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Revert "runtime: make stack traces of endless recursion print only top and bottom 50"

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This reverts commit 3a81338622.

Reason for revert: Some edge cases not properly covered due to changes within runtime traceback generation since 2017, that need to be examined. This change landed very late in the Go1.16 cycle.

Change-Id: I8cf6f46ea0ef6161d878e79943e6c7cdac94bccf
Reviewed-on: https://go-review.googlesource.com/c/go/+/268577
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Emmanuel Odeke 2020-11-09 20:31:58 +00:00 committed by Keith Randall
parent 8badef4cf6
commit d4957122ee
3 changed files with 47 additions and 265 deletions
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126
src/runtime/crash_test.go
View File

@ -240,132 +240,6 @@ func TestStackOverflow(t *testing.T) {
} }
} }
func TestStackOverflowTopAndBottomTraces(t *testing.T) {
output := runTestProg(t, "testprog", "StackOverflowTopAndBottomTraces")
// 1. First things first, we expect to traverse from
// runtime: goroutine stack exceeds 10000-byte limit
// and down to the very end until we see:
// runtime.goexit()
mustHaves := []string{
// Top half expectations
"\\s*runtime: goroutine stack exceeds 10000-byte limit\n",
"\\s*fatal error: stack overflow\n",
"\\s*runtime stack:\n",
"\\s*runtime.throw[^\n]+\n\t.+:\\d+ [^\n]+",
"\\s+runtime\\.newstack[^\n]+\n\t.+:\\d+ [^\n]+",
"\\s+runtime.morestack[^\n]+\n\t.+:\\d+ [^\n]+",
"\\s+goroutine 1 \\[running\\]:",
// Bottom half expectations
"\\s*main.main\\(\\)\n",
"\\s*runtime.main\\(\\)\n",
"\\s*runtime.goexit\\(\\)\n",
}
for _, pat := range mustHaves {
reg := regexp.MustCompile(pat)
match := reg.FindAllString(output, -1)
if len(match) == 0 {
t.Errorf("Failed to find pattern %q", pat)
}
}
// 2. Split top and bottom halves by the "... ({n} stack frames omitted)" message
regHalving := regexp.MustCompile("\\.{3} \\(\\d+ stack frames omitted\\)")
halverMatches := regHalving.FindAllString(output, -1)
if len(halverMatches) != 1 {
t.Fatal("Failed to find the `stack frames omitted` pattern")
}
str := string(output)
halver := halverMatches[0]
midIndex := strings.Index(str, halver)
topHalf, bottomHalf := str[:midIndex], str[midIndex+len(halver):]
// 2.1. Sanity check, len(topHalf) >= halver || len(bottomHalf) >= halver
if len(topHalf) < len(halver) || len(bottomHalf) < len(halver) {
t.Fatalf("Sanity check len(topHalf) = %d len(bottomHalf) = %d; both must be >= len(halver) %d",
len(topHalf), len(bottomHalf), len(halver))
}
// 3. In each of the halves, we should have an equal number
// of stacktraces before and after the "omitted frames" message.
regStackTraces := regexp.MustCompile("\n[^\n]+\n\t.+:\\d+ .+ fp=0x.+ sp=0x.+ pc=0x.+")
topHalfStackTraces := regStackTraces.FindAllString(topHalf, -1)
bottomHalfStackTraces := regStackTraces.FindAllString(bottomHalf, -1)
nTopHalf, nBottomHalf := len(topHalfStackTraces), len(bottomHalfStackTraces)
if nTopHalf == 0 || nBottomHalf == 0 {
t.Fatal("Both lengths of stack-halves should be non-zero")
}
// The bottom half will always have the 50 non-runtime frames along with these 3 frames:
// * main.main()
// * "runtime.main"
// * "runtime.goexit"
// hence we need to decrement 3 counted lines.
if nTopHalf != nBottomHalf-3 {
t.Errorf("len(topHalfStackTraces)=%d len(bottomHalfStackTraces)-3=%d yet must be equal\n", nTopHalf, nBottomHalf-3)
}
// 4. Next, prune out the:
// func...
// line...
