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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import (
"runtime/internal/atomic"
"unsafe"
)
// For gccgo, use go:linkname to export compiler-called functions.
//
//go:linkname deferproc
//go:linkname deferprocStack
//go:linkname deferreturn
//go:linkname setdeferretaddr
//go:linkname checkdefer
//go:linkname gopanic
//go:linkname canrecover
//go:linkname makefuncfficanrecover
//go:linkname makefuncreturning
//go:linkname gorecover
//go:linkname deferredrecover
//go:linkname goPanicIndex
//go:linkname goPanicIndexU
//go:linkname goPanicSliceAlen
//go:linkname goPanicSliceAlenU
//go:linkname goPanicSliceAcap
//go:linkname goPanicSliceAcapU
//go:linkname goPanicSliceB
//go:linkname goPanicSliceBU
//go:linkname goPanicSlice3Alen
//go:linkname goPanicSlice3AlenU
//go:linkname goPanicSlice3Acap
//go:linkname goPanicSlice3AcapU
//go:linkname goPanicSlice3B
//go:linkname goPanicSlice3BU
//go:linkname goPanicSlice3C
//go:linkname goPanicSlice3CU
//go:linkname panicmem
// Temporary for C code to call:
//go:linkname throw
// Check to make sure we can really generate a panic. If the panic
// was generated from the runtime, or from inside malloc, then convert
// to a throw of msg.
// pc should be the program counter of the compiler-generated code that
// triggered this panic.
func panicCheck1(pc uintptr, msg string) {
name, _, _, _ := funcfileline(pc-1, -1)
if hasPrefix(name, "runtime.") {
throw(msg)
}
// TODO: is this redundant? How could we be in malloc
// but not in the runtime? runtime/internal/*, maybe?
gp := getg()
if gp != nil && gp.m != nil && gp.m.mallocing != 0 {
throw(msg)
}
}
// Same as above, but calling from the runtime is allowed.
//
// Using this function is necessary for any panic that may be
// generated by runtime.sigpanic, since those are always called by the
// runtime.
func panicCheck2(err string) {
// panic allocates, so to avoid recursive malloc, turn panics
// during malloc into throws.
gp := getg()
if gp != nil && gp.m != nil && gp.m.mallocing != 0 {
throw(err)
}
}
// Many of the following panic entry-points turn into throws when they
// happen in various runtime contexts. These should never happen in
// the runtime, and if they do, they indicate a serious issue and
// should not be caught by user code.
//
// The panic{Index,Slice,divide,shift} functions are called by
// code generated by the compiler for out of bounds index expressions,
// out of bounds slice expressions, division by zero, and shift by negative.
// The panicdivide (again), panicoverflow, panicfloat, and panicmem
// functions are called by the signal handler when a signal occurs
// indicating the respective problem.
//
// Since panic{Index,Slice,shift} are never called directly, and
// since the runtime package should never have an out of bounds slice
// or array reference or negative shift, if we see those functions called from the
// runtime package we turn the panic into a throw. That will dump the
// entire runtime stack for easier debugging.
//
// The entry points called by the signal handler will be called from
// runtime.sigpanic, so we can't disallow calls from the runtime to
// these (they always look like they're called from the runtime).
// Hence, for these, we just check for clearly bad runtime conditions.
