undo CL 7301062 / 9742f722b558

broke arm garbage collector

traceback_arm fails with a missing pc. It needs CL 7494043.
But that only makes the build break later, this time with
"invalid freelist". Roll back until it can be fixed correctly.

««« original CL description
runtime: restrict stack root scan to locals and arguments

R=rsc
CC=golang-dev
https://golang.org/cl/7301062
»»»

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7493044

src/pkg/runtime/mgc0.c

@@ -1299,53 +1299,52 @@ addroot(Obj obj)
 	work.nroot++;
 }
 
-static void
-addframeroots(Func *f, byte*, byte *sp, void*)
-{
-	if (f->frame > sizeof(uintptr))
-		addroot((Obj){sp, f->frame - sizeof(uintptr), 0});
-	if (f->args > 0)
-		addroot((Obj){sp + f->frame, f->args, 0});
-}
-
 static void
 addstackroots(G *gp)
 {
 	M *mp;
-	Func *f;
-	byte *sp, *pc;
+	int32 n;
+	Stktop *stk;
+	byte *sp, *guard;
+
+	stk = (Stktop*)gp->stackbase;
+	guard = (byte*)gp->stackguard;
 
 	if(gp == g) {
 		// Scanning our own stack: start at &gp.
 		sp = (byte*)&gp;
-		pc = runtime·getcallerpc(&gp);
 	} else if((mp = gp->m) != nil && mp->helpgc) {
 		// gchelper's stack is in active use and has no interesting pointers.
 		return;
-	} else if(gp->gcstack != (uintptr)nil) {
-		// Scanning another goroutine that is about to enter or might
-		// have just exited a system call. It may be executing code such
-		// as schedlock and may have needed to start a new stack segment.
-		// Use the stack segment and stack pointer at the time of
-		// the system call instead, since that won't change underfoot.
-		sp = (byte*)gp->gcsp;
-		pc = gp->gcpc;
 	} else {
 		// Scanning another goroutine's stack.
 		// The goroutine is usually asleep (the world is stopped).
 		sp = (byte*)gp->sched.sp;
-		pc = gp->sched.pc;
-		if (pc == (byte*)runtime·goexit && gp->fnstart != nil) {
-			// The goroutine has not started.  Its incoming
-			// arguments are at the top of the stack and must
-			// be scanned.  No other data on the stack.
-			f = runtime·findfunc((uintptr)gp->fnstart->fn);
-			if (f->args > 0)
-				addroot((Obj){sp, f->args, 0});
-			return;
+
+		// The exception is that if the goroutine is about to enter or might
+		// have just exited a system call, it may be executing code such
+		// as schedlock and may have needed to start a new stack segment.
+		// Use the stack segment and stack pointer at the time of
+		// the system call instead, since that won't change underfoot.
+		if(gp->gcstack != (uintptr)nil) {
+			stk = (Stktop*)gp->gcstack;
+			sp = (byte*)gp->gcsp;
+			guard = (byte*)gp->gcguard;
+		}
 	}
+
+	n = 0;
+	while(stk) {
+		if(sp < guard-StackGuard || (byte*)stk < sp) {
+			runtime·printf("scanstack inconsistent: g%D#%d sp=%p not in [%p,%p]\n", gp->goid, n, sp, guard-StackGuard, stk);
+			runtime·throw("scanstack");
+		}
+		addroot((Obj){sp, (byte*)stk - sp, 0});
+		sp = (byte*)stk->gobuf.sp;
+		guard = stk->stackguard;
+		stk = (Stktop*)stk->stackbase;
+		n++;
 	}
-	runtime·gentraceback(pc, sp, nil, gp, 0, nil, 0x7fffffff, addframeroots, nil);
 }
 
 static void

src/pkg/runtime/mprof.goc

@@ -511,7 +511,7 @@ saveg(byte *pc, byte *sp, G *gp, TRecord *r)
 {
 	int32 n;
 	
-	n = runtime·gentraceback(pc, sp, 0, gp, 0, r->stk, nelem(r->stk), nil, nil);
+	n = runtime·gentraceback(pc, sp, 0, gp, 0, r->stk, nelem(r->stk));
 	if(n < nelem(r->stk))
 		r->stk[n] = 0;
 }

src/pkg/runtime/proc.c

@@ -1710,7 +1710,7 @@ runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp)
 		runtime·unlock(&prof);
 		return;
 	}
-	n = runtime·gentraceback(pc, sp, lr, gp, 0, prof.pcbuf, nelem(prof.pcbuf), nil, nil);
+	n = runtime·gentraceback(pc, sp, lr, gp, 0, prof.pcbuf, nelem(prof.pcbuf));
 	if(n > 0)
 		prof.fn(prof.pcbuf, n);
 	runtime·unlock(&prof);

src/pkg/runtime/runtime.h

@@ -749,7 +749,7 @@ void	runtime·exitsyscall(void);
 G*	runtime·newproc1(FuncVal*, byte*, int32, int32, void*);
 bool	runtime·sigsend(int32 sig);
 int32	runtime·callers(int32, uintptr*, int32);
-int32	runtime·gentraceback(byte*, byte*, byte*, G*, int32, uintptr*, int32,  void (*fn)(Func*, byte*, byte*, void*), void *arg);
+int32	runtime·gentraceback(byte*, byte*, byte*, G*, int32, uintptr*, int32);
 int64	runtime·nanotime(void);
 void	runtime·dopanic(int32);
 void	runtime·startpanic(void);

src/pkg/runtime/sigqueue.goc

@@ -84,7 +84,6 @@ func signal_recv() (m uint32) {
 	static uint32 recv[nelem(sig.mask)];
 	uint32 i, old, new;
 	
