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// Copyright 2009 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 "unsafe"
// The code in this file implements stack trace walking for all architectures.
// The most important fact about a given architecture is whether it uses a link register.
// On systems with link registers, the prologue for a non-leaf function stores the
// incoming value of LR at the bottom of the newly allocated stack frame.
// On systems without link registers, the architecture pushes a return PC during
// the call instruction, so the return PC ends up above the stack frame.
// In this file, the return PC is always called LR, no matter how it was found.
//
// To date, the opposite of a link register architecture is an x86 architecture.
// This code may need to change if some other kind of non-link-register
// architecture comes along.
//
// The other important fact is the size of a pointer: on 32-bit systems the LR
// takes up only 4 bytes on the stack, while on 64-bit systems it takes up 8 bytes.
// Typically this is ptrSize.
//
// As an exception, amd64p32 has ptrSize == 4 but the CALL instruction still
// stores an 8-byte return PC onto the stack. To accommodate this, we use regSize
// as the size of the architecture-pushed return PC.
//
// usesLR is defined below. ptrSize and regSize are defined in stubs.go.
const usesLR = GOARCH != "amd64" && GOARCH != "amd64p32" && GOARCH != "386"
var (
// initialized in tracebackinit
goexitPC uintptr
jmpdeferPC uintptr
mcallPC uintptr
morestackPC uintptr
mstartPC uintptr
rt0_goPC uintptr
sigpanicPC uintptr
runfinqPC uintptr
backgroundgcPC uintptr
bgsweepPC uintptr
forcegchelperPC uintptr
timerprocPC uintptr
gcBgMarkWorkerPC uintptr
systemstack_switchPC uintptr
systemstackPC uintptr
stackBarrierPC uintptr
cgocallback_gofuncPC uintptr
gogoPC uintptr
externalthreadhandlerp uintptr // initialized elsewhere
)
func tracebackinit() {
// Go variable initialization happens late during runtime startup.
// Instead of initializing the variables above in the declarations,
// schedinit calls this function so that the variables are
// initialized and available earlier in the startup sequence.
goexitPC = funcPC(goexit)
jmpdeferPC = funcPC(jmpdefer)
mcallPC = funcPC(mcall)
morestackPC = funcPC(morestack)
mstartPC = funcPC(mstart)
rt0_goPC = funcPC(rt0_go)
sigpanicPC = funcPC(sigpanic)
runfinqPC = funcPC(runfinq)
backgroundgcPC = funcPC(backgroundgc)
bgsweepPC = funcPC(bgsweep)
forcegchelperPC = funcPC(forcegchelper)
timerprocPC = funcPC(timerproc)
gcBgMarkWorkerPC = funcPC(gcBgMarkWorker)
systemstack_switchPC = funcPC(systemstack_switch)
systemstackPC = funcPC(systemstack)
stackBarrierPC = funcPC(stackBarrier)
cgocallback_gofuncPC = funcPC(cgocallback_gofunc)
// used by sigprof handler
gogoPC = funcPC(gogo)
}
// Traceback over the deferred function calls.
// Report them like calls that have been invoked but not started executing yet.
func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
var frame stkframe
for d := gp._defer; d != nil; d = d.link {
fn := d.fn
if fn == nil {
// Defer of nil function. Args don't matter.
frame.pc = 0
frame.fn = nil
frame.argp = 0
frame.arglen = 0
frame.argmap = nil
} else {
frame.pc = uintptr(fn.fn)
f := findfunc(frame.pc)
if f == nil {
print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
throw("unknown pc")
}
frame.fn = f
frame.argp = uintptr(deferArgs(d))
setArgInfo(&frame, f, true)
}
frame.continpc = frame.pc
if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
return
}
}
}
// Generic traceback. Handles runtime stack prints (pcbuf == nil),
// the runtime.Callers function (pcbuf != nil), as well as the garbage
// collector (callback != nil). A little clunky to merge these, but avoids
// duplicating the code and all its subtlety.
func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max int, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) int {
if goexitPC == 0 {
throw("gentraceback before goexitPC initialization")
}
g := getg()
if g == gp && g == g.m.curg {
// The starting sp has been passed in as a uintptr, and the caller may
// have other uintptr-typed stack references as well.
// If during one of the calls that got us here or during one of the
// callbacks below the stack must be grown, all these uintptr references
// to the stack will not be updated, and gentraceback will continue
// to inspect the old stack memory, which may no longer be valid.
