runtime: simplify stack traces

Make the stack traces more readable for new
Go programmers while preserving their utility for old hands.

- Change status number [4] to string.
- Elide frames in runtime package (internal details).
- Swap file:line and arguments.
- Drop 'created by' for main goroutine.
- Show goroutines in order of allocation:
  implies main goroutine first if nothing else.

There is no option to get the extra frames back.
Uncomment 'return 1' at the bottom of symtab.c.

$ 6.out
throw: all goroutines are asleep - deadlock!

goroutine 1 [chan send]:
main.main()
       /Users/rsc/g/go/src/pkg/runtime/x.go:22 +0x8a

goroutine 2 [select (no cases)]:
main.sel()
       /Users/rsc/g/go/src/pkg/runtime/x.go:11 +0x18
created by main.main
       /Users/rsc/g/go/src/pkg/runtime/x.go:19 +0x23

goroutine 3 [chan receive]:
main.recv(0xf8400010a0, 0x0)
       /Users/rsc/g/go/src/pkg/runtime/x.go:15 +0x2e
created by main.main
       /Users/rsc/g/go/src/pkg/runtime/x.go:20 +0x50

goroutine 4 [chan receive (nil chan)]:
main.recv(0x0, 0x0)
       /Users/rsc/g/go/src/pkg/runtime/x.go:15 +0x2e
created by main.main
       /Users/rsc/g/go/src/pkg/runtime/x.go:21 +0x66
$

$ 6.out index
panic: runtime error: index out of range

goroutine 1 [running]:
main.main()
        /Users/rsc/g/go/src/pkg/runtime/x.go:25 +0xb9
$

$ 6.out nil
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x22ca]

goroutine 1 [running]:
main.main()
        /Users/rsc/g/go/src/pkg/runtime/x.go:28 +0x211
$

$ 6.out panic
panic: panic

goroutine 1 [running]:
main.main()
        /Users/rsc/g/go/src/pkg/runtime/x.go:30 +0x101
$

R=golang-dev, qyzhai, n13m3y3r, r
CC=golang-dev
https://golang.org/cl/4907048

1 files changed, 29 insertions, 24 deletions

diff --git a/src/pkg/runtime/amd64/traceback.c b/src/pkg/runtime/amd64/traceback.c
index 3e85d36bd7..6b758c270d 100644
--- a/src/pkg/runtime/amd64/traceback.c
+++ b/src/pkg/runtime/amd64/traceback.c
@@ -123,27 +123,30 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 		else if(pcbuf != nil)
 			pcbuf[n++] = pc;
 		else {
-			// Print during crash.
-			//	main+0xf /home/rsc/go/src/runtime/x.go:23
-			//		main(0x1, 0x2, 0x3)
-			runtime·printf("%S", f->name);
-			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 && !waspanic)
-				tracepc--;
-			runtime·printf(" %S:%d\n", f->src, runtime·funcline(f, tracepc));
-			runtime·printf("\t%S(", f->name);
-			for(i = 0; i < f->args; i++) {
-				if(i != 0)
-					runtime·prints(", ");
-				runtime·printhex(((uintptr*)fp)[i]);
-				if(i >= 4) {
-					runtime·prints(", ...");
-					break;
+			if(showframe(f)) {
+				// Print during crash.
+				//	main(0x1, 0x2, 0x3)
+				//		/home/rsc/go/src/runtime/x.go:23 +0xf
+				//		
+				tracepc = pc;	// back up to CALL instruction for funcline.
+				if(n > 0 && pc > f->entry && !waspanic)
+					tracepc--;
+				runtime·printf("%S(", f->name);
+				for(i = 0; i < f->args; i++) {
+					if(i != 0)
+						runtime·prints(", ");
+					runtime·printhex(((uintptr*)fp)[i]);
+					if(i >= 4) {
+						runtime·prints(", ...");
+						break;
+					}
 				}
+				runtime·prints(")\n");
+				runtime·printf("\t%S:%d", f->src, runtime·funcline(f, tracepc));
+				if(pc > f->entry)
+					runtime·printf(" +%p", (uintptr)(pc - f->entry));
+				runtime·printf("\n");
 			}
-			runtime·prints(")\n");
 			n++;
 		}
 		
@@ -189,14 +192,16 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *g, int32 skip, uintptr
 		fp = nil;
 	}
 	
-	if(pcbuf == nil && (pc = g->gopc) != 0 && (f = runtime·findfunc(pc)) != nil) {
-		runtime·printf("----- goroutine created by -----\n%S", f->name);
-		if(pc > f->entry)
-			runtime·printf("+%p", (uintptr)(pc - f->entry));
+	// Show what created goroutine, except main goroutine (goid 1).
+	if(pcbuf == nil && (pc = g->gopc) != 0 && (f = runtime·findfunc(pc)) != nil && g->goid != 1) {
+		runtime·printf("created by %S\n", f->name);
 		tracepc = pc;	// back up to CALL instruction for funcline.
 		if(n > 0 && pc > f->entry)
 			tracepc--;
-		runtime·printf(" %S:%d\n", f->src, runtime·funcline(f, tracepc));
+		runtime·printf("\t%S:%d", f->src, runtime·funcline(f, tracepc));
+		if(pc > f->entry)
+			runtime·printf(" +%p", (uintptr)(pc - f->entry));
+		runtime·printf("\n");
 	}
 		
 	return n;