// 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"
"runtime/internal/sys"
"unsafe"
)
// We have two different ways of doing defers. The older way involves creating a
// defer record at the time that a defer statement is executing and adding it to a
// defer chain. This chain is inspected by the deferreturn call at all function
// exits in order to run the appropriate defer calls. A cheaper way (which we call
// open-coded defers) is used for functions in which no defer statements occur in
// loops. In that case, we simply store the defer function/arg information into
// specific stack slots at the point of each defer statement, as well as setting a
// bit in a bitmask. At each function exit, we add inline code to directly make
// the appropriate defer calls based on the bitmask and fn/arg information stored
// on the stack. During panic/Goexit processing, the appropriate defer calls are
// made using extra funcdata info that indicates the exact stack slots that
// contain the bitmask and defer fn/args.
// 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) {
if sys.GoarchWasm == 0 && hasPrefix(funcname(findfunc(pc)), "runtime.") {
// Note: wasm can't tail call, so we can't get the original caller's pc.
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.
//
// The panic{Index,Slice} functions are implemented in assembly and tail call
// to the goPanic{Index,Slice} functions below. This is done so we can use
// a space-minimal register calling convention.
// 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})
}
// Implemented in assembly, as they take arguments in registers.
// Declared here to mark them as ABIInternal.
func panicIndex(x int, y int)
func panicIndexU(x uint, y int)
func panicSliceAlen(x int, y int)
func panicSliceAlenU(x uint, y int)
func panicSliceAcap(x int, y int)
func panicSliceAcapU(x uint, y int)
func panicSliceB(x int, y int)
func panicSliceBU(x uint, y int)
func panicSlice3Alen(x int, y int)
func panicSlice3AlenU(x uint, y int)
func panicSlice3Acap(x int, y int)
func panicSlice3AcapU(x uint, y int)
func panicSlice3B(x int, y int)
func panicSlice3BU(x uint, y int)
func panicSlice3C(x int, y int)
func panicSlice3CU(x uint, y int)
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)
}
func panicmemAddr(addr uintptr) {
panicCheck2("invalid memory address or nil pointer dereference")
panic(errorAddressString{msg: "invalid memory address or nil pointer dereference", addr: addr})
}
// Create a new deferred function fn with siz bytes of arguments.
// The compiler turns a defer statement into a call to this.
//go:nosplit
func deferproc(siz int32, fn *funcval) { // arguments of fn follow fn
gp := getg()
if gp.m.curg != gp {
// go code on the system stack can't defer
throw("defer on system stack")
}
// the arguments of fn are in a perilous state. The stack map
// for deferproc does not describe them. So we can't let garbage
// collection or stack copying trigger until we've copied them out
// to somewhere safe. The memmove below does that.
// Until the copy completes, we can only call nosplit routines.
sp := getcallersp()
argp := uintptr(unsafe.Pointer(&fn)) + unsafe.Sizeof(fn)
callerpc := getcallerpc()
d := newdefer(siz)
if d._panic != nil {
throw("deferproc: d.panic != nil after newdefer")
}
d.link = gp._defer
gp._defer = d
d.fn = fn
d.pc = callerpc
d.sp = sp
switch siz {
case 0:
// Do nothing.
case sys.PtrSize:
*(*uintptr)(deferArgs(d)) = *(*uintptr)(unsafe.Pointer(argp))
default:
memmove(deferArgs(d), unsafe.Pointer(argp), uintptr(siz))
}
// deferproc returns 0 normally.
// a deferred func that stops a panic
// makes the deferproc return 1.
// the code the compiler generates always
// checks the return value and jumps to the
// end of the function if deferproc returns != 0.
return0()
// No code can go here - the C return register has
// been set and must not be clobbered.
}
// deferprocStack queues a new deferred function with a defer record on the stack.
// The defer record must have its siz and fn fields initialized.
// All other fields can contain junk.
// The defer record must be immediately followed in memory by
// the arguments of the defer.
// Nosplit because the arguments on the stack won't be scanned
// until the defer record is spliced into the gp._defer list.
