// loop back to the beginning ad nauseam until it's sent
	// exactly the number of bytes told to. As such, we need to
	// know exactly how many bytes to send.
	var remain int64 = 0

	lr, ok := r.(*io.LimitedReader)
	if ok {
		remain, r = lr.N, lr.R
		if remain <= 0 {
			return 0, nil, true
		}
	}
	// r might be an *os.File or an os.fileWithoutWriteTo.

	HasLR:          true,
	FixedFrameSize: 4, // LR
}

var ArchARM64 = &Arch{
	Name:           "arm64",
	Family:         ARM64,
	ByteOrder:      binary.LittleEndian,
	PtrSize:        8,
	RegSize:        8,
	MinLC:          4,
	Alignment:      1,
	CanMergeLoads:  true,
	CanJumpTable:   true,
	HasLR:          true,
	FixedFrameSize: 8, // LR
}

var ArchLoong64 = &Arch{

// license that can be found in the LICENSE file.

package runtime

// NOTE(rsc): _CONTEXT_CONTROL is actually 0x400001 and should include PC, SP, and LR.
// However, empirically, LR doesn't come along on Windows 10
// unless you also set _CONTEXT_INTEGER (0x400002).
// Without LR, we skip over the next-to-bottom function in profiles
// when the bottom function is frameless.
// So we set both here, to make a working _CONTEXT_CONTROL.

	SLD	$56, BYTES, TMP
	LXVL	SRC, TMP, V0
	STXVL	V0, TGT, TMP
	RET
#endif

	MOVD    0(SRC), TMP
	ADD	$8, SRC
	MOVD    TMP, 0(TGT)
	ADD     $8, TGT
checkbytes:
	BC	12, 14, LR		// BEQ lr
#ifdef GOPPC64_power10
	SLD	$56, BYTES, TMP
	LXVL	SRC, TMP, V0
	STXVL	V0, TGT, TMP
	RET
#endif
lt8:	// Move word if possible
	CMP BYTES, $4
	BLT lt4
	MOVWZ 0(SRC), TMP
	ADD $-4, BYTES

	go badLR1()
	select {}
}

//go:noinline
func badLR1() {
	// We need two frames on LR machines because we'll smash this
	// frame's saved LR.
	badLR2(0)
}

//go:noinline
func badLR2(arg int) {
	// Smash the return PC or saved LR.
	lrOff := unsafe.Sizeof(uintptr(0))
	if runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" {
		lrOff = 32 // FIXED_FRAME or sys.MinFrameSize

	lOut := new(strings.Builder)
	log.SetPrefix("lr: ")
	log.SetOutput(lOut)
	log.SetFlags(0)

	data := []byte("Hello, World!")
	p := make([]byte, len(data))

	lr := ErrReader(errors.New("io failure"))
	rl := NewReadLogger("read", lr)
	n, err := rl.Read(p)
	if err == nil {
		t.Fatalf("Unexpectedly succeeded to read: %v", err)
	}

	wantLogWithHex := fmt.Sprintf("lr: read %x: io failure\n", p[:n])

import "unsafe"

// adjust Gobuf as if it executed a call to fn with context ctxt
// and then did an immediate Gosave.
func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
	if buf.lr != 0 {
		throw("invalid use of gostartcall")
	}
	buf.lr = buf.pc
	buf.pc = uintptr(fn)
	buf.ctxt = ctxt

//
// if handled == false, sendFile performed no work.
func sendFile(fd *netFD, r io.Reader) (written int64, err error, handled bool) {
	var n int64 = 0 // by default, copy until EOF.

	lr, ok := r.(*io.LimitedReader)
	if ok {
		n, r = lr.N, lr.R
		if n <= 0 {
			return 0, nil, true
		}
	}

	f, ok := r.(*os.File)
	if !ok {
		return 0, nil, false
	}

import "unsafe"

// adjust Gobuf as if it executed a call to fn with context ctxt
// and then did an immediate Gosave.
func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
	if buf.lr != 0 {
		throw("invalid use of gostartcall")
	}
	buf.lr = buf.pc
	buf.pc = uintptr(fn)
	buf.ctxt = ctxt

	ADD	$(16 + callbackArgs__size), R13	// free locals
	MOVM.IA.W (R13), [R4-R11, R12]	// pop {r4-r11, lr=>r12}
	ADD	$(4*4), R13	// skip r0-r3
	B	(R12)	// return

// uint32 tstart_stdcall(M *newm);
TEXT runtime·tstart_stdcall(SB),NOSPLIT|NOFRAME,$0
	MOVM.DB.W [R4-R11, R14], (R13)		// push {r4-r11, lr}

	MOVW	m_g0(R0), g
	MOVW	R0, g_m(g)
	BL	runtime·save_g(SB)