The low level Operating System Primitives

syscall package

加载动态链接库（DLL）

syscall.LoadDLL

• LoadDLL函数用于显式地加载一个DLL，并返回一个syscall.DLL对象和一个error。syscall.DLL对象包含了DLL的句柄以及导出函数的地址。
• 当使用LoadDLL函数加载DLL时，如果加载失败，会返回一个非nil的error，并且需要检查error来处理加载失败的情况。

// LoadDLL loads the named DLL file into memory.
//
// If name is not an absolute path and is not a known system DLL used by
// Go, Windows will search for the named DLL in many locations, causing
// potential DLL preloading attacks.
//
// Use LazyDLL in golang.org/x/sys/windows for a secure way to
// load system DLLs.
func LoadDLL(name string) (*DLL, error) {
    namep, err := UTF16PtrFromString(name)
    if err != nil {
        return nil, err
    }
    var h uintptr
    var e Errno
    if sysdll.IsSystemDLL[name] {
        h, e = loadsystemlibrary(namep)
    } else {
        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
}

syscall.MustLoadDLL

• MustLoadDLL函数也用于加载一个DLL，但是它会在加载失败时直接panic。因此，MustLoadDLL适用于对加载DLL失败情况没有特别处理逻辑的场景。
• MustLoadDLL函数的使用方式与LoadDLL类似，但不需要检查error，因为它会在加载失败时直接panic。

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

syscall.NewLazyDLL

• NewLazyDLL函数用于创建一个*syscall.LazyDLL对象，该对象包含了DLL的名称和导出函数的延迟加载信息。
• LazyDLL对象并不立即加载DLL，而是在调用其Load方法时才会去加载DLL，并返回一个*syscall.LazyDLL对象和一个error。这样做的好处是可以将DLL的加载延迟到需要使用其中的函数时再进行。

// 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.
//
// LazyDLL is subject to the same DLL preloading attacks as documented
// on LoadDLL.
//
// Use LazyDLL in golang.org/x/sys/windows for a secure way to
// load system DLLs.
type LazyDLL struct {
    mu   sync.Mutex
    dll  *DLL // non nil once DLL is loaded
    Name string
}

// 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 {
        d.mu.Lock()
        defer d.mu.Unlock()
        if d.dll == nil {
            dll, e := LoadDLL(d.Name)
            if e != nil {
                return e
            }
            // 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}
}

windows package

加载动态链接库（DLL）

windows.LoadDLL

• LoadDLL函数用于显式地加载一个非系统的DLL，并返回一个*windows.DLL对象和一个error。*windows.DLL对象包含了DLL的句柄以及导出函数的地址。
• 与syscall.LoadDLL类似，windows.LoadDLL用于显式加载非系统DLL的方法。

// 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
}

windows.MustLoadDLL

• MustLoadDLL函数用于加载一个非系统的DLL。它会在加载失败时直接panic，因此适用于对加载DLL失败情况没有特别处理逻辑的场景。
• MustLoadDLL函数与syscall.MustLoadDLL类似，但是在windows包中专门用于加载非系统DLL。

// 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
}

windows.NewLazyDLL & windows.NewLazySystemDLL

• LazySystemDLL是一个类型，表示系统的动态链接库。它实际上是*windows.LazyDLL类型的实例，用于延迟加载系统DLL。

• NewLazySystemDLL函数用于创建一个*windows.LazyDLL对象，该对象代表系统的动态链接库。这个对象可以延迟加载系统DLL，并提供访问其中导出函数的能力。

• 与syscall.NewLazyDLL类似，windows.NewLazySystemDLL是用于延迟加载系统DLL的方法。

// 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}
}