panic.go

     1  // Copyright 2014 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/goarch"
    10  	"internal/runtime/atomic"
    11  	"internal/runtime/sys"
    12  	"internal/stringslite"
    13  	"unsafe"
    14  )
    15  
    16  // throwType indicates the current type of ongoing throw, which affects the
    17  // amount of detail printed to stderr. Higher values include more detail.
    18  type throwType uint32
    19  
    20  const (
    21  	// throwTypeNone means that we are not throwing.
    22  	throwTypeNone throwType = iota
    23  
    24  	// throwTypeUser is a throw due to a problem with the application.
    25  	//
    26  	// These throws do not include runtime frames, system goroutines, or
    27  	// frame metadata.
    28  	throwTypeUser
    29  
    30  	// throwTypeRuntime is a throw due to a problem with Go itself.
    31  	//
    32  	// These throws include as much information as possible to aid in
    33  	// debugging the runtime, including runtime frames, system goroutines,
    34  	// and frame metadata.
    35  	throwTypeRuntime
    36  )
    37  
    38  // We have two different ways of doing defers. The older way involves creating a
    39  // defer record at the time that a defer statement is executing and adding it to a
    40  // defer chain. This chain is inspected by the deferreturn call at all function
    41  // exits in order to run the appropriate defer calls. A cheaper way (which we call
    42  // open-coded defers) is used for functions in which no defer statements occur in
    43  // loops. In that case, we simply store the defer function/arg information into
    44  // specific stack slots at the point of each defer statement, as well as setting a
    45  // bit in a bitmask. At each function exit, we add inline code to directly make
    46  // the appropriate defer calls based on the bitmask and fn/arg information stored
    47  // on the stack. During panic/Goexit processing, the appropriate defer calls are
    48  // made using extra funcdata info that indicates the exact stack slots that
    49  // contain the bitmask and defer fn/args.
    50  
    51  // Check to make sure we can really generate a panic. If the panic
    52  // was generated from the runtime, or from inside malloc, then convert
    53  // to a throw of msg.
    54  // pc should be the program counter of the compiler-generated code that
    55  // triggered this panic.
    56  func panicCheck1(pc uintptr, msg string) {
    57  	if goarch.IsWasm == 0 && stringslite.HasPrefix(funcname(findfunc(pc)), "runtime.") {
    58  		// Note: wasm can't tail call, so we can't get the original caller's pc.
    59  		throw(msg)
    60  	}
    61  	// TODO: is this redundant? How could we be in malloc
    62  	// but not in the runtime? internal/runtime/*, maybe?
    63  	gp := getg()
    64  	if gp != nil && gp.m != nil && gp.m.mallocing != 0 {
    65  		throw(msg)
    66  	}
    67  }
    68  
    69  // Same as above, but calling from the runtime is allowed.
    70  //
    71  // Using this function is necessary for any panic that may be
    72  // generated by runtime.sigpanic, since those are always called by the
    73  // runtime.
    74  func panicCheck2(err string) {
    75  	// panic allocates, so to avoid recursive malloc, turn panics
    76  	// during malloc into throws.
    77  	gp := getg()
    78  	if gp != nil && gp.m != nil && gp.m.mallocing != 0 {
    79  		throw(err)
    80  	}
    81  }
    82  
    83  // Many of the following panic entry-points turn into throws when they
    84  // happen in various runtime contexts. These should never happen in
    85  // the runtime, and if they do, they indicate a serious issue and
    86  // should not be caught by user code.
    87  //
    88  // The panic{Index,Slice,divide,shift} functions are called by
    89  // code generated by the compiler for out of bounds index expressions,
    90  // out of bounds slice expressions, division by zero, and shift by negative.
    91  // The panicdivide (again), panicoverflow, panicfloat, and panicmem
    92  // functions are called by the signal handler when a signal occurs
    93  // indicating the respective problem.
    94  //
    95  // Since panic{Index,Slice,shift} are never called directly, and
    96  // since the runtime package should never have an out of bounds slice
    97  // or array reference or negative shift, if we see those functions called from the
    98  // runtime package we turn the panic into a throw. That will dump the
    99  // entire runtime stack for easier debugging.
   100  //
   101  // The entry points called by the signal handler will be called from
   102  // runtime.sigpanic, so we can't disallow calls from the runtime to
   103  // these (they always look like they're called from the runtime).
   104  // Hence, for these, we just check for clearly bad runtime conditions.
   105  //
   106  // The panic{Index,Slice} functions are implemented in assembly and tail call
   107  // to the goPanic{Index,Slice} functions below. This is done so we can use
   108  // a space-minimal register calling convention.
   109  
   110  // failures in the comparisons for s[x], 0 <= x < y (y == len(s))
   111  //
   112  //go:yeswritebarrierrec
   113  func goPanicIndex(x int, y int) {
   114  	panicCheck1(sys.GetCallerPC(), "index out of range")
   115  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsIndex})
   116  }
   117  
   118  //go:yeswritebarrierrec
   119  func goPanicIndexU(x uint, y int) {
   120  	panicCheck1(sys.GetCallerPC(), "index out of range")
   121  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsIndex})
   122  }
   123  
   124  // failures in the comparisons for s[:x], 0 <= x <= y (y == len(s) or cap(s))
   125  //
   126  //go:yeswritebarrierrec
   127  func goPanicSliceAlen(x int, y int) {
   128  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   129  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceAlen})
   130  }
   131  
   132  //go:yeswritebarrierrec
   133  func goPanicSliceAlenU(x uint, y int) {
   134  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   135  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceAlen})
   136  }
   137  
   138  //go:yeswritebarrierrec
   139  func goPanicSliceAcap(x int, y int) {
   140  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   141  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceAcap})
   142  }
   143  
   144  //go:yeswritebarrierrec
   145  func goPanicSliceAcapU(x uint, y int) {
   146  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   147  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceAcap})
   148  }
   149  
   150  // failures in the comparisons for s[x:y], 0 <= x <= y
   151  //
   152  //go:yeswritebarrierrec
   153  func goPanicSliceB(x int, y int) {
   154  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   155  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceB})
   156  }
   157  
   158  //go:yeswritebarrierrec
   159  func goPanicSliceBU(x uint, y int) {
   160  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   161  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceB})
   162  }
   163  
   164  // failures in the comparisons for s[::x], 0 <= x <= y (y == len(s) or cap(s))
   165  func goPanicSlice3Alen(x int, y int) {
   166  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   167  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3Alen})
   168  }
   169  func goPanicSlice3AlenU(x uint, y int) {
   170  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   171  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3Alen})
   172  }
   173  func goPanicSlice3Acap(x int, y int) {
   174  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   175  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3Acap})
   176  }
   177  func goPanicSlice3AcapU(x uint, y int) {
   178  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   179  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3Acap})
   180  }
   181  
   182  // failures in the comparisons for s[:x:y], 0 <= x <= y
   183  func goPanicSlice3B(x int, y int) {
   184  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   185  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3B})
   186  }
   187  func goPanicSlice3BU(x uint, y int) {
   188  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   189  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3B})
   190  }
   191  
   192  // failures in the comparisons for s[x:y:], 0 <= x <= y
   193  func goPanicSlice3C(x int, y int) {
   194  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   195  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3C})
   196  }
   197  func goPanicSlice3CU(x uint, y int) {
   198  	panicCheck1(sys.GetCallerPC(), "slice bounds out of range")
   199  	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3C})
   200  }
   201  
   202  // failures in the conversion ([x]T)(s) or (*[x]T)(s), 0 <= x <= y, y == len(s)
   203  func goPanicSliceConvert(x int, y int) {
   204  	panicCheck1(sys.GetCallerPC(), "slice length too short to convert to array or pointer to array")
   205  	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsConvert})
   206  }
   207  
   208  // Implemented in assembly, as they take arguments in registers.
