
    73  	// purposes like signal handling. Used on Windows, Plan 9,
    74  	// and iOS because they do not use a separate stack.
    75  	stackSystem = goos.IsWindows*4096 + goos.IsPlan9*512 + goos.IsIos*goarch.IsArm64*1024
    76  
    77  	// The minimum size of stack used by Go code
    78  	stackMin = 2048
    79  
    80  	// The minimum stack size to allocate.
    81  	// The hackery here rounds fixedStack0 up to a power of 2.
    82  	fixedStack0 = stackMin + stackSystem
    83  	fixedStack1 = fixedStack0 - 1
    84  	fixedStack2 = fixedStack1 | (fixedStack1 >> 1)
    85  	fixedStack3 = fixedStack2 | (fixedStack2 >> 2)
    86  	fixedStack4 = fixedStack3 | (fixedStack3 >> 4)
    87  	fixedStack5 = fixedStack4 | (fixedStack4 >> 8)
    88  	fixedStack6 = fixedStack5 | (fixedStack5 >> 16)
    89  	fixedStack  = fixedStack6 + 1
    90  
    91  	// stackNosplit is the maximum number of bytes that a chain of NOSPLIT
    92  	// functions can use.
    93  	// This arithmetic must match that in cmd/internal/objabi/stack.go:StackNosplit.
    94  	stackNosplit = abi.StackNosplitBase * sys.StackGuardMultiplier
    95  
    96  	// The stack guard is a pointer this many bytes above the
    97  	// bottom of the stack.
    98  	//
    99  	// The guard leaves enough room for a stackNosplit chain of NOSPLIT calls
   100  	// plus one stackSmall frame plus stackSystem bytes for the OS.
   101  	// This arithmetic must match that in cmd/internal/objabi/stack.go:StackLimit.
   102  	stackGuard = stackNosplit + stackSystem + abi.StackSmall
   103  )
   104  
   105  const (
   106  	// stackDebug == 0: no logging
   107  	//            == 1: logging of per-stack operations
   108  	//            == 2: logging of per-frame operations
   109  	//            == 3: logging of per-word updates
   110  	//            == 4: logging of per-word reads
   111  	stackDebug       = 0
   112  	stackFromSystem  = 0 // allocate stacks from system memory instead of the heap
   113  	stackFaultOnFree = 0 // old stacks are mapped noaccess to detect use after free
   114  	stackNoCache     = 0 // disable per-P small stack caches
   115  
   116  	// check the BP links during traceback.
   117  	debugCheckBP = false
   118  )
   119  
   120  var (
   121  	stackPoisonCopy = 0 // fill stack that should not be accessed with garbage, to detect bad dereferences during copy
   122  )
   123  
   124  const (
   125  	uintptrMask = 1<<(8*goarch.PtrSize) - 1
   126  
   127  	// The values below can be stored to g.stackguard0 to force
   128  	// the next stack check to fail.
   129  	// These are all larger than any real SP.
   130  
   131  	// Goroutine preemption request.
   132  	// 0xfffffade in hex.
   133  	stackPreempt = uintptrMask & -1314
   134  
   135  	// Thread is forking. Causes a split stack check failure.
   136  	// 0xfffffb2e in hex.
   137  	stackFork = uintptrMask & -1234
   138  
   139  	// Force a stack movement. Used for debugging.
   140  	// 0xfffffeed in hex.
   141  	stackForceMove = uintptrMask & -275
   142  
   143  	// stackPoisonMin is the lowest allowed stack poison value.
   144  	stackPoisonMin = uintptrMask & -4096
   145  )
   146  
   147  // Global pool of spans that have free stacks.
   148  // Stacks are assigned an order according to size.
   149  //
   150  //	order = log_2(size/FixedStack)
   151  //
   152  // There is a free list for each order.
   153  var stackpool [_NumStackOrders]struct {
   154  	item stackpoolItem
   155  	_    [(cpu.CacheLinePadSize - unsafe.Sizeof(stackpoolItem{})%cpu.CacheLinePadSize) % cpu.CacheLinePadSize]byte
   156  }
   157  
   158  type stackpoolItem struct {
   159  	_    sys.NotInHeap
   160  	mu   mutex
   161  	span mSpanList
   162  }
   163  
   164  // Global pool of large stack spans.
   165  var stackLarge struct {
   166  	lock mutex
   167  	free [heapAddrBits - gc.PageShift]mSpanList // free lists by log_2(s.npages)
   168  }
   169  
   170  func stackinit() {
   171  	if _StackCacheSize&pageMask != 0 {
   172  		throw("cache size must be a multiple of page size")
   173  	}
   174  	for i := range stackpool {
   175  		stackpool[i].item.span.init()
   176  		lockInit(&stackpool[i].item.mu, lockRankStackpool)
   177  	}
   178  	for i := range stackLarge.free {
   179  		stackLarge.free[i].init()
   180  		lockInit(&stackLarge.lock, lockRankStackLarge)
   181  	}
   182  }
   183  
   184  // stacklog2 returns ⌊log_2(n)⌋.
   185  func stacklog2(n uintptr) int {
   186  	if n == 0 {
   187  		return 0
   188  	}
   189  	return bits.Len64(uint64(n))
   190  }
   191  
   192  // Allocates a stack from the free pool. Must be called with
   193  // stackpool[order].item.mu held.
   194  func stackpoolalloc(order uint8) gclinkptr {
   195  	list := &stackpool[order].item.span
   196  	s := list.first
   197  	lockWithRankMayAcquire(&mheap_.lock, lockRankMheap)
   198  	if s == nil {
   199  		// no free stacks. Allocate another span worth.
   200  		s = mheap_.allocManual(_StackCacheSize>>gc.PageShift, spanAllocStack)
   201  		if s == nil {
   202  			throw("out of memory")
   203  		}
   204  		if s.allocCount != 0 {
   205  			throw("bad allocCount")
   206  		}
   207  		if s.manualFreeList.ptr() != nil {
   208  			throw("bad manualFreeList")
   209  		}
   210  		osStackAlloc(s)
   211  		s.elemsize = fixedStack << order
   212  		for i := uintptr(0); i < _StackCacheSize; i += s.elemsize {
   213  			x := gclinkptr(s.base() + i)
   214  			if valgrindenabled {
   215  				// The address of x.ptr() becomes the base of stacks. We need to
   216  				// mark it allocated here and in stackfree and stackpoolfree, and free'd in
   217  				// stackalloc in order to avoid overlapping allocations and
   218  				// uninitialized memory errors in valgrind.
   219  				valgrindMalloc(unsafe.Pointer(x.ptr()), unsafe.Sizeof(x.ptr()))
   220  			}
   221  			x.ptr().next = s.manualFreeList
   222  			s.manualFreeList = x
   223  		}
   224  		list.insert(s)
   225  	}
   226  	x := s.manualFreeList
   227  	if x.ptr() == nil {
   228  		throw("span has no free stacks")
   229  	}
   230  	s.manualFreeList = x.ptr().next
   231  	s.allocCount++
   232  	if s.manualFreeList.ptr() == nil {
   233  		// all stacks in s are allocated.
   234  		list.remove(s)
   235  	}
   236  	return x
   237  }
   238  
   239  // Adds stack x to the free pool. Must be called with stackpool[order].item.mu held.