// pairs in both of the halves.
prunes := []struct {
src *string
matches []string
}{
{src: &topHalf, matches: topHalfStackTraces},
{src: &bottomHalf, matches: bottomHalfStackTraces},
}
for _, prune := range prunes {
str := *prune.src
for _, match := range prune.matches {
index := strings.Index(str, match)
str = str[:index] + str[index+len(match):]
}
*prune.src = str
}
// 5. Now match and prune out the remaining patterns in the top and bottom halves.
// We aren't touching the bottom stack since its patterns are already matched
// by the:
// func...
// line...
// pairs
topPartPrunables := []string{
"^\\s*runtime: goroutine stack exceeds 10000-byte limit\n",
"\\s*fatal error: stack overflow\n",
"\\s*runtime stack:\n",
"\\s*runtime.throw[^\n]+\n\t.+:\\d+ [^\n]+",
"\\s+runtime\\.newstack[^\n]+\n\t.+:\\d+ [^\n]+",
"\\s+runtime.morestack[^\n]+\n\t.+:\\d+ [^\n]+",
"\\s+goroutine 1 \\[running\\]:",
}
for _, pat := range topPartPrunables {
reg := regexp.MustCompile(pat)
matches := reg.FindAllString(topHalf, -1)
if len(matches) == 0 {
t.Errorf("top stack traces do not contain pattern: %q", reg)
} else if len(matches) != 1 {
t.Errorf("inconsistent state got %d matches want only 1", len(matches))
} else {
match := matches[0]
idx := strings.Index(topHalf, match)
topHalf = topHalf[:idx] + topHalf[idx+len(match):]
}
}
// 6. At the end we should only be left with
// newlines in both the top and bottom halves.
topHalf = strings.TrimSpace(topHalf)
bottomHalf = strings.TrimSpace(bottomHalf)
if topHalf != "" && bottomHalf != "" {
t.Fatalf("len(topHalf)=%d len(bottomHalf)=%d\ntopHalf=\n%s\n\nbottomHalf=\n%s",
len(topHalf), len(bottomHalf), topHalf, bottomHalf)
}
}
func TestThreadExhaustion(t *testing.T) { func TestThreadExhaustion(t *testing.T) {
output := runTestProg(t, "testprog", "ThreadExhaustion") output := runTestProg(t, "testprog", "ThreadExhaustion")
want := "runtime: program exceeds 10-thread limit\nfatal error: thread exhaustion" want := "runtime: program exceeds 10-thread limit\nfatal error: thread exhaustion"

13
src/runtime/testdata/testprog/deadlock.go vendored
View File

@ -20,7 +20,6 @@ func init() {
register("LockedDeadlock2", LockedDeadlock2) register("LockedDeadlock2", LockedDeadlock2)
register("GoexitDeadlock", GoexitDeadlock) register("GoexitDeadlock", GoexitDeadlock)
register("StackOverflow", StackOverflow) register("StackOverflow", StackOverflow)
register("StackOverflowTopAndBottomTraces", StackOverflowTopAndBottomTraces)
register("ThreadExhaustion", ThreadExhaustion) register("ThreadExhaustion", ThreadExhaustion)
register("RecursivePanic", RecursivePanic) register("RecursivePanic", RecursivePanic)
register("RecursivePanic2", RecursivePanic2) register("RecursivePanic2", RecursivePanic2)
@ -86,18 +85,6 @@ func StackOverflow() {
f() f()
} }
func StackOverflowTopAndBottomTraces() {
var fi, gi func()
fi = func() {
gi()
}
gi = func() {
fi()
}
debug.SetMaxStack(10000)
fi()
}
func ThreadExhaustion() { func ThreadExhaustion() {
debug.SetMaxThreads(10) debug.SetMaxThreads(10)
c := make(chan int) c := make(chan int)

173
src/runtime/traceback.go
View File

@ -73,34 +73,17 @@ func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v uns
const sizeofSkipFunction = 256 const sizeofSkipFunction = 256
// Generic traceback. Handles runtime stack prints (pcbuf == nil && callback == nil), // Generic traceback. Handles runtime stack prints (pcbuf == nil),
// the runtime.Callers function (pcbuf != nil), as well as the garbage // the runtime.Callers function (pcbuf != nil), as well as the garbage
// collector (callback != nil). A little clunky to merge these, but avoids // collector (callback != nil). A little clunky to merge these, but avoids
// duplicating the code and all its subtlety. // duplicating the code and all its subtlety.