// Even if all the variables were updated correctly, it is not clear that
// we want to expose a traceback that begins on one stack and ends
// on another stack. That could confuse callers quite a bit.
// Instead, we require that gentraceback and any other function that
// accepts an sp for the current goroutine (typically obtained by
// calling getcallersp) must not run on that goroutine's stack but
// instead on the g0 stack.
throw("gentraceback cannot trace user goroutine on its own stack")
}
gotraceback := gotraceback(nil)
// Fix up returns to the stack barrier by fetching the
// original return PC from gp.stkbar.
stkbar := gp.stkbar[gp.stkbarPos:]
if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.
if gp.syscallsp != 0 {
pc0 = gp.syscallpc
sp0 = gp.syscallsp
if usesLR {
lr0 = 0
}
} else {
pc0 = gp.sched.pc
sp0 = gp.sched.sp
if usesLR {
lr0 = gp.sched.lr
}
}
}
nprint := 0
var frame stkframe
frame.pc = pc0
frame.sp = sp0
if usesLR {
frame.lr = lr0
}
waspanic := false
printing := pcbuf == nil && callback == nil
_defer := gp._defer
for _defer != nil && uintptr(_defer.sp) == _NoArgs {
_defer = _defer.link
}
// If the PC is zero, it's likely a nil function call.
// Start in the caller's frame.
if frame.pc == 0 {
if usesLR {
frame.pc = *(*uintptr)(unsafe.Pointer(frame.sp))
frame.lr = 0
} else {
frame.pc = uintptr(*(*uintreg)(unsafe.Pointer(frame.sp)))
frame.sp += regSize
}
}
f := findfunc(frame.pc)
if f == nil {
if callback != nil {
print("runtime: unknown pc ", hex(frame.pc), "\n")
throw("unknown pc")
}
return 0
}
frame.fn = f
n := 0
for n < max {
// Typically:
// pc is the PC of the running function.
// sp is the stack pointer at that program counter.
// fp is the frame pointer (caller's stack pointer) at that program counter, or nil if unknown.
// stk is the stack containing sp.
// The caller's program counter is lr, unless lr is zero, in which case it is *(uintptr*)sp.
f = frame.fn
// Found an actual function.
// Derive frame pointer and link register.
if frame.fp == 0 {
// We want to jump over the systemstack switch. If we're running on the
// g0, this systemstack is at the top of the stack.
// if we're not on g0 or there's a no curg, then this is a regular call.
sp := frame.sp
if flags&_TraceJumpStack != 0 && f.entry == systemstackPC && gp == g.m.g0 && gp.m.curg != nil {
sp = gp.m.curg.sched.sp
stkbar = gp.m.curg.stkbar[gp.m.curg.stkbarPos:]
}
frame.fp = sp + uintptr(funcspdelta(f, frame.pc))
if !usesLR {
// On x86, call instruction pushes return PC before entering new function.
frame.fp += regSize
}
}
var flr *_func
if topofstack(f) {
frame.lr = 0
flr = nil
} else if usesLR && f.entry == jmpdeferPC {
// jmpdefer modifies SP/LR/PC non-atomically.
// If a profiling interrupt arrives during jmpdefer,
// the stack unwind may see a mismatched register set
// and get confused. Stop if we see PC within jmpdefer
// to avoid that confusion.
// See golang.org/issue/8153.
if callback != nil {
throw("traceback_arm: found jmpdefer when tracing with callback")
}
frame.lr = 0
} else {
var lrPtr uintptr
if usesLR {
if n == 0 && frame.sp < frame.fp || frame.lr == 0 {
lrPtr = frame.sp
frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
}
} else {
if frame.lr == 0 {
lrPtr = frame.fp - regSize
frame.lr = uintptr(*(*uintreg)(unsafe.Pointer(lrPtr)))
}
}
if frame.lr == stackBarrierPC {
// Recover original PC.
if stkbar[0].savedLRPtr != lrPtr {
print("found next stack barrier at ", hex(lrPtr), "; expected ")
gcPrintStkbars(stkbar)
print("\n")
throw("missed stack barrier")
}
frame.lr = stkbar[0].savedLRVal
stkbar = stkbar[1:]
}
flr = findfunc(frame.lr)
if flr == nil {
// This happens if you get a profiling interrupt at just the wrong time.
// In that context it is okay to stop early.
