From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: "François Dumont" <frs.dumont@gmail.com>
Cc: "libstdc++" <libstdc++@gcc.gnu.org>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [Bug libstdc++/99402] [10 Regression] std::copy creates _GLIBCXX_DEBUG false positive for attempt to subscript a dereferenceable (start-of-sequence) iterator
Date: Sun, 18 Apr 2021 15:04:12 +0100 [thread overview]
Message-ID: <CAH6eHdSJx=Rq=T65HDw_MoRBmv4zc2stDwg4jRM4T11pXwH+kw@mail.gmail.com> (raw)
In-Reply-To: <70f13ddf-8b3a-1a6b-006f-21a9cb3a5db9@gmail.com>
On Sun, 18 Apr 2021, 15:01 François Dumont via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:
> Hi
>
> Ok to backport this to gcc-10 branch ?
>
Yes please, thanks.
> Tested under Linux x86_64.
>
> François
>
>
> On 13/04/21 10:51 pm, redi at gcc dot gnu.org wrote:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99402
> >
> > Jonathan Wakely <redi at gcc dot gnu.org> changed:
> >
> > What |Removed |Added
> >
> ----------------------------------------------------------------------------
> > Summary|[10/11 Regression] |[10 Regression]
> std::copy
> > |std::copy creates |creates _GLIBCXX_DEBUG
> > |_GLIBCXX_DEBUG false |false positive for
> attempt
> > |positive for attempt to |to subscript a
> > |subscript a dereferenceable |dereferenceable
> > |(start-of-sequence) |(start-of-sequence)
> > |iterator |iterator
> >
> > --- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
> > This was fixed on trunk by r11-8100:
> >
> > libstdc++: [_GLIBCXX_DEBUG] Fix management of __dp_sign_max_size [PR
> 99402]
> >
> > __dp_sign precision indicates that we found out what iterator comes
> first or
> > last in the range. __dp_sign_max_size is the same plus it gives the
> information
> > of the max size of the range that is to say the max_size value such that
> > distance(lhs, rhs) < max_size.
> > Thanks to this additional information we are able to tell when a copy of
> n
> > elements
> > to that range will fail even if we do not know exactly how large it is.
> >
> > This patch makes sure that we are properly using this information.
> >
> > libstdc++-v3/ChangeLog:
> >
> > PR libstdc++/99402
> > * include/debug/helper_functions.h
> (__can_advance(_InputIterator,
> > const std::pair<_Diff, _Distance_precision>&, int)): New.
> > (__can_advance(const _Safe_iterator<>&,
> > const std::pair<_Diff, _Distance_precision>&, int)): New.
> > * include/debug/macros.h (__glibcxx_check_can_increment_dist):
> New,
> > use latter.
> > (__glibcxx_check_can_increment_range): Adapt to use latter.
> > (__glibcxx_check_can_decrement_range): Likewise.
> > * include/debug/safe_iterator.h
> > (_Safe_iterator<>::_M_can_advance(const std::pair<_Diff,
> > _Distance_precision>&,
> > int)): New.
> > (__can_advance(const _Safe_iterator<>&,
> > const std::pair<_Diff, _Distance_precision>&, int)): New.
> > * include/debug/safe_iterator.tcc
> > (_Safe_iterator<>::_M_can_advance(const std::pair<_Diff,
> > _Distance_precision>&,
> > int)): New.
> > (_Safe_iterator<>::_M_valid_range(const _Safe_iterator<>&,
> > std::pair<difference_type, _Distance_precision>&, bool)): Adapt
> for
> > __dp_sign_max_size.
> > (__copy_move_a): Adapt to use
> __glibcxx_check_can_increment_dist.
> > (__copy_move_backward_a): Likewise.
> > (__equal_aux): Likewise.
> > * include/debug/stl_iterator.h (__can_advance(const
> > std::reverse_iterator<>&,
> > const std::pair<_Diff, _Distance_precision>&, int)): New.
> > (__can_advance(const std::move_iterator<>&,
> > const std::pair<_Diff, _Distance_precision>&, int)): New.
> > * testsuite/25_algorithms/copy/debug/99402.cc: New test.
> >
>
>
prev parent reply other threads:[~2021-04-18 14:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-99402-19885@http.gcc.gnu.org/bugzilla/>
[not found] ` <bug-99402-19885-WRC4AU1Dpn@http.gcc.gnu.org/bugzilla/>
2021-03-07 21:30 ` [Bug libstdc++/99402] [10/11 " François Dumont
2021-03-11 17:51 ` François Dumont
2021-04-08 13:07 ` Jonathan Wakely
2021-04-09 20:02 ` François Dumont
[not found] ` <bug-99402-19885-PxIZ3sL1KH@http.gcc.gnu.org/bugzilla/>
2021-04-18 13:28 ` [Bug libstdc++/99402] [10 " François Dumont
2021-04-18 14:04 ` Jonathan Wakely [this message]
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