5l, 6l, 8l: fix stack split logic for stacks near default segment size

Fixes #3310.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5823051

1 files changed, 5 insertions, 0 deletions

diff --git a/src/pkg/runtime/stack.h b/src/pkg/runtime/stack.h
index f56dac120f..d42385d6cb 100644
--- a/src/pkg/runtime/stack.h
+++ b/src/pkg/runtime/stack.h
@@ -94,4 +94,9 @@ enum {
 	// The maximum number of bytes that a chain of NOSPLIT
 	// functions can use.
 	StackLimit = StackGuard - StackSystem - StackSmall,
+	
+	// The assumed size of the top-of-stack data block.
+	// The actual size can be smaller than this but cannot be larger.
+	// Checked in proc.c's runtime.malg.
+	StackTop = 72,
 };