[Bug fortran/64854] New: No bound check for explicit-shape arrays

[Bug fortran/64854] New: No bound check for explicit-shape arrays

[bugs at stellardeath dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

            Bug ID: 64854
           Summary: No bound check for explicit-shape arrays
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugs at stellardeath dot org

I assumed that the following would be catched by -fcheck=bounds,
array "a" is passed as an explicit-shape array to subroutine
"testsub" with the invalid bounds "n1", "n2":

program test
  use m1
  implicit none

  integer :: n1, n2
  real :: a(1:10)

  ! Setup invalid indices:
  n1 = 1024*1024
  n2 = 1024*1024*2

  call testsub(a, n1, n2)

  contains

    subroutine testsub(a, n1, n2)
      integer :: n1, n2
      real :: a(n1:n2)
      integer :: i

      do i = n1, n2
        a(i) = 0
      end do

    end subroutine

end program

But this happily produces a segfault.


My gfortran version:

#> gfortran-4.9 --version
GNU Fortran (SUSE Linux) 4.9.0
Copyright (C) 2014 Free Software Foundation, Inc.

GNU Fortran comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Fortran
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING


Kind regards,
  Lorenz

[Bug fortran/64854] No bound check for explicit-shape arrays

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2015-01-29
     Ever confirmed|0                           |1

--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Well, you give wrong information to the compiler. How do expect it to handle
your mistake: in testsub -fcheck=bounds checks that n1<=i<=n2 which is the
case. What you ask for is a check that a(n1:n2) is inside a(1:10), AFAIK such
check is not implemented and I don't have any idea about how difficult it is to
implement it.

I am inclined to close tis PR as INVALID or WONTFIX.

[Bug fortran/64854] No bound check for explicit-shape arrays

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

Harald Anlauf <anlauf at gmx dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |anlauf at gmx dot de

--- Comment #3 from Harald Anlauf <anlauf at gmx dot de> ---
(In reply to Dominique d'Humieres from comment #1)
> Well, you give wrong information to the compiler. How do expect it to handle
> your mistake: in testsub -fcheck=bounds checks that n1<=i<=n2 which is the
> case. What you ask for is a check that a(n1:n2) is inside a(1:10), AFAIK
> such check is not implemented and I don't have any idea about how difficult
> it is to implement it.

valgrind detects this issue.

I was expected that the address sanitizer is able to handle it,
but I am getting linking errors on my system.

> I am inclined to close tis PR as INVALID or WONTFIX.

The right way to fix the problem is to fix the program
by using an appropriate programming style.  Writing

      real    :: a(n1:)   ! not:  real :: a(n1:n2)

one gets the expected check:

At line 22 of file pr64854.f90
Fortran runtime error: Index '1048586' of dimension 1 of array 'a' above upper
bound of 1048585

Backtrace for this error:
  + function testsub.3321 (0x80486A4)
    from file pr64854.f90
  + in the main program
    from file pr64854.f90
  + /lib/libc.so.6(__libc_start_main+0xf3) [0xb7424003]

I also suggest to close the PR.

[Bug fortran/64854] No bound check for explicit-shape arrays

[bugs at stellardeath dot org]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

--- Comment #4 from Lorenz Hüdepohl <bugs at stellardeath dot org> ---
> The right way to fix the problem is to fix the program
> by using an appropriate programming style.  Writing
>
>      real    :: a(n1:)   ! not:  real :: a(n1:n2)
>
> one gets the expected check

I realize that, and when I write my own code I would never
use such a construction. However, sometimes one is burdened
with existing code in which small treasures such as this kind
of bug are hidden.

I was hoping that with -fcheck=bounds I could find this.

If the code was correct already there would be no need for
any kind of runtime checks, right?
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd351

emsr at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |emsr at gcc dot gnu.org

--- Comment #1 from emsr at gcc dot gnu.org ---
Created attachment 34621
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id4621&actioníit
Just keep trying in generate_canonical...

I'm going to test this...

Just keep looping until you get less that one in generate_canonical.

[Bug fortran/64854] No bound check for explicit-shape arrays

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

--- Comment #5 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Note that the error is detected if the code is compiled with
-fsanitize=address. And IMO the right way to use the array in a 'contains' is
a(:) (for which -fcheck=bounds works).

[Bug fortran/64854] No bound check for explicit-shape arrays

[anlauf at gmx dot de]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

--- Comment #6 from Harald Anlauf <anlauf at gmx dot de> ---
(In reply to Lorenz Hüdepohl from comment #4)
> > The right way to fix the problem is to fix the program
> > by using an appropriate programming style.  Writing
> >
> >      real    :: a(n1:)   ! not:  real :: a(n1:n2)
> >
> > one gets the expected check
> 
> I realize that, and when I write my own code I would never
> use such a construction. However, sometimes one is burdened
> with existing code in which small treasures such as this kind
> of bug are hidden.
> 
> I was hoping that with -fcheck=bounds I could find this.

As Dominique pointed out, this is not the way bounds checking
is usually implemented.  Checks are local.

Fortran allows you to intentionally bypass all checks by
using explicit size specifications.  You can even use different
ranks of the array in the caller and the callee.  If you lie to
the compiler in that situation about proper sizes, then you lose.

> If the code was correct already there would be no need for
> any kind of runtime checks, right?

Right.  But IMHO bounds check are not applicable here.
Try other compilers.  I'd expect them to behave similarly.

Use valgrind or -fsanitize=address to detect this kind of
memory problems.  (I solved my linking problem by updating
to current trunk).
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd803

--- Comment #6 from Dodji Seketeli <dodji at gcc dot gnu.org> ---
Created attachment 34622
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id4622&actioníit
Refined candidate fix patch with regression test and cover letter

I have successfully tested this refined patch locally and I am
currently bootstrapping it.  I'll submit it right away if it passes
bootstrap.  Thanks for testing the previous one!

[Bug fortran/64854] No bound check for explicit-shape arrays

[bugs at stellardeath dot org]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

--- Comment #7 from Lorenz Hüdepohl <bugs at stellardeath dot org> ---
> Use valgrind or -fsanitize=address to detect this kind of
> memory problems.

I can live with that, thanks for your comments!
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd670

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #34487|0                           |1
        is obsolete|                            |

--- Comment #5 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Created attachment 34627
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id4627&actioníit
Updated test case (part 1/2): [main file] compile with g++ -fsanitize=vptr

[Bug fortran/64854] No bound check for explicit-shape arrays

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64854

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #8 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Per comment 7, closing as WONTFIX.