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, 13 insertions, 4 deletions

diff --git a/src/pkg/runtime/runtime.c b/src/pkg/runtime/runtime.c
index 49aba7da01..c4bd408829 100644
--- a/src/pkg/runtime/runtime.c
+++ b/src/pkg/runtime/runtime.c
@@ -51,12 +51,15 @@ runtime·dopanic(int32 unused)
 	static bool didothers;
 
 	if(g->sig != 0)
-		runtime·printf("\n[signal %x code=%p addr=%p pc=%p]\n",
+		runtime·printf("[signal %x code=%p addr=%p pc=%p]\n",
 			g->sig, g->sigcode0, g->sigcode1, g->sigpc);
 
-	runtime·printf("\n");
 	if(runtime·gotraceback()){
-		runtime·traceback(runtime·getcallerpc(&unused), runtime·getcallersp(&unused), 0, g);
+		if(g != m->g0) {
+			runtime·printf("\n");
+			runtime·goroutineheader(g);
+			runtime·traceback(runtime·getcallerpc(&unused), runtime·getcallersp(&unused), 0, g);
+		}
 		if(!didothers) {
 			didothers = true;
 			runtime·tracebackothers(g);
@@ -703,7 +706,13 @@ runtime·Caller(int32 skip, uintptr retpc, String retfile, int32 retline, bool r
 void
 runtime·Callers(int32 skip, Slice pc, int32 retn)
 {
-	retn = runtime·callers(skip, (uintptr*)pc.array, pc.len);
+	// runtime.callers uses pc.array==nil as a signal
+	// to print a stack trace.  Pick off 0-length pc here
+	// so that we don't let a nil pc slice get to it.
+	if(pc.len == 0)
+		retn = 0;
+	else
+		retn = runtime·callers(skip, (uintptr*)pc.array, pc.len);
 	FLUSH(&retn);
 }