   240  func stackpoolfree(x gclinkptr, order uint8) {
   241  	s := spanOfUnchecked(uintptr(x))
   242  	if s.state.get() != mSpanManual {
   243  		throw("freeing stack not in a stack span")
   244  	}
   245  	if s.manualFreeList.ptr() == nil {
   246  		// s will now have a free stack
   247  		stackpool[order].item.span.insert(s)
   248  	}
   249  	x.ptr().next = s.manualFreeList
   250  	s.manualFreeList = x
   251  	s.allocCount--
   252  	if gcphase == _GCoff && s.allocCount == 0 {
   253  		// Span is completely free. Return it to the heap
   254  		// immediately if we're sweeping.
   255  		//
   256  		// If GC is active, we delay the free until the end of
   257  		// GC to avoid the following type of situation:
   258  		//
   259  		// 1) GC starts, scans a SudoG but does not yet mark the SudoG.elem pointer
   260  		// 2) The stack that pointer points to is copied
   261  		// 3) The old stack is freed
   262  		// 4) The containing span is marked free
   263  		// 5) GC attempts to mark the SudoG.elem pointer. The
   264  		//    marking fails because the pointer looks like a
   265  		//    pointer into a free span.
   266  		//
   267  		// By not freeing, we prevent step #4 until GC is done.
   268  		stackpool[order].item.span.remove(s)
   269  		s.manualFreeList = 0
   270  		osStackFree(s)
   271  		mheap_.freeManual(s, spanAllocStack)
   272  	}
   273  }
   274  
   275  // stackcacherefill/stackcacherelease implement a global pool of stack segments.
   276  // The pool is required to prevent unlimited growth of per-thread caches.
   277  //
   278  //go:systemstack
   279  func stackcacherefill(c *mcache, order uint8) {
   280  	if stackDebug >= 1 {
   281  		print("stackcacherefill order=", order, "\n")
   282  	}
   283  
   284  	// Grab some stacks from the global cache.
   285  	// Grab half of the allowed capacity (to prevent thrashing).
   286  	var list gclinkptr
   287  	var size uintptr
   288  	lock(&stackpool[order].item.mu)
   289  	for size < _StackCacheSize/2 {
   290  		x := stackpoolalloc(order)
   291  		x.ptr().next = list
   292  		list = x
   293  		size += fixedStack << order
   294  	}
   295  	unlock(&stackpool[order].item.mu)
   296  	c.stackcache[order].list = list
   297  	c.stackcache[order].size = size
   298  }
   299  
   300  //go:systemstack
   301  func stackcacherelease(c *mcache, order uint8) {
   302  	if stackDebug >= 1 {
   303  		print("stackcacherelease order=", order, "\n")
   304  	}
   305  	x := c.stackcache[order].list
   306  	size := c.stackcache[order].size
   307  	lock(&stackpool[order].item.mu)
   308  	for size > _StackCacheSize/2 {
   309  		y := x.ptr().next
   310  		stackpoolfree(x, order)
   311  		x = y
   312  		size -= fixedStack << order
   313  	}
   314  	unlock(&stackpool[order].item.mu)
   315  	c.stackcache[order].list = x
   316  	c.stackcache[order].size = size
   317  }
   318  
   319  //go:systemstack
   320  func stackcache_clear(c *mcache) {
   321  	if stackDebug >= 1 {
   322  		print("stackcache clear\n")
   323  	}
   324  	for order := uint8(0); order < _NumStackOrders; order++ {
   325  		lock(&stackpool[order].item.mu)
   326  		x := c.stackcache[order].list
   327  		for x.ptr() != nil {
   328  			y := x.ptr().next
   329  			stackpoolfree(x, order)
   330  			x = y
   331  		}
   332  		c.stackcache[order].list = 0
   333  		c.stackcache[order].size = 0
   334  		unlock(&stackpool[order].item.mu)
   335  	}
   336  }
   337  
   338  // stackalloc allocates an n byte stack.
   339  //
   340  // stackalloc must run on the system stack because it uses per-P
   341  // resources and must not split the stack.
   342  //
   343  //go:systemstack
   344  func stackalloc(n uint32) stack {
   345  	// Stackalloc must be called on scheduler stack, so that we
   346  	// never try to grow the stack during the code that stackalloc runs.
   347  	// Doing so would cause a deadlock (issue 1547).
   348  	thisg := getg()
   349  	if thisg != thisg.m.g0 {
   350  		throw("stackalloc not on scheduler stack")
   351  	}
   352  	if n&(n-1) != 0 {
   353  		throw("stack size not a power of 2")
   354  	}
   355  	if stackDebug >= 1 {
   356  		print("stackalloc ", n, "\n")
   357  	}
   358  
   359  	if debug.efence != 0 || stackFromSystem != 0 {
   360  		n = uint32(alignUp(uintptr(n), physPageSize))
   361  		v := sysAlloc(uintptr(n), &memstats.stacks_sys, "goroutine stack (system)")
   362  		if v == nil {
   363  			throw("out of memory (stackalloc)")
   364  		}
   365  		return stack{uintptr(v), uintptr(v) + uintptr(n)}
   366  	}
   367  
   368  	// Small stacks are allocated with a fixed-size free-list allocator.
   369  	// If we need a stack of a bigger size, we fall back on allocating
   370  	// a dedicated span.
   371  	var v unsafe.Pointer
   372  	if n < fixedStack<<_NumStackOrders && n < _StackCacheSize {
   373  		order := uint8(0)
   374  		n2 := n
   375  		for n2 > fixedStack {
   376  			order++
   377  			n2 >>= 1
   378  		}
   379  		var x gclinkptr
   380  		if stackNoCache != 0 || thisg.m.p == 0 || thisg.m.preemptoff != "" {
   381  			// thisg.m.p == 0 can happen in the guts of exitsyscall
   382  			// or procresize. Just get a stack from the global pool.
   383  			// Also don't touch stackcache during gc
   384  			// as it's flushed concurrently.
   385  			lock(&stackpool[order].item.mu)
   386  			x = stackpoolalloc(order)
   387  			unlock(&stackpool[order].item.mu)
   388  		} else {
   389  			c := thisg.m.p.ptr().mcache
   390  			x = c.stackcache[order].list
   391  			if x.ptr() == nil {
   392  				stackcacherefill(c, order)
   393  				x = c.stackcache[order].list
   394  			}
   395  			c.stackcache[order].list = x.ptr().next
   396  			c.stackcache[order].size -= uintptr(n)
   397  		}
   398  		if valgrindenabled {
   399  			// We're about to allocate the stack region starting at x.ptr().
   400  			// To prevent valgrind from complaining about overlapping allocations,
   401  			// we need to mark the (previously allocated) memory as free'd.
   402  			valgrindFree(unsafe.Pointer(x.ptr()))
   403  		}
   404  		v = unsafe.Pointer(x)
   405  	} else {
   406  		var s *mspan
   407  		npage := uintptr(n) >> gc.PageShift
   408  		log2npage := stacklog2(npage)
   409  
   410  		// Try to get a stack from the large stack cache.
   411  		lock(&stackLarge.lock)
   412  		if !stackLarge.free[log2npage].isEmpty() {
   413  			s = stackLarge.free[log2npage].first
   414  			stackLarge.free[log2npage].remove(s)
   415  		}
   416  		unlock(&stackLarge.lock)
   417  
   418  		lockWithRankMayAcquire(&mheap_.lock, lockRankMheap)
   419  
   420  		if s == nil {
   421  			// Allocate a new stack from the heap.
