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From: "xin.liu@compiler-dev.com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/97920] [FINAL] -O2 segment fault due to extend derive type's member being partially allocated
Date: Wed, 16 Dec 2020 00:30:39 +0000 [thread overview]
Message-ID: <bug-97920-4-TArjwhTDfC@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-97920-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97920
--- Comment #5 from xin liu <xin.liu@compiler-dev.com> ---
(In reply to Paul Thomas from comment #2)
> (In reply to Martin Liška from comment #1)
> > Confirmed with valgrind. At least as old as 4.9.0.
>
> Hi,
>
> From a quick perusal of the standard, I find in F2003 16.4.2.1:
>
> "Unless a pointer is initialized (explicitly or by default), it has an
> initial association status of undefined. A pointer may be initialized to
> have an
> association status of disassociated".
>
> In your testcase, the status of b%b is undefined and so the compiler can do
> anything it wants with it, including segfaulting. I think therefore that you
> should initialize the derived types in your application as follows:
>
> type t1
> real, dimension(:), pointer :: a => NULL ()
> contains
> final :: t1f
> end type
>
> type, extends(t1) :: t2
> real, dimension(:), pointer :: b => NULL ()
> contains
> final :: t2f
> end type
>
> This clears the valgrind error "Conditional jump or move depends on
> uninitialised value(s)". Also the finalization is invoked so that the
> programme completes with zero memory allocation,
>
> To my surprise (probably due to standard ignorance), leaving the declared
> type declarations as you have them, and declaring 'b' as
>
> type(t2) :: b = t2 (NULL(), NULL())
>
> clears the valgrind fault but no finalization occurs. I notice that
> finalization does not occur if an entity has the save attribute. gfortran
> assigns 'b' the IMPLICIT-SAVE attribute, which is why the finalization does
> not occur. I have been unable to find whether or not this is conforming.
>
> However, initializing 'b' in an assignment:
> b = t2(NULL(), NULL())
>
> clears the valgrind fault and results in the deallocation of memory. This
> confirms my suspicion about the save attribute.
>
> In conclusion, I do not believe that this is a bug. If you do not use
> pointers as pointers, make them allocatable instead. These are automatically
> nullified on entry into scope.
>
> Thanks for the report by the way!
>
> Paul
I get it, Thanks for your explain.
prev parent reply other threads:[~2020-12-16 0:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 2:08 [Bug fortran/97920] New: " xin.liu@compiler-dev.com
2020-11-20 7:35 ` [Bug fortran/97920] " marxin at gcc dot gnu.org
2020-12-08 17:05 ` pault at gcc dot gnu.org
2020-12-12 13:58 ` tkoenig at gcc dot gnu.org
2020-12-16 0:27 ` xin.liu@compiler-dev.com
2020-12-16 0:30 ` xin.liu@compiler-dev.com [this message]
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