// But if callback is set, we're doing a garbage collection and must
// get everything, so crash loudly.
if callback != nil {
print("runtime: unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
throw("unknown caller pc")
}
}
}
frame.varp = frame.fp
if !usesLR {
// On x86, call instruction pushes return PC before entering new function.
frame.varp -= regSize
}
// If framepointer_enabled and there's a frame, then
// there's a saved bp here.
if framepointer_enabled && GOARCH == "amd64" && frame.varp > frame.sp {
frame.varp -= regSize
}
// Derive size of arguments.
// Most functions have a fixed-size argument block,
// so we can use metadata about the function f.
// Not all, though: there are some variadic functions
// in package runtime and reflect, and for those we use call-specific
// metadata recorded by f's caller.
if callback != nil || printing {
frame.argp = frame.fp
if usesLR {
frame.argp += ptrSize
}
setArgInfo(&frame, f, callback != nil)
}
// Determine frame's 'continuation PC', where it can continue.
// Normally this is the return address on the stack, but if sigpanic
// is immediately below this function on the stack, then the frame
// stopped executing due to a trap, and frame.pc is probably not
// a safe point for looking up liveness information. In this panicking case,
// the function either doesn't return at all (if it has no defers or if the
// defers do not recover) or it returns from one of the calls to
// deferproc a second time (if the corresponding deferred func recovers).
// It suffices to assume that the most recent deferproc is the one that
// returns; everything live at earlier deferprocs is still live at that one.
frame.continpc = frame.pc
if waspanic {
if _defer != nil && _defer.sp == frame.sp {
frame.continpc = _defer.pc
} else {
frame.continpc = 0
}
}
// Unwind our local defer stack past this frame.
for _defer != nil && (_defer.sp == frame.sp || _defer.sp == _NoArgs) {
_defer = _defer.link
}
if skip > 0 {
skip--
goto skipped
}
if pcbuf != nil {
(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
}
if callback != nil {
if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
return n
}
}
if printing {
if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp) {
// Print during crash.
// main(0x1, 0x2, 0x3)
// /home/rsc/go/src/runtime/x.go:23 +0xf
//
tracepc := frame.pc // back up to CALL instruction for funcline.
if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
tracepc--
}
print(funcname(f), "(")
argp := (*[100]uintptr)(unsafe.Pointer(frame.argp))
for i := uintptr(0); i < frame.arglen/ptrSize; i++ {
if i >= 10 {
print(", ...")
break
}
if i != 0 {
print(", ")
}
print(hex(argp[i]))
}
print(")\n")
file, line := funcline(f, tracepc)
print("\t", file, ":", line)
if frame.pc > f.entry {
print(" +", hex(frame.pc-f.entry))
}
if g.m.throwing > 0 && gp == g.m.curg || gotraceback >= 2 {
print(" fp=", hex(frame.fp), " sp=", hex(frame.sp))
}
print("\n")
nprint++
}
}
n++
skipped:
waspanic = f.entry == sigpanicPC
// Do not unwind past the bottom of the stack.
if flr == nil {
break
}
// Unwind to next frame.
frame.fn = flr
frame.pc = frame.lr
frame.lr = 0
frame.sp = frame.fp
frame.fp = 0
frame.argmap = nil
// On link register architectures, sighandler saves the LR on stack
// before faking a call to sigpanic.
if usesLR && waspanic {
x := *(*uintptr)(unsafe.Pointer(frame.sp))
frame.sp += ptrSize
if GOARCH == "arm64" {
// arm64 needs 16-byte aligned SP, always
frame.sp += ptrSize
}
f = findfunc(frame.pc)
frame.fn = f
if f == nil {
frame.pc = x
} else if funcspdelta(f, frame.pc) == 0 {
frame.lr = x
}
}
}
if printing {
n = nprint
}
// If callback != nil, we're being called to gather stack information during
// garbage collection or stack growth. In that context, require that we used
// up the entire defer stack. If not, then there is a bug somewhere and the
// garbage collection or stack growth may not have seen the correct picture
// of the stack. Crash now instead of silently executing the garbage collection
// or stack copy incorrectly and setting up for a mysterious crash later.
//
// Note that panic != nil is okay here: there can be leftover panics,
// because the defers on the panic stack do not nest in frame order as
// they do on the defer stack. If you have:
//
// frame 1 defers d1
// frame 2 defers d2
// frame 3 defers d3
// frame 4 panics
// frame 4's panic starts running defers
// frame 5, running d3, defers d4
// frame 5 panics
// frame 5's panic starts running defers
// frame 6, running d4, garbage collects
// frame 6, running d2, garbage collects
//
// During the execution of d4, the panic stack is d4 -> d3, which
// is nested properly, and we'll treat frame 3 as resumable, because we
// can find d3. (And in fact frame 3 is resumable. If d4 recovers
// and frame 5 continues running, d3, d3 can recover and we'll
// resume execution in (returning from) frame 3.)
