if r == ^uintptr(0) {
		return nil, int(err0)
	}
	return unsafe.Pointer(r), int(err0)
}

//go:nosplit
func munmap(addr unsafe.Pointer, n uintptr) {
	r, err := syscall2(&libc_munmap, uintptr(addr), uintptr(n))
	if int32(r) == -1 {
		println("syscall munmap failed: ", hex(err))
		throw("syscall munmap")
	}
}

//go:nosplit
func madvise(addr unsafe.Pointer, n uintptr, flags int32) {

	prot := syscall.PROT_READ | syscall.PROT_WRITE
	flags := syscall.MAP_FILE | syscall.MAP_SHARED
	region, err := syscall.Mmap(int(f.Fd()), 0, size, prot, flags)
	if err != nil {
		return nil, err
	}

	return &sharedMem{f: f, region: region, removeOnClose: removeOnClose}, nil
}

// Close unmaps the shared memory and closes the temporary file. If this
// sharedMem was created with sharedMemTempFile, Close also removes the file.

//
// Third, it also mmaps the output file (if available). The intended usage is:
//   - Mmap the output file
//   - Write the content
//   - possibly apply any edits in the output buffer
//   - possibly write more content to the file. These writes take place in a heap
//     backed buffer that will get synced to disk.
//   - Munmap the output file
//
// And finally, it provides a mechanism by which you can multithread the

		// Since Linux 3.18, support for madvise is optional.
		// Fall back on mmap if it's not supported.
		// _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE will unmap all the
		// pages in the old mapping, and remap the memory region.
		mmap(v, n, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE, -1, 0)
	}

	if debug.harddecommit > 0 {
		p, err := mmap(v, n, _PROT_NONE, _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE, -1, 0)
		if p != v || err != 0 {

		// bump start to next page
		start = round(limit, pageSize)
	}
	return start, start + n
}

var memmap = mmap.Mmap
var munmap = mmap.Munmap

func (m *mappedFile) close() {
	m.closeOnce.Do(func() {
		if m.mapping != nil {
			munmap(m.mapping)
			m.mapping = nil
		}
		if m.f != nil {
			m.f.Close() // best effort
			m.f = nil
		}
	})
}

//go:cgo_import_dynamic libc_kill kill "libc.so"
//go:cgo_import_dynamic libc_madvise madvise "libc.so"
//go:cgo_import_dynamic libc_malloc malloc "libc.so"
//go:cgo_import_dynamic libc_mmap mmap "libc.so"
//go:cgo_import_dynamic libc_munmap munmap "libc.so"
//go:cgo_import_dynamic libc_open open "libc.so"
//go:cgo_import_dynamic libc_pthread_attr_destroy pthread_attr_destroy "libc.so"

// 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)
}

//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)

//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	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	readlen(fd int, buf *byte, nbuf int) (n int, err error) = SYS_READ

	}
	return
}
func osinit_hack_trampoline()

// mmap is used to do low-level memory allocation via mmap. Don't allow stack
// splits, since this function (used by sysAlloc) is called in a lot of low-level
// parts of the runtime and callers often assume it won't acquire any locks.
//
//go:nosplit
func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) (unsafe.Pointer, int) {