runtime,syscall: move SyscallX implementations from runtime to syscall

There is no need for syscall.Syscall{3,6,9,12,15,18} to be implemented
in the runtime and linknamed from syscall. All of them can be
implemented using the single runtime.syscall_syscalln function.

While here, improve the documentation of syscall.SyscallN.

Change-Id: I0e09d42e855d6baf900354c9b7992a4329c4ffc7
Reviewed-on: https://go-review.googlesource.com/c/go/+/690515
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/runtime/syscall_windows.go

@@ -416,7 +416,7 @@ const _LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800
 
 //go:linkname syscall_loadsystemlibrary syscall.loadsystemlibrary
 func syscall_loadsystemlibrary(filename *uint16) (handle, err uintptr) {
-	handle, _, err = syscall_SyscallN(uintptr(unsafe.Pointer(_LoadLibraryExW)), uintptr(unsafe.Pointer(filename)), 0, _LOAD_LIBRARY_SEARCH_SYSTEM32)
+	handle, _, err = syscall_syscalln(uintptr(unsafe.Pointer(_LoadLibraryExW)), 3, uintptr(unsafe.Pointer(filename)), 0, _LOAD_LIBRARY_SEARCH_SYSTEM32)
 	KeepAlive(filename)
 	if handle != 0 {
 		err = 0
@@ -430,7 +430,7 @@ func syscall_loadsystemlibrary(filename *uint16) (handle, err uintptr) {
 //
 //go:linkname syscall_loadlibrary syscall.loadlibrary
 func syscall_loadlibrary(filename *uint16) (handle, err uintptr) {
-	handle, _, err = syscall_SyscallN(uintptr(unsafe.Pointer(_LoadLibraryW)), uintptr(unsafe.Pointer(filename)))
+	handle, _, err = syscall_syscalln(uintptr(unsafe.Pointer(_LoadLibraryW)), 1, uintptr(unsafe.Pointer(filename)))
 	KeepAlive(filename)
 	if handle != 0 {
 		err = 0
@@ -444,7 +444,7 @@ func syscall_loadlibrary(filename *uint16) (handle, err uintptr) {
 //
 //go:linkname syscall_getprocaddress syscall.getprocaddress
 func syscall_getprocaddress(handle uintptr, procname *byte) (outhandle, err uintptr) {
-	outhandle, _, err = syscall_SyscallN(uintptr(unsafe.Pointer(_GetProcAddress)), handle, uintptr(unsafe.Pointer(procname)))
+	outhandle, _, err = syscall_syscalln(uintptr(unsafe.Pointer(_GetProcAddress)), 2, handle, uintptr(unsafe.Pointer(procname)))
 	KeepAlive(procname)
 	if outhandle != 0 {
 		err = 0
@@ -452,48 +452,7 @@ func syscall_getprocaddress(handle uintptr, procname *byte) (outhandle, err uint
 	return
 }
 
-//go:linkname syscall_Syscall syscall.Syscall
+//go:linkname syscall_syscalln syscall.syscalln
-//go:nosplit
-func syscall_Syscall(fn, nargs, a1, a2, a3 uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, nargs, a1, a2, a3)
-}
-
-//go:linkname syscall_Syscall6 syscall.Syscall6
-//go:nosplit
-func syscall_Syscall6(fn, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, nargs, a1, a2, a3, a4, a5, a6)
-}
-
-//go:linkname syscall_Syscall9 syscall.Syscall9
-//go:nosplit
-func syscall_Syscall9(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9)
-}
-
-//go:linkname syscall_Syscall12 syscall.Syscall12
-//go:nosplit
-func syscall_Syscall12(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12 uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12)
-}
-
-//go:linkname syscall_Syscall15 syscall.Syscall15
-//go:nosplit
-func syscall_Syscall15(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15)
-}
-
-//go:linkname syscall_Syscall18 syscall.Syscall18
-//go:nosplit
-func syscall_Syscall18(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18 uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18)
-}
-
-//go:linkname syscall_SyscallN syscall.SyscallN
-//go:nosplit
-func syscall_SyscallN(fn uintptr, args ...uintptr) (r1, r2, err uintptr) {
-	return syscall_syscalln(fn, uintptr(len(args)), args...)
-}
-
 //go:nosplit
 func syscall_syscalln(fn, n uintptr, args ...uintptr) (r1, r2, err uintptr) {
 	if n > uintptr(len(args)) {

src/syscall/dll_windows.go

@@ -22,28 +22,78 @@ func (e *DLLError) Error() string { return e.Msg }
 
 func (e *DLLError) Unwrap() error { return e.Err }
 
-// Implemented in ../runtime/syscall_windows.go.
+// N.B. For the Syscall functions below:
+//
+// //go:uintptrkeepalive because the uintptr argument may be converted pointers
+// that need to be kept alive in the caller.
+//
+// //go:nosplit because stack copying does not account for uintptrkeepalive, so
+// the stack must not grow. Stack copying cannot blindly assume that all
+// uintptr arguments are pointers, because some values may look like pointers,
+// but not really be pointers, and adjusting their value would break the call.
 
 // Deprecated: Use [SyscallN] instead.
-func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+//
+//go:nosplit
+//go:uintptrkeepalive
+func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(trap, nargs, a1, a2, a3)
+}
 
 // Deprecated: Use [SyscallN] instead.
-func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+//
+//go:nosplit
+//go:uintptrkeepalive
+func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(trap, nargs, a1, a2, a3, a4, a5, a6)
+}
 
 // Deprecated: Use [SyscallN] instead.
-func Syscall9(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno)
+//
+//go:nosplit
+//go:uintptrkeepalive
+func Syscall9(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9)
+}
 
 // Deprecated: Use [SyscallN] instead.
-func Syscall12(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12 uintptr) (r1, r2 uintptr, err Errno)
+//
+//go:nosplit
+//go:uintptrkeepalive
+func Syscall12(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12)
+}
 
 // Deprecated: Use [SyscallN] instead.
-func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr) (r1, r2 uintptr, err Errno)
+//
+//go:nosplit
+//go:uintptrkeepalive
+func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15)
+}
 
 // Deprecated: Use [SyscallN] instead.
-func Syscall18(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18 uintptr) (r1, r2 uintptr, err Errno)
+//
+//go:nosplit
+//go:uintptrkeepalive
+func Syscall18(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18)
+}
 
+// SyscallN executes procedure p with arguments args.
+//
+// See [Proc.Call] for more information.
+//
+//go:nosplit
+//go:uintptrkeepalive
+func SyscallN(p uintptr, args ...uintptr) (r1, r2 uintptr, err Errno) {
+	return syscalln(p, uintptr(len(args)), args...)
+}
+
+// syscalln is implemented in runtime/syscall_windows.go.
+//
 //go:noescape
-func SyscallN(trap uintptr, args ...uintptr) (r1, r2 uintptr, err Errno)
+func syscalln(fn, n uintptr, args ...uintptr) (r1, r2 uintptr, err Errno)
 func loadlibrary(filename *uint16) (handle uintptr, err Errno)
 func loadsystemlibrary(filename *uint16) (handle uintptr, err Errno)
 func getprocaddress(handle uintptr, procname *uint8) (proc uintptr, err Errno)