Method Load

pkg/sentry/arch/stack.go:139–222

Load pushes the given args, env and aux vector to the stack using the well-known format for a new executable. It returns the start and end of the argument and environment vectors.

(args []string, env []string, aux Auxv)

// well-known format for a new executable. It returns the start and end
// of the argument and environment vectors.
func (s *Stack) Load(args []string, env []string, aux Auxv) (StackLayout, error) {
	l := StackLayout{}

	// Make sure we start with a 16-byte alignment.
	s.Align(16)

	// Push the environment vector so the end of the argument vector is adjacent to
	// the beginning of the environment vector.
	// While the System V abi for x86_64 does not specify an ordering to the
	// Information Block (the block holding the arg, env, and aux vectors),
	// support features like setproctitle(3) naturally expect these segments
	// to be in this order. See: https://www.uclibc.org/docs/psABI-x86_64.pdf
	// page 29.
	l.EnvvEnd = s.Bottom
	envAddrs := make([]hostarch.Addr, len(env))
	for i := len(env) - 1; i >= 0; i-- {
		if _, err := s.PushNullTerminatedByteSlice([]byte(env[i])); err != nil {
			return StackLayout{}, err
		}
		envAddrs[i] = s.Bottom
	}
	l.EnvvStart = s.Bottom

	// Push our strings.
	l.ArgvEnd = s.Bottom
	argAddrs := make([]hostarch.Addr, len(args))
	for i := len(args) - 1; i >= 0; i-- {
		if _, err := s.PushNullTerminatedByteSlice([]byte(args[i])); err != nil {
			return StackLayout{}, err
		}
		argAddrs[i] = s.Bottom
	}
	l.ArgvStart = s.Bottom

	// We need to align the arguments appropriately.
	//
	// We must finish on a 16-byte alignment, but we'll play it
	// conservatively and finish at 32-bytes. It would be nice to be able
	// to call Align here, but unfortunately we need to align the stack
	// with all the variable sized arrays pushed. So we just need to do
	// some calculations.
	argvSize := s.Arch.Width() * uint(len(args)+1)
	envvSize := s.Arch.Width() * uint(len(env)+1)
	auxvSize := s.Arch.Width() * 2 * uint(len(aux)+1)
	total := hostarch.Addr(argvSize) + hostarch.Addr(envvSize) + hostarch.Addr(auxvSize) + hostarch.Addr(s.Arch.Width())
	expectedBottom := s.Bottom - total
	if expectedBottom%32 != 0 {
		s.Bottom -= expectedBottom % 32
	}

	// Push our auxvec.
	// NOTE: We need an extra zero here per spec.
	// The Push function will automatically terminate
	// strings and arrays with a single null value.
	auxv := make([]hostarch.Addr, 0, len(aux)*2+1)
	for _, a := range aux {
		auxv = append(auxv, hostarch.Addr(a.Key), a.Value)
	}