cmd/ld, runtime: restrict stack root scan to locals and arguments

Updates #5134

R=golang-dev, bradfitz, cshapiro, daniel.morsing, ality, iant
CC=golang-dev
https://golang.org/cl/8022044

src/cmd/ld/lib.c

@@ -1862,7 +1862,10 @@ genasmsym(void (*put)(Sym*, char*, int, vlong, vlong, int, Sym*))
 		/* frame, locals, args, auto and param after */
 		put(nil, ".frame", 'm', (uint32)s->text->to.offset+PtrSize, 0, 0, 0);
 		put(nil, ".locals", 'm', s->locals, 0, 0, 0);
-		put(nil, ".args", 'm', s->args, 0, 0, 0);
+		if(s->text->textflag & NOSPLIT)
+			put(nil, ".args", 'm', ArgsSizeUnknown, 0, 0, 0);
+		else
+			put(nil, ".args", 'm', s->args, 0, 0, 0);
 
 		for(a=s->autom; a; a=a->link) {
 			// Emit a or p according to actual offset, even if label is wrong.

src/cmd/ld/lib.h

@@ -71,6 +71,13 @@ enum
 	NHASH = 100003,
 };
 
+enum
+{
+	// This value is known to the garbage collector and should be kept in
+	// sync with runtime/pkg/runtime.h
+	ArgsSizeUnknown = 0x80000000
+};
+
 typedef struct Library Library;
 struct Library
 {

src/pkg/runtime/mgc0.c

@@ -18,6 +18,7 @@ enum {
 	Debug = 0,
 	DebugMark = 0,  // run second pass to check mark
 	CollectStats = 0,
+	ScanStackByFrames = 0,
 
 	// Four bits per word (see #defines below).
 	wordsPerBitmapWord = sizeof(void*)*8/4,
@@ -1316,51 +1317,94 @@ addroot(Obj obj)
 	work.nroot++;
 }
 
+// Scan a stack frame.  The doframe parameter is a signal that the previously
+// scanned activation has an unknown argument size.  When *doframe is true the
+// current activation must have its entire frame scanned.  Otherwise, only the
+// locals need to be scanned.
+static void
+addframeroots(Func *f, byte*, byte *sp, void *doframe)
+{
+	uintptr outs;
+
+	if(thechar == '5')
+		sp += sizeof(uintptr);
+	if(f->locals == 0 || *(bool*)doframe == true)
+		addroot((Obj){sp, f->frame - sizeof(uintptr), 0});
+	else if(f->locals > 0) {
+		outs = f->frame - sizeof(uintptr) - f->locals;
+		addroot((Obj){sp + outs, f->locals, 0});
+	}
+	if(f->args > 0)
+		addroot((Obj){sp + f->frame, f->args, 0});
+	*(bool*)doframe = (f->args == ArgsSizeUnknown);
+}
+
 static void
 addstackroots(G *gp)
 {
 	M *mp;
 	int32 n;
 	Stktop *stk;
-	byte *sp, *guard;
+	byte *sp, *guard, *pc;
+	Func *f;
+	bool doframe;
 
 	stk = (Stktop*)gp->stackbase;
 	guard = (byte*)gp->stackguard;
 
 	if(gp == g) {
 		// Scanning our own stack: start at &gp.
-		sp = (byte*)&gp;
+		sp = runtime·getcallersp(&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;
+		stk = (Stktop*)gp->gcstack;
+		guard = (byte*)gp->gcguard;
 	} else {
 		// Scanning another goroutine's stack.
 		// The goroutine is usually asleep (the world is stopped).
 		sp = (byte*)gp->sched.sp;
-
-		// 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;
+		pc = gp->sched.pc;
+		if(ScanStackByFrames && pc == (byte*)runtime·goexit && gp->fnstart != nil) {
+			// The goroutine has not started. However, its incoming
+			// arguments are live at the top of the stack and must
+			// be scanned.  No other live values should be on the
+			// stack.
+			f = runtime·findfunc((uintptr)gp->fnstart->fn);
+			if(f->args > 0) {
+				if(thechar == '5')
+					sp += sizeof(uintptr);
+				addroot((Obj){sp, f->args, 0});
+			}
+			return;
 		}
 	}
-
-	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");
+	if (ScanStackByFrames) {
+		doframe = false;
+		runtime·gentraceback(pc, sp, nil, gp, 0, nil, 0x7fffffff, addframeroots, &doframe);
+	} else {
+		USED(pc);
+		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, (uintptr)defaultProg | PRECISE | LOOP});
+			sp = (byte*)stk->gobuf.sp;
+			guard = stk->stackguard;
+			stk = (Stktop*)stk->stackbase;
+			n++;
 		}
-		addroot((Obj){sp, (byte*)stk - sp, (uintptr)defaultProg | PRECISE | LOOP});
-		sp = (byte*)stk->gobuf.sp;
-		guard = stk->stackguard;
-		stk = (Stktop*)stk->stackbase;
-		n++;
 	}
 }
 