   209  // Declared here to mark them as ABIInternal.
   210  func panicIndex(x int, y int)
   211  func panicIndexU(x uint, y int)
   212  func panicSliceAlen(x int, y int)
   213  func panicSliceAlenU(x uint, y int)
   214  func panicSliceAcap(x int, y int)
   215  func panicSliceAcapU(x uint, y int)
   216  func panicSliceB(x int, y int)
   217  func panicSliceBU(x uint, y int)
   218  func panicSlice3Alen(x int, y int)
   219  func panicSlice3AlenU(x uint, y int)
   220  func panicSlice3Acap(x int, y int)
   221  func panicSlice3AcapU(x uint, y int)
   222  func panicSlice3B(x int, y int)
   223  func panicSlice3BU(x uint, y int)
   224  func panicSlice3C(x int, y int)
   225  func panicSlice3CU(x uint, y int)
   226  func panicSliceConvert(x int, y int)
   227  
   228  var shiftError = error(errorString("negative shift amount"))
   229  
   230  //go:yeswritebarrierrec
   231  func panicshift() {
   232  	panicCheck1(sys.GetCallerPC(), "negative shift amount")
   233  	panic(shiftError)
   234  }
   235  
   236  var divideError = error(errorString("integer divide by zero"))
   237  
   238  //go:yeswritebarrierrec
   239  func panicdivide() {
   240  	panicCheck2("integer divide by zero")
   241  	panic(divideError)
   242  }
   243  
   244  var overflowError = error(errorString("integer overflow"))
   245  
   246  func panicoverflow() {
   247  	panicCheck2("integer overflow")
   248  	panic(overflowError)
   249  }
   250  
   251  var floatError = error(errorString("floating point error"))
   252  
   253  func panicfloat() {
   254  	panicCheck2("floating point error")
   255  	panic(floatError)
   256  }
   257  
   258  var memoryError = error(errorString("invalid memory address or nil pointer dereference"))
   259  
   260  func panicmem() {
   261  	panicCheck2("invalid memory address or nil pointer dereference")
   262  	panic(memoryError)
   263  }
   264  
   265  func panicmemAddr(addr uintptr) {
   266  	panicCheck2("invalid memory address or nil pointer dereference")
   267  	panic(errorAddressString{msg: "invalid memory address or nil pointer dereference", addr: addr})
   268  }
   269  
   270  // Create a new deferred function fn, which has no arguments and results.
   271  // The compiler turns a defer statement into a call to this.
   272  func deferproc(fn func()) {
   273  	gp := getg()
   274  	if gp.m.curg != gp {
   275  		// go code on the system stack can't defer
   276  		throw("defer on system stack")
   277  	}
   278  
   279  	d := newdefer()
   280  	d.link = gp._defer
   281  	gp._defer = d
   282  	d.fn = fn
   283  	d.pc = sys.GetCallerPC()
   284  	// We must not be preempted between calling GetCallerSP and
   285  	// storing it to d.sp because GetCallerSP's result is a
   286  	// uintptr stack pointer.
   287  	d.sp = sys.GetCallerSP()
   288  }
   289  
   290  var rangeDoneError = error(errorString("range function continued iteration after function for loop body returned false"))
   291  var rangePanicError = error(errorString("range function continued iteration after loop body panic"))
   292  var rangeExhaustedError = error(errorString("range function continued iteration after whole loop exit"))
   293  var rangeMissingPanicError = error(errorString("range function recovered a loop body panic and did not resume panicking"))
   294  
   295  //go:noinline
   296  func panicrangestate(state int) {
   297  	switch abi.RF_State(state) {
   298  	case abi.RF_DONE:
   299  		panic(rangeDoneError)
   300  	case abi.RF_PANIC:
   301  		panic(rangePanicError)
   302  	case abi.RF_EXHAUSTED:
   303  		panic(rangeExhaustedError)
   304  	case abi.RF_MISSING_PANIC:
   305  		panic(rangeMissingPanicError)
   306  	}
   307  	throw("unexpected state passed to panicrangestate")
   308  }
   309  
   310  // deferrangefunc is called by functions that are about to
   311  // execute a range-over-function loop in which the loop body
   312  // may execute a defer statement. That defer needs to add to
   313  // the chain for the current function, not the func literal synthesized
   314  // to represent the loop body. To do that, the original function
   315  // calls deferrangefunc to obtain an opaque token representing
   316  // the current frame, and then the loop body uses deferprocat
   317  // instead of deferproc to add to that frame's defer lists.
   318  //
   319  // The token is an 'any' with underlying type *atomic.Pointer[_defer].
   320  // It is the atomically-updated head of a linked list of _defer structs
   321  // representing deferred calls. At the same time, we create a _defer
   322  // struct on the main g._defer list with d.head set to this head pointer.
   323  //
   324  // The g._defer list is now a linked list of deferred calls,
   325  // but an atomic list hanging off:
   326  //
   327  //		g._defer => d4 -> d3 -> drangefunc -> d2 -> d1 -> nil
   328  //	                             | .head
   329  //	                             |
   330  //	                             +--> dY -> dX -> nil
   331  //
   332  // with each -> indicating a d.link pointer, and where drangefunc
   333  // has the d.rangefunc = true bit set.
   334  // Note that the function being ranged over may have added
   335  // its own defers (d4 and d3), so drangefunc need not be at the
   336  // top of the list when deferprocat is used. This is why we pass
   337  // the atomic head explicitly.
   338  //
   339  // To keep misbehaving programs from crashing the runtime,
   340  // deferprocat pushes new defers onto the .head list atomically.
   341  // The fact that it is a separate list from the main goroutine
   342  // defer list means that the main goroutine's defers can still
   343  // be handled non-atomically.
   344  //
   345  // In the diagram, dY and dX are meant to be processed when
   346  // drangefunc would be processed, which is to say the defer order
   347  // should be d4, d3, dY, dX, d2, d1. To make that happen,
   348  // when defer processing reaches a d with rangefunc=true,
   349  // it calls deferconvert to atomically take the extras
   350  // away from d.head and then adds them to the main list.
   351  //
   352  // That is, deferconvert changes this list:
   353  //
   354  //		g._defer => drangefunc -> d2 -> d1 -> nil
   355  //	                 | .head
   356  //	                 |
   357  //	                 +--> dY -> dX -> nil
   358  //
   359  // into this list:
   360  //
   361  //	g._defer => dY -> dX -> d2 -> d1 -> nil
   362  //
   363  // It also poisons *drangefunc.head so that any future
   364  // deferprocat using that head will throw.
   365  // (The atomic head is ordinary garbage collected memory so that
   366  // it's not a problem if user code holds onto it beyond
   367  // the lifetime of drangefunc.)
   368  //
   369  // TODO: We could arrange for the compiler to call into the
   370  // runtime after the loop finishes normally, to do an eager
   371  // deferconvert, which would catch calling the loop body
   372  // and having it defer after the loop is done. If we have a
   373  // more general catch of loop body misuse, though, this
   374  // might not be worth worrying about in addition.
   375  //
   376  // See also ../cmd/compile/internal/rangefunc/rewrite.go.