   422  			s = mheap_.allocManual(npage, spanAllocStack)
   423  			if s == nil {
   424  				throw("out of memory")
   425  			}
   426  			osStackAlloc(s)
   427  			s.elemsize = uintptr(n)
   428  		}
   429  		v = unsafe.Pointer(s.base())
   430  	}
   431  
   432  	if traceAllocFreeEnabled() {
   433  		trace := traceAcquire()
   434  		if trace.ok() {
   435  			trace.GoroutineStackAlloc(uintptr(v), uintptr(n))
   436  			traceRelease(trace)
   437  		}
   438  	}
   439  	if raceenabled {
   440  		racemalloc(v, uintptr(n))
   441  	}
   442  	if msanenabled {
   443  		msanmalloc(v, uintptr(n))
   444  	}
   445  	if asanenabled {
   446  		asanunpoison(v, uintptr(n))
   447  	}
   448  	if valgrindenabled {
   449  		valgrindMalloc(v, uintptr(n))
   450  	}
   451  	if stackDebug >= 1 {
   452  		print("  allocated ", v, "\n")
   453  	}
   454  	return stack{uintptr(v), uintptr(v) + uintptr(n)}
   455  }
   456  
   457  // stackfree frees an n byte stack allocation at stk.
   458  //
   459  // stackfree must run on the system stack because it uses per-P
   460  // resources and must not split the stack.
   461  //
   462  //go:systemstack
   463  func stackfree(stk stack) {
   464  	gp := getg()
   465  	v := unsafe.Pointer(stk.lo)
   466  	n := stk.hi - stk.lo
   467  	if n&(n-1) != 0 {
   468  		throw("stack not a power of 2")
   469  	}
   470  	if stk.lo+n < stk.hi {
   471  		throw("bad stack size")
   472  	}
   473  	if stackDebug >= 1 {
   474  		println("stackfree", v, n)
   475  		memclrNoHeapPointers(v, n) // for testing, clobber stack data
   476  	}
   477  	if debug.efence != 0 || stackFromSystem != 0 {
   478  		if debug.efence != 0 || stackFaultOnFree != 0 {
   479  			sysFault(v, n)
   480  		} else {
   481  			sysFree(v, n, &memstats.stacks_sys)
   482  		}
   483  		return
   484  	}
   485  	if traceAllocFreeEnabled() {
   486  		trace := traceAcquire()
   487  		if trace.ok() {
   488  			trace.GoroutineStackFree(uintptr(v))
   489  			traceRelease(trace)
   490  		}
   491  	}
   492  	if msanenabled {
   493  		msanfree(v, n)
   494  	}
   495  	if asanenabled {
   496  		asanpoison(v, n)
   497  	}
   498  	if valgrindenabled {
   499  		valgrindFree(v)
   500  	}
   501  	if n < fixedStack<<_NumStackOrders && n < _StackCacheSize {
   502  		order := uint8(0)
   503  		n2 := n
   504  		for n2 > fixedStack {
   505  			order++
   506  			n2 >>= 1
   507  		}
   508  		x := gclinkptr(v)
   509  		if stackNoCache != 0 || gp.m.p == 0 || gp.m.preemptoff != "" {
   510  			lock(&stackpool[order].item.mu)
   511  			if valgrindenabled {
   512  				// x.ptr() is the head of the list of free stacks, and will be used
   513  				// when allocating a new stack, so it has to be marked allocated.
   514  				valgrindMalloc(unsafe.Pointer(x.ptr()), unsafe.Sizeof(x.ptr()))
   515  			}
   516  			stackpoolfree(x, order)
   517  			unlock(&stackpool[order].item.mu)
   518  		} else {
   519  			c := gp.m.p.ptr().mcache
   520  			if c.stackcache[order].size >= _StackCacheSize {
   521  				stackcacherelease(c, order)
   522  			}
   523  			if valgrindenabled {
   524  				// x.ptr() is the head of the list of free stacks, and will
   525  				// be used when allocating a new stack, so it has to be
   526  				// marked allocated.
   527  				valgrindMalloc(unsafe.Pointer(x.ptr()), unsafe.Sizeof(x.ptr()))
   528  			}
   529  			x.ptr().next = c.stackcache[order].list
   530  			c.stackcache[order].list = x
   531  			c.stackcache[order].size += n
   532  		}
   533  	} else {
   534  		s := spanOfUnchecked(uintptr(v))
   535  		if s.state.get() != mSpanManual {
   536  			println(hex(s.base()), v)
   537  			throw("bad span state")
   538  		}
   539  		if gcphase == _GCoff {
   540  			// Free the stack immediately if we're
   541  			// sweeping.
   542  			osStackFree(s)
   543  			mheap_.freeManual(s, spanAllocStack)
   544  		} else {
   545  			// If the GC is running, we can't return a
   546  			// stack span to the heap because it could be
   547  			// reused as a heap span, and this state
   548  			// change would race with GC. Add it to the
   549  			// large stack cache instead.
   550  			log2npage := stacklog2(s.npages)
   551  			lock(&stackLarge.lock)
   552  			stackLarge.free[log2npage].insert(s)
   553  			unlock(&stackLarge.lock)
   554  		}
   555  	}
   556  }
   557  
   558  var maxstacksize uintptr = 1 << 20 // enough until runtime.main sets it for real
   559  
   560  var maxstackceiling = maxstacksize
   561  
   562  var ptrnames = []string{
   563  	0: "scalar",
   564  	1: "ptr",
   565  }
   566  
   567  // Stack frame layout
   568  //
   569  // (x86)
   570  // +------------------+
   571  // | args from caller |
   572  // +------------------+ <- frame->argp
   573  // |  return address  |
   574  // +------------------+
   575  // |  caller's BP (*) | (*) if framepointer_enabled && varp > sp
   576  // +------------------+ <- frame->varp
   577  // |     locals       |
   578  // +------------------+
   579  // |  args to callee  |
   580  // +------------------+ <- frame->sp
   581  //
   582  // (arm)
   583  // +------------------+
   584  // | args from caller |
   585  // +------------------+ <- frame->argp
   586  // | caller's retaddr |
   587  // +------------------+
   588  // |  caller's FP (*) | (*) on ARM64, if framepointer_enabled && varp > sp
   589  // +------------------+ <- frame->varp
   590  // |     locals       |
   591  // +------------------+
   592  // |  args to callee  |
   593  // +------------------+
   594  // |  return address  |
   595  // +------------------+ <- frame->sp
   596  //
   597  // varp > sp means that the function has a frame;
   598  // varp == sp means frameless function.
   599  
   600  type adjustinfo struct {
   601  	old   stack
   602  	delta uintptr // ptr distance from old to new stack (newbase - oldbase)
   603  
   604  	// sghi is the highest sudog.elem on the stack.
   605  	sghi uintptr
   606  }
   607  
   608  // adjustpointer checks whether *vpp is in the old stack described by adjinfo.
   609  // If so, it rewrites *vpp to point into the new stack.
   610  func adjustpointer(adjinfo *adjustinfo, vpp unsafe.Pointer) {
   611  	pp := (*uintptr)(vpp)
   612  	p := *pp
   613  	if stackDebug >= 4 {
   614  		print("        ", pp, ":", hex(p), "\n")
   615  	}
   616  	if valgrindenabled {
   617  		// p is a pointer on a stack, it is inherently initialized, as
   618  		// everything on the stack is, but valgrind for _some unknown reason_
   619  		// sometimes thinks it's uninitialized, and flags operations on p below
   620  		// as uninitialized. We just initialize it if valgrind thinks its
   621  		// uninitialized.