//go:nosplit
func deferprocStack(d *_defer) {
gp := getg()
if gp.m.curg != gp {
// go code on the system stack can't defer
throw("defer on system stack")
}
// siz and fn are already set.
// The other fields are junk on entry to deferprocStack and
// are initialized here.
d.started = false
d.heap = false
d.openDefer = false
d.sp = getcallersp()
d.pc = getcallerpc()
d.framepc = 0
d.varp = 0
// The lines below implement:
// d.panic = nil
// d.fd = nil
// d.link = gp._defer
// gp._defer = d
// But without write barriers. The first three 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.
// The fourth write does not require a write barrier because we
// explicitly mark all the defer structures, so we don't need to
// keep track of pointers to them with a write barrier.
*(*uintptr)(unsafe.Pointer(&d._panic)) = 0
*(*uintptr)(unsafe.Pointer(&d.fd)) = 0
*(*uintptr)(unsafe.Pointer(&d.link)) = uintptr(unsafe.Pointer(gp._defer))
*(*uintptr)(unsafe.Pointer(&gp._defer)) = uintptr(unsafe.Pointer(d))
return0()
// No code can go here - the C return register has
// been set and must not be clobbered.
}
// Small malloc size classes >= 16 are the multiples of 16: 16, 32, 48, 64, 80, 96, 112, 128, 144, ...
// Each P holds a pool for defers with small arg sizes.
// Assign defer allocations to pools by rounding to 16, to match malloc size classes.
const (
deferHeaderSize = unsafe.Sizeof(_defer{})
minDeferAlloc = (deferHeaderSize + 15) &^ 15
minDeferArgs = minDeferAlloc - deferHeaderSize
)
// defer size class for arg size sz
//go:nosplit
func deferclass(siz uintptr) uintptr {
if siz <= minDeferArgs {
return 0
}
return (siz - minDeferArgs + 15) / 16
}
// total size of memory block for defer with arg size sz
func totaldefersize(siz uintptr) uintptr {
if siz <= minDeferArgs {
return minDeferAlloc
}
return deferHeaderSize + siz
}
// Ensure that defer arg sizes that map to the same defer size class
// also map to the same malloc size class.
func testdefersizes() {
var m [len(p{}.deferpool)]int32
for i := range m {
m[i] = -1
}
for i := uintptr(0); ; i++ {
defersc := deferclass(i)
if defersc >= uintptr(len(m)) {
break
}
siz := roundupsize(totaldefersize(i))
if m[defersc] < 0 {
m[defersc] = int32(siz)
continue
}
if m[defersc] != int32(siz) {
print("bad defer size class: i=", i, " siz=", siz, " defersc=", defersc, "\n")
throw("bad defer size class")
}
}
}
// The arguments associated with a deferred call are stored
// immediately after the _defer header in memory.
//go:nosplit
func deferArgs(d *_defer) unsafe.Pointer {
if d.siz == 0 {
// Avoid pointer past the defer allocation.
return nil
}
return add(unsafe.Pointer(d), unsafe.Sizeof(*d))
}
var deferType *_type // type of _defer struct
func init() {
var x interface{}
x = (*_defer)(nil)
deferType = (*(**ptrtype)(unsafe.Pointer(&x))).elem
}
// Allocate a Defer, usually using per-P pool.
// Each defer must be released with freedefer. The defer is not
// added to any defer chain yet.
//
// This must not grow the stack because there may be a frame without
// stack map information when this is called.
