[petsc-users] fortran INTENT with petsc object gives segfault after upgrade from 3.8.4 to 3.10.2

[Smith, Barry F.]

> On Oct 22, 2018, at 4:33 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:
> 
> Thanks Barry and Matt, it makes sense if rr is a pointer instead
> of an allocatable. So:
> 
>  Vec, POINTER, INTENT(in) :: rr_system
> 
> would be the proper way, right?

   Yes

> 
> And out of curiosity, why did petsc-3.8.4 tolerate my wrong
> INTENT(out)?

   I think it is a compiler optimization that doesn't pass in the value for intent(out) hence the crash when it is used.
> 
> Chris
> 
> 
> 
> dr. ir. Christiaan Klaij  | Senior Researcher | Research & Development
> MARIN | T +31 317 49 33 44 | mailto:C.Klaij at marin.nl | http://www.marin.nl
> 
> MARIN news: http://www.marin.nl/web/News/News-items/Seminar-Scheepsbrandstof-en-de-mondiale-zwavelnorm-2020.htm
> 
> ________________________________________
> From: Smith, Barry F. <bsmith at mcs.anl.gov>
> Sent: Friday, October 19, 2018 10:26 PM
> To: Klaij, Christiaan
> Cc: petsc-users at mcs.anl.gov
> Subject: Re: [petsc-users] fortran INTENT with petsc object gives segfault after upgrade from 3.8.4 to 3.10.2
> 
>> On Oct 19, 2018, at 9:37 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:
>> 
>> As far as I (mis)understand fortran, this is a data protection
>> thing: all arguments are passed in from above but the subroutine
>> is only allowed to change rr and ierr, not aa and xx (if you try,
>> you get a compiler warning).
> 
>      The routine is not allowed to change rr (it is only allowed to change the values "inside" rr) that is why it needs to be intent in or inout. Otherwise the compiler can optimize and not pass down the value of the rr pointer to the subroutine since by declaring as it as out the compiler thinks your subroutine is going to set is value.
> 
>    Barry
> 
> 
>> That's why I find it very odd to
>> give an intent(in) to rr. But I've tried your suggestion anyway:
>> both intent(in) and intent(inout) for rr do work! Can't say I
>> understand though.
>> 
>> Below's a small example of what I was expecting. Change rr to
>> intent(in) and the compiler complains.
>> 
>> Chris
>> 
>> $ cat intent.f90
>> program intent
>> 
>> implicit none
>> 
>> real, allocatable :: aa(:), xx(:), rr(:)
>> integer :: ierr
>> 
>> allocate(aa(10),xx(10),rr(10))
>> 
>> aa = 1.0
>> xx = 2.0
>> 
>> call matmult(aa,xx,rr,ierr)
>> 
>> print *, rr(1)
>> print *, ierr
>> 
>> deallocate(aa,xx,rr)
>> 
>> contains
>> 
>>   subroutine matmult(aa,xx,rr,ierr)
>>     real, intent(in) :: aa(:), xx(:)
>>     real, intent(out):: rr(:)
>>     integer, intent(out) :: ierr
>>     rr=aa*xx
>>     ierr=0
>>   end subroutine matmult
>> 
>> end program intent
>> $ ./a.out
>>  2.000000
>>          0
>> 
>> 
>> 
>> 
>> dr. ir. Christiaan Klaij  | Senior Researcher | Research & Development
>> MARIN | T +31 317 49 33 44 | mailto:C.Klaij at marin.nl | http://www.marin.nl
>> 
>> MARIN news: http://www.marin.nl/web/News/News-items/Seminar-Scheepsbrandstof-en-de-mondiale-zwavelnorm-2020.htm
>> 
>> ________________________________________
>> From: Smith, Barry F. <bsmith at mcs.anl.gov>
>> Sent: Friday, October 19, 2018 2:32 PM
>> To: Klaij, Christiaan
>> Cc: petsc-users at mcs.anl.gov
>> Subject: Re: [petsc-users] fortran INTENT with petsc object gives segfault after upgrade from 3.8.4 to 3.10.2
>> 
>>  Hmm, the intent of all three first arguments should be in since they are passed in from the routine above. Does it work if you replace
>> 
>>> Vec, INTENT(out) :: rr_system
>> 
>> with
>> 
>>> Vec, INTENT(in) :: rr_system
>> 
>> ?
>> 
>>   Barry
>> 
>> 
>>> On Oct 19, 2018, at 3:51 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:
>>> 
>>> I've recently upgraded from petsc-3.8.4 to petsc-3.10.2 and was
>>> surprised to find a number of segmentation faults in my test
>>> cases. These turned out to be related to user-defined MatMult and
>>> PCApply for shell matrices. For example:
>>> 
>>> SUBROUTINE systemMatMult(aa_system,xx_system,rr_system,ierr)
>>> Mat, INTENT(in) :: aa_system
>>> Vec, INTENT(in) :: xx_system
>>> Vec, INTENT(out) :: rr_system
>>> PetscErrorCode, INTENT(out) :: ierr
>>> ...
>>> END
>>> 
>>> where aa_system is the shell matrix. This code works fine with
>>> 3.8.4 and older, but fails with 3.10.2 due to invalid
>>> pointers (gdb backtrace shows failure of VecSetValues due to
>>> invalid first argument). After replacing by:
>>> 
>>> SUBROUTINE mass_momentum_systemMatMult(aa_system,xx_system,rr_system,ierr)
>>> Mat :: aa_system
>>> Vec :: xx_system
>>> Vec :: rr_system
>>> PetscErrorCode :: ierr
>>> ...
>>> END
>>> 
>>> everything's fine again. So clearly something has changed since
>>> 3.8.4 that now prevents the use of INTENT in Fortran (at least
>>> using intel 17.0.1 compilers). Any reason for this?
>>> 
>>> Chris
>>> 
>>> 
>>> dr. ir. Christiaan Klaij  | Senior Researcher | Research & Development
>>> MARIN | T +31 317 49 33 44 | mailto:C.Klaij at marin.nl | http://www.marin.nl
>>> 
>>> MARIN news: http://www.marin.nl/web/News/News-items/ReFRESCO-successfully-coupled-to-ParaView-Catalyst-for-insitu-analysis-1.htm
>>> 
>> 
>