// //
// The skip argument counts the number of logical frames to skip rather // The skip argument is only valid with pcbuf != nil and counts the number
// than physical frames (with inlining, a PC in pcbuf can represent multiple calls). // of logical frames to skip rather than physical frames (with inlining, a
// PC in pcbuf can represent multiple calls). If a PC is partially skipped
// and max > 1, pcbuf[1] will be runtime.skipPleaseUseCallersFrames+N where
// N indicates the number of logical frames to skip in pcbuf[0].
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 { 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 {
var op operation = traversing
if pcbuf == nil && callback == nil {
op = printing
}
n, _ := ggentraceback(pc0, sp0, lr0, gp, skip, pcbuf, max, op, callback, v, flags)
return n
}
type operation int8
const (
traversing operation = 1 << iota
countingframes
printing
)
// n always returns the number of total frames <= max.
// nregularframes is the count of non-runtime frames.
// nregularframes is only valid if op == countingframes.
func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max int, op operation, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) (ntotalframes, nregularframes int) {
if skip > 0 && callback != nil { if skip > 0 && callback != nil {
throw("gentraceback callback cannot be used with non-zero skip") throw("gentraceback callback cannot be used with non-zero skip")
} }
@ -152,6 +135,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
} }
waspanic := false waspanic := false
cgoCtxt := gp.cgoCtxt cgoCtxt := gp.cgoCtxt
printing := pcbuf == nil && callback == nil
// If the PC is zero, it's likely a nil function call. // If the PC is zero, it's likely a nil function call.
// Start in the caller's frame. // Start in the caller's frame.
@ -165,7 +149,6 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
} }
} }
printing := op == printing
f := findfunc(frame.pc) f := findfunc(frame.pc)
if !f.valid() { if !f.valid() {
if callback != nil || printing { if callback != nil || printing {
@ -175,14 +158,15 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
if callback != nil { if callback != nil {
throw("unknown pc") throw("unknown pc")
} }
return 0, 0 return 0
} }
frame.fn = f frame.fn = f
var cache pcvalueCache var cache pcvalueCache
lastFuncID := funcID_normal lastFuncID := funcID_normal
for ntotalframes < max { n := 0
for n < max {
// Typically: // Typically:
// pc is the PC of the running function. // pc is the PC of the running function.
// sp is the stack pointer at that program counter. // sp is the stack pointer at that program counter.
@ -245,7 +229,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
} else { } else {
var lrPtr uintptr var lrPtr uintptr
if usesLR { if usesLR {
if ntotalframes == 0 && frame.sp < frame.fp || frame.lr == 0 { if n == 0 && frame.sp < frame.fp || frame.lr == 0 {
lrPtr = frame.sp lrPtr = frame.sp
frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr)) frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
} }
@ -336,15 +320,11 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
if callback != nil { if callback != nil {
if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) { if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
return return n
} }
} }
if pcbuf == nil && skip > 0 { if pcbuf != nil {
// In this case we are printing and we still need to count
// the number of frames. See https://golang.org/issues/24628.
skip--
} else if pcbuf != nil {
pc := frame.pc pc := frame.pc
// backup to CALL instruction to read inlining info (same logic as below) // backup to CALL instruction to read inlining info (same logic as below)
tracepc := pc tracepc := pc
@ -359,7 +339,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
// See issue 34123. // See issue 34123.
// The pc can be at function entry when the frame is initialized without // The pc can be at function entry when the frame is initialized without
// actually running code, like runtime.mstart. // actually running code, like runtime.mstart.
if (ntotalframes == 0 && flags&_TraceTrap != 0) || waspanic || pc == f.entry { if (n == 0 && flags&_TraceTrap != 0) || waspanic || pc == f.entry {
pc++ pc++
} else { } else {
tracepc-- tracepc--
@ -377,9 +357,9 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
// ignore wrappers // ignore wrappers
} else if skip > 0 { } else if skip > 0 {
skip-- skip--
} else if ntotalframes < max { } else if n < max {
(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[ntotalframes] = pc (*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
ntotalframes++ n++
} }
lastFuncID = inltree[ix].funcID lastFuncID = inltree[ix].funcID
// Back up to an instruction in the "caller". // Back up to an instruction in the "caller".
@ -392,15 +372,17 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
// Ignore wrapper functions (except when they trigger panics). // Ignore wrapper functions (except when they trigger panics).