   622  		//
   623  		// See go.dev/issues/73801.
   624  		valgrindMakeMemDefined(unsafe.Pointer(&p), unsafe.Sizeof(&p))
   625  	}
   626  	if adjinfo.old.lo <= p && p < adjinfo.old.hi {
   627  		*pp = p + adjinfo.delta
   628  		if stackDebug >= 3 {
   629  			print("        adjust ptr ", pp, ":", hex(p), " -> ", hex(*pp), "\n")
   630  		}
   631  	}
   632  }
   633  
   634  // Information from the compiler about the layout of stack frames.
   635  // Note: this type must agree with reflect.bitVector.
   636  type bitvector struct {
   637  	n        int32 // # of bits
   638  	bytedata *uint8
   639  }
   640  
   641  // ptrbit returns the i'th bit in bv.
   642  // ptrbit is less efficient than iterating directly over bitvector bits,
   643  // and should only be used in non-performance-critical code.
   644  // See adjustpointers for an example of a high-efficiency walk of a bitvector.
   645  func (bv *bitvector) ptrbit(i uintptr) uint8 {
   646  	b := *(addb(bv.bytedata, i/8))
   647  	return (b >> (i % 8)) & 1
   648  }
   649  
   650  // bv describes the memory starting at address scanp.
   651  // Adjust any pointers contained therein.
   652  func adjustpointers(scanp unsafe.Pointer, bv *bitvector, adjinfo *adjustinfo, f funcInfo) {
   653  	minp := adjinfo.old.lo
   654  	maxp := adjinfo.old.hi
   655  	delta := adjinfo.delta
   656  	num := uintptr(bv.n)
   657  	// If this frame might contain channel receive slots, use CAS
   658  	// to adjust pointers. If the slot hasn't been received into
   659  	// yet, it may contain stack pointers and a concurrent send
   660  	// could race with adjusting those pointers. (The sent value
   661  	// itself can never contain stack pointers.)
   662  	useCAS := uintptr(scanp) < adjinfo.sghi
   663  	for i := uintptr(0); i < num; i += 8 {
   664  		if stackDebug >= 4 {
   665  			for j := uintptr(0); j < 8; j++ {
   666  				print("        ", add(scanp, (i+j)*goarch.PtrSize), ":", ptrnames[bv.ptrbit(i+j)], ":", hex(*(*uintptr)(add(scanp, (i+j)*goarch.PtrSize))), " # ", i, " ", *addb(bv.bytedata, i/8), "\n")
   667  			}
   668  		}
   669  		b := *(addb(bv.bytedata, i/8))
   670  		for b != 0 {
   671  			j := uintptr(sys.TrailingZeros8(b))
   672  			b &= b - 1
   673  			pp := (*uintptr)(add(scanp, (i+j)*goarch.PtrSize))
   674  		retry:
   675  			p := *pp
   676  			if f.valid() && 0 < p && p < minLegalPointer && debug.invalidptr != 0 {
   677  				// Looks like a junk value in a pointer slot.
   678  				// Live analysis wrong?
   679  				getg().m.traceback = 2
   680  				print("runtime: bad pointer in frame ", funcname(f), " at ", pp, ": ", hex(p), "\n")
   681  				throw("invalid pointer found on stack")
   682  			}
   683  			if minp <= p && p < maxp {
   684  				if stackDebug >= 3 {
   685  					print("adjust ptr ", hex(p), " ", funcname(f), "\n")
   686  				}
   687  				if useCAS {
   688  					ppu := (*unsafe.Pointer)(unsafe.Pointer(pp))
   689  					if !atomic.Casp1(ppu, unsafe.Pointer(p), unsafe.Pointer(p+delta)) {
   690  						goto retry
   691  					}
   692  				} else {
   693  					*pp = p + delta
   694  				}
   695  			}
   696  		}
   697  	}
   698  }
   699  
   700  // Note: the argument/return area is adjusted by the callee.
   701  func adjustframe(frame *stkframe, adjinfo *adjustinfo) {
   702  	if frame.continpc == 0 {
   703  		// Frame is dead.
   704  		return
   705  	}
   706  	f := frame.fn
   707  	if stackDebug >= 2 {
   708  		print("    adjusting ", funcname(f), " frame=[", hex(frame.sp), ",", hex(frame.fp), "] pc=", hex(frame.pc), " continpc=", hex(frame.continpc), "\n")
   709  	}
   710  
   711  	// Adjust saved frame pointer if there is one.
   712  	if (goarch.ArchFamily == goarch.AMD64 || goarch.ArchFamily == goarch.ARM64) && frame.argp-frame.varp == 2*goarch.PtrSize {
   713  		if stackDebug >= 3 {
   714  			print("      saved bp\n")
   715  		}
   716  		if debugCheckBP {
   717  			// Frame pointers should always point to the next higher frame on
   718  			// the Go stack (or be nil, for the top frame on the stack).
   719  			bp := *(*uintptr)(unsafe.Pointer(frame.varp))
   720  			if bp != 0 && (bp < adjinfo.old.lo || bp >= adjinfo.old.hi) {
   721  				println("runtime: found invalid frame pointer")
   722  				print("bp=", hex(bp), " min=", hex(adjinfo.old.lo), " max=", hex(adjinfo.old.hi), "\n")
   723  				throw("bad frame pointer")
   724  			}
   725  		}
   726  		// On AMD64, this is the caller's frame pointer saved in the current
   727  		// frame.
   728  		// On ARM64, this is the frame pointer of the caller's caller saved
   729  		// by the caller in its frame (one word below its SP).
   730  		adjustpointer(adjinfo, unsafe.Pointer(frame.varp))
   731  	}
   732  
   733  	locals, args, objs := frame.getStackMap(true)
   734  
   735  	// Adjust local variables if stack frame has been allocated.
   736  	if locals.n > 0 {
   737  		size := uintptr(locals.n) * goarch.PtrSize
   738  		adjustpointers(unsafe.Pointer(frame.varp-size), &locals, adjinfo, f)
   739  	}
   740  
   741  	// Adjust arguments.
   742  	if args.n > 0 {
   743  		if stackDebug >= 3 {
   744  			print("      args\n")
   745  		}
   746  		adjustpointers(unsafe.Pointer(frame.argp), &args, adjinfo, funcInfo{})
   747  	}
   748  
   749  	// Adjust pointers in all stack objects (whether they are live or not).
   750  	// See comments in mgcmark.go:scanframeworker.
   751  	if frame.varp != 0 {
   752  		for i := range objs {
   753  			obj := &objs[i]
   754  			off := obj.off
   755  			base := frame.varp // locals base pointer
   756  			if off >= 0 {
   757  				base = frame.argp // arguments and return values base pointer
   758  			}
   759  			p := base + uintptr(off)
   760  			if p < frame.sp {
   761  				// Object hasn't been allocated in the frame yet.
   762  				// (Happens when the stack bounds check fails and
   763  				// we call into morestack.)