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));
+	n = runtime·gentraceback(pc, sp, 0, gp, 0, r->stk, nelem(r->stk), nil, nil);
 	if(n < nelem(r->stk))
 		r->stk[n] = 0;
 }

src/pkg/runtime/proc.c

@@ -1778,7 +1778,7 @@ 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));
+	n = runtime·gentraceback(pc, sp, lr, gp, 0, prof.pcbuf, nelem(prof.pcbuf), nil, nil);
 	if(n > 0)
 		prof.fn(prof.pcbuf, n);
 	runtime·unlock(&prof);

src/pkg/runtime/runtime.h

@@ -147,7 +147,12 @@ enum
 	// Global <-> per-M stack segment cache transfer batch size.
 	StackCacheBatch = 16,
 };
-
+enum
+{
+	// This value is generated by the linker and should be kept in
+	// sync with cmd/ld/lib.h
+	ArgsSizeUnknown = 0x80000000,
+};
 /*
  * structures
  */
@@ -775,7 +780,7 @@ 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);
+int32	runtime·gentraceback(byte*, byte*, byte*, G*, int32, uintptr*, int32, void (*)(Func*, byte*, byte*, void*), void*);
 int64	runtime·nanotime(void);
 void	runtime·dopanic(int32);
 void	runtime·startpanic(void);

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)
+runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max, void (*fn)(Func*, byte*, byte*, void*), void *arg)
 {
-	int32 i, n, iter;
+	int32 i, n;
 	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;
-	for(iter = 0; iter < 100 && n < max; iter++) {	// iter avoids looping forever
+	while(n < max) {
 		// Typically:
 		//	pc is the PC of the running function.
 		//	sp is the stack pointer at that program counter.
@@ -60,14 +60,17 @@ 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 && runtime·showframe(nil, gp == m->curg))
+			if(pcbuf == nil && fn == 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(pc <= 0x1000 || (f = runtime·findfunc(pc)) == nil) {
+			if(fn != nil)
+				runtime·throw("unknown pc");
 			break;
+		}
 		
 		// Found an actual function.
 		if(lr == 0)
@@ -83,6 +86,8 @@ 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.
@@ -114,7 +119,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		
 		waspanic = f->entry == (uintptr)runtime·sigpanic;
 
-		if(pcbuf == nil && f->entry == (uintptr)runtime·newstack && gp == m->g0) {
+		if(pcbuf == nil && fn == 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*);
@@ -125,7 +130,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			continue;
 		}
 		
-		if(pcbuf == nil && f->entry == (uintptr)runtime·lessstack && gp == m->g0) {
+		if(pcbuf == nil && fn == 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;
@@ -136,6 +141,10 @@ 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;
@@ -163,7 +172,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		}
 	}
 	
-	if(pcbuf == nil && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil
+	if(pcbuf == nil && fn == 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.
@@ -187,7 +196,7 @@ 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);
+	runtime·gentraceback(pc0, sp, lr, gp, 0, nil, 100, nil, nil);
 }
 
 // func caller(n int) (pc uintptr, file string, line int, ok bool)
@@ -199,5 +208,5 @@ 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);
+	return runtime·gentraceback(pc, sp, 0, g, skip, pcbuf, m, nil, nil);
 }

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)
-// 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.
+// 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.
 int32
-runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max)
+runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max, void (*fn)(Func*, byte*, byte*, void*), void *arg)
 {
-	int32 i, n, iter, sawnewstack;
+	int32 i, n, 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;
-	for(iter = 0; iter < 100 && n < max; iter++) {	// iter avoids looping forever
+	while(n < max) {
 		// Typically:
 		//	pc is the PC of the running function.
 		//	sp is the stack pointer at that program counter.
@@ -68,13 +68,16 @@ 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 && runtime·showframe(nil, gp == m->curg))
+			if(pcbuf == nil && fn == 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(pc <= 0x1000 || (f = runtime·findfunc(pc)) == nil) {
+			if(fn != nil)
+				runtime·throw("unknown pc");
 			break;
+		}
 
 		// Found an actual function.
 		if(fp == nil) {
@@ -91,6 +94,8 @@ 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.
@@ -129,7 +134,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		if(f->entry == (uintptr)runtime·newstack)
 			sawnewstack = 1;
 
-		if(pcbuf == nil && f->entry == (uintptr)runtime·morestack && gp == m->g0 && sawnewstack) {
+		if(pcbuf == nil && fn == 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.
@@ -144,7 +149,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 			continue;
 		}
 
-		if(pcbuf == nil && f->entry == (uintptr)runtime·lessstack && gp == m->g0) {
+		if(pcbuf == nil && fn == 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;
@@ -156,6 +161,10 @@ 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;
@@ -164,7 +173,7 @@ 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 && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil
+	if(pcbuf == nil && fn == 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.
@@ -187,7 +196,7 @@ 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);
+	runtime·gentraceback(pc0, sp, nil, gp, 0, nil, 100, nil, nil);
 }
 
 int32
@@ -199,5 +208,5 @@ 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);
+	return runtime·gentraceback(pc, sp, nil, g, skip, pcbuf, m, nil, nil);
 }