From bd580a0d10729553a7905481d17eed0436198866 Mon Sep 17 00:00:00 2001
From: Austin Clements <austin@google.com>
Date: Mon, 27 Sep 2021 10:05:13 -0400
Subject: [PATCH] runtime: add a maymorestack hook that moves the stack

This adds a maymorestack hook that moves the stack at every
cooperative preemption point.

For #48297.

Change-Id: Ic15f9bcbc163345e6422586302d57fda4744caec
Reviewed-on: https://go-review.googlesource.com/c/go/+/359797
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: David Chase <drchase@google.com>
---
 src/runtime/debug.go | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/runtime/debug.go b/src/runtime/debug.go
index c343f430cc..2703a0ce01 100644
--- a/src/runtime/debug.go
+++ b/src/runtime/debug.go
@@ -95,3 +95,22 @@ func mayMoreStackPreempt() {
 		g.stackguard0 = stackPreempt
 	}
 }
+
+// mayMoreStackMove is a maymorestack hook that forces stack movement
+// at every possible point.
+//
+// See mayMoreStackPreempt.
+//
+//go:nosplit
+//go:linkname mayMoreStackMove
+func mayMoreStackMove() {
+	// Don't do anything on the g0 or gsignal stack.
+	g := getg()
+	if g == g.m.g0 || g == g.m.gsignal {
+		return
+	}
+	// Force stack movement, unless the stack is already poisoned.
+	if g.stackguard0 < stackPoisonMin {
+		g.stackguard0 = stackForceMove
+	}
+}
-- 
2.50.0