   764  				continue
   765  			}
   766  			ptrBytes, gcData := obj.gcdata()
   767  			for i := uintptr(0); i < ptrBytes; i += goarch.PtrSize {
   768  				if *addb(gcData, i/(8*goarch.PtrSize))>>(i/goarch.PtrSize&7)&1 != 0 {
   769  					adjustpointer(adjinfo, unsafe.Pointer(p+i))
   770  				}
   771  			}
   772  		}
   773  	}
   774  }
   775  
   776  func adjustctxt(gp *g, adjinfo *adjustinfo) {
   777  	adjustpointer(adjinfo, unsafe.Pointer(&gp.sched.ctxt))
   778  	if !framepointer_enabled {
   779  		return
   780  	}
   781  	if debugCheckBP {
   782  		bp := gp.sched.bp
   783  		if bp != 0 && (bp < adjinfo.old.lo || bp >= adjinfo.old.hi) {
   784  			println("runtime: found invalid top frame pointer")
   785  			print("bp=", hex(bp), " min=", hex(adjinfo.old.lo), " max=", hex(adjinfo.old.hi), "\n")
   786  			throw("bad top frame pointer")
   787  		}
   788  	}
   789  	oldfp := gp.sched.bp
   790  	adjustpointer(adjinfo, unsafe.Pointer(&gp.sched.bp))
   791  	if GOARCH == "arm64" {
   792  		// On ARM64, the frame pointer is saved one word *below* the SP,
   793  		// which is not copied or adjusted in any frame. Do it explicitly
   794  		// here.
   795  		if oldfp == gp.sched.sp-goarch.PtrSize {
   796  			memmove(unsafe.Pointer(gp.sched.bp), unsafe.Pointer(oldfp), goarch.PtrSize)
   797  			adjustpointer(adjinfo, unsafe.Pointer(gp.sched.bp))
   798  		}
   799  	}
   800  }
   801  
   802  func adjustdefers(gp *g, adjinfo *adjustinfo) {
   803  	// Adjust pointers in the Defer structs.
   804  	// We need to do this first because we need to adjust the
   805  	// defer.link fields so we always work on the new stack.
   806  	adjustpointer(adjinfo, unsafe.Pointer(&gp._defer))
   807  	for d := gp._defer; d != nil; d = d.link {
   808  		adjustpointer(adjinfo, unsafe.Pointer(&d.fn))
   809  		adjustpointer(adjinfo, unsafe.Pointer(&d.sp))
   810  		adjustpointer(adjinfo, unsafe.Pointer(&d.link))
   811  	}
   812  }
   813  
   814  func adjustpanics(gp *g, adjinfo *adjustinfo) {
   815  	// Panics are on stack and already adjusted.
   816  	// Update pointer to head of list in G.
   817  	adjustpointer(adjinfo, unsafe.Pointer(&gp._panic))
   818  }
   819  
   820  func adjustsudogs(gp *g, adjinfo *adjustinfo) {
   821  	// the data elements pointed to by a SudoG structure
   822  	// might be in the stack.
   823  	for s := gp.waiting; s != nil; s = s.waitlink {
   824  		adjustpointer(adjinfo, unsafe.Pointer(&s.elem.vu))
   825  		adjustpointer(adjinfo, unsafe.Pointer(&s.elem.vp))
   826  	}
   827  }
   828  
   829  func fillstack(stk stack, b byte) {
   830  	for p := stk.lo; p < stk.hi; p++ {
   831  		*(*byte)(unsafe.Pointer(p)) = b
   832  	}
   833  }
   834  
   835  func findsghi(gp *g, stk stack) uintptr {
   836  	var sghi uintptr
   837  	for sg := gp.waiting; sg != nil; sg = sg.waitlink {
   838  		p := sg.elem.uintptr() + uintptr(sg.c.get().elemsize)
   839  		if stk.lo <= p && p < stk.hi && p > sghi {
   840  			sghi = p
   841  		}
   842  	}
   843  	return sghi
   844  }
   845  
   846  // syncadjustsudogs adjusts gp's sudogs and copies the part of gp's
   847  // stack they refer to while synchronizing with concurrent channel
   848  // operations. It returns the number of bytes of stack copied.
   849  func syncadjustsudogs(gp *g, used uintptr, adjinfo *adjustinfo) uintptr {
   850  	if gp.waiting == nil {
   851  		return 0
   852  	}
   853  
   854  	// Lock channels to prevent concurrent send/receive.
   855  	var lastc *hchan
   856  	for sg := gp.waiting; sg != nil; sg = sg.waitlink {
   857  		if sg.c.get() != lastc {
   858  			// There is a ranking cycle here between gscan bit and
   859  			// hchan locks. Normally, we only allow acquiring hchan
   860  			// locks and then getting a gscan bit. In this case, we
   861  			// already have the gscan bit. We allow acquiring hchan
   862  			// locks here as a special case, since a deadlock can't
   863  			// happen because the G involved must already be
   864  			// suspended. So, we get a special hchan lock rank here
   865  			// that is lower than gscan, but doesn't allow acquiring
   866  			// any other locks other than hchan.
   867  			lockWithRank(&sg.c.get().lock, lockRankHchanLeaf)
   868  		}
   869  		lastc = sg.c.get()
   870  	}
   871  
   872  	// Adjust sudogs.
   873  	adjustsudogs(gp, adjinfo)
   874  
   875  	// Copy the part of the stack the sudogs point in to
   876  	// while holding the lock to prevent races on
   877  	// send/receive slots.
   878  	var sgsize uintptr
   879  	if adjinfo.sghi != 0 {
   880  		oldBot := adjinfo.old.hi - used
   881  		newBot := oldBot + adjinfo.delta
   882  		sgsize = adjinfo.sghi - oldBot
   883  		memmove(unsafe.Pointer(newBot), unsafe.Pointer(oldBot), sgsize)
   884  	}
   885  
   886  	// Unlock channels.
   887  	lastc = nil
   888  	for sg := gp.waiting; sg != nil; sg = sg.waitlink {
   889  		if sg.c.get() != lastc {
   890  			unlock(&sg.c.get().lock)
   891  		}
   892  		lastc = sg.c.get()
   893  	}
   894  
   895  	return sgsize
   896  }
   897  
   898  // Copies gp's stack to a new stack of a different size.
   899  // Caller must have changed gp status to Gcopystack.
   900  func copystack(gp *g, newsize uintptr) {
   901  	if gp.syscallsp != 0 {
   902  		throw("stack growth not allowed in system call")
   903  	}
   904  	old := gp.stack
   905  	if old.lo == 0 {
   906  		throw("nil stackbase")
   907  	}
   908  	used := old.hi - gp.sched.sp
   909  	// Add just the difference to gcController.addScannableStack.
   910  	// g0 stacks never move, so this will never account for them.
   911  	// It's also fine if we have no P, addScannableStack can deal with
   912  	// that case.
   913  	gcController.addScannableStack(getg().m.p.ptr(), int64(newsize)-int64(old.hi-old.lo))
   914  
   915  	// allocate new stack
   916  	new := stackalloc(uint32(newsize))
   917  	if stackPoisonCopy != 0 {
   918  		fillstack(new, 0xfd)
   919  	}
   920  	if stackDebug >= 1 {
   921  		print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]", " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
   922  	}
   923  
   924  	// Compute adjustment.
   925  	var adjinfo adjustinfo
   926  	adjinfo.old = old
   927  	adjinfo.delta = new.hi - old.hi
   928  
   929  	// Adjust sudogs, synchronizing with channel ops if necessary.
   930  	ncopy := used
   931  	if !gp.activeStackChans {
   932  		if newsize < old.hi-old.lo && gp.parkingOnChan.Load() {
   933  			// It's not safe for someone to shrink this stack while we're actively
   934  			// parking on a channel, but it is safe to grow since we do that
   935  			// ourselves and explicitly don't want to synchronize with channels
   936  			// since we could self-deadlock.
