runtime: clean up windows a bit

Document the various hard-coded architecture checks
or remove them in favor of more general checks.
This should be a no-op now but will make the arm64 port
have fewer diffs.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.
This CL is, however, not windows/arm64-specific.
It is cleanup meant to make the port (and future ports) easier.

Change-Id: Ifd6b19e44e8c9ca4a0d2590f314928ce235821b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/288813
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/runtime/os_windows.go

@@ -236,6 +236,8 @@ func windowsLoadSystemLib(name []byte) uintptr {
 	}
 }
 
+const haveCputicksAsm = GOARCH == "386" || GOARCH == "amd64"
+
 func loadOptionalSyscalls() {
 	var kernel32dll = []byte("kernel32.dll\000")
 	k32 := stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&kernel32dll[0])))
@@ -262,7 +264,7 @@ func loadOptionalSyscalls() {
 	}
 	_NtWaitForSingleObject = windowsFindfunc(n32, []byte("NtWaitForSingleObject\000"))
 
-	if GOARCH == "arm" {
+	if !haveCputicksAsm {
 		_QueryPerformanceCounter = windowsFindfunc(k32, []byte("QueryPerformanceCounter\000"))
 		if _QueryPerformanceCounter == nil {
 			throw("could not find QPC syscalls")
@@ -452,8 +454,10 @@ func createHighResTimer() uintptr {
 		_SYNCHRONIZE|_TIMER_QUERY_STATE|_TIMER_MODIFY_STATE)
 }
 
+const highResTimerSupported = GOARCH == "386" || GOARCH == "amd64"
+
 func initHighResTimer() {
-	if GOARCH == "arm" {
+	if !highResTimerSupported {
 		// TODO: Not yet implemented.
 		return
 	}
@@ -1217,14 +1221,14 @@ func setThreadCPUProfiler(hz int32) {
 	atomic.Store((*uint32)(unsafe.Pointer(&getg().m.profilehz)), uint32(hz))
 }
 
-const preemptMSupported = GOARCH != "arm"
+const preemptMSupported = GOARCH == "386" || GOARCH == "amd64"
 
 // suspendLock protects simultaneous SuspendThread operations from
 // suspending each other.
 var suspendLock mutex
 
 func preemptM(mp *m) {
-	if GOARCH == "arm" {
+	if !preemptMSupported {
 		// TODO: Implement call injection
 		return
 	}

src/runtime/signal_windows.go

@@ -5,6 +5,7 @@
 package runtime
 
 import (
+	"runtime/internal/sys"
 	"unsafe"
 )
 
@@ -132,16 +133,14 @@ func exceptionhandler(info *exceptionrecord, r *context, gp *g) int32 {
 	// overwrite the PC. (See issue #35773)
 	if r.ip() != 0 && r.ip() != funcPC(asyncPreempt) {
 		sp := unsafe.Pointer(r.sp())
-		sp = add(sp, ^(unsafe.Sizeof(uintptr(0)) - 1)) // sp--
+		delta := uintptr(sys.StackAlign)
+		sp = add(sp, -delta)
 		r.set_sp(uintptr(sp))
-		switch GOARCH {
-		default:
-			panic("unsupported architecture")
-		case "386", "amd64":
-			*((*uintptr)(sp)) = r.ip()
-		case "arm":
+		if usesLR {
 			*((*uintptr)(sp)) = r.lr()
 			r.set_lr(r.ip())
+		} else {
+			*((*uintptr)(sp)) = r.ip()
 		}
 	}
 	r.set_ip(funcPC(sigpanic))

src/runtime/syscall_windows.go

@@ -116,13 +116,14 @@ func compileCallback(fn eface, cdecl bool) (code uintptr) {
 			// registers and the stack.
 			panic("compileCallback: argument size is larger than uintptr")
 		}
-		if k := t.kind & kindMask; (GOARCH == "amd64" || GOARCH == "arm") && (k == kindFloat32 || k == kindFloat64) {
+		if k := t.kind & kindMask; GOARCH != "386" && (k == kindFloat32 || k == kindFloat64) {
 			// In fastcall, floating-point arguments in
 			// the first four positions are passed in
 			// floating-point registers, which we don't
 			// currently spill. arm passes floating-point
 			// arguments in VFP registers, which we also
 			// don't support.
+			// So basically we only support 386.
 			panic("compileCallback: float arguments not supported")
 		}