   377  func deferrangefunc() any {
   378  	gp := getg()
   379  	if gp.m.curg != gp {
   380  		// go code on the system stack can't defer
   381  		throw("defer on system stack")
   382  	}
   383  
   384  	d := newdefer()
   385  	d.link = gp._defer
   386  	gp._defer = d
   387  	d.pc = sys.GetCallerPC()
   388  	// We must not be preempted between calling GetCallerSP and
   389  	// storing it to d.sp because GetCallerSP's result is a
   390  	// uintptr stack pointer.
   391  	d.sp = sys.GetCallerSP()
   392  
   393  	d.rangefunc = true
   394  	d.head = new(atomic.Pointer[_defer])
   395  
   396  	return d.head
   397  }
   398  
   399  // badDefer returns a fixed bad defer pointer for poisoning an atomic defer list head.
   400  func badDefer() *_defer {
   401  	return (*_defer)(unsafe.Pointer(uintptr(1)))
   402  }
   403  
   404  // deferprocat is like deferproc but adds to the atomic list represented by frame.
   405  // See the doc comment for deferrangefunc for details.
   406  func deferprocat(fn func(), frame any) {
   407  	head := frame.(*atomic.Pointer[_defer])
   408  	if raceenabled {
   409  		racewritepc(unsafe.Pointer(head), sys.GetCallerPC(), abi.FuncPCABIInternal(deferprocat))
   410  	}
   411  	d1 := newdefer()
   412  	d1.fn = fn
   413  	for {
   414  		d1.link = head.Load()
   415  		if d1.link == badDefer() {
   416  			throw("defer after range func returned")
   417  		}
   418  		if head.CompareAndSwap(d1.link, d1) {
   419  			break
   420  		}
   421  	}
   422  }
   423  
   424  // deferconvert converts the rangefunc defer list of d0 into an ordinary list
   425  // following d0.
   426  // See the doc comment for deferrangefunc for details.
   427  func deferconvert(d0 *_defer) {
   428  	head := d0.head
   429  	if raceenabled {
   430  		racereadpc(unsafe.Pointer(head), sys.GetCallerPC(), abi.FuncPCABIInternal(deferconvert))
   431  	}
   432  	tail := d0.link
   433  	d0.rangefunc = false
   434  
   435  	var d *_defer
   436  	for {
   437  		d = head.Load()
   438  		if head.CompareAndSwap(d, badDefer()) {
   439  			break
   440  		}
   441  	}
   442  	if d == nil {
   443  		return
   444  	}
   445  	for d1 := d; ; d1 = d1.link {
   446  		d1.sp = d0.sp
   447  		d1.pc = d0.pc
   448  		if d1.link == nil {
   449  			d1.link = tail
   450  			break
   451  		}
   452  	}
   453  	d0.link = d
   454  	return
   455  }
   456  
   457  // deferprocStack queues a new deferred function with a defer record on the stack.
   458  // The defer record must have its fn field initialized.
   459  // All other fields can contain junk.
   460  // Nosplit because of the uninitialized pointer fields on the stack.
   461  //
   462  //go:nosplit
   463  func deferprocStack(d *_defer) {
   464  	gp := getg()
   465  	if gp.m.curg != gp {
   466  		// go code on the system stack can't defer
   467  		throw("defer on system stack")
   468  	}
   469  
   470  	// fn is already set.
   471  	// The other fields are junk on entry to deferprocStack and
   472  	// are initialized here.
   473  	d.heap = false
   474  	d.rangefunc = false
   475  	d.sp = sys.GetCallerSP()
   476  	d.pc = sys.GetCallerPC()
   477  	// The lines below implement:
   478  	//   d.panic = nil
   479  	//   d.fd = nil
   480  	//   d.link = gp._defer
   481  	//   d.head = nil
   482  	//   gp._defer = d
   483  	// But without write barriers. The first three are writes to
   484  	// the stack so they don't need a write barrier, and furthermore
   485  	// are to uninitialized memory, so they must not use a write barrier.
   486  	// The fourth write does not require a write barrier because we
   487  	// explicitly mark all the defer structures, so we don't need to
   488  	// keep track of pointers to them with a write barrier.
   489  	*(*uintptr)(unsafe.Pointer(&d.link)) = uintptr(unsafe.Pointer(gp._defer))
   490  	*(*uintptr)(unsafe.Pointer(&d.head)) = 0
   491  	*(*uintptr)(unsafe.Pointer(&gp._defer)) = uintptr(unsafe.Pointer(d))
   492  }
   493  
   494  // Each P holds a pool for defers.
   495  
   496  // Allocate a Defer, usually using per-P pool.
   497  // Each defer must be released with freedefer.  The defer is not
   498  // added to any defer chain yet.
   499  func newdefer() *_defer {
   500  	var d *_defer
   501  	mp := acquirem()
   502  	pp := mp.p.ptr()
   503  	if len(pp.deferpool) == 0 && sched.deferpool != nil {
   504  		lock(&sched.deferlock)
   505  		for len(pp.deferpool) < cap(pp.deferpool)/2 && sched.deferpool != nil {
   506  			d := sched.deferpool
   507  			sched.deferpool = d.link
   508  			d.link = nil
   509  			pp.deferpool = append(pp.deferpool, d)
   510  		}
   511  		unlock(&sched.deferlock)
   512  	}
   513  	if n := len(pp.deferpool); n > 0 {
   514  		d = pp.deferpool[n-1]
   515  		pp.deferpool[n-1] = nil
   516  		pp.deferpool = pp.deferpool[:n-1]
   517  	}
   518  	releasem(mp)
   519  	mp, pp = nil, nil
   520  
   521  	if d == nil {
   522  		// Allocate new defer.
   523  		d = new(_defer)
   524  	}
   525  	d.heap = true
   526  	return d
   527  }
   528  
   529  // popDefer pops the head of gp's defer list and frees it.
   530  func popDefer(gp *g) {
   531  	d := gp._defer
   532  	d.fn = nil // Can in theory point to the stack
   533  	// We must not copy the stack between the updating gp._defer and setting
   534  	// d.link to nil. Between these two steps, d is not on any defer list, so
   535  	// stack copying won't adjust stack pointers in it (namely, d.link). Hence,
   536  	// if we were to copy the stack, d could then contain a stale pointer.
   537  	gp._defer = d.link
   538  	d.link = nil
   539  	// After this point we can copy the stack.
   540  
   541  	if !d.heap {
   542  		return
   543  	}
   544  
   545  	mp := acquirem()
   546  	pp := mp.p.ptr()
   547  	if len(pp.deferpool) == cap(pp.deferpool) {
   548  		// Transfer half of local cache to the central cache.
   549  		var first, last *_defer
   550  		for len(pp.deferpool) > cap(pp.deferpool)/2 {
   551  			n := len(pp.deferpool)
   552  			d := pp.deferpool[n-1]
   553  			pp.deferpool[n-1] = nil
   554  			pp.deferpool = pp.deferpool[:n-1]
   555  			if first == nil {
   556  				first = d
   557  			} else {
   558  				last.link = d
   559  			}
   560  			last = d
   561  		}
   562  		lock(&sched.deferlock)
   563  		last.link = sched.deferpool
   564  		sched.deferpool = first
   565  		unlock(&sched.deferlock)
   566  	}
   567  
   568  	*d = _defer{}
   569  
   570  	pp.deferpool = append(pp.deferpool, d)
   571  
   572  	releasem(mp)
   573  	mp, pp = nil, nil
   574  }
   575  
   576  // deferreturn runs deferred functions for the caller's frame.
   577  // The compiler inserts a call to this at the end of any
   578  // function which calls defer.