   937  			throw("racy sudog adjustment due to parking on channel")
   938  		}
   939  		adjustsudogs(gp, &adjinfo)
   940  	} else {
   941  		// sudogs may be pointing in to the stack and gp has
   942  		// released channel locks, so other goroutines could
   943  		// be writing to gp's stack. Find the highest such
   944  		// pointer so we can handle everything there and below
   945  		// carefully. (This shouldn't be far from the bottom
   946  		// of the stack, so there's little cost in handling
   947  		// everything below it carefully.)
   948  		adjinfo.sghi = findsghi(gp, old)
   949  
   950  		// Synchronize with channel ops and copy the part of
   951  		// the stack they may interact with.
   952  		ncopy -= syncadjustsudogs(gp, used, &adjinfo)
   953  	}
   954  
   955  	// Copy the stack (or the rest of it) to the new location
   956  	memmove(unsafe.Pointer(new.hi-ncopy), unsafe.Pointer(old.hi-ncopy), ncopy)
   957  
   958  	// Adjust remaining structures that have pointers into stacks.
   959  	// We have to do most of these before we traceback the new
   960  	// stack because gentraceback uses them.
   961  	adjustctxt(gp, &adjinfo)
   962  	adjustdefers(gp, &adjinfo)
   963  	adjustpanics(gp, &adjinfo)
   964  	if adjinfo.sghi != 0 {
   965  		adjinfo.sghi += adjinfo.delta
   966  	}
   967  
   968  	// Swap out old stack for new one
   969  	gp.stack = new
   970  	gp.stackguard0 = new.lo + stackGuard // NOTE: might clobber a preempt request
   971  	gp.sched.sp = new.hi - used
   972  	gp.stktopsp += adjinfo.delta
   973  
   974  	// Adjust pointers in the new stack.
   975  	var u unwinder
   976  	for u.init(gp, 0); u.valid(); u.next() {
   977  		adjustframe(&u.frame, &adjinfo)
   978  	}
   979  
   980  	if valgrindenabled {
   981  		if gp.valgrindStackID == 0 {
   982  			gp.valgrindStackID = valgrindRegisterStack(unsafe.Pointer(new.lo), unsafe.Pointer(new.hi))
   983  		} else {
   984  			valgrindChangeStack(gp.valgrindStackID, unsafe.Pointer(new.lo), unsafe.Pointer(new.hi))
   985  		}
   986  	}
   987  
   988  	// free old stack
   989  	if goexperiment.RuntimeSecret && gp.secret > 0 {
   990  		// Some portion of the old stack has secret stuff on it.
   991  		// We don't really know where we entered secret mode,
   992  		// so just clear the whole thing.
   993  		// TODO(dmo): traceback until we hit secret.Do? clearing
   994  		// is fast and optimized, might not be worth it.
   995  		memclrNoHeapPointers(unsafe.Pointer(old.lo), old.hi-old.lo)
   996  		// The memmove call above might put secrets from the stack into registers.
   997  		secretEraseRegisters()
   998  	}
   999  	if stackPoisonCopy != 0 {
  1000  		fillstack(old, 0xfc)
  1001  	}
  1002  	stackfree(old)
  1003  }
  1004  
  1005  // round x up to a power of 2.
  1006  func round2(x int32) int32 {
  1007  	s := uint(0)
  1008  	for 1<<s < x {
  1009  		s++
  1010  	}
  1011  	return 1 << s
  1012  }
  1013  
  1014  // Called from runtime·morestack when more stack is needed.
  1015  // Allocate larger stack and relocate to new stack.
  1016  // Stack growth is multiplicative, for constant amortized cost.
  1017  //
  1018  // g->atomicstatus will be Grunning or Gscanrunning upon entry.
  1019  // If the scheduler is trying to stop this g, then it will set preemptStop.
  1020  //
  1021  // This must be nowritebarrierrec because it can be called as part of
  1022  // stack growth from other nowritebarrierrec functions, but the
  1023  // compiler doesn't check this.
  1024  //
  1025  //go:nowritebarrierrec
  1026  func newstack() {
  1027  	thisg := getg()
  1028  	// TODO: double check all gp. shouldn't be getg().
  1029  	if thisg.m.morebuf.g.ptr().stackguard0 == stackFork {
  1030  		throw("stack growth after fork")
  1031  	}
  1032  	if thisg.m.morebuf.g.ptr() != thisg.m.curg {
  1033  		print("runtime: newstack called from g=", hex(thisg.m.morebuf.g), "\n"+"\tm=", thisg.m, " m->curg=", thisg.m.curg, " m->g0=", thisg.m.g0, " m->gsignal=", thisg.m.gsignal, "\n")
  1034  		morebuf := thisg.m.morebuf
  1035  		traceback(morebuf.pc, morebuf.sp, morebuf.lr, morebuf.g.ptr())
  1036  		throw("runtime: wrong goroutine in newstack")
  1037  	}
  1038  
  1039  	gp := thisg.m.curg
  1040  	if goexperiment.RuntimeSecret && gp.secret > 0 {
  1041  		// If we're entering here from a secret context, clear
  1042  		// all the registers. This is important because we
  1043  		// might context switch to a different goroutine which
  1044  		// is not in secret mode, and it will not be careful
  1045  		// about clearing its registers.
  1046  		secretEraseRegisters()
  1047  	}
  1048  
  1049  	if thisg.m.curg.throwsplit {
  1050  		// Update syscallsp, syscallpc in case traceback uses them.
  1051  		morebuf := thisg.m.morebuf
  1052  		gp.syscallsp = morebuf.sp
  1053  		gp.syscallpc = morebuf.pc
  1054  		pcname, pcoff := "(unknown)", uintptr(0)
  1055  		f := findfunc(gp.sched.pc)
  1056  		if f.valid() {
  1057  			pcname = funcname(f)
  1058  			pcoff = gp.sched.pc - f.entry()
  1059  		}
  1060  		print("runtime: newstack at ", pcname, "+", hex(pcoff),
  1061  			" sp=", hex(gp.sched.sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
  1062  			"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
  1063  			"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
  1064  
  1065  		thisg.m.traceback = 2 // Include runtime frames
  1066  		traceback(morebuf.pc, morebuf.sp, morebuf.lr, gp)
  1067  		throw("runtime: stack split at bad time")
  1068  	}
  1069  
  1070  	morebuf := thisg.m.morebuf
  1071  	thisg.m.morebuf.pc = 0
  1072  	thisg.m.morebuf.lr = 0
  1073  	thisg.m.morebuf.sp = 0
  1074  	thisg.m.morebuf.g = 0
  1075  
  1076  	// NOTE: stackguard0 may change underfoot, if another thread
  1077  	// is about to try to preempt gp. Read it just once and use that same
  1078  	// value now and below.
  1079  	stackguard0 := atomic.Loaduintptr(&gp.stackguard0)
  1080  
  1081  	// Be conservative about where we preempt.
  1082  	// We are interested in preempting user Go code, not runtime code.
  1083  	// If we're holding locks, mallocing, or preemption is disabled, don't
  1084  	// preempt.
  1085  	// This check is very early in newstack so that even the status change
  1086  	// from Grunning to Gwaiting and back doesn't happen in this case.
  1087  	// That status change by itself can be viewed as a small preemption,
  1088  	// because the GC might change Gwaiting to Gscanwaiting, and then
  1089  	// this goroutine has to wait for the GC to finish before continuing.
