dll_windows.go
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	// Copyright 2011 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.

	package windows

	import (
	"sync"
	"sync/atomic"
	"syscall"
	"unsafe"
	)

	// DLLError describes reasons for DLL load failures.
	type DLLError struct {
	Err error
	ObjName string
	Msg string
	}

	func (e *DLLError) Error() string { return e.Msg }

	// Implemented in runtime/syscall_windows.goc; we provide jumps to them in our assembly file.
	func loadlibrary(filename *uint16) (handle uintptr, err syscall.Errno)
	func getprocaddress(handle uintptr, procname *uint8) (proc uintptr, err syscall.Errno)

	// A DLL implements access to a single DLL.
	type DLL struct {
	Name string
	Handle Handle
	}

	// LoadDLL loads DLL file into memory.
	//
	// Warning: using LoadDLL without an absolute path name is subject to
	// DLL preloading attacks. To safely load a system DLL, use LazyDLL
	// with System set to true, or use LoadLibraryEx directly.
	func LoadDLL(name string) (dll *DLL, err error) {
	namep, err := UTF16PtrFromString(name)
	if err != nil {
	return nil, err
	}
	h, e := loadlibrary(namep)
	if e != 0 {
	return nil, &DLLError{
	Err: e,
	ObjName: name,
	Msg: "Failed to load " + name + ": " + e.Error(),
	}
	}
	d := &DLL{
	Name: name,
	Handle: Handle(h),
	}
	return d, nil
	}

	// MustLoadDLL is like LoadDLL but panics if load operation failes.
	func MustLoadDLL(name string) *DLL {
	d, e := LoadDLL(name)
	if e != nil {
	panic(e)
	}
	return d
	}

	// FindProc searches DLL d for procedure named name and returns *Proc
	// if found. It returns an error if search fails.
	func (d DLL) FindProc(name string) (proc Proc, err error) {
	namep, err := BytePtrFromString(name)
	if err != nil {
	return nil, err
	}
	a, e := getprocaddress(uintptr(d.Handle), namep)
	if e != 0 {
	return nil, &DLLError{
	Err: e,
	ObjName: name,
	Msg: "Failed to find " + name + " procedure in " + d.Name + ": " + e.Error(),
	}
	}
	p := &Proc{
	Dll: d,
	Name: name,
	addr: a,
	}
	return p, nil
	}

	// MustFindProc is like FindProc but panics if search fails.
	func (d DLL) MustFindProc(name string) Proc {
	p, e := d.FindProc(name)
	if e != nil {
	panic(e)
	}
	return p
	}

	// Release unloads DLL d from memory.
	func (d *DLL) Release() (err error) {
	return FreeLibrary(d.Handle)
	}

	// A Proc implements access to a procedure inside a DLL.
	type Proc struct {
	Dll *DLL
	Name string
	addr uintptr
	}

	// Addr returns the address of the procedure represented by p.
	// The return value can be passed to Syscall to run the procedure.
	func (p *Proc) Addr() uintptr {
	return p.addr
	}

	//go:uintptrescapes

	// Call executes procedure p with arguments a. It will panic, if more than 15 arguments
	// are supplied.
	//
	// The returned error is always non-nil, constructed from the result of GetLastError.
	// Callers must inspect the primary return value to decide whether an error occurred
	// (according to the semantics of the specific function being called) before consulting
	// the error. The error will be guaranteed to contain windows.Errno.
	func (p *Proc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {
	switch len(a) {
	case 0:
	return syscall.Syscall(p.Addr(), uintptr(len(a)), 0, 0, 0)
	case 1:
	return syscall.Syscall(p.Addr(), uintptr(len(a)), a[0], 0, 0)
	case 2:
	return syscall.Syscall(p.Addr(), uintptr(len(a)), a[0], a[1], 0)
	case 3:
	return syscall.Syscall(p.Addr(), uintptr(len(a)), a[0], a[1], a[2])
	case 4:
	return syscall.Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], 0, 0)
	case 5:
	return syscall.Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], 0)
	case 6:
	return syscall.Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5])
	case 7:
	return syscall.Syscall9(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], 0, 0)
	case 8:
	return syscall.Syscall9(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], 0)
	case 9:
	return syscall.Syscall9(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8])
	case 10:
	return syscall.Syscall12(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], 0, 0)
	case 11:
	return syscall.Syscall12(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], 0)
	case 12:
	return syscall.Syscall12(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11])
	case 13:
	return syscall.Syscall15(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], 0, 0)
	case 14:
	return syscall.Syscall15(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], 0)
	case 15:
	return syscall.Syscall15(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], a[14])
	default:
	panic("Call " + p.Name + " with too many arguments " + itoa(len(a)) + ".")
	}
	}

	// A LazyDLL implements access to a single DLL.
	// It will delay the load of the DLL until the first
	// call to its Handle method or to one of its
	// LazyProc's Addr method.
	type LazyDLL struct {
	Name string

	// System determines whether the DLL must be loaded from the
	// Windows System directory, bypassing the normal DLL search
	// path.
	System bool

	mu sync.Mutex
	dll *DLL // non nil once DLL is loaded
	}

	// Load loads DLL file d.Name into memory. It returns an error if fails.
	// Load will not try to load DLL, if it is already loaded into memory.
	func (d *LazyDLL) Load() error {
	// Non-racy version of:
	// if d.dll != nil {
	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&d.dll))) != nil {
	return nil
	}
	d.mu.Lock()
	defer d.mu.Unlock()
	if d.dll != nil {
	return nil
	}

	// kernel32.dll is special, since it's where LoadLibraryEx comes from.
	// The kernel already special-cases its name, so it's always
	// loaded from system32.
	var dll *DLL
	var err error
	if d.Name == "kernel32.dll" {
	dll, err = LoadDLL(d.Name)
	} else {
	dll, err = loadLibraryEx(d.Name, d.System)
	}
	if err != nil {
	return err
	}

