runtime: introduce GOTRACEBACK=single, now the default

Abandon (but still support) the old numbering system.

GOTRACEBACK=none is old 0
GOTRACEBACK=single is the new behavior
GOTRACEBACK=all is old 1
GOTRACEBACK=system is old 2
GOTRACEBACK=crash is unchanged

See doc comment change in runtime1.go for details.

Filed #13107 to decide whether to change default back to GOTRACEBACK=all for Go 1.6 release.
If you run into programs where printing only the current goroutine omits
needed information, please add details in a comment on that issue.

Fixes #12366.

Change-Id: I82ca8b99b5d86dceb3f7102d38d2659d45dbe0db
Reviewed-on: https://go-review.googlesource.com/16512
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/extern.go

@@ -106,15 +106,20 @@ the limit.
 
 The GOTRACEBACK variable controls the amount of output generated when a Go
 program fails due to an unrecovered panic or an unexpected runtime condition.
-By default, a failure prints a stack trace for every extant goroutine, eliding functions
+By default, a failure prints a stack trace for the current goroutine,
-internal to the run-time system, and then exits with exit code 2.
+eliding functions internal to the run-time system, and then exits with exit code 2.
-If GOTRACEBACK=0, the per-goroutine stack traces are omitted entirely.
+The failure prints stack traces for all goroutines if there is no current goroutine
-If GOTRACEBACK=1, the default behavior is used.
+or the failure is internal to the run-time.
-If GOTRACEBACK=2, the per-goroutine stack traces include run-time functions.
+GOTRACEBACK=none omits the goroutine stack traces entirely.
-If GOTRACEBACK=crash, the per-goroutine stack traces include run-time functions,
+GOTRACEBACK=single (the default) behaves as described above.
-and if possible the program crashes in an operating-specific manner instead of
+GOTRACEBACK=all adds stack traces for all user-created goroutines.
-exiting. For example, on Unix systems, the program raises SIGABRT to trigger a
+GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
-core dump.
+and shows goroutines created internally by the run-time.
+GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
+manner instead of exiting. For example, on Unix systems, the crash raises
+SIGABRT to trigger a core dump.
+For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
+none, all, and system, respectively.
 
 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
 the set of Go environment variables. They influence the building of Go programs

src/runtime/os3_plan9.go

@@ -14,6 +14,7 @@ func sighandler(_ureg *ureg, note *byte, gp *g) int {
 	var docrash bool
 	var sig int
 	var flags int
+	var level int32
 
 	c := &sigctxt{_ureg}
 	notestr := gostringnocopy(note)
@@ -97,7 +98,8 @@ Throw:
 	print(notestr, "\n")
 	print("PC=", hex(c.pc()), "\n")
 	print("\n")
-	if gotraceback(&docrash) > 0 {
+	level, _, docrash = gotraceback()
+	if level > 0 {
 		goroutineheader(gp)
 		tracebacktrap(c.pc(), c.sp(), 0, gp)
 		tracebackothers(gp)

src/runtime/panic.go

@@ -605,18 +605,21 @@ func dopanic_m(gp *g, pc, sp uintptr) {
 		print("[signal ", hex(gp.sig), " code=", hex(gp.sigcode0), " addr=", hex(gp.sigcode1), " pc=", hex(gp.sigpc), "]\n")
 	}
 
-	var docrash bool
+	level, all, docrash := gotraceback()
 	_g_ := getg()
-	if t := gotraceback(&docrash); t > 0 {
+	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 t >= 2 || _g_.m.throwing > 0 {
+		} else if level >= 2 || _g_.m.throwing > 0 {
 			print("\nruntime stack:\n")
 			traceback(pc, sp, 0, gp)
 		}
-		if !didothers {
+		if !didothers && all {
 			didothers = true
 			tracebackothers(gp)
 		}

src/runtime/runtime1.go

@@ -8,30 +8,37 @@ import "unsafe"
 