   579  func deferreturn() {
   580  	var p _panic
   581  	p.deferreturn = true
   582  
   583  	p.start(sys.GetCallerPC(), unsafe.Pointer(sys.GetCallerSP()))
   584  	for {
   585  		fn, ok := p.nextDefer()
   586  		if !ok {
   587  			break
   588  		}
   589  		fn()
   590  	}
   591  }
   592  
   593  // Goexit terminates the goroutine that calls it. No other goroutine is affected.
   594  // Goexit runs all deferred calls before terminating the goroutine. Because Goexit
   595  // is not a panic, any recover calls in those deferred functions will return nil.
   596  //
   597  // Calling Goexit from the main goroutine terminates that goroutine
   598  // without func main returning. Since func main has not returned,
   599  // the program continues execution of other goroutines.
   600  // If all other goroutines exit, the program crashes.
   601  //
   602  // It crashes if called from a thread not created by the Go runtime.
   603  func Goexit() {
   604  	// Create a panic object for Goexit, so we can recognize when it might be
   605  	// bypassed by a recover().
   606  	var p _panic
   607  	p.goexit = true
   608  
   609  	p.start(sys.GetCallerPC(), unsafe.Pointer(sys.GetCallerSP()))
   610  	for {
   611  		fn, ok := p.nextDefer()
   612  		if !ok {
   613  			break
   614  		}
   615  		fn()
   616  	}
   617  
   618  	goexit1()
   619  }
   620  
   621  // Call all Error and String methods before freezing the world.
   622  // Used when crashing with panicking.
   623  func preprintpanics(p *_panic) {
   624  	defer func() {
   625  		text := "panic while printing panic value"
   626  		switch r := recover().(type) {
   627  		case nil:
   628  			// nothing to do
   629  		case string:
   630  			throw(text + ": " + r)
   631  		default:
   632  			throw(text + ": type " + toRType(efaceOf(&r)._type).string())
   633  		}
   634  	}()
   635  	for p != nil {
   636  		if p.link != nil && *efaceOf(&p.link.arg) == *efaceOf(&p.arg) {
   637  			// This panic contains the same value as the next one in the chain.
   638  			// Mark it as repanicked. We will skip printing it twice in a row.
   639  			p.link.repanicked = true
   640  			p = p.link
   641  			continue
   642  		}
   643  		switch v := p.arg.(type) {
   644  		case error:
   645  			p.arg = v.Error()
   646  		case stringer:
   647  			p.arg = v.String()
   648  		}
   649  		p = p.link
   650  	}
   651  }
   652  
   653  // Print all currently active panics. Used when crashing.
   654  // Should only be called after preprintpanics.
   655  func printpanics(p *_panic) {
   656  	if p.link != nil {
   657  		printpanics(p.link)
   658  		if p.link.repanicked {
   659  			return
   660  		}
   661  		if !p.link.goexit {
   662  			print("\t")
   663  		}
   664  	}
   665  	if p.goexit {
   666  		return
   667  	}
   668  	print("panic: ")
   669  	printpanicval(p.arg)
   670  	if p.repanicked {
   671  		print(" [recovered, repanicked]")
   672  	} else if p.recovered {
   673  		print(" [recovered]")
   674  	}
   675  	print("\n")
   676  }
   677  
   678  // readvarintUnsafe reads the uint32 in varint format starting at fd, and returns the
   679  // uint32 and a pointer to the byte following the varint.
   680  //
   681  // The implementation is the same with runtime.readvarint, except that this function
   682  // uses unsafe.Pointer for speed.
   683  func readvarintUnsafe(fd unsafe.Pointer) (uint32, unsafe.Pointer) {
   684  	var r uint32
   685  	var shift int
   686  	for {
   687  		b := *(*uint8)(fd)
   688  		fd = add(fd, unsafe.Sizeof(b))
   689  		if b < 128 {
   690  			return r + uint32(b)<<shift, fd
   691  		}
   692  		r += uint32(b&0x7F) << (shift & 31)
   693  		shift += 7
   694  		if shift > 28 {
   695  			panic("Bad varint")
   696  		}
   697  	}
   698  }
   699  
   700  // A PanicNilError happens when code calls panic(nil).
   701  //
   702  // Before Go 1.21, programs that called panic(nil) observed recover returning nil.
   703  // Starting in Go 1.21, programs that call panic(nil) observe recover returning a *PanicNilError.
   704  // Programs can change back to the old behavior by setting GODEBUG=panicnil=1.
   705  type PanicNilError struct {
   706  	// This field makes PanicNilError structurally different from
   707  	// any other struct in this package, and the _ makes it different
   708  	// from any struct in other packages too.
   709  	// This avoids any accidental conversions being possible
   710  	// between this struct and some other struct sharing the same fields,
   711  	// like happened in go.dev/issue/56603.
   712  	_ [0]*PanicNilError
   713  }
   714  
   715  func (*PanicNilError) Error() string { return "panic called with nil argument" }
   716  func (*PanicNilError) RuntimeError() {}
   717  
   718  var panicnil = &godebugInc{name: "panicnil"}
   719  
   720  // The implementation of the predeclared function panic.
   721  // The compiler emits calls to this function.
   722  //
   723  // gopanic should be an internal detail,
   724  // but widely used packages access it using linkname.
   725  // Notable members of the hall of shame include:
   726  //   - go.undefinedlabs.com/scopeagent
   727  //   - github.com/goplus/igop
   728  //
   729  // Do not remove or change the type signature.
   730  // See go.dev/issue/67401.
   731  //
   732  //go:linkname gopanic
   733  func gopanic(e any) {
   734  	if e == nil {
   735  		if debug.panicnil.Load() != 1 {
   736  			e = new(PanicNilError)
   737  		} else {
   738  			panicnil.IncNonDefault()
   739  		}
   740  	}
   741  
   742  	gp := getg()
   743  	if gp.m.curg != gp {
   744  		print("panic: ")
   745  		printpanicval(e)
   746  		print("\n")
   747  		throw("panic on system stack")
   748  	}
   749  
   750  	if gp.m.mallocing != 0 {
   751  		print("panic: ")
   752  		printpanicval(e)
   753  		print("\n")
   754  		throw("panic during malloc")
   755  	}
   756  	if gp.m.preemptoff != "" {
   757  		print("panic: ")
   758  		printpanicval(e)
   759  		print("\n")
   760  		print("preempt off reason: ")
   761  		print(gp.m.preemptoff)
   762  		print("\n")
   763  		throw("panic during preemptoff")
   764  	}
   765  	if gp.m.locks != 0 {
   766  		print("panic: ")
   767  		printpanicval(e)
   768  		print("\n")
   769  		throw("panic holding locks")
   770  	}
   771  
   772  	var p _panic
   773  	p.arg = e
   774  
   775  	runningPanicDefers.Add(1)
   776  
   777  	p.start(sys.GetCallerPC(), unsafe.Pointer(sys.GetCallerSP()))
   778  	for {
   779  		fn, ok := p.nextDefer()
   780  		if !ok {
   781  			break
   782  		}
   783  		fn()
   784  	}
   785  
   786  	// If we're tracing, flush the current generation to make the trace more
   787  	// readable.
   788  	//
   789  	// TODO(aktau): Handle a panic from within traceAdvance more gracefully.
   790  	// Currently it would hang. Not handled now because it is very unlikely, and
   791  	// already unrecoverable.
