runtime: accept GOTRACEBACK=crash to mean 'crash after panic'

This provides a way to generate core dumps when people need them.
The settings are:

        GOTRACEBACK=0  no traceback on panic, just exit
        GOTRACEBACK=1  default - traceback on panic, then exit
        GOTRACEBACK=2  traceback including runtime frames on panic, then exit
        GOTRACEBACK=crash traceback including runtime frames on panic, then crash

Fixes #3257.

R=golang-dev, devon.odell, r, daniel.morsing, ality
CC=golang-dev
https://golang.org/cl/7666044

src/pkg/runtime/extern.go

@@ -7,6 +7,50 @@
 such as functions to control goroutines. It also includes the low-level type information
 used by the reflect package; see reflect's documentation for the programmable
 interface to the run-time type system.
+
+Environment Variables
+
+The following environment variables ($name or %name%, depending on the host
+operating system) control the run-time behavior of Go programs. The meanings
+and use may change from release to release.
+
+The GOGC variable sets the initial garbage collection target percentage.
+A collection is triggered when the ratio of freshly allocated data to live data
+remaining after the previous collection reaches this percentage. The default
+is GOGC=100. Setting GOGC=off disables the garbage collector entirely.
+The runtime/debug package's SetGCPercent function allows changing this
+percentage at run time. See http://golang.org/pkg/runtime/debug/#SetGCPercent.
+
+The GOGCTRACE variable controls debug output from the garbage collector.
+Setting GOGCTRACE=1 causes the garbage collector to emit a single line to standard
+error at each collection, summarizing the amount of memory collected and the
+length of the pause. Setting GOGCTRACE=2 emits the same summary but also
+repeats each collection.
+
+The GOMAXPROCS variable limits the number of operating system threads that
+can execute user-level Go code simultaneously. There is no limit to the number of threads
+that can be blocked in system calls on behalf of Go code; those do not count against
+the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
+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
+internal to the run-time system, and then exits with exit code 2.
+If GOTRACEBACK=0, the per-goroutine stack traces are omitted entirely.
+If GOTRACEBACK=1, the default behavior is used.
+If GOTRACEBACK=2, the per-goroutine stack traces include run-time functions.
+If GOTRACEBACK=crash, the per-goroutine stack traces include run-time functions,
+and if possible the program crashes in an operating-specific manner instead of
+exiting. For example, on Unix systems, the program raises SIGABRT to trigger a
+core dump.
+
+The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
+the set of Go environment variables. They influence the building of Go programs
+(see http://golang.org/cmd/go and http://golang.org/pkg/go/build).
+GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
+constants or functions in this package, but they do not influence the execution
+of the run-time system.
 */
 package runtime
 

src/pkg/runtime/os_plan9.c

@@ -91,6 +91,13 @@ runtime·osinit(void)
 	runtime·notify(runtime·sigtramp);
 }
 
+void
+runtime·crash(void)
+{
+	runtime·notify(nil);
+	*(int32*)0 = 0;
+}
+
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {

src/pkg/runtime/os_plan9_386.c

@@ -28,6 +28,7 @@ runtime·dumpregs(Ureg *u)
 int32
 runtime·sighandler(void *v, int8 *s, G *gp)
 {
+	bool crash;
 	Ureg *ureg;
 	uintptr *sp;
 	SigTab *sig, *nsig;
@@ -93,11 +94,15 @@ Throw:
 	runtime·printf("PC=%X\n", ureg->pc);
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()) {
+	if(runtime·gotraceback(&crash)) {
 		runtime·traceback((void*)ureg->pc, (void*)ureg->sp, 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·dumpregs(ureg);
 	}
+	
+	if(crash)
+		runtime·crash();
+
 	runtime·goexitsall("");
 	runtime·exits(s);
 

