syscall: redirect writes to runtime.write in faketime mode

If the faketime build tag is set, this causes syscall.Write for FDs 1
and 2 to redirect to runtime.write, since that's where we'll apply the
faketime framing. This is equivalent to what nacl currently does in
naclFile.write.

We do this on all of the platforms except nacl, which has its own
faketime support and we're about to remove, and Windows, which would
require other changes to support faketime so we're leaving alone for
now.

Updates #30439.

Change-Id: I138a5ca63577d92d15b5437d037bd3159fa84ee7
Reviewed-on: https://go-review.googlesource.com/c/go/+/192739
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/fs_js.go

@@ -404,6 +404,14 @@ func Write(fd int, b []byte) (int, error) {
 		return n, err
 	}
 
+	if faketime && (fd == 1 || fd == 2) {
+		n := faketimeWrite(fd, b)
+		if n < 0 {
+			return 0, errnoErr(Errno(-n))
+		}
+		return n, nil
+	}
+
 	buf := uint8Array.New(len(b))
 	js.CopyBytesToJS(buf, b)
 	n, err := fsCall("write", fd, buf, 0, len(b), nil)

src/syscall/syscall_plan9.go

@@ -167,6 +167,14 @@ func Read(fd int, p []byte) (n int, err error) {
 }
 
 func Write(fd int, p []byte) (n int, err error) {
+	if faketime && (fd == 1 || fd == 2) {
+		n = faketimeWrite(fd, p)
+		if n < 0 {
+			return 0, ErrorString("error")
+		}
+		return n, nil
+	}
+
 	return Pwrite(fd, p, -1)
 }
 

src/syscall/syscall_unix.go

@@ -205,7 +205,14 @@ func Write(fd int, p []byte) (n int, err error) {
 	if race.Enabled {
 		race.ReleaseMerge(unsafe.Pointer(&ioSync))
 	}
-	n, err = write(fd, p)
+	if faketime && (fd == 1 || fd == 2) {
+		n = faketimeWrite(fd, p)
+		if n < 0 {
+			n, err = 0, errnoErr(Errno(-n))
+		}
+	} else {
+		n, err = write(fd, p)
+	}
 	if race.Enabled && n > 0 {
 		race.ReadRange(unsafe.Pointer(&p[0]), n)
 	}

src/syscall/time_fake.go

@@ -0,0 +1,26 @@
+// Copyright 2019 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.
+
+// +build faketime
+
+package syscall
+
+import "unsafe"
+
+const faketime = true
+
+// When faketime is enabled, we redirect writes to FDs 1 and 2 through
+// the runtime's write function, since that adds the framing that
+// reports the emulated time.
+
+//go:linkname runtimeWrite runtime.write
+func runtimeWrite(fd uintptr, p unsafe.Pointer, n int32) int32
+
+func faketimeWrite(fd int, p []byte) int {
+	var pp *byte
+	if len(p) > 0 {
+		pp = &p[0]
+	}
+	return int(runtimeWrite(uintptr(fd), unsafe.Pointer(pp), int32(len(p))))
+}

src/syscall/time_nofake.go

@@ -0,0 +1,14 @@
+// Copyright 2019 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.
+
+// +build !faketime
+
+package syscall
+
+const faketime = false
+
+func faketimeWrite(fd int, p []byte) int {
+	// This should never be called since faketime is false.
+	panic("not implemented")
+}