//
//go:nosplit
func newdefer(siz int32) *_defer {
var d *_defer
sc := deferclass(uintptr(siz))
gp := getg()
if sc < uintptr(len(p{}.deferpool)) {
pp := gp.m.p.ptr()
if len(pp.deferpool[sc]) == 0 && sched.deferpool[sc] != nil {
// Take the slow path on the system stack so
// we don't grow newdefer's stack.
systemstack(func() {
lock(&sched.deferlock)
for len(pp.deferpool[sc]) < cap(pp.deferpool[sc])/2 && sched.deferpool[sc] != nil {
d := sched.deferpool[sc]
sched.deferpool[sc] = d.link
d.link = nil
pp.deferpool[sc] = append(pp.deferpool[sc], d)
}
unlock(&sched.deferlock)
})
}
if n := len(pp.deferpool[sc]); n > 0 {
d = pp.deferpool[sc][n-1]
pp.deferpool[sc][n-1] = nil
pp.deferpool[sc] = pp.deferpool[sc][:n-1]
}
}
if d == nil {
// Allocate new defer+args.
systemstack(func() {
total := roundupsize(totaldefersize(uintptr(siz)))
d = (*_defer)(mallocgc(total, deferType, true))
})
}
d.siz = siz
d.heap = true
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.fn != nil {
freedeferfn()
}
if !d.heap {
return
}
sc := deferclass(uintptr(d.siz))
if sc >= uintptr(len(p{}.deferpool)) {
return
}
pp := getg().m.p.ptr()
if len(pp.deferpool[sc]) == cap(pp.deferpool[sc]) {
// 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[sc]) > cap(pp.deferpool[sc])/2 {
n := len(pp.deferpool[sc])
d := pp.deferpool[sc][n-1]
pp.deferpool[sc][n-1] = nil
pp.deferpool[sc] = pp.deferpool[sc][:n-1]
if first == nil {
first = d
} else {
last.link = d
}
last = d
}
lock(&sched.deferlock)
last.link = sched.deferpool[sc]
sched.deferpool[sc] = first
unlock(&sched.deferlock)
})
}
// These lines used to be simply `*d = _defer{}` but that
// started causing a nosplit stack overflow via typedmemmove.
d.siz = 0
d.started = false
d.openDefer = false
d.sp = 0
d.pc = 0
d.framepc = 0
d.varp = 0
d.fd = nil
// d._panic and d.fn must be nil already.
// If not, we would have called freedeferpanic or freedeferfn above,
// both of which throw.
d.link = nil
pp.deferpool[sc] = append(pp.deferpool[sc], 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")
}
// Run a deferred function if there is one.
// The compiler inserts a call to this at the end of any
// function which calls defer.
// If there is a deferred function, this will call runtime·jmpdefer,
// which will jump to the deferred function such that it appears
// to have been called by the caller of deferreturn at the point
// just before deferreturn was called. The effect is that deferreturn
// is called again and again until there are no more deferred functions.
//
// Declared as nosplit, because the function should not be preempted once we start
// modifying the caller's frame in order to reuse the frame to call the deferred
// function.
//
// The single argument isn't actually used - it just has its address
// taken so it can be matched against pending defers.
//go:nosplit
func deferreturn(arg0 uintptr) {
gp := getg()
d := gp._defer
if d == nil {
return
}
sp := getcallersp()
if d.sp != sp {
return
}
if d.openDefer {
done := runOpenDeferFrame(gp, d)
if !done {
throw("unfinished open-coded defers in deferreturn")
}
gp._defer = d.link
freedefer(d)
return
}
// Moving arguments around.
//
// Everything called after this point must be recursively
// nosplit because the garbage collector won't know the form
// of the arguments until the jmpdefer can flip the PC over to
// fn.
switch d.siz {
case 0:
// Do nothing.
case sys.PtrSize:
*(*uintptr)(unsafe.Pointer(&arg0)) = *(*uintptr)(deferArgs(d))
default:
memmove(unsafe.Pointer(&arg0), deferArgs(d), uintptr(d.siz))
}
fn := d.fn
d.fn = nil
gp._defer = d.link
freedefer(d)
// If the defer function pointer is nil, force the seg fault to happen
// here rather than in jmpdefer. gentraceback() throws an error if it is
// called with a callback on an LR architecture and jmpdefer is on the
// stack, because the stack trace can be incorrect in that case - see
// issue #8153).