} else if skip > 0 { } else if skip > 0 {
skip-- skip--
} else if ntotalframes < max { } else if n < max {
(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[ntotalframes] = pc (*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
ntotalframes++ n++
} }
lastFuncID = f.funcID lastFuncID = f.funcID
ntotalframes-- // offset ntotalframes++ below n-- // offset n++ below
} }
if printing && skip <= 0 { if printing {
// assume skip=0 for printing.
//
// Never elide wrappers if we haven't printed // Never elide wrappers if we haven't printed
// any frames. And don't elide wrappers that // any frames. And don't elide wrappers that
// called panic rather than the wrapped // called panic rather than the wrapped
@ -408,7 +390,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
// backup to CALL instruction to read inlining info (same logic as below) // backup to CALL instruction to read inlining info (same logic as below)
tracepc := frame.pc tracepc := frame.pc
if (ntotalframes > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic { if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
tracepc-- tracepc--
} }
// If there is inlining info, print the inner frames. // If there is inlining info, print the inner frames.
@ -466,14 +448,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
} }
lastFuncID = f.funcID lastFuncID = f.funcID
} }
n++
if op == countingframes {
name := fullfuncname(f, frame.pc)
if len(name) < len("runtime.") || name[:len("runtime.")] != "runtime." {
nregularframes++
}
}
ntotalframes++
if f.funcID == funcID_cgocallback && len(cgoCtxt) > 0 { if f.funcID == funcID_cgocallback && len(cgoCtxt) > 0 {
ctxt := cgoCtxt[len(cgoCtxt)-1] ctxt := cgoCtxt[len(cgoCtxt)-1]
@ -483,7 +458,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
// callback != nil only used when we only care // callback != nil only used when we only care
// about Go frames. // about Go frames.
if skip == 0 && callback == nil { if skip == 0 && callback == nil {
ntotalframes = tracebackCgoContext(pcbuf, printing, ctxt, ntotalframes, max) n = tracebackCgoContext(pcbuf, printing, ctxt, n, max)
} }
} }
@ -523,7 +498,7 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
} }
if printing { if printing {
ntotalframes = nprint n = nprint
} }
// Note that panic != nil is okay here: there can be leftover panics, // Note that panic != nil is okay here: there can be leftover panics,
@ -566,13 +541,13 @@ func ggentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max i
// At other times, such as when gathering a stack for a profiling signal // 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 // or when printing a traceback during a crash, everything may not be
// stopped nicely, and the stack walk may not be able to complete. // stopped nicely, and the stack walk may not be able to complete.
if callback != nil && ntotalframes < max && frame.sp != gp.stktopsp { if callback != nil && n < max && frame.sp != gp.stktopsp {
print("runtime: g", gp.goid, ": frame.sp=", hex(frame.sp), " top=", hex(gp.stktopsp), "\n") print("runtime: g", gp.goid, ": frame.sp=", hex(frame.sp), " top=", hex(gp.stktopsp), "\n")
print("\tstack=[", hex(gp.stack.lo), "-", hex(gp.stack.hi), "] n=", ntotalframes, " max=", max, "\n") print("\tstack=[", hex(gp.stack.lo), "-", hex(gp.stack.hi), "] n=", n, " max=", max, "\n")
throw("traceback did not unwind completely") throw("traceback did not unwind completely")
} }
return return n
} }
// reflectMethodValue is a partial duplicate of reflect.makeFuncImpl // reflectMethodValue is a partial duplicate of reflect.makeFuncImpl
@ -737,15 +712,24 @@ func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
printCgoTraceback(&cgoCallers) printCgoTraceback(&cgoCallers)
} }
var n int
if readgstatus(gp)&^_Gscan == _Gsyscall { if readgstatus(gp)&^_Gscan == _Gsyscall {
// Override registers if blocked in system call. // Override registers if blocked in system call.
pc = gp.syscallpc pc = gp.syscallpc
sp = gp.syscallsp sp = gp.syscallsp
flags &^= _TraceTrap flags &^= _TraceTrap
} }
// Print traceback. By default, omits runtime frames.
printtraceback(pc, sp, lr, gp, flags) // 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) printcreatedby(gp)
if gp.ancestors == nil { if gp.ancestors == nil {
return return
} }
@ -754,62 +738,6 @@ func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
} }
} }
// countframes traverses the current stacktrace from the top of pc0 to its bottom, excluding runtime frames.
