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, 5 insertions, 3 deletions

diff --git a/src/pkg/runtime/traceback_arm.c b/src/pkg/runtime/traceback_arm.c
index 3c23cd9fcd..171672a89d 100644
--- a/src/pkg/runtime/traceback_arm.c
+++ b/src/pkg/runtime/traceback_arm.c
@@ -10,7 +10,7 @@
 void runtime·sigpanic(void);
 
 int32
-runtime·gentraceback(uintptr pc0, uintptr sp0, uintptr lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max, void (*callback)(Stkframe*, void*), void *v, bool printall)
+runtime·gentraceback(uintptr pc0, uintptr sp0, uintptr lr0, G *gp, int32 skip, uintptr *pcbuf, int32 max, bool (*callback)(Stkframe*, void*), void *v, bool printall)
 {
 	int32 i, n, nprint, line;
 	uintptr x, tracepc;
@@ -140,8 +140,10 @@ runtime·gentraceback(uintptr pc0, uintptr sp0, uintptr lr0, G *gp, int32 skip,
 
 		if(pcbuf != nil)
 			pcbuf[n] = frame.pc;
-		if(callback != nil)
-			callback(&frame, v);
+		if(callback != nil) {
+			if(!callback(&frame, v))
+				return n;
+		}
 		if(printing) {
 			if(printall || runtime·showframe(f, gp)) {
 				// Print during crash.