src/pkg/runtime/os_plan9_amd64.c

@@ -36,6 +36,7 @@ runtime·dumpregs(Ureg *u)
 int32
 runtime·sighandler(void *v, int8 *s, G *gp)
 {
+	bool crash;
 	Ureg *ureg;
 	uintptr *sp;
 	SigTab *sig, *nsig;
@@ -101,11 +102,15 @@ Throw:
 	runtime·printf("PC=%X\n", ureg->ip);
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()) {
+	if(runtime·gotraceback(&crash)) {
 		runtime·traceback((void*)ureg->ip, (void*)ureg->sp, 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·dumpregs(ureg);
 	}
+	
+	if(crash)
+		runtime·crash();
+
 	runtime·goexitsall("");
 	runtime·exits(s);
 

src/pkg/runtime/os_windows.c

@@ -455,3 +455,16 @@ int32 runtime·badcallbacklen = sizeof runtime·badcallbackmsg - 1;
 
 int8 runtime·badsignalmsg[] = "runtime: signal received on thread not created by Go.\n";
 int32 runtime·badsignallen = sizeof runtime·badsignalmsg - 1;
+
+void
+runtime·crash(void)
+{
+	// TODO: This routine should do whatever is needed
+	// to make the Windows program abort/crash as it
+	// would if Go was not intercepting signals.
+	// On Unix the routine would remove the custom signal
+	// handler and then raise a signal (like SIGABRT).
+	// Something like that should happen here.
+	// It's okay to leave this empty for now: if crash returns
+	// the ordinary exit-after-panic happens.
+}

src/pkg/runtime/os_windows_386.c

@@ -27,6 +27,7 @@ runtime·dumpregs(Context *r)
 uint32
 runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 {
+	bool crash;
 	uintptr *sp;
 
 	switch(info->ExceptionCode) {
@@ -74,12 +75,16 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 	}
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()){
+	if(runtime·gotraceback(&crash)){
 		runtime·traceback((void*)r->Eip, (void*)r->Esp, 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 	
+	if(crash)
+		runtime·crash();
+
+
 	runtime·exit(2);
 	return 0;
 }

src/pkg/runtime/os_windows_amd64.c

@@ -35,6 +35,7 @@ runtime·dumpregs(Context *r)
 uint32
 runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 {
+	bool crash;
 	uintptr *sp;
 
 	switch(info->ExceptionCode) {
@@ -81,12 +82,15 @@ runtime·sighandler(ExceptionRecord *info, Context *r, G *gp)
 	}
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()){
+	if(runtime·gotraceback(&crash)){
 		runtime·traceback((void*)r->Rip, (void*)r->Rsp, 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·dumpregs(r);
 	}
 	
+	if(crash)
+		runtime·crash();
+
 	runtime·exit(2);
 	return 0;
 }

src/pkg/runtime/panic.c

@@ -402,12 +402,13 @@ void
 runtime·dopanic(int32 unused)
 {
 	static bool didothers;
+	bool crash;
 
 	if(g->sig != 0)
 		runtime·printf("[signal %x code=%p addr=%p pc=%p]\n",
 			g->sig, g->sigcode0, g->sigcode1, g->sigpc);
 
-	if(runtime·gotraceback()){
+	if(runtime·gotraceback(&crash)){
 		if(g != m->g0) {
 			runtime·printf("\n");
 			runtime·goroutineheader(g);
@@ -429,6 +430,9 @@ runtime·dopanic(int32 unused)
 		runtime·lock(&deadlock);
 	}
 	
+	if(crash)
+		runtime·crash();
+
 	runtime·exit(2);
 }
 

src/pkg/runtime/proc.c

@@ -232,7 +232,7 @@ runtime·tracebackothers(G *me)
 	G *gp;
 	int32 traceback;
 
-	traceback = runtime·gotraceback();
+	traceback = runtime·gotraceback(nil);
 	for(gp = runtime·allg; gp != nil; gp = gp->alllink) {
 		if(gp == me || gp->status == Gdead)
 			continue;

src/pkg/runtime/runtime.c

@@ -17,14 +17,27 @@ enum {
  */
 void	runtime·sigpanic(void);
 
