[PATCH] libstdc++: Fix access issue in iota_view::_Sentinel [PR100690]

[Jonathan Wakely]

On Thu, 20 May 2021, 19:35 Patrick Palka via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> Tested on x86_64-pc-linux-gnu, does this look OK for trunk/11/10?
>


Yes/yes/yes

Thanks.

>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/100690
>         * include/std/ranges (iota_view::_Sentinel::_M_distance_from):
>         Split out into this member function from ...
>         (iota_view::_Sentinel::operator-): ... here, for sake of access
>         checking.
>         * testsuite/std/ranges/iota/iota_view.cc:
> ---
>  libstdc++-v3/include/std/ranges                     |  8 ++++++--
>  libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc | 11 +++++++++++
>  2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges
> b/libstdc++-v3/include/std/ranges
> index 704f924557c..76add252ca6 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -499,6 +499,10 @@ namespace ranges
>         _M_equal(const _Iterator& __x) const
>         { return __x._M_value == _M_bound; }
>
> +       constexpr auto
> +       _M_distance_from(const _Iterator& __x) const
> +       { return _M_bound - __x._M_value; }
> +
>         _Bound _M_bound = _Bound();
>
>        public:
> @@ -515,12 +519,12 @@ namespace ranges
>         friend constexpr iter_difference_t<_Winc>
>         operator-(const _Iterator& __x, const _Sentinel& __y)
>           requires sized_sentinel_for<_Bound, _Winc>
> -       { return __x._M_value - __y._M_bound; }
> +       { return -__y._M_distance_from(__x); }
>
>         friend constexpr iter_difference_t<_Winc>
>         operator-(const _Sentinel& __x, const _Iterator& __y)
>           requires sized_sentinel_for<_Bound, _Winc>
> -       { return -(__y - __x); }
> +       { return __x._M_distance_from(__y); }
>        };
>
>        _Winc _M_value = _Winc();
> diff --git a/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> b/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> index be8695120ad..362ef1f7f78 100644
> --- a/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> @@ -80,6 +80,16 @@ test04()
>  // Verify we optimize away the 'bound' data member of an unbounded
> iota_view.
>  static_assert(sizeof(std::ranges::iota_view<char>) == 1);
>
> +void
> +test05()
> +{
> +  // PR libstdc++/100690
> +  int x[] = {42, 42, 42};
> +  auto r = std::views::iota(std::ranges::begin(x), std::ranges::cbegin(x)
> + 3);
> +  VERIFY( r.end() - r.begin() == 3 );
> +  VERIFY( r.begin() - r.end() == -3 );
> +}
> +
>  int
>  main()
>  {
> @@ -87,4 +97,5 @@ main()
>    test02();
>    test03();
>    test04();
> +  test05();
>  }
> --
> 2.32.0.rc0
>
>