   792  	if traceEnabled() {
   793  		traceAdvance(false)
   794  	}
   795  
   796  	// ran out of deferred calls - old-school panic now
   797  	// Because it is unsafe to call arbitrary user code after freezing
   798  	// the world, we call preprintpanics to invoke all necessary Error
   799  	// and String methods to prepare the panic strings before startpanic.
   800  	preprintpanics(&p)
   801  
   802  	fatalpanic(&p)   // should not return
   803  	*(*int)(nil) = 0 // not reached
   804  }
   805  
   806  // start initializes a panic to start unwinding the stack.
   807  //
   808  // If p.goexit is true, then start may return multiple times.
   809  func (p *_panic) start(pc uintptr, sp unsafe.Pointer) {
   810  	gp := getg()
   811  
   812  	// Record the caller's PC and SP, so recovery can identify panics
   813  	// that have been recovered. Also, so that if p is from Goexit, we
   814  	// can restart its defer processing loop if a recovered panic tries
   815  	// to jump past it.
   816  	p.startPC = sys.GetCallerPC()
   817  	p.startSP = unsafe.Pointer(sys.GetCallerSP())
   818  
   819  	if p.deferreturn {
   820  		p.sp = sp
   821  
   822  		if s := (*savedOpenDeferState)(gp.param); s != nil {
   823  			// recovery saved some state for us, so that we can resume
   824  			// calling open-coded defers without unwinding the stack.
   825  
   826  			gp.param = nil
   827  
   828  			p.retpc = s.retpc
   829  			p.deferBitsPtr = (*byte)(add(sp, s.deferBitsOffset))
   830  			p.slotsPtr = add(sp, s.slotsOffset)
   831  		}
   832  
   833  		return
   834  	}
   835  
   836  	p.link = gp._panic
   837  	gp._panic = (*_panic)(noescape(unsafe.Pointer(p)))
   838  
   839  	// Initialize state machine, and find the first frame with a defer.
   840  	//
   841  	// Note: We could use startPC and startSP here, but callers will
   842  	// never have defer statements themselves. By starting at their
   843  	// caller instead, we avoid needing to unwind through an extra
   844  	// frame. It also somewhat simplifies the terminating condition for
   845  	// deferreturn.
   846  	p.lr, p.fp = pc, sp
   847  	p.nextFrame()
   848  }
   849  
   850  // nextDefer returns the next deferred function to invoke, if any.
   851  //
   852  // Note: The "ok bool" result is necessary to correctly handle when
   853  // the deferred function itself was nil (e.g., "defer (func())(nil)").
   854  func (p *_panic) nextDefer() (func(), bool) {
   855  	gp := getg()
   856  
   857  	if !p.deferreturn {
   858  		if gp._panic != p {
   859  			throw("bad panic stack")
   860  		}
   861  
   862  		if p.recovered {
   863  			mcall(recovery) // does not return
   864  			throw("recovery failed")
   865  		}
   866  	}
   867  
   868  	// The assembler adjusts p.argp in wrapper functions that shouldn't
   869  	// be visible to recover(), so we need to restore it each iteration.
   870  	p.argp = add(p.startSP, sys.MinFrameSize)
   871  
   872  	for {
   873  		for p.deferBitsPtr != nil {
   874  			bits := *p.deferBitsPtr
   875  
   876  			// Check whether any open-coded defers are still pending.
   877  			//
   878  			// Note: We need to check this upfront (rather than after
   879  			// clearing the top bit) because it's possible that Goexit
   880  			// invokes a deferred call, and there were still more pending
   881  			// open-coded defers in the frame; but then the deferred call
   882  			// panic and invoked the remaining defers in the frame, before
   883  			// recovering and restarting the Goexit loop.
   884  			if bits == 0 {
   885  				p.deferBitsPtr = nil
   886  				break
   887  			}
   888  
   889  			// Find index of top bit set.
   890  			i := 7 - uintptr(sys.LeadingZeros8(bits))
   891  
   892  			// Clear bit and store it back.
   893  			bits &^= 1 << i
   894  			*p.deferBitsPtr = bits
   895  
   896  			return *(*func())(add(p.slotsPtr, i*goarch.PtrSize)), true
   897  		}
   898  
   899  	Recheck:
   900  		if d := gp._defer; d != nil && d.sp == uintptr(p.sp) {
   901  			if d.rangefunc {
   902  				deferconvert(d)
   903  				popDefer(gp)
   904  				goto Recheck
   905  			}
   906  
   907  			fn := d.fn
   908  
   909  			p.retpc = d.pc
   910  
   911  			// Unlink and free.
   912  			popDefer(gp)
   913  
   914  			return fn, true
   915  		}
   916  
   917  		if !p.nextFrame() {
   918  			return nil, false
   919  		}
   920  	}
   921  }
   922  
   923  // nextFrame finds the next frame that contains deferred calls, if any.
   924  func (p *_panic) nextFrame() (ok bool) {
   925  	if p.lr == 0 {
   926  		return false
   927  	}
   928  
   929  	gp := getg()
   930  	systemstack(func() {
   931  		var limit uintptr
   932  		if d := gp._defer; d != nil {
   933  			limit = d.sp
   934  		}
   935  
   936  		var u unwinder
   937  		u.initAt(p.lr, uintptr(p.fp), 0, gp, 0)
   938  		for {
   939  			if !u.valid() {
   940  				p.lr = 0
   941  				return // ok == false
   942  			}
   943  
   944  			// TODO(mdempsky): If we populate u.frame.fn.deferreturn for
   945  			// every frame containing a defer (not just open-coded defers),
   946  			// then we can simply loop until we find the next frame where
   947  			// it's non-zero.
   948  
   949  			if u.frame.sp == limit {
   950  				break // found a frame with linked defers
   951  			}
   952  
   953  			if p.initOpenCodedDefers(u.frame.fn, unsafe.Pointer(u.frame.varp)) {
   954  				break // found a frame with open-coded defers
   955  			}
   956  
   957  			u.next()
   958  		}
   959  
   960  		p.lr = u.frame.lr
   961  		p.sp = unsafe.Pointer(u.frame.sp)
   962  		p.fp = unsafe.Pointer(u.frame.fp)
   963  
   964  		ok = true
   965  	})
   966  
   967  	return
   968  }
   969  
   970  func (p *_panic) initOpenCodedDefers(fn funcInfo, varp unsafe.Pointer) bool {
   971  	fd := funcdata(fn, abi.FUNCDATA_OpenCodedDeferInfo)
   972  	if fd == nil {
   973  		return false
   974  	}
   975  
   976  	if fn.deferreturn == 0 {
   977  		throw("missing deferreturn")
   978  	}
   979  
   980  	deferBitsOffset, fd := readvarintUnsafe(fd)
   981  	deferBitsPtr := (*uint8)(add(varp, -uintptr(deferBitsOffset)))
   982  	if *deferBitsPtr == 0 {
   983  		return false // has open-coded defers, but none pending
   984  	}
   985  
   986  	slotsOffset, fd := readvarintUnsafe(fd)
   987  
   988  	p.retpc = fn.entry() + uintptr(fn.deferreturn)
   989  	p.deferBitsPtr = deferBitsPtr
   990  	p.slotsPtr = add(varp, -uintptr(slotsOffset))
   991  
   992  	return true
   993  }
   994  
   995  // The implementation of the predeclared function recover.
   996  // Cannot split the stack because it needs to reliably
   997  // find the stack segment of its caller.
   998  //
   999  // TODO(rsc): Once we commit to CopyStackAlways,
  1000  // this doesn't need to be nosplit.
  1001  //
  1002  //go:nosplit
  1003  func gorecover(argp uintptr) any {
  1004  	// Must be in a function running as part of a deferred call during the panic.