//
// During the execution of d2, however, the panic stack is d2 -> d3,
// which is inverted. The scan will match d2 to frame 2 but having
// d2 on the stack until then means it will not match d3 to frame 3.
// This is okay: if we're running d2, then all the defers after d2 have
// completed and their corresponding frames are dead. Not finding d3
// for frame 3 means we'll set frame 3's continpc == 0, which is correct
// (frame 3 is dead). At the end of the walk the panic stack can thus
// contain defers (d3 in this case) for dead frames. The inversion here
// always indicates a dead frame, and the effect of the inversion on the
// scan is to hide those dead frames, so the scan is still okay:
// what's left on the panic stack are exactly (and only) the dead frames.
//
// We require callback != nil here because only when callback != nil
// do we know that gentraceback is being called in a "must be correct"
// context as opposed to a "best effort" context. The tracebacks with
// callbacks only happen when everything is stopped nicely.
// At other times, such as when gathering a stack for a profiling signal
// or when printing a traceback during a crash, everything may not be
// stopped nicely, and the stack walk may not be able to complete.
// It's okay in those situations not to use up the entire defer stack:
// incomplete information then is still better than nothing.
if callback != nil && n < max && _defer != nil {
if _defer != nil {
print("runtime: g", gp.goid, ": leftover defer sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
}
for _defer = gp._defer; _defer != nil; _defer = _defer.link {
print("\tdefer ", _defer, " sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
}
throw("traceback has leftover defers")
}
if callback != nil && n < max && len(stkbar) > 0 {
print("runtime: g", gp.goid, ": leftover stack barriers ")
gcPrintStkbars(stkbar)
print("\n")
throw("traceback has leftover stack barriers")
}
return n
}
func setArgInfo(frame *stkframe, f *_func, needArgMap bool) {
frame.arglen = uintptr(f.args)
if needArgMap && f.args == _ArgsSizeUnknown {
// Extract argument bitmaps for reflect stubs from the calls they made to reflect.
switch funcname(f) {
case "reflect.makeFuncStub", "reflect.methodValueCall":
arg0 := frame.sp
if usesLR {
arg0 += ptrSize
}
fn := *(**[2]uintptr)(unsafe.Pointer(arg0))
if fn[0] != f.entry {
print("runtime: confused by ", funcname(f), "\n")
throw("reflect mismatch")
}
bv := (*bitvector)(unsafe.Pointer(fn[1]))
frame.arglen = uintptr(bv.n * ptrSize)
frame.argmap = bv
}
}
}
func printcreatedby(gp *g) {
// Show what created goroutine, except main goroutine (goid 1).
pc := gp.gopc
f := findfunc(pc)
if f != nil && showframe(f, gp) && gp.goid != 1 {
print("created by ", funcname(f), "\n")
tracepc := pc // back up to CALL instruction for funcline.
if pc > f.entry {
tracepc -= _PCQuantum
}
file, line := funcline(f, tracepc)
print("\t", file, ":", line)
if pc > f.entry {
print(" +", hex(pc-f.entry))
}
print("\n")
}
}
func traceback(pc, sp, lr uintptr, gp *g) {
traceback1(pc, sp, lr, gp, 0)
}
// tracebacktrap is like traceback but expects that the PC and SP were obtained
// from a trap, not from gp->sched or gp->syscallpc/gp->syscallsp or getcallerpc/getcallersp.
// Because they are from a trap instead of from a saved pair,
// the initial PC must not be rewound to the previous instruction.
// (All the saved pairs record a PC that is a return address, so we
// rewind it into the CALL instruction.)
func tracebacktrap(pc, sp, lr uintptr, gp *g) {
traceback1(pc, sp, lr, gp, _TraceTrap)
}
func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
var n int
if readgstatus(gp)&^_Gscan == _Gsyscall {
// Override registers if blocked in system call.
pc = gp.syscallpc
sp = gp.syscallsp
flags &^= _TraceTrap
}
// Print traceback. By default, omits runtime frames.
