From 35c7234601c409a1d1595e4eb9fe72e8ba4e6464 Mon Sep 17 00:00:00 2001
From: Austin Clements <austin@google.com>
Date: Wed, 15 Sep 2021 17:14:21 -0400
Subject: runtime: add always-preempt maymorestack hook

This adds a maymorestack hook that forces a preemption at every
possible cooperative preemption point. This would have helped us catch
several recent preemption-related bugs earlier, including #47302,
 #47304, and #47441.

For #48297.

Change-Id: Ib82c973589c8a7223900e1842913b8591938fb9f
Reviewed-on: https://go-review.googlesource.com/c/go/+/359796
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/stack.go | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'src/runtime/stack.go')

diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index 52d21e4ee4..7d9ae1e9d2 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -144,6 +144,9 @@ const (
 	// Force a stack movement. Used for debugging.
 	// 0xfffffeed in hex.
 	stackForceMove = uintptrMask & -275
+
+	// stackPoisonMin is the lowest allowed stack poison value.
+	stackPoisonMin = uintptrMask & -4096
 )
 
 // Global pool of spans that have free stacks.
-- 
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