runtime: add windows/arm64 cgo-linking code

This code is needed for use with cgo proper
(as opposed to hand-written DLL calls, which
we always use but only exercise cgo execution,
not cgo linking).

Change-Id: Iddc31d9c1c924d83d032b80dca65ddfda6624046
Reviewed-on: https://go-review.googlesource.com/c/go/+/312041
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/cgo/gcc_windows_arm64.c

@@ -0,0 +1,46 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#include <process.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include "libcgo.h"
+#include "libcgo_windows.h"
+
+static void threadentry(void*);
+static void (*setg_gcc)(void*);
+
+void
+x_cgo_init(G *g, void (*setg)(void*))
+{
+	setg_gcc = setg;
+}
+
+void
+_cgo_sys_thread_start(ThreadStart *ts)
+{
+	uintptr_t thandle;
+
+	thandle = _beginthread(threadentry, 0, ts);
+	if(thandle == -1) {
+		fprintf(stderr, "runtime: failed to create new OS thread (%d)\n", errno);
+		abort();
+	}
+}
+
+extern void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
+
+static void
+threadentry(void *v)
+{
+	ThreadStart ts;
+
+	ts = *(ThreadStart*)v;
+	free(v);
+
+	crosscall1(ts.fn, setg_gcc, (void *)ts.g);
+}

src/runtime/rt0_windows_arm64.s

@@ -10,3 +10,20 @@
 // kernel for an ordinary -buildmode=exe program.
 TEXT _rt0_arm64_windows(SB),NOSPLIT|NOFRAME,$0
 	B	·rt0_go(SB)
+
+TEXT _rt0_arm64_windows_lib(SB),NOSPLIT|NOFRAME,$0
+	MOVD	$_rt0_arm64_windows_lib_go(SB), R0
+	MOVD	$0, R1
+	MOVD	_cgo_sys_thread_create(SB), R2
+	B	(R2)
+
+TEXT _rt0_arm64_windows_lib_go(SB),NOSPLIT|NOFRAME,$0
+	MOVD	$0, R0
+	MOVD	$0, R1
+	MOVD	$runtime·rt0_go(SB), R2
+	B	(R2)
+
+TEXT main(SB),NOSPLIT,$0
+	MOVD	$runtime·rt0_go(SB), R2
+	B	(R2)
+

src/runtime/sys_windows_arm.s

@@ -335,7 +335,7 @@ TEXT runtime·switchtothread(SB),NOSPLIT|NOFRAME,$0
 TEXT ·publicationBarrier(SB),NOSPLIT|NOFRAME,$0-0
 	B	runtime·armPublicationBarrier(SB)
 
-// never called (cgo not supported)
+// never called (this is a GOARM=7 platform)
 TEXT runtime·read_tls_fallback(SB),NOSPLIT|NOFRAME,$0
 	MOVW	$0xabcd, R0
 	MOVW	R0, (R0)