_ = fn.fn
jmpdefer(fn, uintptr(unsafe.Pointer(&arg0)))
}
// 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()
// Create a panic object for Goexit, so we can recognize when it might be
// bypassed by a recover().
var p _panic
p.goexit = true
p.link = gp._panic
gp._panic = (*_panic)(noescape(unsafe.Pointer(&p)))
addOneOpenDeferFrame(gp, getcallerpc(), unsafe.Pointer(getcallersp()))
for {
d := gp._defer
if d == nil {
break
}
if d.started {
if d._panic != nil {
d._panic.aborted = true
d._panic = nil
}
if !d.openDefer {
d.fn = nil
gp._defer = d.link
freedefer(d)
continue
}
}
d.started = true
d._panic = (*_panic)(noescape(unsafe.Pointer(&p)))
if d.openDefer {
done := runOpenDeferFrame(gp, d)
if !done {
// We should always run all defers in the frame,
// since there is no panic associated with this
// defer that can be recovered.
throw("unfinished open-coded defers in Goexit")
}
if p.aborted {
// Since our current defer caused a panic and may
// have been already freed, just restart scanning
// for open-coded defers from this frame again.
addOneOpenDeferFrame(gp, getcallerpc(), unsafe.Pointer(getcallersp()))
} else {
addOneOpenDeferFrame(gp, 0, nil)
}
} else {
// Save the pc/sp in reflectcallSave(), so we can "recover" back to this
// loop if necessary.
reflectcallSave(&p, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz))
}
if p.aborted {
// We had a recursive panic in the defer d we started, and
// then did a recover in a defer that was further down the
// defer chain than d. In the case of an outstanding Goexit,
// we force the recover to return back to this loop. d will
// have already been freed if completed, so just continue
// immediately to the next defer on the chain.
p.aborted = false
continue
}
if gp._defer != d {
throw("bad defer entry in Goexit")
}
d._panic = nil
d.fn = nil
gp._defer = d.link
freedefer(d)
// Note: we ignore recovers here because Goexit isn't a panic
}
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)
if !p.link.goexit {
print("\t")
}
}
if p.goexit {
return
}
print("panic: ")
printany(p.arg)
if p.recovered {
print(" [recovered]")
}
print("\n")
}
// addOneOpenDeferFrame scans the stack for the first frame (if any) with
// open-coded defers and if it finds one, adds a single record to the defer chain
// for that frame. If sp is non-nil, it starts the stack scan from the frame
// specified by sp. If sp is nil, it uses the sp from the current defer record
// (which has just been finished). Hence, it continues the stack scan from the
// frame of the defer that just finished. It skips any frame that already has an
// open-coded _defer record, which would have been been created from a previous
// (unrecovered) panic.
//
// Note: All entries of the defer chain (including this new open-coded entry) have
// their pointers (including sp) adjusted properly if the stack moves while
// running deferred functions. Also, it is safe to pass in the sp arg (which is
// the direct result of calling getcallersp()), because all pointer variables
// (including arguments) are adjusted as needed during stack copies.
func addOneOpenDeferFrame(gp *g, pc uintptr, sp unsafe.Pointer) {
var prevDefer *_defer
if sp == nil {
prevDefer = gp._defer
pc = prevDefer.framepc
sp = unsafe.Pointer(prevDefer.sp)
}
systemstack(func() {
gentraceback(pc, uintptr(sp), 0, gp, 0, nil, 0x7fffffff,
func(frame *stkframe, unused unsafe.Pointer) bool {
if prevDefer != nil && prevDefer.sp == frame.sp {
// Skip the frame for the previous defer that
// we just finished (and was used to set
// where we restarted the stack scan)
return true
}
f := frame.fn
fd := funcdata(f, _FUNCDATA_OpenCodedDeferInfo)
if fd == nil {
return true
}
// Insert the open defer record in the
// chain, in order sorted by sp.
