runtime: use libc for signal functions on iOS

Also:
 - Add extra SystemStack space for darwin/arm64 just
like for darwin/arm.
 - Removed redundant stack alignment; the arm64 hardware enforces
 the 16 byte alignment.
 - Save and restore the g registers at library initialization.
 - Zero g registers since libpreinit can call libc functions
 that in turn use asmcgocall. asmcgocall requires an initialized g.
 - Change asmcgocall to work even if no g is set. The change mimics
 amd64.

Change-Id: I1b8c63b07cfec23b909c0d215b50dc229f8adbc8
Reviewed-on: https://go-review.googlesource.com/117176
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index e40fa9cc1b..d83e9d6722 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -64,8 +64,8 @@ const (
 	// StackSystem is a number of additional bytes to add
 	// to each stack below the usual guard area for OS-specific
 	// purposes like signal handling. Used on Windows, Plan 9,
-	// and Darwin/ARM because they do not use a separate stack.
-	_StackSystem = sys.GoosWindows*512*sys.PtrSize + sys.GoosPlan9*512 + sys.GoosDarwin*sys.GoarchArm*1024
+	// and iOS because they do not use a separate stack.
+	_StackSystem = sys.GoosWindows*512*sys.PtrSize + sys.GoosPlan9*512 + sys.GoosDarwin*sys.GoarchArm*1024 + sys.GoosDarwin*sys.GoarchArm64*1024
 
 	// The minimum size of stack used by Go code
 	_StackMin = 2048