// failures in the comparisons for s[x], 0 <= x < y (y == len(s))
func goPanicIndex(x int, y int) {
panicCheck1(getcallerpc(), "index out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsIndex})
}
func goPanicIndexU(x uint, y int) {
panicCheck1(getcallerpc(), "index out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsIndex})
}
// failures in the comparisons for s[:x], 0 <= x <= y (y == len(s) or cap(s))
func goPanicSliceAlen(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceAlen})
}
func goPanicSliceAlenU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceAlen})
}
func goPanicSliceAcap(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceAcap})
}
func goPanicSliceAcapU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceAcap})
}
// failures in the comparisons for s[x:y], 0 <= x <= y
func goPanicSliceB(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceB})
}
func goPanicSliceBU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceB})
}
// failures in the comparisons for s[::x], 0 <= x <= y (y == len(s) or cap(s))
func goPanicSlice3Alen(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3Alen})
}
func goPanicSlice3AlenU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3Alen})
}
func goPanicSlice3Acap(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3Acap})
}
func goPanicSlice3AcapU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3Acap})
}
// failures in the comparisons for s[:x:y], 0 <= x <= y
func goPanicSlice3B(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3B})
}
func goPanicSlice3BU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3B})
}
// failures in the comparisons for s[x:y:], 0 <= x <= y
func goPanicSlice3C(x int, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSlice3C})
}
func goPanicSlice3CU(x uint, y int) {
panicCheck1(getcallerpc(), "slice bounds out of range")
panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3C})
}
var shiftError = error(errorString("negative shift amount"))
func panicshift() {
panicCheck1(getcallerpc(), "negative shift amount")
panic(shiftError)
}
var divideError = error(errorString("integer divide by zero"))
func panicdivide() {
panicCheck2("integer divide by zero")
panic(divideError)
}
var overflowError = error(errorString("integer overflow"))
func panicoverflow() {
panicCheck2("integer overflow")
panic(overflowError)
}
var floatError = error(errorString("floating point error"))
func panicfloat() {
panicCheck2("floating point error")
panic(floatError)
}
var memoryError = error(errorString("invalid memory address or nil pointer dereference"))
func panicmem() {
panicCheck2("invalid memory address or nil pointer dereference")
panic(memoryError)
}
// deferproc creates a new deferred function.
// The compiler turns a defer statement into a call to this.
// frame points into the stack frame; it is used to determine which
// deferred functions are for the current stack frame, and whether we
// have already deferred functions for this frame.
// pfn is a C function pointer.
// arg is a value to pass to pfn.
func deferproc(frame *bool, pfn uintptr, arg unsafe.Pointer) {
d := newdefer()
if d._panic != nil {
throw("deferproc: d.panic != nil after newdefer")
}
d.frame = frame
d.panicStack = getg()._panic
d.pfn = pfn
d.arg = arg
d.retaddr = 0
d.makefunccanrecover = false
}
// deferprocStack queues a new deferred function with a defer record on the stack.
// The defer record, d, does not need to be initialized.
// Other arguments are the same as in deferproc.
//go:nosplit
func deferprocStack(d *_defer, frame *bool, pfn uintptr, arg unsafe.Pointer) {
gp := getg()
if gp.m.curg != gp {
// go code on the system stack can't defer
throw("defer on system stack")
}
d.pfn = pfn
d.retaddr = 0
d.makefunccanrecover = false
d.heap = false
// The lines below implement:
// d.frame = frame
// d.arg = arg
// d._panic = nil
// d.panicStack = gp._panic
// d.link = gp._defer
// But without write barriers. They are writes to the stack so they
// don't need a write barrier, and furthermore are to uninitialized
// memory, so they must not use a write barrier.
*(*uintptr)(unsafe.Pointer(&d.frame)) = uintptr(unsafe.Pointer(frame))
*(*uintptr)(unsafe.Pointer(&d.arg)) = uintptr(unsafe.Pointer(arg))
*(*uintptr)(unsafe.Pointer(&d._panic)) = 0
*(*uintptr)(unsafe.Pointer(&d.panicStack)) = uintptr(unsafe.Pointer(gp._panic))
*(*uintptr)(unsafe.Pointer(&d.link)) = uintptr(unsafe.Pointer(gp._defer))
gp._defer = d
}
// Allocate a Defer, usually using per-P pool.
// Each defer must be released with freedefer.
func newdefer() *_defer {
var d *_defer
gp := getg()
pp := gp.m.p.ptr()
if len(pp.deferpool) == 0 && sched.deferpool != nil {
systemstack(func() {
lock(&sched.deferlock)
for len(pp.deferpool) < cap(pp.deferpool)/2 && sched.deferpool != nil {
d := sched.deferpool
sched.deferpool = d.link
d.link = nil
pp.deferpool = append(pp.deferpool, d)
}
unlock(&sched.deferlock)
})
}
if n := len(pp.deferpool); n > 0 {
d = pp.deferpool[n-1]
pp.deferpool[n-1] = nil
pp.deferpool = pp.deferpool[:n-1]
}
if d == nil {
systemstack(func() {
d = new(_defer)
})
if debugCachedWork {
// Duplicate the tail below so if there's a
// crash in checkPut we can tell if d was just
// allocated or came from the pool.
d.heap = true
d.link = gp._defer
gp._defer = d
return d
}
}
d.heap = true
d.link = gp._defer
gp._defer = d
return d
}
// Free the given defer.
