syscall: mark SyscallN as noescape

qmuntal · qmuntal · commit 7fff741016c8 · 2024-11-06T16:35:17.000Z
syscall.SyscallN is implemented by runtime.syscall_syscalln, which makes sure that the variadic argument doesn't escape. There is no need to worry about the lifetime of the elements of the variadic argument, as the compiler will keep them live until the function returns. Fixes #70197. Cq-Include-Trybots: luci.golang.try:gotip-windows-amd64-longtest,gotip-windows-amd64-race Change-Id: I12991f0be12062eea68f2b103fa0a794c1b527eb Reviewed-on: https://go-review.googlesource.com/c/go/+/625297 Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Alex Brainman <alex.brainman@gmail.com> Reviewed-by: David Chase <drchase@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
diff --git a/src/syscall/dll_windows.go b/src/syscall/dll_windows.go
@@ -42,6 +42,7 @@ func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a
 // 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:noescape
 func SyscallN(trap uintptr, args ...uintptr) (r1, r2 uintptr, err Errno)
 func loadlibrary(filename *uint16) (handle uintptr, err Errno)
 func loadsystemlibrary(filename *uint16) (handle uintptr, err Errno)
diff --git a/src/syscall/syscall_windows_test.go b/src/syscall/syscall_windows_test.go
@@ -227,6 +227,53 @@ func TestGetStartupInfo(t *testing.T) {
 	}
 }
 
+func TestSyscallAllocations(t *testing.T) {
+	testenv.SkipIfOptimizationOff(t)
+
+	t.Parallel()
+
+	// Test that syscall.SyscallN arguments do not escape.
+	// The function used (in this case GetVersion) doesn't matter
+	// as long as it is always available and doesn't panic.
+	h, err := syscall.LoadLibrary("kernel32.dll")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer syscall.FreeLibrary(h)
+	proc, err := syscall.GetProcAddress(h, "GetVersion")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	testAllocs := func(t *testing.T, name string, fn func() error) {
+		t.Run(name, func(t *testing.T) {
+			n := int(testing.AllocsPerRun(10, func() {
+				if err := fn(); err != nil {
+					t.Fatalf("%s: %v", name, err)
+				}
+			}))
+			if n > 0 {
+				t.Errorf("allocs = %d, want 0", n)
+			}
+		})
+	}
+
+	testAllocs(t, "SyscallN", func() error {
+		r0, _, e1 := syscall.SyscallN(proc, 0, 0, 0)
+		if r0 == 0 {
+			return syscall.Errno(e1)
+		}
+		return nil
+	})
+	testAllocs(t, "Syscall", func() error {
+		r0, _, e1 := syscall.Syscall(proc, 3, 0, 0, 0)
+		if r0 == 0 {
+			return syscall.Errno(e1)
+		}
+		return nil
+	})
+}
+
 func FuzzUTF16FromString(f *testing.F) {
 	f.Add("hi")           // ASCII
 	f.Add("â")            // latin1