	// Non-racy version of:
	// d.dll = dll
	atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&d.dll)), unsafe.Pointer(dll))
	return nil
	}

	// mustLoad is like Load but panics if search fails.
	func (d *LazyDLL) mustLoad() {
	e := d.Load()
	if e != nil {
	panic(e)
	}
	}

	// Handle returns d's module handle.
	func (d *LazyDLL) Handle() uintptr {
	d.mustLoad()
	return uintptr(d.dll.Handle)
	}

	// NewProc returns a LazyProc for accessing the named procedure in the DLL d.
	func (d LazyDLL) NewProc(name string) LazyProc {
	return &LazyProc{l: d, Name: name}
	}

	// NewLazyDLL creates new LazyDLL associated with DLL file.
	func NewLazyDLL(name string) *LazyDLL {
	return &LazyDLL{Name: name}
	}

	// NewLazySystemDLL is like NewLazyDLL, but will only
	// search Windows System directory for the DLL if name is
	// a base name (like "advapi32.dll").
	func NewLazySystemDLL(name string) *LazyDLL {
	return &LazyDLL{Name: name, System: true}
	}

	// A LazyProc implements access to a procedure inside a LazyDLL.
	// It delays the lookup until the Addr method is called.
	type LazyProc struct {
	Name string

	mu sync.Mutex
	l *LazyDLL
	proc *Proc
	}

	// Find searches DLL for procedure named p.Name. It returns
	// an error if search fails. Find will not search procedure,
	// if it is already found and loaded into memory.
	func (p *LazyProc) Find() error {
	// Non-racy version of:
	// if p.proc == nil {
	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc))) == nil {
	p.mu.Lock()
	defer p.mu.Unlock()
	if p.proc == nil {
	e := p.l.Load()
	if e != nil {
	return e
	}
	proc, e := p.l.dll.FindProc(p.Name)
	if e != nil {
	return e
	}
	// Non-racy version of:
	// p.proc = proc
	atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc)), unsafe.Pointer(proc))
	}
	}
	return nil
	}

	// mustFind is like Find but panics if search fails.
	func (p *LazyProc) mustFind() {
	e := p.Find()
	if e != nil {
	panic(e)
	}
	}

	// Addr returns the address of the procedure represented by p.
	// The return value can be passed to Syscall to run the procedure.
	// It will panic if the procedure cannot be found.
	func (p *LazyProc) Addr() uintptr {
	p.mustFind()
	return p.proc.Addr()
	}

	//go:uintptrescapes

	// Call executes procedure p with arguments a. It will panic, if more than 15 arguments
	// are supplied. It will also panic if the procedure cannot be found.
	//
	// The returned error is always non-nil, constructed from the result of GetLastError.
	// Callers must inspect the primary return value to decide whether an error occurred
	// (according to the semantics of the specific function being called) before consulting
	// the error. The error will be guaranteed to contain windows.Errno.
	func (p *LazyProc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {
	p.mustFind()
	return p.proc.Call(a...)
	}

	var canDoSearchSystem32Once struct {
	sync.Once
	v bool
	}

	func initCanDoSearchSystem32() {
	// https://msdn.microsoft.com/en-us/library/ms684179(v=vs.85).aspx says:
	// "Windows 7, Windows Server 2008 R2, Windows Vista, and Windows
	// Server 2008: The LOAD_LIBRARY_SEARCH_* flags are available on
	// systems that have KB2533623 installed. To determine whether the
	// flags are available, use GetProcAddress to get the address of the
	// AddDllDirectory, RemoveDllDirectory, or SetDefaultDllDirectories
	// function. If GetProcAddress succeeds, the LOAD_LIBRARY_SEARCH_*
	// flags can be used with LoadLibraryEx."
	canDoSearchSystem32Once.v = (modkernel32.NewProc("AddDllDirectory").Find() == nil)
	}

	func canDoSearchSystem32() bool {
	canDoSearchSystem32Once.Do(initCanDoSearchSystem32)
	return canDoSearchSystem32Once.v
	}

	func isBaseName(name string) bool {
	for _, c := range name {
	if c == ':' \|\| c == '/' \|\| c == '\\' {
	return false
	}
	}
	return true
	}

	// loadLibraryEx wraps the Windows LoadLibraryEx function.
	//
	// See https://msdn.microsoft.com/en-us/library/windows/desktop/ms684179(v=vs.85).aspx
	//
	// If name is not an absolute path, LoadLibraryEx searches for the DLL
	// in a variety of automatic locations unless constrained by flags.
	// See: https://msdn.microsoft.com/en-us/library/ff919712%28VS.85%29.aspx
	func loadLibraryEx(name string, system bool) (*DLL, error) {
	loadDLL := name
	var flags uintptr
	if system {
	if canDoSearchSystem32() {
	const LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800
	flags = LOAD_LIBRARY_SEARCH_SYSTEM32
	} else if isBaseName(name) {
	// WindowsXP or unpatched Windows machine
	// trying to load "foo.dll" out of the system
	// folder, but LoadLibraryEx doesn't support
	// that yet on their system, so emulate it.
	windir, _ := Getenv("WINDIR") // old var; apparently works on XP
	if windir == "" {
	return nil, errString("%WINDIR% not defined")
	}
	loadDLL = windir + "\\System32\\" + name
	}
	}
	h, err := LoadLibraryEx(loadDLL, 0, flags)
	if err != nil {
	return nil, err
	}
	return &DLL{Name: name, Handle: h}, nil
	}

	type errString string

	func (s errString) Error() string { return string(s) }

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