// The defer cannot be used after this call.
//
// This must not grow the stack because there may be a frame without a
// stack map when this is called.
//
//go:nosplit
func freedefer(d *_defer) {
if d._panic != nil {
freedeferpanic()
}
if d.pfn != 0 {
freedeferfn()
}
if !d.heap {
return
}
pp := getg().m.p.ptr()
if len(pp.deferpool) == cap(pp.deferpool) {
// Transfer half of local cache to the central cache.
//
// Take this slow path on the system stack so
// we don't grow freedefer's stack.
systemstack(func() {
var first, last *_defer
for len(pp.deferpool) > cap(pp.deferpool)/2 {
n := len(pp.deferpool)
d := pp.deferpool[n-1]
pp.deferpool[n-1] = nil
pp.deferpool = pp.deferpool[:n-1]
if first == nil {
first = d
} else {
last.link = d
}
last = d
}
lock(&sched.deferlock)
last.link = sched.deferpool
sched.deferpool = first
unlock(&sched.deferlock)
})
}
// These lines used to be simply `*d = _defer{}` but that
// started causing a nosplit stack overflow via typedmemmove.
d.link = nil
d.frame = nil
d.panicStack = nil
d.arg = nil
d.retaddr = 0
d.makefunccanrecover = false
// d._panic and d.pfn must be nil already.
// If not, we would have called freedeferpanic or freedeferfn above,
// both of which throw.
pp.deferpool = append(pp.deferpool, d)
}
// Separate function so that it can split stack.
// Windows otherwise runs out of stack space.
func freedeferpanic() {
// _panic must be cleared before d is unlinked from gp.
throw("freedefer with d._panic != nil")
}
func freedeferfn() {
// fn must be cleared before d is unlinked from gp.
throw("freedefer with d.fn != nil")
}
// deferreturn is called to undefer the stack.
// The compiler inserts a call to this function as a finally clause
// wrapped around the body of any function that calls defer.
// The frame argument points to the stack frame of the function.
func deferreturn(frame *bool) {
gp := getg()
for gp._defer != nil && gp._defer.frame == frame {
d := gp._defer
pfn := d.pfn
d.pfn = 0
if pfn != 0 {
// This is rather awkward.
// The gc compiler does this using assembler
// code in jmpdefer.
var fn func(unsafe.Pointer)
*(*uintptr)(unsafe.Pointer(&fn)) = uintptr(noescape(unsafe.Pointer(&pfn)))
gp.deferring = true
fn(d.arg)
gp.deferring = false
}
// If that was CgocallBackDone, it will have freed the
// defer for us, since we are no longer running as Go code.
if getg() == nil {
*frame = true
return
}
if gp.ranCgocallBackDone {
gp.ranCgocallBackDone = false
*frame = true
return
}
gp._defer = d.link
freedefer(d)
// Since we are executing a defer function now, we
// know that we are returning from the calling
// function. If the calling function, or one of its
// callees, panicked, then the defer functions would
// be executed by panic.
*frame = true
}
}
// __builtin_extract_return_addr is a GCC intrinsic that converts an
// address returned by __builtin_return_address(0) to a real address.
// On most architectures this is a nop.