// If that means we print nothing at all, repeat forcing all frames printed.
n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags|_TraceRuntimeFrames)
}
if n == _TracebackMaxFrames {
print("...additional frames elided...\n")
}
printcreatedby(gp)
}
func callers(skip int, pcbuf []uintptr) int {
sp := getcallersp(unsafe.Pointer(&skip))
pc := uintptr(getcallerpc(unsafe.Pointer(&skip)))
gp := getg()
var n int
systemstack(func() {
n = gentraceback(pc, sp, 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
})
return n
}
func gcallers(gp *g, skip int, pcbuf []uintptr) int {
return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
}
func showframe(f *_func, gp *g) bool {
g := getg()
if g.m.throwing > 0 && gp != nil && (gp == g.m.curg || gp == g.m.caughtsig.ptr()) {
return true
}
traceback := gotraceback(nil)
name := funcname(f)
// Special case: always show runtime.panic frame, so that we can
// see where a panic started in the middle of a stack trace.
// See golang.org/issue/5832.
if name == "runtime.panic" {
return true
}
return traceback > 1 || f != nil && contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name))
}
// isExportedRuntime reports whether name is an exported runtime function.
// It is only for runtime functions, so ASCII A-Z is fine.
func isExportedRuntime(name string) bool {
const n = len("runtime.")
return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
}
var gStatusStrings = [...]string{
_Gidle: "idle",
_Grunnable: "runnable",
_Grunning: "running",
_Gsyscall: "syscall",
_Gwaiting: "waiting",
_Gdead: "dead",
_Genqueue: "enqueue",
_Gcopystack: "copystack",
}
var gScanStatusStrings = [...]string{
0: "scan",
_Grunnable: "scanrunnable",
_Grunning: "scanrunning",
_Gsyscall: "scansyscall",
_Gwaiting: "scanwaiting",
_Gdead: "scandead",
_Genqueue: "scanenqueue",
}
func goroutineheader(gp *g) {
gpstatus := readgstatus(gp)
// Basic string status
var status string
if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
status = gStatusStrings[gpstatus]
} else if gpstatus&_Gscan != 0 && 0 <= gpstatus&^_Gscan && gpstatus&^_Gscan < uint32(len(gStatusStrings)) {
status = gStatusStrings[gpstatus&^_Gscan]
} else {
status = "???"
}
// Override.
if (gpstatus == _Gwaiting || gpstatus == _Gscanwaiting) && gp.waitreason != "" {
status = gp.waitreason
}
// approx time the G is blocked, in minutes
var waitfor int64
gpstatus &^= _Gscan // drop the scan bit
if (gpstatus == _Gwaiting || gpstatus == _Gsyscall) && gp.waitsince != 0 {
waitfor = (nanotime() - gp.waitsince) / 60e9
}
print("goroutine ", gp.goid, " [", status)
if waitfor >= 1 {
print(", ", waitfor, " minutes")
}
if gp.lockedm != nil {
print(", locked to thread")
}
print("]:\n")
}
func tracebackothers(me *g) {
level := gotraceback(nil)
// Show the current goroutine first, if we haven't already.
g := getg()
gp := g.m.curg
if gp != nil && gp != me {
print("\n")
goroutineheader(gp)
traceback(^uintptr(0), ^uintptr(0), 0, gp)
}
lock(&allglock)
for _, gp := range allgs {
if gp == me || gp == g.m.curg || readgstatus(gp) == _Gdead || isSystemGoroutine(gp) && level < 2 {
continue
}
print("\n")
goroutineheader(gp)
// Note: gp.m == g.m occurs when tracebackothers is
// called from a signal handler initiated during a
// systemstack call. The original G is still in the
// running state, and we want to print its stack.
if gp.m != g.m && readgstatus(gp)&^_Gscan == _Grunning {
print("\tgoroutine running on other thread; stack unavailable\n")
printcreatedby(gp)
} else {
traceback(^uintptr(0), ^uintptr(0), 0, gp)
}
}
unlock(&allglock)
}
// Does f mark the top of a goroutine stack?
func topofstack(f *_func) bool {
pc := f.entry
return pc == goexitPC ||
pc == mstartPC ||
pc == mcallPC ||
pc == morestackPC ||
pc == rt0_goPC ||
externalthreadhandlerp != 0 && pc == externalthreadhandlerp
}
// isSystemGoroutine reports whether the goroutine g must be omitted in
// stack dumps and deadlock detector.
func isSystemGoroutine(gp *g) bool {
pc := gp.startpc
return pc == runfinqPC && !fingRunning ||
pc == backgroundgcPC ||
pc == bgsweepPC ||
pc == forcegchelperPC ||
pc == timerprocPC ||
pc == gcBgMarkWorkerPC
}