d := gp._defer
var prev *_defer
for d != nil {
dsp := d.sp
if frame.sp < dsp {
break
}
if frame.sp == dsp {
if !d.openDefer {
throw("duplicated defer entry")
}
return true
}
prev = d
d = d.link
}
if frame.fn.deferreturn == 0 {
throw("missing deferreturn")
}
maxargsize, _ := readvarintUnsafe(fd)
d1 := newdefer(int32(maxargsize))
d1.openDefer = true
d1._panic = nil
// These are the pc/sp to set after we've
// run a defer in this frame that did a
// recover. We return to a special
// deferreturn that runs any remaining
// defers and then returns from the
// function.
d1.pc = frame.fn.entry + uintptr(frame.fn.deferreturn)
d1.varp = frame.varp
d1.fd = fd
// Save the SP/PC associated with current frame,
// so we can continue stack trace later if needed.
d1.framepc = frame.pc
d1.sp = frame.sp
d1.link = d
if prev == nil {
gp._defer = d1
} else {
prev.link = d1
}
// Stop stack scanning after adding one open defer record
return false
},
nil, 0)
})
}
// readvarintUnsafe reads the uint32 in varint format starting at fd, and returns the
// uint32 and a pointer to the byte following the varint.
//
// There is a similar function runtime.readvarint, which takes a slice of bytes,
// rather than an unsafe pointer. These functions are duplicated, because one of
// the two use cases for the functions would get slower if the functions were
// combined.
func readvarintUnsafe(fd unsafe.Pointer) (uint32, unsafe.Pointer) {
var r uint32
var shift int
for {
b := *(*uint8)((unsafe.Pointer(fd)))
fd = add(fd, unsafe.Sizeof(b))
if b < 128 {
return r + uint32(b)<<shift, fd
}
r += ((uint32(b) &^ 128) << shift)
shift += 7
if shift > 28 {
panic("Bad varint")
}
}
}
// runOpenDeferFrame runs the active open-coded defers in the frame specified by
// d. It normally processes all active defers in the frame, but stops immediately
// if a defer does a successful recover. It returns true if there are no
// remaining defers to run in the frame.
func runOpenDeferFrame(gp *g, d *_defer) bool {
done := true
fd := d.fd
// Skip the maxargsize
_, fd = readvarintUnsafe(fd)
deferBitsOffset, fd := readvarintUnsafe(fd)
nDefers, fd := readvarintUnsafe(fd)
deferBits := *(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset)))
for i := int(nDefers) - 1; i >= 0; i-- {
// read the funcdata info for this defer
var argWidth, closureOffset, nArgs uint32
argWidth, fd = readvarintUnsafe(fd)
closureOffset, fd = readvarintUnsafe(fd)
nArgs, fd = readvarintUnsafe(fd)
if deferBits&(1<<i) == 0 {
for j := uint32(0); j < nArgs; j++ {
_, fd = readvarintUnsafe(fd)
_, fd = readvarintUnsafe(fd)
_, fd = readvarintUnsafe(fd)
}
continue
}
closure := *(**funcval)(unsafe.Pointer(d.varp - uintptr(closureOffset)))
d.fn = closure
deferArgs := deferArgs(d)
// If there is an interface receiver or method receiver, it is
// described/included as the first arg.
for j := uint32(0); j < nArgs; j++ {
var argOffset, argLen, argCallOffset uint32
argOffset, fd = readvarintUnsafe(fd)
argLen, fd = readvarintUnsafe(fd)
argCallOffset, fd = readvarintUnsafe(fd)
memmove(unsafe.Pointer(uintptr(deferArgs)+uintptr(argCallOffset)),
unsafe.Pointer(d.varp-uintptr(argOffset)),
uintptr(argLen))
}
deferBits = deferBits &^ (1 << i)
*(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset))) = deferBits
p := d._panic
reflectcallSave(p, unsafe.Pointer(closure), deferArgs, argWidth)
if p != nil && p.aborted {
break
}
d.fn = nil
// These args are just a copy, so can be cleared immediately
memclrNoHeapPointers(deferArgs, uintptr(argWidth))
if d._panic != nil && d._panic.recovered {
done = deferBits == 0
break
}
}
return done
}
// reflectcallSave calls reflectcall after saving the caller's pc and sp in the
// panic record. This allows the runtime to return to the Goexit defer processing
// loop, in the unusual case where the Goexit may be bypassed by a successful
// recover.
