runtime: grow stack by copying

On stack overflow, if all frames on the stack are
copyable, we copy the frames to a new stack twice
as large as the old one.  During GC, if a G is using
less than 1/4 of its stack, copy the stack to a stack
half its size.

TODO
- Do something about C frames.  When a C frame is in the
  stack segment, it isn't copyable.  We allocate a new segment
  in this case.
  - For idempotent C code, we can abort it, copy the stack,
    then retry.  I'm working on a separate CL for this.
  - For other C code, we can raise the stackguard
    to the lowest Go frame so the next call that Go frame
    makes triggers a copy, which will then succeed.
- Pick a starting stack size?

The plan is that eventually we reach a point where the
stack contains only copyable frames.

LGTM=rsc
R=dvyukov, rsc
CC=golang-codereviews
https://golang.org/cl/54650044

1 files changed, 3 insertions, 1 deletions

diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index f833642707..5ecb7827a9 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -589,6 +589,7 @@ struct DebugVars
 };
 
 extern bool runtime·precisestack;
+extern bool runtime·copystack;
 
 /*
  * defined macros
@@ -732,7 +733,7 @@ struct Stkframe
 	uintptr	arglen;	// number of bytes at argp
 };
 
-int32	runtime·gentraceback(uintptr, uintptr, uintptr, G*, int32, uintptr*, int32, void(*)(Stkframe*, void*), void*, bool);
+int32	runtime·gentraceback(uintptr, uintptr, uintptr, G*, int32, uintptr*, int32, bool(*)(Stkframe*, void*), void*, bool);
 void	runtime·traceback(uintptr pc, uintptr sp, uintptr lr, G* gp);
 void	runtime·tracebackothers(G*);
 bool	runtime·haszeroargs(uintptr pc);
@@ -860,6 +861,7 @@ int8*	runtime·funcname(Func*);
 int32	runtime·pcdatavalue(Func*, int32, uintptr);
 void*	runtime·stackalloc(uint32);
 void	runtime·stackfree(void*, uintptr);
+void	runtime·shrinkstack(G*);
 MCache*	runtime·allocmcache(void);
 void	runtime·freemcache(MCache*);
 void	runtime·mallocinit(void);