// os/file.go

// 新建文件
func Create(name string) (*File, error) {
	// 跳转到下面的OpenFile
	return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)

// OpenFile在这里还是平台无关的代码
func OpenFile(name string, flag int, perm FileMode) (*File, error) {
	// 从openFileNolog开始,不同平台代码会有不同
	f, err := openFileNolog(name, flag, perm)
	if err != nil {
		return nil, err
	f.appendMode = flag&O_APPEND != 0

	return f, nil
// os/file_unix.go

// openFileNolog的unix实现
func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
	setSticky := false
	if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
		if _, err := Stat(name); IsNotExist(err) {
			setSticky = true

	var r int
	var s poll.SysFile
	for {
		var e error
		r, s, e = open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
		if e == nil {

		// We have to check EINTR here, per issues 11180 and 39237.
		if e == syscall.EINTR {

		return nil, &PathError{Op: "open", Path: name, Err: e}

	// open(2) itself won't handle the sticky bit on *BSD and Solaris
	if setSticky {

	// There's a race here with fork/exec, which we are
	// content to live with. See ../syscall/exec_unix.go.
	if !supportsCloseOnExec {

	kind := kindOpenFile
	if unix.HasNonblockFlag(flag) {
		kind = kindNonBlock

	// 封装为File结构
	f := newFile(r, name, kind)
	f.pfd.SysFile = s
	return f, nil
// os/file_open_unix.go

func open(path string, flag int, perm uint32) (int, poll.SysFile, error) {
	// 跳转到syscall.Open
	fd, err := syscall.Open(path, flag, perm)
	return fd, poll.SysFile{}, err
// syscall/zsyscall_darwin_amd64.go

func Open(path string, mode int, perm uint32) (fd int, err error) {
	var _p0 *byte
	_p0, err = BytePtrFromString(path)
	if err != nil {
	// 调用syscall
	r0, _, e1 := syscall(abi.FuncPCABI0(libc_open_trampoline), uintptr(unsafe.Pointer(_p0)), uintptr(mode), uintptr(perm))
	fd = int(r0)
	if e1 != 0 {
		err = errnoErr(e1)
// syscall/syscall_darwin.go
func syscall(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)

// internal/abi/funcpc.go
func FuncPCABI0(f interface{}) uintptr

// syscall/zsyscall_darwin_amd64.go
func libc_open_trampoline()
//go:cgo_import_dynamic libc_open open "/usr/lib/libSystem.B.dylib"

// 先通过abi.FuncPCABI0(libc_open_trampoline)先获取到open函数的地址
// 然后通过syscall调用open函数
// open函数是libc标准库中的函数,C语言定义为
int open(const char *pathname, int flags, mode_t mode);

//go:linkname syscall_syscall syscall.syscall
func syscall_syscall(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) {
	args := struct{ fn, a1, a2, a3, r1, r2, err uintptr }{fn, a1, a2, a3, r1, r2, err}
	libcCall(unsafe.Pointer(abi.FuncPCABI0(syscall)), unsafe.Pointer(&args))
	return args.r1, args.r2, args.err
func syscall()

// runtime/sys_libc.go
func libcCall(fn, arg unsafe.Pointer) int32 {
	// Leave caller's PC/SP/G around for traceback.
	gp := getg()
	var mp *m
	if gp != nil {
		mp = gp.m
	if mp != nil && mp.libcallsp == 0 {
		mp.libcallpc = getcallerpc()
		// sp must be the last, because once async cpu profiler finds
		// all three values to be non-zero, it will use them
		mp.libcallsp = getcallersp()
	} else {
		// Make sure we don't reset libcallsp. This makes
		// libcCall reentrant; We remember the g/pc/sp for the
		// first call on an M, until that libcCall instance
		// returns.  Reentrance only matters for signals, as
		// libc never calls back into Go.  The tricky case is
		// where we call libcX from an M and record g/pc/sp.
		// Before that call returns, a signal arrives on the
		// same M and the signal handling code calls another
		// libc function.  We don't want that second libcCall
		// from within the handler to be recorded, and we
		// don't want that call's completion to zero
		// libcallsp.
		// We don't need to set libcall* while we're in a sighandler
		// (even if we're not currently in libc) because we block all
		// signals while we're handling a signal. That includes the
		// profile signal, which is the one that uses the libcall* info.
		mp = nil
	// 跳转到asmcgocall
	res := asmcgocall(fn, arg)
	if mp != nil {
		mp.libcallsp = 0
	return res

// 硬件平台相关代码
// runtime/asm_arm64.s
// func asmcgocall(fn, arg unsafe.Pointer) int32
// Call fn(arg) on the scheduler stack,
// aligned appropriately for the gcc ABI.
// See cgocall.go for more details.
TEXT ·asmcgocall(SB),NOSPLIT,$0-20
	MOVD	fn+0(FP), R1
	MOVD	arg+8(FP), R0