-	g->issystem = true;
 	for(;;) {
 		// Serve from local copy if there are bits left.
 		for(i=0; i<NSIG; i++) {

src/pkg/runtime/traceback_arm.c

@@ -17,9 +17,9 @@ void _divu(void);
 void _modu(void);
 
 int32
-runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max, void (*fn)(Func*, byte*, byte*, void*), void *arg)
+runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max)
 {
-	int32 i, n;
+	int32 i, n, iter;
 	uintptr pc, lr, tracepc, x;
 	byte *fp;
 	bool waspanic;
@@ -46,7 +46,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 
 	n = 0;
 	stk = (Stktop*)gp->stackbase;
-	while(n < max) {
+	for(iter = 0; iter < 100 && n < max; iter++) {	// iter avoids looping forever
 		// Typically:
 		//	pc is the PC of the running function.
 		//	sp is the stack pointer at that program counter.
@@ -60,17 +60,14 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			sp = (byte*)stk->gobuf.sp;
 			lr = 0;
 			fp = nil;
-			if(pcbuf == nil && fn == nil && runtime·showframe(nil, gp == m->curg))
+			if(pcbuf == nil && runtime·showframe(nil, gp == m->curg))
 				runtime·printf("----- stack segment boundary -----\n");
 			stk = (Stktop*)stk->stackbase;
 			continue;
 		}
 		
-		if(pc <= 0x1000 || (f = runtime·findfunc(pc)) == nil) {
-			if(fn != nil)
-				runtime·throw("unknown pc");
+		if(pc <= 0x1000 || (f = runtime·findfunc(pc)) == nil)
 			break;
-		}
 		
 		// Found an actual function.
 		if(lr == 0)
@@ -85,8 +82,6 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			skip--;
 		else if(pcbuf != nil)
 			pcbuf[n++] = pc;
-		else if(fn != nil)
-			(*fn)(f, (byte*)pc, sp, arg);
 		else {
 			if(runtime·showframe(f, gp == m->curg)) {
 				// Print during crash.
@@ -118,7 +113,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		
 		waspanic = f->entry == (uintptr)runtime·sigpanic;
 
-		if(pcbuf == nil && fn == nil && f->entry == (uintptr)runtime·newstack && gp == m->g0) {
+		if(pcbuf == nil && f->entry == (uintptr)runtime·newstack && gp == m->g0) {
 			runtime·printf("----- newstack called from goroutine %D -----\n", m->curg->goid);
 			pc = (uintptr)m->morepc;
 			sp = (byte*)m->moreargp - sizeof(void*);
@@ -129,7 +124,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			continue;
 		}
 		
-		if(pcbuf == nil && fn == nil && f->entry == (uintptr)runtime·lessstack && gp == m->g0) {
+		if(pcbuf == nil && f->entry == (uintptr)runtime·lessstack && gp == m->g0) {
 			runtime·printf("----- lessstack called from goroutine %D -----\n", m->curg->goid);
 			gp = m->curg;
 			stk = (Stktop*)gp->stackbase;
@@ -140,10 +135,6 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			continue;
 		}	
 		
-		// Do not unwind past the bottom of the stack.
-		if(pc == (uintptr)runtime·goexit)
-			break;
-
 		// Unwind to next frame.
 		pc = lr;
 		lr = 0;
@@ -171,7 +162,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		}
 	}
 	
-	if(pcbuf == nil && fn == nil && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil
+	if(pcbuf == nil && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil
 			&& runtime·showframe(f, gp == m->curg) && gp->goid != 1) {
 		runtime·printf("created by %S\n", f->name);
 		tracepc = pc;	// back up to CALL instruction for funcline.
@@ -195,7 +186,7 @@ runtime·traceback(byte *pc0, byte *sp, byte *lr, G *gp)
 		sp = (byte*)gp->sched.sp;
 		lr = nil;
 	}
-	runtime·gentraceback(pc0, sp, lr, gp, 0, nil, 100, nil, nil);
+	runtime·gentraceback(pc0, sp, lr, gp, 0, nil, 100);
 }
 
 // func caller(n int) (pc uintptr, file string, line int, ok bool)
@@ -207,5 +198,5 @@ runtime·callers(int32 skip, uintptr *pcbuf, int32 m)
 	sp = runtime·getcallersp(&skip);
 	pc = runtime·getcallerpc(&skip);
 
-	return runtime·gentraceback(pc, sp, 0, g, skip, pcbuf, m, nil, nil);
+	return runtime·gentraceback(pc, sp, 0, g, skip, pcbuf, m);
 }

src/pkg/runtime/traceback_x86.c

@@ -17,14 +17,14 @@ void runtime·sigpanic(void);
 // This code is also used for the 386 tracebacks.
 // Use uintptr for an appropriate word-sized integer.
 
