runtime: make sure associated defers are copyable before trying to copy a stack.

Defers generated from cgo lie to us about their argument layout.
Mark those defers as not copyable.

CL 83820043 contains an additional test for this code and should be
checked in (and enabled) after this change is in.

Fixes bug 7695.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/84740043

src/pkg/runtime/stack.c

@@ -194,7 +194,7 @@ runtime·oldstack(void)
 			top->gobuf.pc, top->gobuf.sp, top->gobuf.lr, (uintptr)m->cret, (uintptr)argsize);
 	}
 
-	// gp->status is usually Grunning, but it could be Gsyscall if a stack split
+	// gp->status is usually Grunning, but it could be Gsyscall if a stack overflow
 	// happens during a function call inside entersyscall.
 	oldstatus = gp->status;
 	
@@ -318,13 +318,61 @@ static int32
 copyabletopsegment(G *gp)
 {
 	CopyableInfo cinfo;
+	Defer *d;
+	Func *f;
+	FuncVal *fn;
+	StackMap *stackmap;
 
 	cinfo.stk = (byte*)gp->stackguard - StackGuard;
 	cinfo.base = (byte*)gp->stackbase + sizeof(Stktop);
 	cinfo.frames = 0;
+
+	// Check that each frame is copyable.  As a side effect,
+	// count the frames.
 	runtime·gentraceback(~(uintptr)0, ~(uintptr)0, 0, gp, 0, nil, 0x7fffffff, checkframecopy, &cinfo, false);
 	if(StackDebug >= 1 && cinfo.frames != -1)
 		runtime·printf("copystack: %d copyable frames\n", cinfo.frames);
+
+	// Check to make sure all Defers are copyable
+	for(d = gp->defer; d != nil; d = d->link) {
+		if(cinfo.stk <= (byte*)d && (byte*)d < cinfo.base) {
+			// Defer is on the stack.  Its copyableness has
+			// been established during stack walking.
+			// For now, this only happens with the Defer in runtime.main.
+			continue;
+		}
+		if(d->argp < cinfo.stk || cinfo.base <= d->argp)
+			break; // a defer for the next segment
+		fn = d->fn;
+		f = runtime·findfunc((uintptr)fn->fn);
+		if(f == nil)
+			return -1;
+
+		// Check to make sure we have an args pointer map for the defer's args.
+		// We only need the args map, but we check
+		// for the locals map also, because when the locals map
+		// isn't provided it means the ptr map came from C and
+		// C (particularly, cgo) lies to us.  See issue 7695.
+		stackmap = runtime·funcdata(f, FUNCDATA_ArgsPointerMaps);
+		if(stackmap == nil || stackmap->n <= 0)
+			return -1;
+		stackmap = runtime·funcdata(f, FUNCDATA_LocalsPointerMaps);
+		if(stackmap == nil || stackmap->n <= 0)
+			return -1;
+
+		if(cinfo.stk <= (byte*)fn && (byte*)fn < cinfo.base) {
+			// FuncVal is on the stack.  Again, its copyableness
+			// was established during stack walking.
+			continue;
+		}
+		// The FuncVal may have pointers in it, but fortunately for us
+		// the compiler won't put pointers into the stack in a
+		// heap-allocated FuncVal.
+		// One day if we do need to check this, we'll need maps of the
+		// pointerness of the closure args.  The only place we have that map
+		// right now is in the gc program for the FuncVal.  Ugh.
+	}
+
 	return cinfo.frames;
 }
 
