Revert "internal/abi, runtime, cmd: merge StackSmall, StackBig consts into internal/abi"

This reverts commit CL 486379.

Submitted out of order and breaks bootstrap.

Change-Id: Ie20a61cc56efc79a365841293ca4e7352b02d86b
Reviewed-on: https://go-review.googlesource.com/c/go/+/486917
TryBot-Bypass: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index 39dbed5114..e1e6c7e82a 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -85,6 +85,13 @@ const (
 	_FixedStack6 = _FixedStack5 | (_FixedStack5 >> 16)
 	_FixedStack  = _FixedStack6 + 1
 
+	// Functions that need frames bigger than this use an extra
+	// instruction to do the stack split check, to avoid overflow
+	// in case SP - framesize wraps below zero.
+	// This value can be no bigger than the size of the unmapped
+	// space at zero.
+	_StackBig = 4096
+
 	// The stack guard is a pointer this many bytes above the
 	// bottom of the stack.
 	//
@@ -94,10 +101,15 @@ const (
 	// This arithmetic must match that in cmd/internal/objabi/stack.go:StackLimit.
 	_StackGuard = 928*sys.StackGuardMultiplier + _StackSystem
 
+	// After a stack split check the SP is allowed to be this
+	// many bytes below the stack guard. This saves an instruction
+	// in the checking sequence for tiny frames.
+	_StackSmall = 128
+
 	// The maximum number of bytes that a chain of NOSPLIT
 	// functions can use.
 	// This arithmetic must match that in cmd/internal/objabi/stack.go:StackLimit.
-	_StackLimit = _StackGuard - _StackSystem - abi.StackSmall
+	_StackLimit = _StackGuard - _StackSystem - _StackSmall
 )
 
 const (