-// Generic traceback.  Handles runtime stack prints (pcbuf == nil),
-// the runtime.Callers function (pcbuf != nil), as well as the garbage
-// collector (fn != nil).  A little clunky to merge the two but avoids
-// duplicating the code and all its subtlety.
+// Generic traceback.  Handles runtime stack prints (pcbuf == nil)
+// as well as the runtime.Callers function (pcbuf != nil).
+// A little clunky to merge the two but avoids duplicating
+// the code and all its subtlety.
 int32
-runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max, void (*fn)(Func*, byte*, byte*, void*), void *arg)
+runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max)
 {
-	int32 i, n, sawnewstack;
+	int32 i, n, iter, sawnewstack;
 	uintptr pc, lr, tracepc;
 	byte *fp;
 	Stktop *stk;
@@ -54,7 +54,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 	n = 0;
 	sawnewstack = 0;
 	stk = (Stktop*)gp->stackbase;
-	while(n < max) {
+	for(iter = 0; iter < 100 && n < max; iter++) {	// iter avoids looping forever
 		// Typically:
 		//	pc is the PC of the running function.
 		//	sp is the stack pointer at that program counter.
@@ -68,16 +68,13 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			sp = (byte*)stk->gobuf.sp;
 			lr = 0;
 			fp = nil;
-			if(pcbuf == nil && fn == nil && runtime·showframe(nil, gp == m->curg))
+			if(pcbuf == nil && runtime·showframe(nil, gp == m->curg))
 				runtime·printf("----- stack segment boundary -----\n");
 			stk = (Stktop*)stk->stackbase;
 			continue;
 		}
-		if(pc <= 0x1000 || (f = runtime·findfunc(pc)) == nil) {
-			if(fn != nil)
-				runtime·throw("unknown pc");
+		if(pc <= 0x1000 || (f = runtime·findfunc(pc)) == nil)
 			break;
-		}
 
 		// Found an actual function.
 		if(fp == nil) {
@@ -94,8 +91,6 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			skip--;
 		else if(pcbuf != nil)
 			pcbuf[n++] = pc;
-		else if(fn != nil)
-			(*fn)(f, (byte*)pc, sp, arg);
 		else {
 			if(runtime·showframe(f, gp == m->curg)) {
 				// Print during crash.
@@ -134,7 +129,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		if(f->entry == (uintptr)runtime·newstack)
 			sawnewstack = 1;
 
-		if(pcbuf == nil && fn == nil && f->entry == (uintptr)runtime·morestack && gp == m->g0 && sawnewstack) {
+		if(pcbuf == nil && f->entry == (uintptr)runtime·morestack && gp == m->g0 && sawnewstack) {
 			// The fact that we saw newstack means that morestack
 			// has managed to record its information in m, so we can
 			// use it to keep unwinding the stack.
@@ -149,7 +144,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			continue;
 		}
 
-		if(pcbuf == nil && fn == nil && f->entry == (uintptr)runtime·lessstack && gp == m->g0) {
+		if(pcbuf == nil && f->entry == (uintptr)runtime·lessstack && gp == m->g0) {
 			// Lessstack is running on scheduler stack.  Switch to original goroutine.
 			runtime·printf("----- lessstack called from goroutine %D -----\n", m->curg->goid);
 			gp = m->curg;
@@ -161,10 +156,6 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			continue;
 		}
 
-		// Do not unwind past the bottom of the stack.
-		if(pc == (uintptr)runtime·goexit)
-			break;
-
 		// Unwind to next frame.
 		pc = lr;
 		lr = 0;
@@ -173,7 +164,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 	}
 	
 	// Show what created goroutine, except main goroutine (goid 1).
-	if(pcbuf == nil && fn == nil && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil
+	if(pcbuf == nil && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil
 			&& runtime·showframe(f, gp == m->curg) && gp->goid != 1) {
 		runtime·printf("created by %S\n", f->name);
 		tracepc = pc;	// back up to CALL instruction for funcline.
@@ -196,7 +187,7 @@ runtime·traceback(byte *pc0, byte *sp, byte*, G *gp)
 		pc0 = gp->sched.pc;
 		sp = (byte*)gp->sched.sp;
 	}
-	runtime·gentraceback(pc0, sp, nil, gp, 0, nil, 100, nil, nil);
+	runtime·gentraceback(pc0, sp, nil, gp, 0, nil, 100);
 }
 
 int32
@@ -208,5 +199,5 @@ runtime·callers(int32 skip, uintptr *pcbuf, int32 m)
 	sp = (byte*)&skip;
 	pc = runtime·getcallerpc(&skip);
 
-	return runtime·gentraceback(pc, sp, nil, g, skip, pcbuf, m, nil, nil);
+	return runtime·gentraceback(pc, sp, nil, g, skip, pcbuf, m);
 }