code review 100870044: runtime: make continuation pc available to stack walk

src/pkg/runtime/panic.c

 // Copyright 2012 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.
 
 #include "runtime.h"
 #include "arch_GOARCH.h"
 #include "stack.h"
 #include "malloc.h"
 #include "../../cmd/ld/textflag.h"
 
@@ skipping 202 matching lines @@
 runtime·panic(Eface e)
 {
         Defer *d, dabort;
         Panic p;
         void *pc, *argp;
 
         runtime·memclr((byte*)&p, sizeof p);
         p.arg = e;
         p.link = g->panic;
         p.stackbase = g->stackbase;
-        p.defer = nil;

[iant, 2014/05/30 21:50:09]

Why bother?  We just did a memclr of the entire struct.

[rsc, 2014/05/30 22:36:39]

So we did; I missed that. There was a mysterious crash and I thought this might
be it (it didn't help, obviously). Will revert.

         g->panic = &p;
 
         dabort.fn = &abortpanicV;
         dabort.siz = sizeof(&p);
         dabort.args[0] = &p;
-        dabort.argp = (void*)-1;  // unused because abortpanic never recovers
+        dabort.argp = NoArgs;
         dabort.special = true;
 
         for(;;) {
                 d = g->defer;
                 if(d == nil)
                         break;
                 // take defer off list in case of recursive panic
                 g->defer = d->link;
                 g->ispanic = true;      // rock for runtime·newstack, where runtime·newstackcall ends up
                 argp = d->argp;
@@ skipping 318 matching lines @@
 {
         rundefer();
         runtime·goexit();
 }
 
 void
 runtime·panicdivide(void)
 {
         runtime·panicstring("integer divide by zero");
 }