	MOVD	RSP, R2		// save original stack pointer
	CBZ	g, nosave
	MOVD	g, R4

	// Figure out if we need to switch to m->g0 stack.
	// We get called to create new OS threads too, and those
	// come in on the m->g0 stack already. Or we might already
	// be on the m->gsignal stack.
	MOVD	g_m(g), R8
	MOVD	m_gsignal(R8), R3
	CMP	R3, g
	BEQ	nosave
	MOVD	m_g0(R8), R3
	CMP	R3, g
	BEQ	nosave

	// Switch to system stack.
	MOVD	R0, R9	// gosave_systemstack_switch<> and save_g might clobber R0
	BL	gosave_systemstack_switch<>(SB)
	MOVD	R3, g
	BL	runtime·save_g(SB)
	MOVD	(g_sched+gobuf_sp)(g), R0
	MOVD	(g_sched+gobuf_bp)(g), R29
	MOVD	R9, R0

	// Now on a scheduling stack (a pthread-created stack).
	// Save room for two of our pointers /*, plus 32 bytes of callee
	// save area that lives on the caller stack. */
	SUB	$16, R13
	MOVD	R4, 0(RSP)	// save old g on stack
	MOVD	(g_stack+stack_hi)(R4), R4
	SUB	R2, R4
	MOVD	R4, 8(RSP)	// save depth in old g stack (can't just save SP, as stack might be copied during a callback)
	BL	(R1)
	MOVD	R0, R9

	// Restore g, stack pointer. R0 is errno, so don't touch it
	MOVD	0(RSP), g
	BL	runtime·save_g(SB)
	MOVD	(g_stack+stack_hi)(g), R5
	MOVD	8(RSP), R6
	SUB	R6, R5
	MOVD	R9, R0

	MOVW	R0, ret+16(FP)

	// Running on a system stack, perhaps even without a g.
	// Having no g can happen during thread creation or thread teardown
	// (see needm/dropm on Solaris, for example).
	// This code is like the above sequence but without saving/restoring g
	// and without worrying about the stack moving out from under us
	// (because we're on a system stack, not a goroutine stack).
	// The above code could be used directly if already on a system stack,
	// but then the only path through this code would be a rare case on Solaris.
	// Using this code for all "already on system stack" calls exercises it more,
	// which should help keep it correct.
	SUB	$16, R13
	MOVD	$0, R4
	MOVD	R4, 0(RSP)	// Where above code stores g, in case someone looks during debugging.
	MOVD	R2, 8(RSP)	// Save original stack pointer.
	BL	(R1)
	// Restore stack pointer.
	MOVD	8(RSP), R2
	MOVD	R0, ret+16(FP)

// 然后回到openFileNolog中
// 在openFileNolog中,继续调用newFile,整体封装为File结构,原路返回
func newFile(fd int, name string, kind newFileKind) *File {
	f := &File{&file{
		pfd: poll.FD{
			Sysfd:         fd,
			IsStream:      true,
			ZeroReadIsEOF: true,
		name:        name,
		stdoutOrErr: fd == 1 || fd == 2,

	pollable := kind == kindOpenFile || kind == kindPipe || kind == kindNonBlock

	// If the caller passed a non-blocking filedes (kindNonBlock),
	// we assume they know what they are doing so we allow it to be
	// used with kqueue.
	if kind == kindOpenFile {
		switch runtime.GOOS {
		case "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd":
			var st syscall.Stat_t
			err := ignoringEINTR(func() error {
				return syscall.Fstat(fd, &st)
			typ := st.Mode & syscall.S_IFMT
			// Don't try to use kqueue with regular files on *BSDs.
			// On FreeBSD a regular file is always
			// reported as ready for writing.
			// On Dragonfly, NetBSD and OpenBSD the fd is signaled
			// only once as ready (both read and write).
			// Issue 19093.
			// Also don't add directories to the netpoller.
			if err == nil && (typ == syscall.S_IFREG || typ == syscall.S_IFDIR) {
				pollable = false

			// In addition to the behavior described above for regular files,
			// on Darwin, kqueue does not work properly with fifos:
			// closing the last writer does not cause a kqueue event
			// for any readers. See issue #24164.
			if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && typ == syscall.S_IFIFO {
				pollable = false

	clearNonBlock := false
	if pollable {
		if kind == kindNonBlock {
			// The descriptor is already in non-blocking mode.
			// We only set f.nonblock if we put the file into
			// non-blocking mode.
		} else if err := syscall.SetNonblock(fd, true); err == nil {
			f.nonblock = true
			clearNonBlock = true
		} else {
			pollable = false

	// An error here indicates a failure to register
	// with the netpoll system. That can happen for
	// a file descriptor that is not supported by
	// epoll/kqueue; for example, disk files on
	// Linux systems. We assume that any real error
	// will show up in later I/O.
	// We do restore the blocking behavior if it was set by us.
	if pollErr := f.pfd.Init("file", pollable); pollErr != nil && clearNonBlock {
		if err := syscall.SetNonblock(fd, false); err == nil {
			f.nonblock = false

	runtime.SetFinalizer(f.file, (*file).close)
	return f

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