 // Keep a cached value to make gotraceback fast,
 // since we call it on every call to gentraceback.
-// The cached value is a uint32 in which the low bit
+// The cached value is a uint32 in which the low bits
-// is the "crash" setting and the top 31 bits are the
+// are the "crash" and "all" settings and the remaining
-// gotraceback value.
+// bits are the traceback value (0 off, 1 on, 2 include system).
-var traceback_cache uint32 = 2 << 1
+const (
+	tracebackCrash = 1 << iota
+	tracebackAll
+	tracebackShift = iota
+)
 
-// The GOTRACEBACK environment variable controls the
+var traceback_cache uint32 = 2 << tracebackShift
-// behavior of a Go program that is crashing and exiting.
+
-//	GOTRACEBACK=0   suppress all tracebacks
+// gotraceback returns the current traceback settings.
-//	GOTRACEBACK=1   default behavior - show tracebacks but exclude runtime frames
+//
-//	GOTRACEBACK=2   show tracebacks including runtime frames
+// If level is 0, suppress all tracebacks.
-//	GOTRACEBACK=crash   show tracebacks including runtime frames, then crash (core dump etc)
+// If level is 1, show tracebacks, but exclude runtime frames.
+// If level is 2, show tracebacks including runtime frames.
+// If all is set, print all goroutine stacks. Otherwise, print just the current goroutine.
+// If crash is set, crash (core dump, etc) after tracebacking.
+//
 //go:nosplit
-func gotraceback(crash *bool) int32 {
+func gotraceback() (level int32, all, crash bool) {
 	_g_ := getg()
-	if crash != nil {
+	all = _g_.m.throwing > 0
-		*crash = false
-	}
 	if _g_.m.traceback != 0 {
-		return int32(_g_.m.traceback)
+		level = int32(_g_.m.traceback)
+		return
 	}
-	if crash != nil {
+	crash = traceback_cache&tracebackCrash != 0
-		*crash = traceback_cache&1 != 0
+	all = all || traceback_cache&tracebackAll != 0
-	}
+	level = int32(traceback_cache >> tracebackShift)
-	return int32(traceback_cache >> 1)
+	return
 }
 
 var (
@@ -365,17 +372,23 @@ func parsedebugvars() {
 	}
 
 	switch p := gogetenv("GOTRACEBACK"); p {
-	case "":
+	case "none":
-		traceback_cache = 1 << 1
+		traceback_cache = 0
+	case "single", "":
+		traceback_cache = 1 << tracebackShift
+	case "all":
+		traceback_cache = 1<<tracebackShift | tracebackAll
+	case "system":
+		traceback_cache = 2<<tracebackShift | tracebackAll
 	case "crash":
-		traceback_cache = 2<<1 | 1
+		traceback_cache = 2<<tracebackShift | tracebackAll | tracebackCrash
 	default:
-		traceback_cache = uint32(atoi(p)) << 1
+		traceback_cache = uint32(atoi(p))<<tracebackShift | tracebackAll
 	}
 	// when C owns the process, simply exit'ing the process on fatal errors
 	// and panics is surprising. Be louder and abort instead.
 	if islibrary || isarchive {
-		traceback_cache |= 1
+		traceback_cache |= tracebackCrash
 	}
 
 	if debug.gcstackbarrierall > 0 {

src/runtime/signal_386.go

@@ -131,8 +131,8 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 	print("\n")
 
-	var docrash bool
+	level, _, docrash := gotraceback()
-	if gotraceback(&docrash) > 0 {
+	if level > 0 {
 		goroutineheader(gp)
 
 		// On Linux/386, all system calls go through the vdso kernel_vsyscall routine.

src/runtime/signal_amd64x.go

@@ -165,8 +165,8 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 	print("\n")
 
-	var docrash bool
+	level, _, docrash := gotraceback()
-	if gotraceback(&docrash) > 0 {
+	if level > 0 {
 		goroutineheader(gp)
 		tracebacktrap(uintptr(c.rip()), uintptr(c.rsp()), 0, gp)
 		if crashing > 0 && gp != _g_.m.curg && _g_.m.curg != nil && readgstatus(_g_.m.curg)&^_Gscan == _Grunning {

src/runtime/signal_arm.go

@@ -126,8 +126,8 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 	print("\n")
 