func reflectcallSave(p *_panic, fn, arg unsafe.Pointer, argsize uint32) {
if p != nil {
p.argp = unsafe.Pointer(getargp(0))
p.pc = getcallerpc()
p.sp = unsafe.Pointer(getcallersp())
}
reflectcall(nil, fn, arg, argsize, argsize)
if p != nil {
p.pc = 0
p.sp = unsafe.Pointer(nil)
}
}
// 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")
}
var p _panic
p.arg = e
p.link = gp._panic
gp._panic = (*_panic)(noescape(unsafe.Pointer(&p)))
atomic.Xadd(&runningPanicDefers, 1)
// By calculating getcallerpc/getcallersp here, we avoid scanning the
// gopanic frame (stack scanning is slow...)
addOneOpenDeferFrame(gp, getcallerpc(), unsafe.Pointer(getcallersp()))
for {
d := gp._defer
if d == nil {
break
}
// If defer was started by earlier panic or Goexit (and, since we're back here, that triggered a new panic),
// take defer off list. An earlier panic will not continue running, but we will make sure below that an
// earlier Goexit does continue running.
if d.started {
if d._panic != nil {
d._panic.aborted = true
}
d._panic = nil
if !d.openDefer {
// For open-coded defers, we need to process the
// defer again, in case there are any other defers
// to call in the frame (not including the defer
// call that caused the panic).
d.fn = nil
gp._defer = d.link
freedefer(d)
continue
}
}
// Mark defer as started, but keep on list, so that traceback
// can find and update the defer's argument frame if stack growth
// or a garbage collection happens before reflectcall starts executing d.fn.
d.started = true
// 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 = (*_panic)(noescape(unsafe.Pointer(&p)))
done := true
if d.openDefer {
done = runOpenDeferFrame(gp, d)
if done && !d._panic.recovered {
addOneOpenDeferFrame(gp, 0, nil)
}
} else {
p.argp = unsafe.Pointer(getargp(0))
reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
}
p.argp = nil
// reflectcall did not panic. Remove d.
if gp._defer != d {
throw("bad defer entry in panic")
}
d._panic = nil
// trigger shrinkage to test stack copy. See stack_test.go:TestStackPanic
//GC()
pc := d.pc
sp := unsafe.Pointer(d.sp) // must be pointer so it gets adjusted during stack copy
if done {
d.fn = nil
gp._defer = d.link
freedefer(d)
}
if p.recovered {
gp._panic = p.link
if gp._panic != nil && gp._panic.goexit && gp._panic.aborted {
// A normal recover would bypass/abort the Goexit. Instead,
// we return to the processing loop of the Goexit.
gp.sigcode0 = uintptr(gp._panic.sp)
gp.sigcode1 = uintptr(gp._panic.pc)
mcall(recovery)
throw("bypassed recovery failed") // mcall should not return
}
atomic.Xadd(&runningPanicDefers, -1)
// Remove any remaining non-started, open-coded
// defer entries after a recover, since the
// corresponding defers will be executed normally
// (inline). Any such entry will become stale once
// we run the corresponding defers inline and exit
// the associated stack frame.
d := gp._defer
var prev *_defer
if !done {
// Skip our current frame, if not done. It is
// needed to complete any remaining defers in
// deferreturn()
prev = d
d = d.link
}
for d != nil {
if d.started {
// This defer is started but we
// are in the middle of a
// defer-panic-recover inside of
// it, so don't remove it or any
// further defer entries
break
}
if d.openDefer {
if prev == nil {
gp._defer = d.link
} else {
prev.link = d.link
}
newd := d.link
freedefer(d)
d = newd
} else {
prev = d
d = d.link
}
}
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
}
// Pass information about recovering frame to recovery.
gp.sigcode0 = uintptr(sp)
gp.sigcode1 = pc
mcall(recovery)
throw("recovery failed") // mcall should not return
}
}
// 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
}
// getargp returns the location where the caller
// writes outgoing function call arguments.