+// The GOTRACEBACK environment variable controls the
+// behavior of a Go program that is crashing and exiting.
+//	GOTRACEBACK=0   suppress all tracebacks
+//	GOTRACEBACK=1   default behavior - show tracebacks but exclude runtime frames
+//	GOTRACEBACK=2   show tracebacks including runtime frames
+//	GOTRACEBACK=crash   show tracebacks including runtime frames, then crash (core dump etc)
 int32
-runtime·gotraceback(void)
+runtime·gotraceback(bool *crash)
 {
 	byte *p;
 
+	if(crash != nil)
+		*crash = false;
 	p = runtime·getenv("GOTRACEBACK");
 	if(p == nil || p[0] == '\0')
 		return 1;	// default is on
+	if(runtime·strcmp(p, (byte*)"crash") == 0) {
+		if(crash != nil)
+			*crash = true;
+		return 2;	// extra information
+	}
 	return runtime·atoi(p);
 }
 

src/pkg/runtime/runtime.h

@@ -699,7 +699,7 @@ String	runtime·gostringw(uint16*);
 void	runtime·initsig(void);
 void	runtime·sigenable(uint32 sig);
 void	runtime·sigdisable(uint32 sig);
-int32	runtime·gotraceback(void);
+int32	runtime·gotraceback(bool *crash);
 void	runtime·goroutineheader(G*);
 void	runtime·traceback(uint8 *pc, uint8 *sp, uint8 *lr, G* gp);
 void	runtime·tracebackothers(G*);
@@ -793,6 +793,7 @@ G*	runtime·netpoll(bool);
 void	runtime·netpollinit(void);
 int32	runtime·netpollopen(int32, PollDesc*);
 void	runtime·netpollready(G**, PollDesc*, int32);
+void	runtime·crash(void);
 
 #pragma	varargck	argpos	runtime·printf	1
 #pragma	varargck	type	"d"	int32

src/pkg/runtime/signal_386.c

@@ -36,6 +36,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *ctxt, G *gp)
 {
 	uintptr *sp;
 	SigTab *t;
+	bool crash;
 
 	if(sig == SIGPROF) {
 		if(gp != m->g0 && gp != m->gsignal)
@@ -109,11 +110,14 @@ Throw:
 	}	
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()){
+	if(runtime·gotraceback(&crash)){
 		runtime·traceback((void*)SIG_EIP(info, ctxt), (void*)SIG_ESP(info, ctxt), 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·dumpregs(info, ctxt);
 	}
 	
+	if(crash)
+		runtime·crash();
+
 	runtime·exit(2);
 }

src/pkg/runtime/signal_amd64.c

@@ -44,6 +44,7 @@ runtime·sighandler(int32 sig, Siginfo *info, void *ctxt, G *gp)
 {
 	uintptr *sp;
 	SigTab *t;
+	bool crash;
 
 	if(sig == SIGPROF) {
 		if(gp != m->g0 && gp != m->gsignal)
@@ -119,11 +120,14 @@ Throw:
 	}
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()){
+	if(runtime·gotraceback(&crash)){
 		runtime·traceback((void*)SIG_RIP(info, ctxt), (void*)SIG_RSP(info, ctxt), 0, gp);
 		runtime·tracebackothers(gp);
 		runtime·dumpregs(info, ctxt);
 	}
 	
+	if(crash)
+		runtime·crash();
+
 	runtime·exit(2);
 }

src/pkg/runtime/signal_arm.c

@@ -43,6 +43,7 @@ void
 runtime·sighandler(int32 sig, Siginfo *info, void *ctxt, G *gp)
 {
 	SigTab *t;
+	bool crash;
 
 	if(sig == SIGPROF) {
 		if(gp != m->g0 && gp != m->gsignal)
@@ -109,12 +110,15 @@ Throw:
 	}
 	runtime·printf("\n");
 
