code review 2609041: 6l: correct logic for morestack choice

src/pkg/runtime/proc.c

 // Copyright 2009 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.h"
 #include "defs.h"
 #include "malloc.h"
 #include "os.h"
 
@@ skipping 731 matching lines @@
         Stktop *top;
         byte *stk, *sp;
         G *g1;
         Gobuf label;
         bool free;
 
         frame = m->moreframe;
         args = m->moreargs;
         g1 = m->curg;
 
+        if(m->morebuf.sp < g1->stackguard - StackGuard)
+                throw("split stack overflow");
 
         if(frame == 1 && args > 0 && m->morebuf.sp - sizeof(Stktop) - args - 32 > g1->stackguard) {
                 // special case: called from reflect.call (frame == 1)
                 // to call code with an arbitrary argument size,
                 // and we have enough space on the current stack.
                 // the new Stktop* is necessary to unwind, but
                 // we don't need to create a new segment.
                 top = (Stktop*)(m->morebuf.sp - sizeof(*top));
                 stk = g1->stackguard - StackGuard;
                 free = false;
@@ skipping 421 matching lines @@
         g->lockedm = nil;
 }
 
 // for testing of wire, unwire
 void
 ·mid(uint32 ret)
 {
         ret = m->id;
         FLUSH(&ret);
 }