Use NewLazySystemDLL instead of NewLazyDLL (#132)

* Use NewLazySystemDLL instead of NewLazyDLL

The ensures that the code only search for DLLs in the Windows system directory.

* Remove old go:generate call

Putting this into doc.go which does not have build tags allows the code to be generated from non-windows OSes.

CHANGELOG.md

@@ -12,6 +12,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Load DLLs only from Windows system directory.
+
 ### Deprecated
 
 ## [0.10.4]

sys/windows/doc.go

@@ -1,2 +1,8 @@
 // Package windows contains various Windows system call.
 package windows
+
+// Use "go generate -v -x ." to generate the source.
+
+// Add -trace to enable debug prints around syscalls.
+//go:generate go run $GOROOT/src/syscall/mksyscall_windows.go -systemdll=true -output zsyscall_windows.go syscall_windows.go
+//go:generate go run fix_generated.go -input zsyscall_windows.go

sys/windows/fix_generated.go

@@ -0,0 +1,60 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//+build ignore
+
+package main
+
+import (
+	"flag"
+	"io/ioutil"
+	"log"
+	"regexp"
+)
+
+func main() {
+	var filename string
+
+	log.SetFlags(0)
+	flag.StringVar(&filename, "input", "", "name of generated source file to fix")
+	flag.Parse()
+
+	if filename == "" {
+		log.Fatal("Name of generated file must be specified with -input flag")
+	}
+
+	if err := fixGeneratedCode(filename); err != nil {
+		log.Fatal(err)
+	}
+}
+
+var lazySystemRegex = regexp.MustCompile(`(?m)\sNewLazySystemDLL`)
+var unsafeImportRegex = regexp.MustCompile(`(?m)"unsafe"`)
+
+// fixGeneratedCode adds "windows." to locations in the generated source code
+// that reference "NewLazySystemDLL" without the package name.
+func fixGeneratedCode(filename string) error {
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return err
+	}
+
+	data = lazySystemRegex.ReplaceAll(data, []byte(" windows.NewLazySystemDLL"))
+	data = unsafeImportRegex.ReplaceAll(data, []byte(`"unsafe"`+"\n\n\t"+`"golang.org/x/sys/windows"`))
+
+	return ioutil.WriteFile(filename, data, 0644)
+}

sys/windows/syscall_windows.go

@@ -580,11 +580,6 @@ func GetTickCount64() (uptime uint64, err error) {
 	return uptime, nil
 }
 
-// Use "GOOS=windows go generate -v -x ." to generate the source.
-
-// Add -trace to enable debug prints around syscalls.
-//go:generate go run $GOROOT/src/syscall/mksyscall_windows.go -systemdll=false -output zsyscall_windows.go syscall_windows.go
-
 // Windows API calls
 //sys   _GlobalMemoryStatusEx(buffer *MemoryStatusEx) (err error) = kernel32.GlobalMemoryStatusEx
 //sys   _GetLogicalDriveStringsW(bufferLength uint32, buffer *uint16) (length uint32, err error) = kernel32.GetLogicalDriveStringsW