@@ -371,7 +419,7 @@ adjustpointers(byte **scanp, BitVector *bv, AdjustInfo *adjinfo, Func *f)
 			}
 			if(minp <= p && p < maxp) {
 				if(StackDebug >= 3)
-					runtime·printf("adjust ptr %p\n", p);
+					runtime·printf("adjust ptr %p %s\n", p, runtime·funcname(f));
 				scanp[i] = p + delta;
 			}
 			break;
@@ -505,11 +553,8 @@ adjustdefers(G *gp, AdjustInfo *adjinfo)
 		if(d->argp < adjinfo->oldstk || adjinfo->oldbase <= d->argp)
 			break; // a defer for the next segment
 		f = runtime·findfunc((uintptr)d->fn->fn);
-		if(f == nil) {
-			runtime·printf("runtime: bad defer %p %d %d %p %p\n", d->fn->fn, d->siz, d->special, d->argp, d->pc);
-			runtime·printf("caller %s\n", runtime·funcname(runtime·findfunc((uintptr)d->pc)));
+		if(f == nil)
 			runtime·throw("can't adjust unknown defer");
-		}
 		if(StackDebug >= 4)
 			runtime·printf("  checking defer %s\n", runtime·funcname(f));
 		// Defer's FuncVal might be on the stack
@@ -519,7 +564,7 @@ adjustdefers(G *gp, AdjustInfo *adjinfo)
 				runtime·printf("    adjust defer fn %s\n", runtime·funcname(f));
 			d->fn = (FuncVal*)((byte*)fn + adjinfo->delta);
 		} else {
-			// deferred function's closure args might point into the stack.
+			// deferred function's args might point into the stack.
 			if(StackDebug >= 3)
 				runtime·printf("    adjust deferred args for %s\n", runtime·funcname(f));
 			stackmap = runtime·funcdata(f, FUNCDATA_ArgsPointerMaps);
@@ -626,7 +671,7 @@ runtime·newstack(void)
 		runtime·throw("runtime: wrong goroutine in newstack");
 	}
 
-	// gp->status is usually Grunning, but it could be Gsyscall if a stack split
+	// gp->status is usually Grunning, but it could be Gsyscall if a stack overflow
 	// happens during a function call inside entersyscall.
 	gp = m->curg;
 	oldstatus = gp->status;
@@ -640,7 +685,7 @@ runtime·newstack(void)
 	m->morebuf.lr = (uintptr)nil;
 	m->morebuf.sp = (uintptr)nil;
 	gp->status = Gwaiting;
-	gp->waitreason = "stack split";
+	gp->waitreason = "stack growth";
 	newstackcall = framesize==1;
 	if(newstackcall)
 		framesize = 0;
@@ -668,8 +713,8 @@ runtime·newstack(void)
 	}
 
 	if(argsize % sizeof(uintptr) != 0) {
-		runtime·printf("runtime: stack split with misaligned argsize %d\n", argsize);
-		runtime·throw("runtime: stack split argsize");
+		runtime·printf("runtime: stack growth with misaligned argsize %d\n", argsize);
+		runtime·throw("runtime: stack growth argsize");
 	}
 
 	if(gp->stackguard0 == (uintptr)StackPreempt) {
@@ -678,7 +723,7 @@ runtime·newstack(void)
 		if(oldstatus == Grunning && m->p == nil && m->locks == 0)
 			runtime·throw("runtime: g is running but p is not");
 		if(oldstatus == Gsyscall && m->locks == 0)
-			runtime·throw("runtime: stack split during syscall");
+			runtime·throw("runtime: stack growth during syscall");
 		// Be conservative about where we preempt.
 		// We are interested in preempting user Go code, not runtime code.
 		if(oldstatus != Grunning || m->locks || m->mallocing || m->gcing || m->p->status != Prunning) {

src/pkg/runtime/stack_test.go

@@ -257,3 +257,20 @@ func growStackWithCallback(cb func()) {
 		f(i)
 	}
 }
+
+// TestDeferPtrs tests the adjustment of Defer's argument pointers (p aka &y)
+// during a stack copy.
+func set(p *int, x int) {
+	*p = x
+}
+func TestDeferPtrs(t *testing.T) {
+	var y int
+
+	defer func() {
+		if y != 42 {
+			t.Errorf("defer's stack references were not adjusted appropriately")
+		}
+	}()
+	defer set(&y, 42)
+	growStack()
+}