-	if(runtime·gotraceback()){
+	if(runtime·gotraceback(&crash)){
 		runtime·traceback((void*)SIG_PC(info, ctxt), (void*)SIG_SP(info, ctxt), (void*)SIG_LR(info, ctxt), gp);
 		runtime·tracebackothers(gp);
 		runtime·printf("\n");
 		runtime·dumpregs(info, ctxt);
 	}
 	
+	if(crash)
+		runtime·crash();
+
 	runtime·exit(2);
 }

src/pkg/runtime/signal_unix.c

@@ -98,5 +98,23 @@ void
 os·sigpipe(void)
 {
 	runtime·setsig(SIGPIPE, SIG_DFL, false);
-	runtime·raisesigpipe();
+	runtime·raise(SIGPIPE);
+}
+
+void
+runtime·crash(void)
+{
+#ifdef GOOS_darwin
+	// OS X core dumps are linear dumps of the mapped memory,
+	// from the first virtual byte to the last, with zeros in the gaps.
+	// Because of the way we arrange the address space on 64-bit systems,
+	// this means the OS X core file will be >128 GB and even on a zippy
+	// workstation can take OS X well over an hour to write (uninterruptible).
+	// Save users from making that mistake.
+	if(sizeof(void*) == 8)
+		return;
+#endif
+
+	runtime·setsig(SIGABRT, SIG_DFL, false);
+	runtime·raise(SIGABRT);
 }

src/pkg/runtime/signal_unix.h

@@ -10,4 +10,5 @@ void	runtime·setsig(int32, GoSighandler*, bool);
 GoSighandler* runtime·getsig(int32);
 
 void	runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp);
-void	runtime·raisesigpipe(void);
+void	runtime·raise(int32);
+

src/pkg/runtime/symtab.c

@@ -670,6 +670,6 @@ runtime·showframe(Func *f, bool current)
 	if(current && m->throwing > 0)
 		return 1;
 	if(traceback < 0)
-		traceback = runtime·gotraceback();
+		traceback = runtime·gotraceback(nil);
 	return traceback > 1 || f != nil && contains(f->name, ".") && !hasprefix(f->name, "runtime.");
 }

src/pkg/runtime/sys_darwin_386.s

@@ -44,13 +44,14 @@ TEXT runtime·write(SB),7,$0
 	INT	$0x80
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$8
+TEXT runtime·raise(SB),7,$16
-	get_tls(CX)
+	MOVL	$20, AX // getpid
-	MOVL	m(CX), DX
+	INT	$0x80
-	MOVL	m_procid(DX), DX
+	MOVL	AX, 4(SP)	// pid
-	MOVL	DX, 0(SP)	// thread_port
+	MOVL	sig+0(FP), AX
-	MOVL	$13, 4(SP)	// signal: SIGPIPE
+	MOVL	AX, 8(SP)	// signal
-	MOVL	$328, AX	// __pthread_kill
+	MOVL	$1, 12(SP)	// posix
+	MOVL	$37, AX // kill
 	INT	$0x80
 	RET
 

src/pkg/runtime/sys_darwin_amd64.s

@@ -60,12 +60,13 @@ TEXT runtime·write(SB),7,$0
 	SYSCALL
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$24
+TEXT runtime·raise(SB),7,$24
-	get_tls(CX)
+	MOVL	$(0x2000000+20), AX // getpid
-	MOVQ	m(CX), DX
+	SYSCALL
-	MOVL	$13, DI	// arg 1 SIGPIPE
+	MOVQ	AX, DI	// arg 1 - pid
-	MOVQ	m_procid(DX), SI	// arg 2 thread_port
+	MOVL	sig+0(FP), SI	// arg 2 - signal
-	MOVL	$(0x2000000+328), AX	// syscall entry __pthread_kill
+	MOVL	$1, DX	// arg 3 - posix
+	MOVL	$(0x2000000+37), AX // kill
 	SYSCALL
 	RET
 