//extern __builtin_extract_return_addr
func __builtin_extract_return_addr(uintptr) uintptr
// setdeferretaddr records the address to which the deferred function
// returns. This is check by canrecover. The frontend relies on this
// function returning false.
func setdeferretaddr(retaddr uintptr) bool {
gp := getg()
if gp._defer != nil {
gp._defer.retaddr = __builtin_extract_return_addr(retaddr)
}
return false
}
// checkdefer is called by exception handlers used when unwinding the
// stack after a recovered panic. The exception handler is simply
// checkdefer(frame)
// return;
// If we have not yet reached the frame we are looking for, we
// continue unwinding.
func checkdefer(frame *bool) {
gp := getg()
if gp == nil {
// We should never wind up here. Even if some other
// language throws an exception, the cgo code
// should ensure that g is set.
throw("no g in checkdefer")
} else if gp.isforeign {
// Some other language has thrown an exception.
// We need to run the local defer handlers.
// If they call recover, we stop unwinding here.
var p _panic
p.isforeign = true
p.link = gp._panic
gp._panic = (*_panic)(noescape(unsafe.Pointer(&p)))
for {
d := gp._defer
if d == nil || d.frame != frame || d.pfn == 0 {
break
}
pfn := d.pfn
gp._defer = d.link
var fn func(unsafe.Pointer)
*(*uintptr)(unsafe.Pointer(&fn)) = uintptr(noescape(unsafe.Pointer(&pfn)))
gp.deferring = true
fn(d.arg)
gp.deferring = false
freedefer(d)
if p.recovered {
// The recover function caught the panic
// thrown by some other language.
break
}
}
recovered := p.recovered
gp._panic = p.link
if recovered {
// Just return and continue executing Go code.
*frame = true
return
}
// We are panicking through this function.
*frame = false
} else if gp._defer != nil && gp._defer.pfn == 0 && gp._defer.frame == frame {
// This is the defer function that called recover.
// Simply return to stop the stack unwind, and let the
// Go code continue to execute.
d := gp._defer
gp._defer = d.link
freedefer(d)
// We are returning from this function.
*frame = true
return
}
// This is some other defer function. It was already run by
// the call to panic, or just above. Rethrow the exception.
rethrowException()
throw("rethrowException returned")
}
// unwindStack starts unwinding the stack for a panic. We unwind
// function calls until we reach the one which used a defer function
// which called recover. Each function which uses a defer statement
// will have an exception handler, as shown above for checkdefer.
func unwindStack() {
// Allocate the exception type used by the unwind ABI.
// It would be nice to define it in runtime_sysinfo.go,
// but current definitions don't work because the required
// alignment is larger than can be represented in Go.
// The type never contains any Go pointers.
size := unwindExceptionSize()
usize := uintptr(unsafe.Sizeof(uintptr(0)))
c := (size + usize - 1) / usize
s := make([]uintptr, c)
getg().exception = unsafe.Pointer(&s[0])
throwException()
}
// Goexit terminates the goroutine that calls it. No other goroutine is affected.
// Goexit runs all deferred calls before terminating the goroutine. Because Goexit
// is not a panic, any recover calls in those deferred functions will return nil.
//
// Calling Goexit from the main goroutine terminates that goroutine
// without func main returning. Since func main has not returned,
// the program continues execution of other goroutines.
// If all other goroutines exit, the program crashes.
func Goexit() {
// Run all deferred functions for the current goroutine.
// This code is similar to gopanic, see that implementation
// for detailed comments.
gp := getg()
gp.goexiting = true
for {
d := gp._defer
if d == nil {
break
}
pfn := d.pfn
if pfn == 0 {
if d._panic != nil {
d._panic.aborted = true
d._panic = nil
}
gp._defer = d.link
freedefer(d)
continue
}
d.pfn = 0
var fn func(unsafe.Pointer)
*(*uintptr)(unsafe.Pointer(&fn)) = uintptr(noescape(unsafe.Pointer(&pfn)))
gp.deferring = true
fn(d.arg)
gp.deferring = false
if gp._defer != d {
throw("bad defer entry in Goexit")
}
d._panic = nil
gp._defer = d.link
freedefer(d)
// Note: we ignore recovers here because Goexit isn't a panic
}
gp.goexiting = false
goexit1()
}
// Call all Error and String methods before freezing the world.