  1005  	// Must be called from the topmost function of the call
  1006  	// (the function used in the defer statement).
  1007  	// p.argp is the argument pointer of that topmost deferred function call.
  1008  	// Compare against argp reported by caller.
  1009  	// If they match, the caller is the one who can recover.
  1010  	gp := getg()
  1011  	p := gp._panic
  1012  	if p != nil && !p.goexit && !p.recovered && argp == uintptr(p.argp) {
  1013  		p.recovered = true
  1014  		return p.arg
  1015  	}
  1016  	return nil
  1017  }
  1018  
  1019  //go:linkname sync_throw sync.throw
  1020  func sync_throw(s string) {
  1021  	throw(s)
  1022  }
  1023  
  1024  //go:linkname sync_fatal sync.fatal
  1025  func sync_fatal(s string) {
  1026  	fatal(s)
  1027  }
  1028  
  1029  //go:linkname rand_fatal crypto/rand.fatal
  1030  func rand_fatal(s string) {
  1031  	fatal(s)
  1032  }
  1033  
  1034  //go:linkname sysrand_fatal crypto/internal/sysrand.fatal
  1035  func sysrand_fatal(s string) {
  1036  	fatal(s)
  1037  }
  1038  
  1039  //go:linkname fips_fatal crypto/internal/fips140.fatal
  1040  func fips_fatal(s string) {
  1041  	fatal(s)
  1042  }
  1043  
  1044  //go:linkname maps_fatal internal/runtime/maps.fatal
  1045  func maps_fatal(s string) {
  1046  	fatal(s)
  1047  }
  1048  
  1049  //go:linkname internal_sync_throw internal/sync.throw
  1050  func internal_sync_throw(s string) {
  1051  	throw(s)
  1052  }
  1053  
  1054  //go:linkname internal_sync_fatal internal/sync.fatal
  1055  func internal_sync_fatal(s string) {
  1056  	fatal(s)
  1057  }
  1058  
  1059  //go:linkname cgroup_throw internal/runtime/cgroup.throw
  1060  func cgroup_throw(s string) {
  1061  	throw(s)
  1062  }
  1063  
  1064  // throw triggers a fatal error that dumps a stack trace and exits.
  1065  //
  1066  // throw should be used for runtime-internal fatal errors where Go itself,
  1067  // rather than user code, may be at fault for the failure.
  1068  //
  1069  // throw should be an internal detail,
  1070  // but widely used packages access it using linkname.
  1071  // Notable members of the hall of shame include:
  1072  //   - github.com/bytedance/sonic
  1073  //   - github.com/cockroachdb/pebble
  1074  //   - github.com/dgraph-io/ristretto
  1075  //   - github.com/outcaste-io/ristretto
  1076  //   - github.com/pingcap/br
  1077  //   - gvisor.dev/gvisor
  1078  //   - github.com/sagernet/gvisor
  1079  //
  1080  // Do not remove or change the type signature.
  1081  // See go.dev/issue/67401.
  1082  //
  1083  //go:linkname throw
  1084  //go:nosplit
  1085  func throw(s string) {
  1086  	// Everything throw does should be recursively nosplit so it
  1087  	// can be called even when it's unsafe to grow the stack.
  1088  	systemstack(func() {
  1089  		print("fatal error: ")
  1090  		printindented(s) // logically printpanicval(s), but avoids convTstring write barrier
  1091  		print("\n")
  1092  	})
  1093  
  1094  	fatalthrow(throwTypeRuntime)
  1095  }
  1096  
  1097  // fatal triggers a fatal error that dumps a stack trace and exits.
  1098  //
  1099  // fatal is equivalent to throw, but is used when user code is expected to be
  1100  // at fault for the failure, such as racing map writes.
  1101  //
  1102  // fatal does not include runtime frames, system goroutines, or frame metadata
  1103  // (fp, sp, pc) in the stack trace unless GOTRACEBACK=system or higher.
  1104  //
  1105  //go:nosplit
  1106  func fatal(s string) {
  1107  	// Everything fatal does should be recursively nosplit so it
  1108  	// can be called even when it's unsafe to grow the stack.
  1109  	printlock() // Prevent multiple interleaved fatal reports. See issue 69447.
  1110  	systemstack(func() {
  1111  		print("fatal error: ")
  1112  		printindented(s) // logically printpanicval(s), but avoids convTstring write barrier
  1113  		print("\n")
  1114  	})
  1115  
  1116  	fatalthrow(throwTypeUser)
  1117  	printunlock()
  1118  }
  1119  
  1120  // runningPanicDefers is non-zero while running deferred functions for panic.
  1121  // This is used to try hard to get a panic stack trace out when exiting.
  1122  var runningPanicDefers atomic.Uint32
  1123  
  1124  // panicking is non-zero when crashing the program for an unrecovered panic.
  1125  var panicking atomic.Uint32
  1126  
  1127  // paniclk is held while printing the panic information and stack trace,
  1128  // so that two concurrent panics don't overlap their output.
  1129  var paniclk mutex
  1130  
  1131  // Unwind the stack after a deferred function calls recover
  1132  // after a panic. Then arrange to continue running as though
  1133  // the caller of the deferred function returned normally.
  1134  //
  1135  // However, if unwinding the stack would skip over a Goexit call, we
  1136  // return into the Goexit loop instead, so it can continue processing
  1137  // defers instead.
  1138  func recovery(gp *g) {
  1139  	p := gp._panic
  1140  	pc, sp, fp := p.retpc, uintptr(p.sp), uintptr(p.fp)
  1141  	p0, saveOpenDeferState := p, p.deferBitsPtr != nil && *p.deferBitsPtr != 0
  1142  
  1143  	// The linker records the f-relative address of a call to deferreturn in f's funcInfo.
  1144  	// Assuming a "normal" call to recover() inside one of f's deferred functions
  1145  	// invoked for a panic, that is the desired PC for exiting f.
  1146  	f := findfunc(pc)
  1147  	if f.deferreturn == 0 {
  1148  		throw("no deferreturn")
  1149  	}
  1150  	gotoPc := f.entry() + uintptr(f.deferreturn)
  1151  
  1152  	// Unwind the panic stack.
  1153  	for ; p != nil && uintptr(p.startSP) < sp; p = p.link {
  1154  		// Don't allow jumping past a pending Goexit.
  1155  		// Instead, have its _panic.start() call return again.
  1156  		//
  1157  		// TODO(mdempsky): In this case, Goexit will resume walking the
  1158  		// stack where it left off, which means it will need to rewalk
  1159  		// frames that we've already processed.
  1160  		//
  1161  		// There's a similar issue with nested panics, when the inner
  1162  		// panic supersedes the outer panic. Again, we end up needing to
  1163  		// walk the same stack frames.
  1164  		//
  1165  		// These are probably pretty rare occurrences in practice, and
  1166  		// they don't seem any worse than the existing logic. But if we
  1167  		// move the unwinding state into _panic, we could detect when we
  1168  		// run into where the last panic started, and then just pick up
  1169  		// where it left off instead.
  1170  		//
  1171  		// With how subtle defer handling is, this might not actually be
  1172  		// worthwhile though.