src/pkg/runtime/sys_freebsd_386.s

@@ -81,16 +81,17 @@ TEXT runtime·getrlimit(SB),7,$-4
 	INT	$0x80
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$12
+TEXT runtime·raise(SB),7,$16
 	// thr_self(&8(SP))
 	LEAL	8(SP), AX
-	MOVL	AX, 0(SP)
+	MOVL	AX, 4(SP)
 	MOVL	$432, AX
 	INT	$0x80
 	// thr_kill(self, SIGPIPE)
 	MOVL	8(SP), AX
-	MOVL	AX, 0(SP)
+	MOVL	AX, 4(SP)
-	MOVL	$13, 4(SP)
+	MOVL	sig+0(FP), AX
+	MOVL	AX, 8(SP)
 	MOVL	$433, AX
 	INT	$0x80
 	RET

src/pkg/runtime/sys_freebsd_amd64.s

@@ -95,14 +95,14 @@ TEXT runtime·getrlimit(SB),7,$-8
 	SYSCALL
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$16
+TEXT runtime·raise(SB),7,$16
 	// thr_self(&8(SP))
 	LEAQ	8(SP), DI	// arg 1 &8(SP)
 	MOVL	$432, AX
 	SYSCALL
 	// thr_kill(self, SIGPIPE)
 	MOVQ	8(SP), DI	// arg 1 id
-	MOVQ	$13, SI	// arg 2 SIGPIPE
+	MOVL	sig+0(FP), SI	// arg 2
 	MOVL	$433, AX
 	SYSCALL
 	RET

src/pkg/runtime/sys_freebsd_arm.s

@@ -87,13 +87,13 @@ TEXT runtime·getrlimit(SB),7,$-8
 	SWI $194
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$8
+TEXT runtime·raise(SB),7,$8
 	// thr_self(&4(R13))
 	MOVW $4(R13), R0 // arg 1 &4(R13)
 	SWI $432
 	// thr_kill(self, SIGPIPE)
 	MOVW 4(R13), R0	// arg 1 id
-	MOVW $13, R1	// arg 2 SIGPIPE
+	MOVW sig+0(FP), R1	// arg 2 - signal
 	SWI $433
 	RET
 

src/pkg/runtime/sys_linux_386.s

@@ -77,11 +77,11 @@ TEXT runtime·usleep(SB),7,$8
 	CALL	*runtime·_vdso(SB)
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$12
+TEXT runtime·raise(SB),7,$12
 	MOVL	$224, AX	// syscall - gettid
 	CALL	*runtime·_vdso(SB)
-	MOVL	AX, 0(SP)	// arg 1 tid
+	MOVL	AX, BX	// arg 1 tid
-	MOVL	$13, 4(SP)	// arg 2 SIGPIPE
+	MOVL	sig+0(FP), CX	// arg 2 signal
 	MOVL	$238, AX	// syscall - tkill
 	CALL	*runtime·_vdso(SB)
 	RET

src/pkg/runtime/sys_linux_amd64.s

@@ -75,11 +75,11 @@ TEXT runtime·usleep(SB),7,$16
 	SYSCALL
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$12
+TEXT runtime·raise(SB),7,$12
 	MOVL	$186, AX	// syscall - gettid
 	SYSCALL
 	MOVL	AX, DI	// arg 1 tid
-	MOVL	$13, SI	// arg 2 SIGPIPE
+	MOVL	sig+0(FP), SI	// arg 2
 	MOVL	$200, AX	// syscall - tkill
 	SYSCALL
 	RET

src/pkg/runtime/sys_linux_arm.s

@@ -92,11 +92,11 @@ TEXT runtime·exit1(SB),7,$-4
 	MOVW	$1003, R1
 	MOVW	R0, (R1)	// fail hard
 
