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List:       gcc-fortran
Subject:    Re: [Patch, Fortran] Prevent segfault with dump-*-original for implicit class expressions.
From:       Mikael Morin <mikael.morin () sfr ! fr>
Date:       2015-04-25 21:13:34
Message-ID: 553C037E.3090006 () sfr ! fr
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Hello,

Le 13/03/2015 11:33, Andre Vehreschild a écrit :
> Hi all,
> 
> this is another patch preventing a segfault. This time the segfault occurred,
> when -fdump-(fortran|tree)-original was given with the program having an
> implicit class set. The issue is that the _data component is assumed to be
> present in a BT_CLASS w/o checking and trying to access the unlimited
> polymorphic flag there. The patch fixes this by redirecting the access to the
> flag to the correct position whether the _data component is present or not.
> 
> Building a testcase for this is difficult for me. May be I am just blocked in
> the head there. The issue occurred when trying to dump the
> (fortran|tree)-original of the testcase gfortran.dg/implicit_class_1.f90. So
> one could argue to add the flag to that testcase, but does it pay in contrast
> to the additional effort each time the testsuite is executed? I have added the
> test now, not being happy with it, but having no clue how to do it better.
> 
> Bootstraps and regtests ok on x86_64-linux-gnu/F20.
> 
> Ok, for trunk?
> 

Comments below:

 b/gcc/fortran/symbol.c
> index 32eea21..3379f47 100644
> --- a/gcc/fortran/symbol.c
> +++ b/gcc/fortran/symbol.c

(skipped)

The beginning looks good.
I suggest using 'ts->u.derived->attr.is_class' instead of
'strcmp (ts->u.derived.components->name, "_data") == 0'.
No strong opinion, your choice.


> @@ -4576,13 +4579,14 @@ gfc_type_compatible (gfc_typespec *ts1, gfc_typespec *ts2)
> if (is_derived1 && is_derived2)
> return gfc_compare_derived_types (ts1->u.derived, ts2->u.derived);
> 
> -  if (is_derived1 && is_class2)
> +  if (is_derived1 && is_class2 && ts2->u.derived->components)
> return gfc_compare_derived_types (ts1->u.derived,
> 				      ts2->u.derived->components->ts.u.derived);
> -  if (is_class1 && is_derived2)
> +  if (is_class1 && is_derived2 && ts1->u.derived->components)
> return gfc_type_is_extension_of (ts1->u.derived->components->ts.u.derived,
> 				     ts2->u.derived);
> -  else if (is_class1 && is_class2)
> +  else if (is_class1 && is_class2 && ts1->u.derived->components
> +	   && ts2->u.derived->components)
> return gfc_type_is_extension_of (ts1->u.derived->components->ts.u.derived,
> 				     ts2->u.derived->components->ts.u.derived);
> else

The above change don't seem right.
In the case where the class container is missing, you want to use
"ts->u.derived" instead of "ts->u.derived->components->ts.u.derived",
not skip the procedure call entirely.

> diff --git a/gcc/testsuite/gfortran.dg/implicit_class_1.f90 \
> b/gcc/testsuite/gfortran.dg/implicit_class_1.f90 index 329f57a..fff1f2b 100644
> --- a/gcc/testsuite/gfortran.dg/implicit_class_1.f90
> +++ b/gcc/testsuite/gfortran.dg/implicit_class_1.f90
> @@ -4,6 +4,10 @@
> !
> ! Contributed by Reinhold Bader <Reinhold.Bader@lrz.de>
> 
> +! Add dump-tree-original to check, if the patch preventing a gfortran
> +! segfault is working correctly.
> +! { dg-options "-fdump-tree-original" }
> +
-fdump-tree-original doesn't trigger any bug here.
So use -fdump-fortran-original (I'm not sure the testsuite will like it).

Mikael


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