  1090  	// If the GC is in some way dependent on this goroutine (for example,
  1091  	// it needs a lock held by the goroutine), that small preemption turns
  1092  	// into a real deadlock.
  1093  	preempt := stackguard0 == stackPreempt
  1094  	if preempt {
  1095  		if !canPreemptM(thisg.m) {
  1096  			// Let the goroutine keep running for now.
  1097  			// gp->preempt is set, so it will be preempted next time.
  1098  			gp.stackguard0 = gp.stack.lo + stackGuard
  1099  			gogo(&gp.sched) // never return
  1100  		}
  1101  	}
  1102  
  1103  	if gp.stack.lo == 0 {
  1104  		throw("missing stack in newstack")
  1105  	}
  1106  	sp := gp.sched.sp
  1107  	if goarch.ArchFamily == goarch.AMD64 || goarch.ArchFamily == goarch.I386 || goarch.ArchFamily == goarch.WASM {
  1108  		// The call to morestack cost a word.
  1109  		sp -= goarch.PtrSize
  1110  	}
  1111  	if stackDebug >= 1 || sp < gp.stack.lo {
  1112  		print("runtime: newstack sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
  1113  			"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
  1114  			"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
  1115  	}
  1116  	if sp < gp.stack.lo {
  1117  		print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->status=", hex(readgstatus(gp)), "\n ")
  1118  		print("runtime: split stack overflow: ", hex(sp), " < ", hex(gp.stack.lo), "\n")
  1119  		throw("runtime: split stack overflow")
  1120  	}
  1121  
  1122  	if preempt {
  1123  		if gp == thisg.m.g0 {
  1124  			throw("runtime: preempt g0")
  1125  		}
  1126  		if thisg.m.p == 0 && thisg.m.locks == 0 {
  1127  			throw("runtime: g is running but p is not")
  1128  		}
  1129  
  1130  		if gp.preemptShrink {
  1131  			// We're at a synchronous safe point now, so
  1132  			// do the pending stack shrink.
  1133  			gp.preemptShrink = false
  1134  			shrinkstack(gp)
  1135  		}
  1136  
  1137  		// Set a flag indicated that we've been synchronously preempted.
  1138  		gp.syncSafePoint = true
  1139  
  1140  		if gp.preemptStop {
  1141  			preemptPark(gp) // never returns
  1142  		}
  1143  
  1144  		// Act like goroutine called runtime.Gosched.
  1145  		gopreempt_m(gp) // never return
  1146  	}
  1147  
  1148  	// Allocate a bigger segment and move the stack.
  1149  	oldsize := gp.stack.hi - gp.stack.lo
  1150  	newsize := oldsize * 2
  1151  
  1152  	// Make sure we grow at least as much as needed to fit the new frame.
  1153  	// (This is just an optimization - the caller of morestack will
  1154  	// recheck the bounds on return.)
  1155  	if f := findfunc(gp.sched.pc); f.valid() {
  1156  		max := uintptr(funcMaxSPDelta(f))
  1157  		needed := max + stackGuard
  1158  		used := gp.stack.hi - gp.sched.sp
  1159  		for newsize-used < needed {
  1160  			newsize *= 2
  1161  		}
  1162  	}
  1163  
  1164  	if stackguard0 == stackForceMove {
  1165  		// Forced stack movement used for debugging.
  1166  		// Don't double the stack (or we may quickly run out
  1167  		// if this is done repeatedly).
  1168  		newsize = oldsize
  1169  	}
  1170  
  1171  	if newsize > maxstacksize || newsize > maxstackceiling {
  1172  		if maxstacksize < maxstackceiling {
  1173  			print("runtime: goroutine stack exceeds ", maxstacksize, "-byte limit\n")
  1174  		} else {
  1175  			print("runtime: goroutine stack exceeds ", maxstackceiling, "-byte limit\n")
  1176  		}
  1177  		print("runtime: sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n")
  1178  		throw("stack overflow")
  1179  	}
  1180  
  1181  	// The goroutine must be executing in order to call newstack,
  1182  	// so it must be Grunning (or Gscanrunning).
  1183  	casgstatus(gp, _Grunning, _Gcopystack)
  1184  
  1185  	// The concurrent GC will not scan the stack while we are doing the copy since
  1186  	// the gp is in a Gcopystack status.
  1187  	copystack(gp, newsize)
  1188  	if stackDebug >= 1 {
  1189  		print("stack grow done\n")
  1190  	}
  1191  	casgstatus(gp, _Gcopystack, _Grunning)
  1192  	gogo(&gp.sched)
  1193  }
  1194  
  1195  //go:nosplit
  1196  func nilfunc() {
  1197  	*(*uint8)(nil) = 0
  1198  }
  1199  
  1200  // adjust Gobuf as if it executed a call to fn
  1201  // and then stopped before the first instruction in fn.
  1202  func gostartcallfn(gobuf *gobuf, fv *funcval) {
  1203  	var fn unsafe.Pointer
  1204  	if fv != nil {
  1205  		fn = unsafe.Pointer(fv.fn)
  1206  	} else {
  1207  		fn = unsafe.Pointer(abi.FuncPCABIInternal(nilfunc))
  1208  	}
  1209  	gostartcall(gobuf, fn, unsafe.Pointer(fv))
  1210  }
  1211  
  1212  // isShrinkStackSafe returns whether it's safe to attempt to shrink
  1213  // gp's stack. Shrinking the stack is only safe when we have precise
  1214  // pointer maps for all frames on the stack. The caller must hold the
  1215  // _Gscan bit for gp or must be running gp itself.
  1216  func isShrinkStackSafe(gp *g) bool {
  1217  	// We can't copy the stack if we're in a syscall.
  1218  	// The syscall might have pointers into the stack and
  1219  	// often we don't have precise pointer maps for the innermost
  1220  	// frames.
  1221  	if gp.syscallsp != 0 {
  1222  		return false
  1223  	}
  1224  	// We also can't copy the stack if we're at an asynchronous
  1225  	// safe-point because we don't have precise pointer maps for
  1226  	// all frames.
  1227  	if gp.asyncSafePoint {
  1228  		return false
  1229  	}
  1230  	// We also can't *shrink* the stack in the window between the
  1231  	// goroutine calling gopark to park on a channel and
  1232  	// gp.activeStackChans being set.
  1233  	if gp.parkingOnChan.Load() {
  1234  		return false
  1235  	}
  1236  	// We also can't copy the stack while a gp is in _Gwaiting solely
  1237  	// to make itself available to suspendG.
  1238  	//
  1239  	// In these cases, the G is actually executing on the system
  1240  	// stack, and the execution tracer, mutex profiler, etc. may want
  1241  	// to take a stack trace of the G's stack.
  1242  	//
  1243  	// Note: it's safe to access gp.waitreason here.
  1244  	// We're only calling isShrinkStackSafe if we took ownership of the
  1245  	// G with the _Gscan bit. This prevents the goroutine from transitioning,
  1246  	// which prevents gp.waitreason from changing.
  1247  	if readgstatus(gp)&^_Gscan == _Gwaiting && gp.waitreason.isWaitingForSuspendG() {
  1248  		return false
  1249  	}
  1250  	return true
  1251  }
  1252  
  1253  // Maybe shrink the stack being used by gp.
  1254  //
  1255  // gp must be stopped and we must own its stack. It may be in
  1256  // _Grunning, but only if this is our own user G.