  1173  		if p.goexit {
  1174  			gotoPc, sp = p.startPC, uintptr(p.startSP)
  1175  			saveOpenDeferState = false // goexit is unwinding the stack anyway
  1176  			break
  1177  		}
  1178  
  1179  		runningPanicDefers.Add(-1)
  1180  	}
  1181  	gp._panic = p
  1182  
  1183  	if p == nil { // must be done with signal
  1184  		gp.sig = 0
  1185  	}
  1186  
  1187  	if gp.param != nil {
  1188  		throw("unexpected gp.param")
  1189  	}
  1190  	if saveOpenDeferState {
  1191  		// If we're returning to deferreturn and there are more open-coded
  1192  		// defers for it to call, save enough state for it to be able to
  1193  		// pick up where p0 left off.
  1194  		gp.param = unsafe.Pointer(&savedOpenDeferState{
  1195  			retpc: p0.retpc,
  1196  
  1197  			// We need to save deferBitsPtr and slotsPtr too, but those are
  1198  			// stack pointers. To avoid issues around heap objects pointing
  1199  			// to the stack, save them as offsets from SP.
  1200  			deferBitsOffset: uintptr(unsafe.Pointer(p0.deferBitsPtr)) - uintptr(p0.sp),
  1201  			slotsOffset:     uintptr(p0.slotsPtr) - uintptr(p0.sp),
  1202  		})
  1203  	}
  1204  
  1205  	// TODO(mdempsky): Currently, we rely on frames containing "defer"
  1206  	// to end with "CALL deferreturn; RET". This allows deferreturn to
  1207  	// finish running any pending defers in the frame.
  1208  	//
  1209  	// But we should be able to tell whether there are still pending
  1210  	// defers here. If there aren't, we can just jump directly to the
  1211  	// "RET" instruction. And if there are, we don't need an actual
  1212  	// "CALL deferreturn" instruction; we can simulate it with something
  1213  	// like:
  1214  	//
  1215  	//	if usesLR {
  1216  	//		lr = pc
  1217  	//	} else {
  1218  	//		sp -= sizeof(pc)
  1219  	//		*(*uintptr)(sp) = pc
  1220  	//	}
  1221  	//	pc = funcPC(deferreturn)
  1222  	//
  1223  	// So that we effectively tail call into deferreturn, such that it
  1224  	// then returns to the simple "RET" epilogue. That would save the
  1225  	// overhead of the "deferreturn" call when there aren't actually any
  1226  	// pending defers left, and shrink the TEXT size of compiled
  1227  	// binaries. (Admittedly, both of these are modest savings.)
  1228  
  1229  	// Ensure we're recovering within the appropriate stack.
  1230  	if sp != 0 && (sp < gp.stack.lo || gp.stack.hi < sp) {
  1231  		print("recover: ", hex(sp), " not in [", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n")
  1232  		throw("bad recovery")
  1233  	}
  1234  
  1235  	// branch directly to the deferreturn
  1236  	gp.sched.sp = sp
  1237  	gp.sched.pc = gotoPc
  1238  	gp.sched.lr = 0
  1239  	// Restore the bp on platforms that support frame pointers.
  1240  	// N.B. It's fine to not set anything for platforms that don't
  1241  	// support frame pointers, since nothing consumes them.
  1242  	switch {
  1243  	case goarch.IsAmd64 != 0:
  1244  		// on x86, fp actually points one word higher than the top of
  1245  		// the frame since the return address is saved on the stack by
  1246  		// the caller
  1247  		gp.sched.bp = fp - 2*goarch.PtrSize
  1248  	case goarch.IsArm64 != 0:
  1249  		// on arm64, the architectural bp points one word higher
  1250  		// than the sp. fp is totally useless to us here, because it
  1251  		// only gets us to the caller's fp.
  1252  		gp.sched.bp = sp - goarch.PtrSize
  1253  	}
  1254  	gogo(&gp.sched)
  1255  }
  1256  
  1257  // fatalthrow implements an unrecoverable runtime throw. It freezes the
  1258  // system, prints stack traces starting from its caller, and terminates the
  1259  // process.
  1260  //
  1261  //go:nosplit
  1262  func fatalthrow(t throwType) {
  1263  	pc := sys.GetCallerPC()
  1264  	sp := sys.GetCallerSP()
  1265  	gp := getg()
  1266  
  1267  	if gp.m.throwing == throwTypeNone {
  1268  		gp.m.throwing = t
  1269  	}
  1270  
  1271  	// Switch to the system stack to avoid any stack growth, which may make
  1272  	// things worse if the runtime is in a bad state.
  1273  	systemstack(func() {
  1274  		if isSecureMode() {
  1275  			exit(2)
  1276  		}
  1277  
  1278  		startpanic_m()
  1279  
  1280  		if dopanic_m(gp, pc, sp, nil) {
  1281  			// crash uses a decent amount of nosplit stack and we're already
  1282  			// low on stack in throw, so crash on the system stack (unlike
  1283  			// fatalpanic).
  1284  			crash()
  1285  		}
  1286  
  1287  		exit(2)
  1288  	})
  1289  
  1290  	*(*int)(nil) = 0 // not reached
  1291  }
  1292  
  1293  // fatalpanic implements an unrecoverable panic. It is like fatalthrow, except
  1294  // that if msgs != nil, fatalpanic also prints panic messages and decrements
  1295  // runningPanicDefers once main is blocked from exiting.
  1296  //
  1297  //go:nosplit
  1298  func fatalpanic(msgs *_panic) {
  1299  	pc := sys.GetCallerPC()
  1300  	sp := sys.GetCallerSP()
  1301  	gp := getg()
  1302  	var docrash bool
  1303  	// Switch to the system stack to avoid any stack growth, which
  1304  	// may make things worse if the runtime is in a bad state.
  1305  	systemstack(func() {
  1306  		if startpanic_m() && msgs != nil {
  1307  			// There were panic messages and startpanic_m
  1308  			// says it's okay to try to print them.
  1309  
  1310  			// startpanic_m set panicking, which will
  1311  			// block main from exiting, so now OK to
  1312  			// decrement runningPanicDefers.
  1313  			runningPanicDefers.Add(-1)
  1314  
  1315  			printpanics(msgs)
  1316  		}
  1317  
  1318  		// If this panic is the result of a synctest bubble deadlock,
  1319  		// print stacks for the goroutines in the bubble.
  1320  		var bubble *synctestBubble
  1321  		if de, ok := msgs.arg.(synctestDeadlockError); ok {
  1322  			bubble = de.bubble
  1323  		}
  1324  
  1325  		docrash = dopanic_m(gp, pc, sp, bubble)
  1326  	})
  1327  
  1328  	if docrash {
  1329  		// By crashing outside the above systemstack call, debuggers
  1330  		// will not be confused when generating a backtrace.
  1331  		// Function crash is marked nosplit to avoid stack growth.
  1332  		crash()
  1333  	}
  1334  
  1335  	systemstack(func() {
  1336  		exit(2)
  1337  	})
  1338  
  1339  	*(*int)(nil) = 0 // not reached
  1340  }
  1341  
  1342  // startpanic_m prepares for an unrecoverable panic.
  1343  //
  1344  // It returns true if panic messages should be printed, or false if
  1345  // the runtime is in bad shape and should just print stacks.
  1346  //
  1347  // It must not have write barriers even though the write barrier
  1348  // explicitly ignores writes once dying > 0. Write barriers still
  1349  // assume that g.m.p != nil, and this function may not have P
  1350  // in some contexts (e.g. a panic in a signal handler for a signal
  1351  // sent to an M with no P).
  1352  //
  1353  //go:nowritebarrierrec
  1354  func startpanic_m() bool {
  1355  	gp := getg()
  1356  	if mheap_.cachealloc.size == 0 { // very early
  1357  		print("runtime: panic before malloc heap initialized\n")
  1358  	}
  1359  	// Disallow malloc during an unrecoverable panic. A panic
  1360  	// could happen in a signal handler, or in a throw, or inside
  1361  	// malloc itself. We want to catch if an allocation ever does
  1362  	// happen (even if we're not in one of these situations).