// Used when crashing with panicking.
func preprintpanics(p *_panic) {
defer func() {
if recover() != nil {
throw("panic while printing panic value")
}
}()
for p != nil {
switch v := p.arg.(type) {
case error:
p.arg = v.Error()
case stringer:
p.arg = v.String()
}
p = p.link
}
}
// Print all currently active panics. Used when crashing.
// Should only be called after preprintpanics.
func printpanics(p *_panic) {
if p.link != nil {
printpanics(p.link)
print("\t")
}
print("panic: ")
printany(p.arg)
if p.recovered {
print(" [recovered]")
}
print("\n")
}
// The implementation of the predeclared function panic.
func gopanic(e interface{}) {
gp := getg()
if gp.m.curg != gp {
print("panic: ")
printany(e)
print("\n")
throw("panic on system stack")
}
if gp.m.mallocing != 0 {
print("panic: ")
printany(e)
print("\n")
throw("panic during malloc")
}
if gp.m.preemptoff != "" {
print("panic: ")
printany(e)
print("\n")
print("preempt off reason: ")
print(gp.m.preemptoff)
print("\n")
throw("panic during preemptoff")
}
if gp.m.locks != 0 {
print("panic: ")
printany(e)
print("\n")
throw("panic holding locks")
}
// The gc compiler allocates this new _panic struct on the
// stack. We can't do that, because when a deferred function
// recovers the panic we unwind the stack. We unlink this
// entry before unwinding the stack, but that doesn't help in
// the case where we panic, a deferred function recovers and
// then panics itself, that panic is in turn recovered, and
// unwinds the stack past this stack frame.
p := &_panic{
arg: e,
link: gp._panic,
}
gp._panic = p
atomic.Xadd(&runningPanicDefers, 1)
for {
d := gp._defer
if d == nil {
break
}
pfn := d.pfn
// If defer was started by earlier panic or Goexit (and, since we're back here, that triggered a new panic),
// take defer off list. The earlier panic or Goexit will not continue running.
if pfn == 0 {
if d._panic != nil {
d._panic.aborted = true
}
d._panic = nil
gp._defer = d.link
freedefer(d)
continue
}
d.pfn = 0
// Record the panic that is running the defer.
// If there is a new panic during the deferred call, that panic
// will find d in the list and will mark d._panic (this panic) aborted.
d._panic = p
var fn func(unsafe.Pointer)
*(*uintptr)(unsafe.Pointer(&fn)) = uintptr(noescape(unsafe.Pointer(&pfn)))
gp.deferring = true
fn(d.arg)
gp.deferring = false
if gp._defer != d {
throw("bad defer entry in panic")
}
d._panic = nil
if p.recovered {
atomic.Xadd(&runningPanicDefers, -1)
gp._panic = p.link
// Aborted panics are marked but remain on the g.panic list.
// Remove them from the list.
for gp._panic != nil && gp._panic.aborted {
gp._panic = gp._panic.link
}
if gp._panic == nil { // must be done with signal
gp.sig = 0
}
// Unwind the stack by throwing an exception.
// The compiler has arranged to create
// exception handlers in each function
// that uses a defer statement. These
// exception handlers will check whether
// the entry on the top of the defer stack
// is from the current function. If it is,
// we have unwound the stack far enough.
unwindStack()
throw("unwindStack returned")
}
// Because we executed that defer function by a panic,
// and it did not call recover, we know that we are
// not returning from the calling function--we are
// panicking through it.
*d.frame = false
// Deferred function did not panic. Remove d.
// In the p.recovered case, d will be removed by checkdefer.
gp._defer = d.link
freedefer(d)
}
// ran out of deferred calls - old-school panic now
// Because it is unsafe to call arbitrary user code after freezing
// the world, we call preprintpanics to invoke all necessary Error
// and String methods to prepare the panic strings before startpanic.
preprintpanics(gp._panic)
fatalpanic(gp._panic) // should not return
*(*int)(nil) = 0 // not reached
}
// currentDefer returns the top of the defer stack if it can be recovered.