  1257  func shrinkstack(gp *g) {
  1258  	if gp.stack.lo == 0 {
  1259  		throw("missing stack in shrinkstack")
  1260  	}
  1261  	if s := readgstatus(gp); s&_Gscan == 0 {
  1262  		// We don't own the stack via _Gscan. We could still
  1263  		// own it if this is our own user G and we're on the
  1264  		// system stack.
  1265  		if !(gp == getg().m.curg && getg() != getg().m.curg && s == _Grunning) {
  1266  			// We don't own the stack.
  1267  			throw("bad status in shrinkstack")
  1268  		}
  1269  	}
  1270  	if !isShrinkStackSafe(gp) {
  1271  		throw("shrinkstack at bad time")
  1272  	}
  1273  	// Check for self-shrinks while in a libcall. These may have
  1274  	// pointers into the stack disguised as uintptrs, but these
  1275  	// code paths should all be nosplit.
  1276  	if gp == getg().m.curg && gp.m.libcallsp != 0 {
  1277  		throw("shrinking stack in libcall")
  1278  	}
  1279  
  1280  	if debug.gcshrinkstackoff > 0 {
  1281  		return
  1282  	}
  1283  
  1284  	oldsize := gp.stack.hi - gp.stack.lo
  1285  	newsize := oldsize / 2
  1286  	// Don't shrink the allocation below the minimum-sized stack
  1287  	// allocation.
  1288  	if newsize < fixedStack {
  1289  		return
  1290  	}
  1291  	// Compute how much of the stack is currently in use and only
  1292  	// shrink the stack if gp is using less than a quarter of its
  1293  	// current stack. The currently used stack includes everything
  1294  	// down to the SP plus the stack guard space that ensures
  1295  	// there's room for nosplit functions.
  1296  	avail := gp.stack.hi - gp.stack.lo
  1297  	if used := gp.stack.hi - gp.sched.sp + stackNosplit; used >= avail/4 {
  1298  		return
  1299  	}
  1300  
  1301  	if stackDebug > 0 {
  1302  		print("shrinking stack ", oldsize, "->", newsize, "\n")
  1303  	}
  1304  
  1305  	copystack(gp, newsize)
  1306  }
  1307  
  1308  // freeStackSpans frees unused stack spans at the end of GC.
  1309  func freeStackSpans() {
  1310  	// Scan stack pools for empty stack spans.
  1311  	for order := range stackpool {
  1312  		lock(&stackpool[order].item.mu)
  1313  		list := &stackpool[order].item.span
  1314  		for s := list.first; s != nil; {
  1315  			next := s.next
  1316  			if s.allocCount == 0 {
  1317  				list.remove(s)
  1318  				s.manualFreeList = 0
  1319  				osStackFree(s)
  1320  				mheap_.freeManual(s, spanAllocStack)
  1321  			}
  1322  			s = next
  1323  		}
  1324  		unlock(&stackpool[order].item.mu)
  1325  	}
  1326  
  1327  	// Free large stack spans.
  1328  	lock(&stackLarge.lock)
  1329  	for i := range stackLarge.free {
  1330  		for s := stackLarge.free[i].first; s != nil; {
  1331  			next := s.next
  1332  			stackLarge.free[i].remove(s)
  1333  			osStackFree(s)
  1334  			mheap_.freeManual(s, spanAllocStack)
  1335  			s = next
  1336  		}
  1337  	}
  1338  	unlock(&stackLarge.lock)
  1339  }
  1340  
  1341  // A stackObjectRecord is generated by the compiler for each stack object in a stack frame.
  1342  // This record must match the generator code in cmd/compile/internal/liveness/plive.go:emitStackObjects.
  1343  type stackObjectRecord struct {
  1344  	// offset in frame
  1345  	// if negative, offset from varp
  1346  	// if non-negative, offset from argp
  1347  	off       int32
  1348  	size      int32
  1349  	ptrBytes  int32
  1350  	gcdataoff uint32 // offset to gcdata from moduledata.rodata
  1351  }
  1352  
  1353  // gcdata returns the number of bytes that contain pointers, and
  1354  // a ptr/nonptr bitmask covering those bytes.
  1355  // Note that this bitmask might be larger than internal/abi.MaxPtrmaskBytes.
  1356  func (r *stackObjectRecord) gcdata() (uintptr, *byte) {
  1357  	ptr := uintptr(unsafe.Pointer(r))
  1358  	var mod *moduledata
  1359  	for datap := &firstmoduledata; datap != nil; datap = datap.next {
  1360  		if datap.gofunc <= ptr && ptr < datap.end {
  1361  			mod = datap
  1362  			break
  1363  		}
  1364  	}
  1365  	// If you get a panic here due to a nil mod,
  1366  	// you may have made a copy of a stackObjectRecord.
  1367  	// You must use the original pointer.
  1368  	res := mod.rodata + uintptr(r.gcdataoff)
  1369  	return uintptr(r.ptrBytes), (*byte)(unsafe.Pointer(res))
  1370  }
  1371  
  1372  // This is exported as ABI0 via linkname so obj can call it.
  1373  //
  1374  //go:nosplit
  1375  //go:linkname morestackc
  1376  func morestackc() {
  1377  	throw("attempt to execute system stack code on user stack")
  1378  }
  1379  
  1380  // startingStackSize is the amount of stack that new goroutines start with.
  1381  // It is a power of 2, and between fixedStack and maxstacksize, inclusive.
  1382  // startingStackSize is updated every GC by tracking the average size of
  1383  // stacks scanned during the GC.
  1384  var startingStackSize uint32 = fixedStack
  1385  
  1386  func gcComputeStartingStackSize() {
  1387  	if debug.adaptivestackstart == 0 {
  1388  		return
  1389  	}
  1390  	// For details, see the design doc at
  1391  	// https://docs.google.com/document/d/1YDlGIdVTPnmUiTAavlZxBI1d9pwGQgZT7IKFKlIXohQ/edit?usp=sharing
  1392  	// The basic algorithm is to track the average size of stacks
  1393  	// and start goroutines with stack equal to that average size.
  1394  	// Starting at the average size uses at most 2x the space that
  1395  	// an ideal algorithm would have used.
  1396  	// This is just a heuristic to avoid excessive stack growth work
  1397  	// early in a goroutine's lifetime. See issue 18138. Stacks that
  1398  	// are allocated too small can still grow, and stacks allocated
  1399  	// too large can still shrink.
  1400  	var scannedStackSize uint64
  1401  	var scannedStacks uint64
  1402  	for _, p := range allp {
  1403  		scannedStackSize += p.scannedStackSize
  1404  		scannedStacks += p.scannedStacks
  1405  		// Reset for next time
  1406  		p.scannedStackSize = 0
  1407  		p.scannedStacks = 0
  1408  	}
  1409  	if scannedStacks == 0 {
  1410  		startingStackSize = fixedStack
  1411  		return
  1412  	}
  1413  	avg := scannedStackSize/scannedStacks + stackGuard
  1414  	// Note: we add stackGuard to ensure that a goroutine that
  1415  	// uses the average space will not trigger a growth.
  1416  	if avg > uint64(maxstacksize) {
  1417  		avg = uint64(maxstacksize)
  1418  	}
  1419  	if avg < fixedStack {
  1420  		avg = fixedStack
  1421  	}
  1422  	// Note: maxstacksize fits in 30 bits, so avg also does.
  1423  	startingStackSize = uint32(round2(int32(avg)))
  1424  }
  1425  

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