func osStackAlloc(s *mspan) {
	osStackRemap(s, _MAP_STACK)
}

func osStackFree(s *mspan) {
	// Undo MAP_STACK.
	osStackRemap(s, 0)
}

func osStackRemap(s *mspan, flags int32) {
	a, err := mmap(unsafe.Pointer(s.base()), s.npages*pageSize, _PROT_READ|_PROT_WRITE, _MAP_PRIVATE|_MAP_ANON|_MAP_FIXED|flags, -1, 0)
	if err != 0 || uintptr(a) != s.base() {

// mmap varies by architecture; see syscall_linux_*.go.
//sys	munmap(addr uintptr, length uintptr) (err error)

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

func Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
	return mapper.Mmap(fd, offset, length, prot, flags)
}

func setTimeval(sec, usec int64) Timeval {
	return Timeval{Sec: int32(sec), Usec: int32(usec)}
}

//sys	mmap2(addr uintptr, length uintptr, prot int, flags int, fd int, pageOffset uintptr) (xaddr uintptr, err error)

func mmap(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error) {
	page := uintptr(offset / 4096)
	if offset != int64(page)*4096 {
		return 0, EINVAL
	}

func GetMmap(c Cache, id ActionID) ([]byte, Entry, error) {
	entry, err := c.Get(id)
	if err != nil {
		return nil, entry, err
	}
	md, err := mmap.Mmap(c.OutputFile(entry.OutputID))
	if err != nil {
		return nil, Entry{}, err
	}
	if int64(len(md.Data)) != entry.Size {
		return nil, Entry{}, &entryNotFoundError{Err: errors.New("file incomplete")}
	}

	// initialize essential registers
	XOR	R0, R0
	MOVD	-32(R15), R7
	CMP	R7, $1234
	BEQ	2(PC)
	MOVD	R0, 0(R0)

	// Initialize m->procid to Linux tid
	SYSCALL $SYS_gettid

	MOVD	-24(R15), R9        // fn
	MOVD	-16(R15), R8        // g
	MOVD	-8(R15), R7         // m

	CMPBEQ	R7, $0, nog
	CMP	R8, $0
	BEQ	nog

	MOVD	R2, m_procid(R7)

	// In child, set up new stack

//sys	sendto(s int, buf []byte, flags int, to unsafe.Pointer, addrlen _Socklen) (err error)
//sys	recvmsg(s int, msg *Msghdr, flags int) (n int, err error)
//sys	sendmsg(s int, msg *Msghdr, flags int) (n int, err error)
//sys	mmap(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error)

//sys	futimesat(dirfd int, path string, times *[2]Timeval) (err error)
//sysnb	Gettimeofday(tv *Timeval) (err error)

//sys	sendto(s int, buf []byte, flags int, to unsafe.Pointer, addrlen _Socklen) (err error)
//sys	recvmsg(s int, msg *Msghdr, flags int) (n int, err error)
//sys	sendmsg(s int, msg *Msghdr, flags int) (n int, err error)
//sys	mmap(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error)

//sysnb	Gettimeofday(tv *Timeval) (err error)

func setTimespec(sec, nsec int64) Timespec {

func setTimeval(sec, usec int64) Timeval {
	return Timeval{Sec: int32(sec), Usec: int32(usec)}
}

//sys	mmap2(addr uintptr, length uintptr, prot int, flags int, fd int, pageOffset uintptr) (xaddr uintptr, err error)

func mmap(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error) {
	page := uintptr(offset / 4096)
	if offset != int64(page)*4096 {
		return 0, EINVAL
	}

		},
		{
			name:            "success case - existing node - no change in CMAD",
			newNode:         newNode(true),
			createError:     alreadyExists,
			existingNode:    newNode(true),
			expectedResult:  true,
			expectedActions: 2,
		},
		{
			name:            "success case - existing node - CMAD disabled",
			newNode:         newNode(false),
			createError:     alreadyExists,

	// Notes:
	// - this version writes everything little-endian, which means
	//   a call is needed to encode every value (expensive)
	// - we may want to move to a model in which we just blast out
	//   all counters, or possibly mmap the file and do the write
	//   implicitly.
	ctrb := make([]byte, 4)
	wrval := func(val uint32) error {
		var buf []byte
		var towr int
		if cfw.cflavor == coverage.CtrRaw {