func callCgoMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) uintptr

// sysMunmap calls the munmap system call. It is implemented in assembly.
func sysMunmap(addr unsafe.Pointer, n uintptr)

// callCgoMunmap calls the munmap function in the runtime/cgo package
// using the GCC calling convention. It is implemented in assembly.

}

var mapper = &mremapMmapper{
	mmapper: mmapper{
		active: make(map[*byte][]byte),
		mmap:   mmap,
		munmap: munmap,
	},
	mremap: mremap,
}

func (m *mremapMmapper) Mremap(oldData []byte, newLength int, flags int) (data []byte, err error) {

func TestMmap(t *testing.T) {
	b, err := syscall.Mmap(-1, 0, syscall.Getpagesize(), syscall.PROT_NONE, syscall.MAP_ANON|syscall.MAP_PRIVATE)
	if err != nil {
		t.Fatalf("Mmap: %v", err)
	}
	if err := syscall.Munmap(b); err != nil {
		t.Fatalf("Munmap: %v", err)
	}

// The err result is an OS error code such as ENOMEM.
func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) (p unsafe.Pointer, err int)

// munmap calls the munmap system call. It is implemented in assembly.
func munmap(addr unsafe.Pointer, n uintptr)

func nanotime1() int64

//go:noescape
func sigaltstack(new, old *stackt)

func fcntl(fd, cmd, arg int32) (ret int32, errno int32)

// if it is already mapped. It also flushes any in-heap data to the new
// mapping.
func (out *OutBuf) Mmap(filesize uint64) error {
	oldlen := len(out.buf)
	if oldlen != 0 {
		out.munmap()
	}

	err := out.f.Truncate(int64(filesize))
	if err != nil {
		Exitf("resize output file failed: %v", err)
	}

	low, high := uint32(filesize), uint32(filesize>>32)

	mem, err := syscall.Mmap(-1, 0, 1<<20, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANON|syscall.MAP_PRIVATE)
	if err != nil {
		t.Fatalf("mmap failed: %v", err)
	}
	defer syscall.Munmap(mem)
	a := (*uint64)(unsafe.Pointer(&mem[0]))
	if *a != 0 {
		t.Fatalf("bad atomic value: %v, want 0", *a)
	}
	atomic.AddUint64(a, 1)
	if *a != 1 {
		t.Fatalf("bad atomic value: %v, want 1", *a)
	}

	data, err := syscall.Mmap(-1, 0, 4096, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANON|syscall.MAP_PRIVATE)
	if err != nil {
		t.Fatalf("failed to mmap memory: %v", err)
	}
	defer syscall.Munmap(data)
	p := (*uint32)(unsafe.Pointer(&data[0]))
	atomic.AddUint32(p, 1)
	(*p)++
	if *p != 2 {
		t.Fatalf("data[0] = %v, expect 2", *p)
	}

	oldheap := out.heap
	if filesize < uint64(len(oldheap)) {
		panic("mmap size too small")
	}
	out.heap = make([]byte, filesize)
	copy(out.heap, oldheap)
	return nil
}

	}
	m, err := syscall.Mmap(-1, 0, 0x1000, syscall.PROT_READ /* Note: no PROT_WRITE */, syscall.MAP_SHARED|syscall.MAP_ANON)
	if err != nil {
		t.Fatalf("can't map anonymous memory: %s", err)
	}
	defer syscall.Munmap(m)
	old := debug.SetPanicOnFault(true)
	defer debug.SetPanicOnFault(old)
	const lowBits = 0x3e7
	defer func() {
		r := recover()
		if r == nil {
			t.Fatalf("write did not fault")
		}

	closefd(fd)
	newP := uintptr(addr)
	if mmapErr != 0 {
		newP = ^uintptr(0)
	}
	if !atomic.Casuintptr(&hpetDevMap[idx], 0, newP) && mmapErr == 0 {
		munmap(addr, physPageSize)
	}
}

//go:nosplit
func (th *vdsoTimehands) getTimecounter() (uint32, bool) {
	switch th.algo {
	case _VDSO_TH_ALGO_X86_TSC:
		return th.getTSCTimecounter(), true