gc, runtime: fix range+panic line number bugs

Fixes #1856.

R=ken2
CC=golang-dev
https://golang.org/cl/4810054

src/cmd/gc/range.c

@@ -98,11 +98,13 @@ walkrange(Node *n)
 	Node *fn, *tmp;
 	NodeList *body, *init;
 	Type *th, *t;
+	int lno;
 
 	t = n->type;
 	init = nil;
 
 	a = n->right;
+	lno = setlineno(a);
 	if(t->etype == TSTRING && !eqtype(t, types[TSTRING])) {
 		a = nod(OCONV, n->right, N);
 		a->type = types[TSTRING];
@@ -248,5 +250,7 @@ walkrange(Node *n)
 	typechecklist(body, Etop);
 	n->nbody = concat(body, n->nbody);
 	walkstmt(&n);
+	
+	lineno = lno;
 }
 

src/pkg/runtime/amd64/traceback.c

@@ -10,6 +10,7 @@ void runtime·deferproc(void);
 void runtime·newproc(void);
 void runtime·newstack(void);
 void runtime·morestack(void);
+void runtime·sigpanic(void);
 
 // This code is also used for the 386 tracebacks.
 // Use uintptr for an appropriate word-sized integer.
@@ -27,11 +28,13 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 	byte *fp;
 	Stktop *stk;
 	Func *f;
+	bool waspanic;
 
 	USED(lr0);
 	pc = (uintptr)pc0;
 	lr = 0;
 	fp = nil;
+	waspanic = false;
 	
 	// If the PC is goexit, the goroutine hasn't started yet.
 	if(pc0 == g->sched.pc && sp == g->sched.sp && pc0 == (byte*)runtime·goexit) {
@@ -127,7 +130,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 			if(pc > f->entry)
 				runtime·printf("+%p", (uintptr)(pc - f->entry));
 			tracepc = pc;	// back up to CALL instruction for funcline.
-			if(n > 0 && pc > f->entry)
+			if(n > 0 && pc > f->entry && !waspanic)
 				tracepc--;
 			runtime·printf(" %S:%d\n", f->src, runtime·funcline(f, tracepc));
 			runtime·printf("\t%S(", f->name);
@@ -144,6 +147,8 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 			n++;
 		}
 		
+		waspanic = f->entry == (uintptr)runtime·sigpanic;
+
 		if(f->entry == (uintptr)runtime·deferproc || f->entry == (uintptr)runtime·newproc)
 			fp += 2*sizeof(uintptr);
 

src/pkg/runtime/arm/traceback.c

@@ -9,6 +9,7 @@ void runtime·deferproc(void);
 void runtime·newproc(void);
 void runtime·newstack(void);
 void runtime·morestack(void);
+void runtime·sigpanic(void);
 void _div(void);
 void _mod(void);
 void _divu(void);
@@ -20,12 +21,14 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 	int32 i, n, iter;
 	uintptr pc, lr, tracepc, x;
 	byte *fp, *p;
+	bool waspanic;
 	Stktop *stk;
 	Func *f;
 	
 	pc = (uintptr)pc0;
 	lr = (uintptr)lr0;
 	fp = nil;
+	waspanic = false;
 
 	// If the PC is goexit, the goroutine hasn't started yet.
 	if(pc == (uintptr)runtime·goexit) {
@@ -121,7 +124,7 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 			if(pc > f->entry)
 				runtime·printf("+%p", (uintptr)(pc - f->entry));
 			tracepc = pc;	// back up to CALL instruction for funcline.
-			if(n > 0 && pc > f->entry)
+			if(n > 0 && pc > f->entry && !waspanic)
 				tracepc -= sizeof(uintptr);
 			runtime·printf(" %S:%d\n", f->src, runtime·funcline(f, tracepc));
 			runtime·printf("\t%S(", f->name);
@@ -137,6 +140,8 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 			runtime·prints(")\n");
 			n++;
 		}
+		
+		waspanic = f->entry == (uintptr)runtime·sigpanic;
 
 		if(pcbuf == nil && f->entry == (uintptr)runtime·newstack && g == m->g0) {
 			runtime·printf("----- newstack called from goroutine %d -----\n", m->curg->goid);

src/pkg/runtime/plan9/thread.c

@@ -167,3 +167,14 @@ os·sigpipe(void)
 {
 	runtime·throw("too many writes on closed pipe");
 }
+
+/*
+ * placeholder - once notes are implemented,
+ * a signal generating a panic must appear as
+ * a call to this function for correct handling by
+ * traceback.
+ */
+void
+runtime·sigpanic(void)
+{
+}

src/pkg/runtime/runtime.c

@@ -11,6 +11,14 @@ enum {
 
 uint32	runtime·panicking;
 
+/*
+ * We assume that all architectures turn faults and the like
+ * into apparent calls to runtime.sigpanic.  If we see a "call"
+ * to runtime.sigpanic, we do not back up the PC to find the
+ * line number of the CALL instruction, because there is no CALL.
+ */
+void	runtime·sigpanic(void);
+
 int32
 runtime·gotraceback(void)
 {
@@ -519,25 +527,35 @@ runtime·nanotime(void)
 void
 runtime·Caller(int32 skip, uintptr retpc, String retfile, int32 retline, bool retbool)
 {
-	Func *f;
+	Func *f, *g;
 	uintptr pc;
+	uintptr rpc[2];
 
-	if(runtime·callers(1+skip, &retpc, 1) == 0) {
+	/*
+	 * Ask for two PCs: the one we were asked for
+	 * and what it called, so that we can see if it
+	 * "called" sigpanic.
+	 */
+	retpc = 0;
+	if(runtime·callers(1+skip-1, rpc, 2) < 2) {
 		retfile = runtime·emptystring;
 		retline = 0;
 		retbool = false;
-	} else if((f = runtime·findfunc(retpc)) == nil) {
+	} else if((f = runtime·findfunc(rpc[1])) == nil) {
 		retfile = runtime·emptystring;
 		retline = 0;
 		retbool = true;  // have retpc at least
 	} else {
+		retpc = rpc[1];
 		retfile = f->src;
 		pc = retpc;
-		if(pc > f->entry)
+		g = runtime·findfunc(rpc[0]);
+		if(pc > f->entry && (g == nil || g->entry != (uintptr)runtime·sigpanic))
 			pc--;
 		retline = runtime·funcline(f, pc);
 		retbool = true;
 	}
+	FLUSH(&retpc);
 	FLUSH(&retfile);
 	FLUSH(&retline);
 	FLUSH(&retbool);

test/fixedbugs/bug348.go

@@ -0,0 +1,46 @@
+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"runtime"
+	"strings"
+)
+
+func f() {
+	var x *string
+	
+	for _, i := range *x {  // THIS IS LINE 17
+		println(i)
+	}
+}
+
+func g() {
+}
+
+func main() {
+	defer func() {
+		for i := 0;; i++ {
+			pc, file, line, ok := runtime.Caller(i)
+			if !ok {
+				print("BUG: bug348: cannot find caller\n")
+				return
+			}
+			if !strings.Contains(file, "bug348.go") || runtime.FuncForPC(pc).Name() != "main.f" {
+				// walk past runtime frames
+				continue
+			}
+			if line != 17 {
+				print("BUG: bug348: panic at ", file, ":", line, " in ", runtime.FuncForPC(pc).Name(), "\n")
+				return
+			}
+			recover()
+			return
+		}
+	}()
+	f()
+}