  1363  	gp.m.mallocing++
  1364  
  1365  	// If we're dying because of a bad lock count, set it to a
  1366  	// good lock count so we don't recursively panic below.
  1367  	if gp.m.locks < 0 {
  1368  		gp.m.locks = 1
  1369  	}
  1370  
  1371  	switch gp.m.dying {
  1372  	case 0:
  1373  		// Setting dying >0 has the side-effect of disabling this G's writebuf.
  1374  		gp.m.dying = 1
  1375  		panicking.Add(1)
  1376  		lock(&paniclk)
  1377  		if debug.schedtrace > 0 || debug.scheddetail > 0 {
  1378  			schedtrace(true)
  1379  		}
  1380  		freezetheworld()
  1381  		return true
  1382  	case 1:
  1383  		// Something failed while panicking.
  1384  		// Just print a stack trace and exit.
  1385  		gp.m.dying = 2
  1386  		print("panic during panic\n")
  1387  		return false
  1388  	case 2:
  1389  		// This is a genuine bug in the runtime, we couldn't even
  1390  		// print the stack trace successfully.
  1391  		gp.m.dying = 3
  1392  		print("stack trace unavailable\n")
  1393  		exit(4)
  1394  		fallthrough
  1395  	default:
  1396  		// Can't even print! Just exit.
  1397  		exit(5)
  1398  		return false // Need to return something.
  1399  	}
  1400  }
  1401  
  1402  var didothers bool
  1403  var deadlock mutex
  1404  
  1405  // gp is the crashing g running on this M, but may be a user G, while getg() is
  1406  // always g0.
  1407  // If bubble is non-nil, print the stacks for goroutines in this group as well.
  1408  func dopanic_m(gp *g, pc, sp uintptr, bubble *synctestBubble) bool {
  1409  	if gp.sig != 0 {
  1410  		signame := signame(gp.sig)
  1411  		if signame != "" {
  1412  			print("[signal ", signame)
  1413  		} else {
  1414  			print("[signal ", hex(gp.sig))
  1415  		}
  1416  		print(" code=", hex(gp.sigcode0), " addr=", hex(gp.sigcode1), " pc=", hex(gp.sigpc), "]\n")
  1417  	}
  1418  
  1419  	level, all, docrash := gotraceback()
  1420  	if level > 0 {
  1421  		if gp != gp.m.curg {
  1422  			all = true
  1423  		}
  1424  		if gp != gp.m.g0 {
  1425  			print("\n")
  1426  			goroutineheader(gp)
  1427  			traceback(pc, sp, 0, gp)
  1428  		} else if level >= 2 || gp.m.throwing >= throwTypeRuntime {
  1429  			print("\nruntime stack:\n")
  1430  			traceback(pc, sp, 0, gp)
  1431  		}
  1432  		if !didothers {
  1433  			if all {
  1434  				didothers = true
  1435  				tracebackothers(gp)
  1436  			} else if bubble != nil {
  1437  				// This panic is caused by a synctest bubble deadlock.
  1438  				// Print stacks for goroutines in the deadlocked bubble.
  1439  				tracebacksomeothers(gp, func(other *g) bool {
  1440  					return bubble == other.bubble
  1441  				})
  1442  			}
  1443  		}
  1444  
  1445  	}
  1446  	unlock(&paniclk)
  1447  
  1448  	if panicking.Add(-1) != 0 {
  1449  		// Some other m is panicking too.
  1450  		// Let it print what it needs to print.
  1451  		// Wait forever without chewing up cpu.
  1452  		// It will exit when it's done.
  1453  		lock(&deadlock)
  1454  		lock(&deadlock)
  1455  	}
  1456  
  1457  	printDebugLog()
  1458  
  1459  	return docrash
  1460  }
  1461  
  1462  // canpanic returns false if a signal should throw instead of
  1463  // panicking.
  1464  //
  1465  //go:nosplit
  1466  func canpanic() bool {
  1467  	gp := getg()
  1468  	mp := acquirem()
  1469  
  1470  	// Is it okay for gp to panic instead of crashing the program?
  1471  	// Yes, as long as it is running Go code, not runtime code,
  1472  	// and not stuck in a system call.
  1473  	if gp != mp.curg {
  1474  		releasem(mp)
  1475  		return false
  1476  	}
  1477  	// N.B. mp.locks != 1 instead of 0 to account for acquirem.
  1478  	if mp.locks != 1 || mp.mallocing != 0 || mp.throwing != throwTypeNone || mp.preemptoff != "" || mp.dying != 0 {
  1479  		releasem(mp)
  1480  		return false
  1481  	}
  1482  	status := readgstatus(gp)
  1483  	if status&^_Gscan != _Grunning || gp.syscallsp != 0 {
  1484  		releasem(mp)
  1485  		return false
  1486  	}
  1487  	if GOOS == "windows" && mp.libcallsp != 0 {
  1488  		releasem(mp)
  1489  		return false
  1490  	}
  1491  	releasem(mp)
  1492  	return true
  1493  }
  1494  
  1495  // shouldPushSigpanic reports whether pc should be used as sigpanic's
  1496  // return PC (pushing a frame for the call). Otherwise, it should be
  1497  // left alone so that LR is used as sigpanic's return PC, effectively
  1498  // replacing the top-most frame with sigpanic. This is used by
  1499  // preparePanic.
  1500  func shouldPushSigpanic(gp *g, pc, lr uintptr) bool {
  1501  	if pc == 0 {
  1502  		// Probably a call to a nil func. The old LR is more
  1503  		// useful in the stack trace. Not pushing the frame
  1504  		// will make the trace look like a call to sigpanic
  1505  		// instead. (Otherwise the trace will end at sigpanic
  1506  		// and we won't get to see who faulted.)
  1507  		return false
  1508  	}
  1509  	// If we don't recognize the PC as code, but we do recognize
  1510  	// the link register as code, then this assumes the panic was
  1511  	// caused by a call to non-code. In this case, we want to
  1512  	// ignore this call to make unwinding show the context.
  1513  	//
  1514  	// If we running C code, we're not going to recognize pc as a
  1515  	// Go function, so just assume it's good. Otherwise, traceback
  1516  	// may try to read a stale LR that looks like a Go code
  1517  	// pointer and wander into the woods.
  1518  	if gp.m.incgo || findfunc(pc).valid() {
  1519  		// This wasn't a bad call, so use PC as sigpanic's
  1520  		// return PC.
  1521  		return true
  1522  	}
  1523  	if findfunc(lr).valid() {
  1524  		// This was a bad call, but the LR is good, so use the
  1525  		// LR as sigpanic's return PC.
  1526  		return false
  1527  	}
  1528  	// Neither the PC or LR is good. Hopefully pushing a frame
  1529  	// will work.
  1530  	return true
  1531  }
  1532  
  1533  // isAbortPC reports whether pc is the program counter at which
  1534  // runtime.abort raises a signal.
  1535  //
  1536  // It is nosplit because it's part of the isgoexception
  1537  // implementation.
  1538  //
  1539  //go:nosplit
  1540  func isAbortPC(pc uintptr) bool {
  1541  	f := findfunc(pc)
  1542  	if !f.valid() {
  1543  		return false
  1544  	}
  1545  	return f.funcID == abi.FuncID_abort
  1546  }
  1547
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