// Otherwise it returns nil.
func currentDefer() *_defer {
gp := getg()
d := gp._defer
if d == nil {
return nil
}
// The panic that would be recovered is the one on the top of
// the panic stack. We do not want to recover it if that panic
// was on the top of the panic stack when this function was
// deferred.
if d.panicStack == gp._panic {
return nil
}
// The deferred thunk will call setdeferretaddr. If this has
// not happened, then we have not been called via defer, and
// we can not recover.
if d.retaddr == 0 {
return nil
}
return d
}
// canrecover is called by a thunk to see if the real function would
// be permitted to recover a panic value. Recovering a value is
// permitted if the thunk was called directly by defer. retaddr is the
// return address of the function that is calling canrecover--that is,
// the thunk.
func canrecover(retaddr uintptr) bool {
d := currentDefer()
if d == nil {
return false
}
ret := __builtin_extract_return_addr(retaddr)
dret := d.retaddr
if ret <= dret && ret+16 >= dret {
return true
}
// On some systems, in some cases, the return address does not
// work reliably. See http://gcc.gnu.org/PR60406. If we are
// permitted to call recover, the call stack will look like this:
// runtime.gopanic, runtime.deferreturn, etc.
// thunk to call deferred function (calls __go_set_defer_retaddr)
// function that calls __go_can_recover (passing return address)
// runtime.canrecover
// Calling callers will skip the thunks. So if our caller's
// caller starts with "runtime.", then we are permitted to
// call recover.
var locs [16]location
if callers(1, locs[:2]) < 2 {
return false
}
name := locs[1].function
if hasPrefix(name, "runtime.") {
return true
}
// If the function calling recover was created by reflect.MakeFunc,
// then makefuncfficanrecover will have set makefunccanrecover.
if !d.makefunccanrecover {
return false
}
// We look up the stack, ignoring libffi functions and
// functions in the reflect package, until we find
// reflect.makeFuncStub or reflect.ffi_callback called by FFI
// functions. Then we check the caller of that function.
n := callers(2, locs[:])
foundFFICallback := false
i := 0
for ; i < n; i++ {
name = locs[i].function
if name == "" {
// No function name means this caller isn't Go code.
// Assume that this is libffi.
continue
}
// Ignore function in libffi.
if hasPrefix(name, "ffi_") {
continue
}
if foundFFICallback {
break
}
if name == "reflect.ffi_callback" {
foundFFICallback = true
continue
}
// Ignore other functions in the reflect package.
if hasPrefix(name, "reflect.") || hasPrefix(name, ".1reflect.") {
continue
}
// We should now be looking at the real caller.
break
}
if i < n {
name = locs[i].function
if hasPrefix(name, "runtime.") {
return true
}
}
return false
}
// This function is called when code is about to enter a function
// created by the libffi version of reflect.MakeFunc. This function is
// passed the names of the callers of the libffi code that called the
// stub. It uses them to decide whether it is permitted to call
// recover, and sets d.makefunccanrecover so that gorecover can make
// the same decision.
func makefuncfficanrecover(loc []location) {
d := currentDefer()
if d == nil {
return
}
// If we are already in a call stack of MakeFunc functions,
// there is nothing we can usefully check here.
if d.makefunccanrecover {
return
}
// loc starts with the caller of our caller. That will be a thunk.
// If its caller was a function function, then it was called
// directly by defer.
if len(loc) < 2 {
return
}
name := loc[1].function
if hasPrefix(name, "runtime.") {
d.makefunccanrecover = true
}
}
// makefuncreturning is called when code is about to exit a function
// created by reflect.MakeFunc. It is called by the function stub used
// by reflect.MakeFunc. It clears the makefunccanrecover field. It's
// OK to always clear this field, because canrecover will only be
// called by a stub created for a function that calls recover. That
// stub will not call a function created by reflect.MakeFunc, so by
// the time we get here any caller higher up on the call stack no
// longer needs the information.
func makefuncreturning() {
d := getg()._defer
if d != nil {
d.makefunccanrecover = false
}
}
// The implementation of the predeclared function recover.
func gorecover() interface{} {
gp := getg()
p := gp._panic
if p != nil && !p.recovered {
p.recovered = true
return p.arg
}
return nil
}
// deferredrecover is called when a call to recover is deferred. That
// is, something like
// defer recover()
//
// We need to handle this specially. In gc, the recover function
// looks up the stack frame. In particular, that means that a deferred
// recover will not recover a panic thrown in the same function that
// defers the recover. It will only recover a panic thrown in a
// function that defers the deferred call to recover.
