runtime: Update open/close/read/write to return -1 on error.

Error detection code copied from syscall, where presumably
we actually do it right.

Note that we throw the errno away.  The runtime doesn't use it.

Fixes #10052

Change-Id: I8de77dda6bf287276b137646c26b84fa61554ec8
Reviewed-on: https://go-review.googlesource.com/6571
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/runtime_test.go

@@ -292,3 +292,29 @@ func TestTrailingZero(t *testing.T) {
 		t.Errorf("sizeof(%#v)==%d, want 0", T5{}, unsafe.Sizeof(T5{}))
 	}
 }
+
+func TestBadOpen(t *testing.T) {
+	if GOOS == "windows" || GOOS == "nacl" {
+		t.Skip("skipping OS that doesn't have open/read/write/close")
+	}
+	// make sure we get the correct error code if open fails.  Same for
+	// read/write/close on the resulting -1 fd.  See issue 10052.
+	nonfile := []byte("/notreallyafile")
+	fd := Open(&nonfile[0], 0, 0)
+	if fd != -1 {
+		t.Errorf("open(\"%s\")=%d, want -1", string(nonfile), fd)
+	}
+	var buf [32]byte
+	r := Read(-1, unsafe.Pointer(&buf[0]), int32(len(buf)))
+	if r != -1 {
+		t.Errorf("read()=%d, want -1", r)
+	}
+	w := Write(^uintptr(0), unsafe.Pointer(&buf[0]), int32(len(buf)))
+	if w != -1 {
+		t.Errorf("write()=%d, want -1", w)
+	}
+	c := Close(-1)
+	if c != -1 {
+		t.Errorf("close()=%d, want -1", c)
+	}
+}