-	var docrash bool
+	level, _, docrash := gotraceback()
-	if gotraceback(&docrash) > 0 {
+	if level > 0 {
 		goroutineheader(gp)
 		tracebacktrap(uintptr(c.pc()), uintptr(c.sp()), uintptr(c.lr()), gp)
 		if crashing > 0 && gp != _g_.m.curg && _g_.m.curg != nil && readgstatus(_g_.m.curg)&^_Gscan == _Grunning {

src/runtime/signal_arm64.go

@@ -139,8 +139,8 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 	print("\n")
 
-	var docrash bool
+	level, _, docrash := gotraceback()
-	if gotraceback(&docrash) > 0 {
+	if level > 0 {
 		goroutineheader(gp)
 		tracebacktrap(uintptr(c.pc()), uintptr(c.sp()), uintptr(c.lr()), gp)
 		if crashing > 0 && gp != _g_.m.curg && _g_.m.curg != nil && readgstatus(_g_.m.curg)&^_Gscan == _Grunning {

src/runtime/signal_ppc64x.go

@@ -144,8 +144,8 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 	print("\n")
 
-	var docrash bool
+	level, _, docrash := gotraceback()
-	if gotraceback(&docrash) > 0 {
+	if level > 0 {
 		goroutineheader(gp)
 		tracebacktrap(uintptr(c.pc()), uintptr(c.sp()), uintptr(c.link()), gp)
 		if crashing > 0 && gp != _g_.m.curg && _g_.m.curg != nil && readgstatus(_g_.m.curg)&^_Gscan == _Grunning {

src/runtime/signal_windows.go

@@ -134,8 +134,8 @@ func lastcontinuehandler(info *exceptionrecord, r *context, gp *g) int32 {
 	}
 	print("\n")
 
-	var docrash bool
+	level, _, docrash := gotraceback()
-	if gotraceback(&docrash) > 0 {
+	if level > 0 {
 		tracebacktrap(r.ip(), r.sp(), 0, gp)
 		tracebackothers(gp)
 		dumpregs(r)

src/runtime/traceback.go

@@ -139,7 +139,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 		// instead on the g0 stack.
 		throw("gentraceback cannot trace user goroutine on its own stack")
 	}
-	gotraceback := gotraceback(nil)
+	level, _, _ := gotraceback()
 
 	// Fix up returns to the stack barrier by fetching the
 	// original return PC from gp.stkbar.
@@ -367,7 +367,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 				if frame.pc > f.entry {
 					print(" +", hex(frame.pc-f.entry))
 				}
-				if g.m.throwing > 0 && gp == g.m.curg || gotraceback >= 2 {
+				if g.m.throwing > 0 && gp == g.m.curg || level >= 2 {
 					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp))
 				}
 				print("\n")
@@ -582,7 +582,7 @@ func showframe(f *_func, gp *g) bool {
 	if g.m.throwing > 0 && gp != nil && (gp == g.m.curg || gp == g.m.caughtsig.ptr()) {
 		return true
 	}
-	traceback := gotraceback(nil)
+	level, _, _ := gotraceback()
 	name := funcname(f)
 
 	// Special case: always show runtime.panic frame, so that we can
@@ -592,7 +592,7 @@ func showframe(f *_func, gp *g) bool {
 		return true
 	}
 
-	return traceback > 1 || f != nil && contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name))
+	return level > 1 || f != nil && contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name))
 }
 
 // isExportedRuntime reports whether name is an exported runtime function.
@@ -658,7 +658,7 @@ func goroutineheader(gp *g) {
 }
 
 func tracebackothers(me *g) {
-	level := gotraceback(nil)
+	level, _, _ := gotraceback()
 
 	// Show the current goroutine first, if we haven't already.
 	g := getg()