-TEXT	runtime·raisesigpipe(SB),7,$-4
+TEXT	runtime·raise(SB),7,$-4
 	MOVW	$SYS_gettid, R7
 	SWI	$0
 	// arg 1 tid already in R0 from gettid
-	MOVW	$13, R1	// arg 2 SIGPIPE
+	MOVW	sig+0(FP), R1	// arg 2 - signal
 	MOVW	$SYS_tkill, R7
 	SWI	$0
 	RET

src/pkg/runtime/sys_netbsd_386.s

@@ -61,12 +61,13 @@ TEXT runtime·usleep(SB),7,$24
 	INT	$0x80
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$12
+TEXT runtime·raise(SB),7,$12
 	MOVL	$311, AX		// sys__lwp_self
 	INT	$0x80
 	MOVL	$0, 0(SP)
 	MOVL	AX, 4(SP)		// arg 1 - target
-	MOVL	$13, 8(SP)		// arg 2 - signo == SIGPIPE
+	MOVL	sig+0(FP), AX
+	MOVL	AX, 8(SP)		// arg 2 - signo
 	MOVL	$318, AX		// sys__lwp_kill
 	INT	$0x80
 	RET

src/pkg/runtime/sys_netbsd_amd64.s

@@ -125,11 +125,11 @@ TEXT runtime·usleep(SB),7,$16
 	SYSCALL
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$16
+TEXT runtime·raise(SB),7,$16
 	MOVL	$311, AX		// sys__lwp_self
 	SYSCALL
 	MOVQ	AX, DI			// arg 1 - target
-	MOVQ	$13, SI			// arg 2 - signo == SIGPIPE
+	MOVL	sig+0(FP), SI		// arg 2 - signo
 	MOVL	$318, AX		// sys__lwp_kill
 	SYSCALL
 	RET

src/pkg/runtime/sys_netbsd_arm.s

@@ -88,9 +88,9 @@ TEXT runtime·usleep(SB),7,$16
 	SWI $0xa001ae	// sys_nanosleep
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$16
+TEXT runtime·raise(SB),7,$16
 	SWI $0xa00137	// sys__lwp_self, the returned R0 is arg 1
-	MOVW $13, R1	// arg 2 - signo == SIGPIPE
+	MOVW	sig+0(FP), R1	// arg 2 - signal
 	SWI $0xa0013e	// sys__lwp_kill
 	RET
 

src/pkg/runtime/sys_openbsd_386.s

@@ -62,12 +62,13 @@ TEXT runtime·usleep(SB),7,$20
 	INT	$0x80
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$12
+TEXT runtime·raise(SB),7,$12
 	MOVL	$299, AX		// sys_getthrid
 	INT	$0x80
 	MOVL	$0, 0(SP)
 	MOVL	AX, 4(SP)		// arg 1 - pid
-	MOVL	$13, 8(SP)		// arg 2 - signum == SIGPIPE
+	MOVL	sig+0(FP), AX
+	MOVL	AX, 8(SP)		// arg 2 - signum
 	MOVL	$37, AX			// sys_kill
 	INT	$0x80
 	RET

src/pkg/runtime/sys_openbsd_amd64.s

@@ -133,11 +133,11 @@ TEXT runtime·usleep(SB),7,$16
 	SYSCALL
 	RET
 
-TEXT runtime·raisesigpipe(SB),7,$16
+TEXT runtime·raise(SB),7,$16
 	MOVL	$299, AX		// sys_getthrid
 	SYSCALL
 	MOVQ	AX, DI			// arg 1 - pid
-	MOVQ	$13, SI			// arg 2 - signum == SIGPIPE
+	MOVL	sig+0(FP), SI			// arg 2 - signum
 	MOVL	$37, AX			// sys_kill
 	SYSCALL
 	RET