//go:nosplit
//go:noinline
func getargp(x int) uintptr {
// x is an argument mainly so that we can return its address.
return uintptr(noescape(unsafe.Pointer(&x)))
}
// The implementation of the predeclared function recover.
// Cannot split the stack because it needs to reliably
// find the stack segment of its caller.
//
// TODO(rsc): Once we commit to CopyStackAlways,
// this doesn't need to be nosplit.
//go:nosplit
func gorecover(argp uintptr) interface{} {
// Must be in a function running as part of a deferred call during the panic.
// Must be called from the topmost function of the call
// (the function used in the defer statement).
// p.argp is the argument pointer of that topmost deferred function call.
// Compare against argp reported by caller.
// If they match, the caller is the one who can recover.
gp := getg()
p := gp._panic
if p != nil && !p.goexit && !p.recovered && argp == uintptr(p.argp) {
p.recovered = true
return p.arg
}
return nil
}
//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
// Unwind the stack after a deferred function calls recover
// after a panic. Then arrange to continue running as though
// the caller of the deferred function returned normally.
func recovery(gp *g) {
// Info about defer passed in G struct.
sp := gp.sigcode0
pc := gp.sigcode1
// d's arguments need to be in the stack.
if sp != 0 && (sp < gp.stack.lo || gp.stack.hi < sp) {
print("recover: ", hex(sp), " not in [", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n")
throw("bad recovery")
}
// Make the deferproc for this d return again,
// this time returning 1. The calling function will
// jump to the standard return epilogue.
gp.sched.sp = sp
gp.sched.pc = pc
gp.sched.lr = 0
gp.sched.ret = 1
gogo(&gp.sched)
}
// 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()
// Switch to the system stack to avoid any stack growth, which
// may make things worse if the runtime is in a bad state.
systemstack(func() {
startpanic_m()
if dopanic_m(gp, pc, sp) {
// crash uses a decent amount of nosplit stack and we're already
// low on stack in throw, so crash on the system stack (unlike
// fatalpanic).
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
// Switch to the system stack to avoid any stack growth, which
// may make things worse if the runtime is in a bad state.
systemstack(func() {
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(pc, sp, 0, gp)
} else if level >= 2 || _g_.m.throwing > 0 {
print("\nruntime stack:\n")
traceback(pc, sp, 0, gp)
}
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
}
if GOOS == "windows" && _m_.libcallsp != 0 {
return false
}
return true
}
// shouldPushSigpanic reports whether pc should be used as sigpanic's
// return PC (pushing a frame for the call). Otherwise, it should be
// left alone so that LR is used as sigpanic's return PC, effectively
// replacing the top-most frame with sigpanic. This is used by
// preparePanic.
func shouldPushSigpanic(gp *g, pc, lr uintptr) bool {
if pc == 0 {
// Probably a call to a nil func. The old LR is more
// useful in the stack trace. Not pushing the frame
// will make the trace look like a call to sigpanic
// instead. (Otherwise the trace will end at sigpanic
// and we won't get to see who faulted.)
return false
}
// If we don't recognize the PC as code, but we do recognize
// the link register as code, then this assumes the panic was
// caused by a call to non-code. In this case, we want to
// ignore this call to make unwinding show the context.
//
// If we running C code, we're not going to recognize pc as a
// Go function, so just assume it's good. Otherwise, traceback
// may try to read a stale LR that looks like a Go code
// pointer and wander into the woods.
if gp.m.incgo || findfunc(pc).valid() {
// This wasn't a bad call, so use PC as sigpanic's
// return PC.
return true
}
if findfunc(lr).valid() {
// This was a bad call, but the LR is good, so use the
// LR as sigpanic's return PC.
return false
}
// Neither the PC or LR is good. Hopefully pushing a frame
// will work.
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 pc == funcPC(abort) || ((GOARCH == "arm" || GOARCH == "arm64") && pc == funcPC(abort)+sys.PCQuantum)
}
 |
The pages are generated with Golds v0.4.2. (GOOS=darwin GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
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