windows/dll_windows.go - sys - Git at Google

 // 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"
 )

 // We need to use LoadLibrary and GetProcAddress from the Go runtime, because
 // the these symbols are loaded by the system linker and are required to
 // dynamically load additional symbols. Note that in the Go runtime, these
 // return syscall.Handle and syscall.Errno, but these are the same, in fact,
 // as windows.Handle and windows.Errno, and we intend to keep these the same.

 //go:linkname syscall_loadlibrary syscall.loadlibrary
 func syscall_loadlibrary(filename *uint16) (handle Handle, err Errno)

 //go:linkname syscall_getprocaddress syscall.getprocaddress
 func syscall_getprocaddress(handle Handle, procname *uint8) (proc uintptr, err Errno)

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

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

 // 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 := syscall_loadlibrary(namep)
 	if e != 0 {
 		return nil, &DLLError{
 			Err:     e,
 			ObjName: name,
 			Msg:     "Failed to load " + name + ": " + e.Error(),
 		}
 	}
 	d := &DLL{
 		Name:   name,
 		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 := syscall_getprocaddress(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.
 			systemdir, err := GetSystemDirectory()
 			if err != nil {
 				return nil, err
 			}
 			loadDLL = systemdir + "\\" + 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) }
	// 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"
	)

	// We need to use LoadLibrary and GetProcAddress from the Go runtime, because
	// the these symbols are loaded by the system linker and are required to
	// dynamically load additional symbols. Note that in the Go runtime, these
	// return syscall.Handle and syscall.Errno, but these are the same, in fact,
	// as windows.Handle and windows.Errno, and we intend to keep these the same.

	//go:linkname syscall_loadlibrary syscall.loadlibrary
	func syscall_loadlibrary(filename *uint16) (handle Handle, err Errno)

	//go:linkname syscall_getprocaddress syscall.getprocaddress
	func syscall_getprocaddress(handle Handle, procname *uint8) (proc uintptr, err Errno)

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

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

	// 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 := syscall_loadlibrary(namep)
	if e != 0 {
	return nil, &DLLError{
	Err: e,
	ObjName: name,
	Msg: "Failed to load " + name + ": " + e.Error(),
	}
	}
	d := &DLL{
	Name: name,
	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 := syscall_getprocaddress(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.
	systemdir, err := GetSystemDirectory()
	if err != nil {
	return nil, err
	}
	loadDLL = systemdir + "\\" + 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) }