// If flags&_TraceRuntimeframes != 0, it'll include the number of runtime frames in the count.
func countframes(pc0, sp0, lr0 uintptr, gp *g, flags uint) (nframes int) {
ntotalframes, nregularframes := ggentraceback(pc0, sp0, lr0, gp, 0, nil, 1<<31-1, countingframes, nil, nil, flags)
nframes = nregularframes
if flags&_TraceRuntimeFrames != 0 {
nframes = ntotalframes
}
return nframes
}
func printtraceback(pc, sp, lr uintptr, gp *g, flags uint) {
// We'd like to print:
// * top nMaxFramesPerPrint frames
// * bottom nMaxFramesPerPrint frames.
// See https://golang.org/issue/7181.
nMaxFramesPerPrint := _TracebackMaxFrames / 2
nTop := gentraceback(pc, sp, lr, gp, 0, nil, nMaxFramesPerPrint, nil, nil, flags)
if nTop < nMaxFramesPerPrint {
// The common case, in which the traceback has less than nMaxFramesPerPrint.
// By default, omits runtime frames.
// If nTop == 0, it means we printed nothing at all, so repeat,
// and this time force all frames to be printed.
if nTop == 0 && (flags&_TraceRuntimeFrames) == 0 {
// Try again to print the frames, but this time with _TraceRuntimeFrames.
printtraceback(pc, sp, lr, gp, flags|_TraceRuntimeFrames)
}
return
}
// Figure out the stack size in order to print the bottom max(nMaxFramesPerPrint) frames.
//
// TODO(odeke-em, iant, khr): perhaps investigate and revise the solution in
// https://go-review.googlesource.com/c/go/+/37222/9/src/runtime/traceback.go
// so that we'll always only need 1 stack walk, instead of 2 as in this worst case.
nframes := countframes(pc, sp, lr, gp, flags)
if nframes <= _TracebackMaxFrames {
// In this case, we'll just print out from where we left off until the end.
gentraceback(pc, sp, lr, gp, nMaxFramesPerPrint /* skip */, nil, 1<<31-1, nil, nil, flags)
return
}
// Otherwise, now skip until the bottom last nMaxFramesPerPrint.
// Calculate the number of stack frames to elide since we
// are printing top and bottom each of nMaxFramesPerPrint.
if elide := nframes - _TracebackMaxFrames; elide > 0 {
print("\n... (")
println(elide, "stack frames omitted)\n")
}
skip := nframes - nMaxFramesPerPrint
_ = gentraceback(pc, sp, lr, gp, skip, nil, 1<<31-1 /* max int32 as the biggest frame number */, nil, nil, flags)
}
// printAncestorTraceback prints the traceback of the given ancestor. // printAncestorTraceback prints the traceback of the given ancestor.
// TODO: Unify this with gentraceback and CallersFrames. // TODO: Unify this with gentraceback and CallersFrames.
func printAncestorTraceback(ancestor ancestorInfo) { func printAncestorTraceback(ancestor ancestorInfo) {
@ -830,9 +758,11 @@ func printAncestorTraceback(ancestor ancestorInfo) {
} }
} }
// fullfuncname retrieves the name for a funcInfo, but if perhaps it was inlined, it'll retrieve // printAncestorTraceback prints the given function info at a given pc
// unwind and retrieve the original name. // within an ancestor traceback. The precision of this info is reduced
func fullfuncname(f funcInfo, pc uintptr) string { // due to only have access to the pcs at the time of the caller
// goroutine being created.
func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) {
name := funcname(f) name := funcname(f)
if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil { if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
inltree := (*[1 << 20]inlinedCall)(inldata) inltree := (*[1 << 20]inlinedCall)(inldata)
@ -841,15 +771,6 @@ func fullfuncname(f funcInfo, pc uintptr) string {
name = funcnameFromNameoff(f, inltree[ix].func_) name = funcnameFromNameoff(f, inltree[ix].func_)
} }
} }
return name
}
// printAncestorTraceback prints the given function info at a given pc
// within an ancestor traceback. The precision of this info is reduced
// due to only have access to the pcs at the time of the caller
// goroutine being created.
func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) {
name := fullfuncname(f, pc)
file, line := funcline(f, pc) file, line := funcline(f, pc)
if name == "runtime.gopanic" { if name == "runtime.gopanic" {
name = "panic" name = "panic"