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")}
	}

	MOVW	R2, 8(R15)
	MOVD	R3, 16(R15)
	MOVD	R4, 24(R15)
	MOVD	$runtime·sigtrampgo(SB), R5
	BL	R5
	RET

TEXT runtime·cgoSigtramp(SB),NOSPLIT,$0
	BR	runtime·sigtramp(SB)

// func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) unsafe.Pointer
TEXT runtime·mmap(SB),NOSPLIT,$48-48
	MOVD	addr+0(FP), R2
	MOVD	n+8(FP), R3
	MOVW	prot+16(FP), R4
	MOVW	flags+20(FP), R5

//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)

type sigset_t struct {
	X__val [16]uint64
}

//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	Unlink(path string) (err error)
//sys	Unmount(path string, flags int) (err error)
//sys	write(fd int, p []byte) (n int, err error)
//sys	writev(fd int, iovecs []Iovec) (n uintptr, err error)
//sys	mmap(addr uintptr, length uintptr, prot int, flag int, fd int, pos int64) (ret uintptr, err error)
//sys	munmap(addr uintptr, length uintptr) (err error)
//sys	getfsstat(stat *Statfs_t, bufsize uintptr, flags int) (n int, err error)

	switch runtime.GOOS {
	case "linux", "android", "netbsd":
		// Figure out two addresses from /proc/self/maps.
		mmap, err := os.ReadFile("/proc/self/maps")
		if err != nil {
			t.Fatal(err)
		}
		var mappings []*profile.Mapping
		id := uint64(1)
		parseProcSelfMaps(mmap, func(lo, hi, offset uint64, file, buildID string) {
			mappings = append(mappings, &profile.Mapping{
				ID:      id,
				Start:   lo,

//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	EpollWait(epfd int, events []EpollEvent, msec int) (n int, err error)

type sigset_t struct {
	X__val [16]uint64
}

//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 {

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

	// 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 {