[petsc-users] Segfaults when calling some PETSc functions in Fortran with variables initialized to PETSC_NULL_XX

[Matthew Knepley]

On Mon, Jul 21, 2025 at 7:49 AM Mark Adams <mfadams at lbl.gov> wrote:

> Hi Robert, [I don't see this message to PETSc users in my email so cc'ing
> manually]
>
> This is odd, something is messed up.
> These NULL things are certainly 0 and the initial value of these objects
> is not defined by the compiler, and they could be 0 in some cases.
>

Hi Robert,

I am not the Fortran expert, but I believe that passing PETSC_NULL_XXX to a
creation routine is not correct. Here is my logic.

In the wrapper, PETSC_NULL_XXX is converted to a NULL pointer (_not_ a
pointer whose value is NULL). Thus KSPCreate would try to set a NULL
pointer and you get the SEGV. I think it may have worked before because
this was not automated, so these routines did not check for PETSC_NULL_XXX
since it is not a case handled by the C function.

Could you try without initializing? Barry would have to tell you what they
should be initialized to.

  Thanks,

     Matt


> Others are more up on the new Fortran stuff, but I would do a clean build
> of PETSc (rm -fr arch...), and turn debugging on.
> You will get a stack trace and it might find something and give a useful
> error message, or "fix" the problem mysteriously.
>
> You could put a print statement in before these are initialized to see
> what *was* in it that you are clobbering.
>
> Mark
>
>
> On Sun, Jul 20, 2025 at 10:33 AM Robert Hager <rhager at pppl.gov> wrote:
>
>> FYI
>>
>> ---------- Forwarded message ---------
>> From: Robert Hager <rhager at pppl.gov>
>> Date: Sun, Jul 20, 2025 at 10:32 AM
>> Subject: Segfaults when calling some PETSc functions in Fortran with
>> variables initialized to PETSC_NULL_XX
>> To: <petsc-users at mcs.anl.gov>
>>
>>
>> Hello,
>>
>> I am in the process of updating my code to use PETSc versions >=3.22. (I
>> am using v3.22.3 compiled with GCC on Perlmutter-CPU at NERSC for debugging
>> at this time.) After updating all the Fortran function calls that have
>> changed from v3.21 to v3.22 I am now getting segfaults in some PETSc
>> routines. In the two instances I was able to identify, the problem seems to
>> be calling the PETSc function with a PETSc variable that has been
>> initialized to PETSC_NULL_XX:
>>
>> solver%rhs2_mat = PETSC_NULL_MAT
>>
>> [...]
>>
>> *call* MatDuplicate(solver%Amat,MAT_DO_NOT_COPY_VALUES,solver%rhs2
>> _mat,ierr)
>>
>> --> Segfault
>>
>>
>> solver%ksp      = PETSC_NULL_KSP
>>
>> [...]
>>
>> *call* KSPCreate(solver%comm,solver%ksp,ierr)
>>
>> --> Segfault
>>
>>
>> When I comment out the assignments to PETSC_NULL_XX in the above
>> examples, the code works just fine.
>>
>> Is this the intended behavior or a bug that you might have fixed by now?
>>
>> Best,
>>
>> Robert
>>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

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