//
// In other words:
//
// func f1() {
// defer recover() // does not stop panic
// panic(0)
// }
//
// func f2() {
// defer func() {
// defer recover() // stops panic(0)
// }()
// panic(0)
// }
//
// func f3() {
// defer func() {
// defer recover() // does not stop panic
// panic(0)
// }()
// panic(1)
// }
//
// func f4() {
// defer func() {
// defer func() {
// defer recover() // stops panic(0)
// }()
// panic(0)
// }()
// panic(1)
// }
//
// The interesting case here is f3. As can be seen from f2, the
// deferred recover could pick up panic(1). However, this does not
// happen because it is blocked by the panic(0).
//
// When a function calls recover, then when we invoke it we pass a
// hidden parameter indicating whether it should recover something.
// This parameter is set based on whether the function is being
// invoked directly from defer. The parameter winds up determining
// whether __go_recover or __go_deferred_recover is called at all.
//
// In the case of a deferred recover, the hidden parameter that
// controls the call is actually the one set up for the function that
// runs the defer recover() statement. That is the right thing in all
// the cases above except for f3. In f3 the function is permitted to
// call recover, but the deferred recover call is not. We address that
// here by checking for that specific case before calling recover. If
// this function was deferred when there is already a panic on the
// panic stack, then we can only recover that panic, not any other.
// Note that we can get away with using a special function here
// because you are not permitted to take the address of a predeclared
// function like recover.
func deferredrecover() interface{} {
gp := getg()
if gp._defer == nil || gp._defer.panicStack != gp._panic {
return nil
}
return gorecover()
}
//go:linkname sync_throw sync.throw
func sync_throw(s string) {
throw(s)
}
//go:nosplit
func throw(s string) {
// Everything throw does should be recursively nosplit so it
// can be called even when it's unsafe to grow the stack.
systemstack(func() {
print("fatal error: ", s, "\n")
})
gp := getg()
if gp.m.throwing == 0 {
gp.m.throwing = 1
}
fatalthrow()
*(*int)(nil) = 0 // not reached
}
// runningPanicDefers is non-zero while running deferred functions for panic.
// runningPanicDefers is incremented and decremented atomically.
// This is used to try hard to get a panic stack trace out when exiting.
var runningPanicDefers uint32
// panicking is non-zero when crashing the program for an unrecovered panic.
// panicking is incremented and decremented atomically.
var panicking uint32
// paniclk is held while printing the panic information and stack trace,
// so that two concurrent panics don't overlap their output.
var paniclk mutex
// fatalthrow implements an unrecoverable runtime throw. It freezes the
// system, prints stack traces starting from its caller, and terminates the
// process.
//
//go:nosplit
func fatalthrow() {
pc := getcallerpc()
sp := getcallersp()
gp := getg()
startpanic_m()
if dopanic_m(gp, pc, sp) {
crash()
}
exit(2)
*(*int)(nil) = 0 // not reached
}
// fatalpanic implements an unrecoverable panic. It is like fatalthrow, except
// that if msgs != nil, fatalpanic also prints panic messages and decrements
// runningPanicDefers once main is blocked from exiting.
//
//go:nosplit
func fatalpanic(msgs *_panic) {
pc := getcallerpc()
sp := getcallersp()
gp := getg()
var docrash bool
if startpanic_m() && msgs != nil {
// There were panic messages and startpanic_m
// says it's okay to try to print them.
// startpanic_m set panicking, which will
// block main from exiting, so now OK to
// decrement runningPanicDefers.
atomic.Xadd(&runningPanicDefers, -1)
printpanics(msgs)
}
docrash = dopanic_m(gp, pc, sp)
if docrash {
// By crashing outside the above systemstack call, debuggers
// will not be confused when generating a backtrace.
