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Diffstat (limited to 'src/runtime/panic.go')
| -rw-r--r-- | src/runtime/panic.go | 1413 |
1 files changed, 1413 insertions, 0 deletions
diff --git a/src/runtime/panic.go b/src/runtime/panic.go new file mode 100644 index 0000000..5b2ccdd --- /dev/null +++ b/src/runtime/panic.go @@ -0,0 +1,1413 @@ +// 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) +} |