// Function crash is marked nosplit to avoid stack growth.
crash()
}
systemstack(func() {
exit(2)
})
*(*int)(nil) = 0 // not reached
}
// startpanic_m prepares for an unrecoverable panic.
//
// It returns true if panic messages should be printed, or false if
// the runtime is in bad shape and should just print stacks.
//
// It must not have write barriers even though the write barrier
// explicitly ignores writes once dying > 0. Write barriers still
// assume that g.m.p != nil, and this function may not have P
// in some contexts (e.g. a panic in a signal handler for a signal
// sent to an M with no P).
//
//go:nowritebarrierrec
func startpanic_m() bool {
_g_ := getg()
if mheap_.cachealloc.size == 0 { // very early
print("runtime: panic before malloc heap initialized\n")
}
// Disallow malloc during an unrecoverable panic. A panic
// could happen in a signal handler, or in a throw, or inside
// malloc itself. We want to catch if an allocation ever does
// happen (even if we're not in one of these situations).
_g_.m.mallocing++
// If we're dying because of a bad lock count, set it to a
// good lock count so we don't recursively panic below.
if _g_.m.locks < 0 {
_g_.m.locks = 1
}
switch _g_.m.dying {
case 0:
// Setting dying >0 has the side-effect of disabling this G's writebuf.
_g_.m.dying = 1
atomic.Xadd(&panicking, 1)
lock(&paniclk)
if debug.schedtrace > 0 || debug.scheddetail > 0 {
schedtrace(true)
}
freezetheworld()
return true
case 1:
// Something failed while panicking.
// Just print a stack trace and exit.
_g_.m.dying = 2
print("panic during panic\n")
return false
case 2:
// This is a genuine bug in the runtime, we couldn't even
// print the stack trace successfully.
_g_.m.dying = 3
print("stack trace unavailable\n")
exit(4)
fallthrough
default:
// Can't even print! Just exit.
exit(5)
return false // Need to return something.
}
}
var didothers bool
var deadlock mutex
func dopanic_m(gp *g, pc, sp uintptr) bool {
if gp.sig != 0 {
signame := signame(gp.sig)
if signame != "" {
print("[signal ", signame)
} else {
print("[signal ", hex(gp.sig))
}
print(" code=", hex(gp.sigcode0), " addr=", hex(gp.sigcode1), " pc=", hex(gp.sigpc), "]\n")
}
level, all, docrash := gotraceback()
_g_ := getg()
if level > 0 {
if gp != gp.m.curg {
all = true
}
if gp != gp.m.g0 {
print("\n")
goroutineheader(gp)
traceback(0)
} else if level >= 2 || _g_.m.throwing > 0 {
print("\nruntime stack:\n")
traceback(0)
}
if !didothers && all {
didothers = true
tracebackothers(gp)
}
}
unlock(&paniclk)
if atomic.Xadd(&panicking, -1) != 0 {
// Some other m is panicking too.
// Let it print what it needs to print.
// Wait forever without chewing up cpu.
// It will exit when it's done.
lock(&deadlock)
lock(&deadlock)
}
printDebugLog()
return docrash
}
// canpanic returns false if a signal should throw instead of
// panicking.
//
//go:nosplit
func canpanic(gp *g) bool {
// Note that g is m->gsignal, different from gp.
// Note also that g->m can change at preemption, so m can go stale
// if this function ever makes a function call.
_g_ := getg()
_m_ := _g_.m
// Is it okay for gp to panic instead of crashing the program?
// Yes, as long as it is running Go code, not runtime code,
// and not stuck in a system call.
if gp == nil || gp != _m_.curg {
return false
}
if _m_.locks != 0 || _m_.mallocing != 0 || _m_.throwing != 0 || _m_.preemptoff != "" || _m_.dying != 0 {
return false
}
status := readgstatus(gp)
if status&^_Gscan != _Grunning || gp.syscallsp != 0 {
return false
}
return true
}
// isAbortPC reports whether pc is the program counter at which
// runtime.abort raises a signal.
//
// It is nosplit because it's part of the isgoexception
// implementation.
//
//go:nosplit
func isAbortPC(pc uintptr) bool {
return false
}