I'm calling (external) subroutine Objee from within another subroutine (FindVee):
subroutine FindVee(EVone,Vw0,Ve,Fye)
use nag_library, only: nag_wp
use My_interface_blocks, only: Objee
...
implicit none
real(kind=nag_wp) :: apmax, Val
...
call Objee(apmax,Val)
write(*,*) 'After Objee', apmax, Val
...
end subroutine FindVee
Subroutine Objee is:
subroutine Objee(ap,V)
use nag_library, only: nag_wp
...
implicit none
real(kind=nag_wp), intent(in) :: ap
real(kind=nag_wp), intent(out):: V
...
V = U(x,sigma) + beta*piy*yhat1(Nav*(Nav+1)/2) + &
& beta*eta*(1.0e0-piy)*yhat2(Nav*(Nav+1)/2)
V = - V
write(*,*) 'Exit Objee', ap, V
end subroutine Objee
Running the code like this, produces the following print on screen:
Exit Objee 0.0000000000000000 9997.5723796583643
Program received signal SIGBUS: Access to an undefined portion of a memory object.
Backtrace for this error:
#0 0x7FAA7ADFF7D7
#1 0x7FAA7ADFFDDE
#2 0x7FAA7A533FEF
#3 0x423B29 in findvee_Program received signal SIGSEGV: Segmentation fault - invalid memory reference.
Backtrace for this error:
#0 0x7FAA7ADFF7D7
#1 0x7FAA7ADFFDDE
#2 0x7FAA7A533FEF
#3 0x7FAA7A0B9BA0
#4 0x7FAA7A0BAEFD
#5 0x7FAA7ADFF7D7
#6 0x7FAA7ADFFDDE
#7 0x7FAA7A533FEF
#8 0x423B29 in findvee_ Segmentation fault (core dumped)
I'm using gfortran 4.8.1, using the following options: -fopenmp -fcheck=all -fcheck=bounds -Wall -Wimplicit-interface -Wimplicit-procedure. The compiler doesn't show any warnings.
After a week of trying all sorts of things and scanning half the internet for a clue of what was happening, I thought I'd print the shape of V in Objee and see what fortran gave me- somehow it turns out it solves the problem:
subroutine Objee(ap,V)
...
write(*,*) 'Exit Objee', ap, V, shape(V)
end subroutine Objee
produces the following on screen:
Exit Objee 0.0000000000000000 9997.5723796583643
After Objee 0.0000000000000000 9997.5723796583643
Magic! Everything works and it seems like everything's right. Could somebody explain to me what's going on here? And also, how I can solve whatever was going on without printing shape(V) on screen with every call to Objee (which will be in the thousands...)
After running valgrind ./programa --leak-check=full, I obtain the following output:
==2784== Invalid write of size 8
==2784== at 0x423B3F: findvee_ (FindVee.f95:66)
==2784== by 0x8: ???
==2784== Address 0x7ffffffffffffda8 is not stack'd, malloc'd or (recently) free'd
==2784==
Program received signal SIGSEGV: Segmentation fault - invalid memory reference.
Backtrace for this error:
#0 0x4E4D7D7
#1 0x4E4DDDE
#2 0x56A3FEF
#3 0x423B3F in findvee_ at FindVee.f95:66
==2784== Invalid read of size 8
==2784== at 0x5C7FBA0: ??? (in /lib/x86_64-linux-gnu/libgcc_s.so.1)
==2784== by 0x5C80EFD: _Unwind_Backtrace (in /lib/x86_64-linux-gnu/libgcc_s.so.1)
==2784== by 0x4E4D7D7: _gfortran_backtrace (in /usr/lib/x86_64-linux-gnu/libgfortran.so.3.0.0)
==2784== by 0x4E4DDDE: ??? (in /usr/lib/x86_64-linux-gnu/libgfortran.so.3.0.0)
==2784== by 0x56A3FEF: ??? (in /lib/x86_64-linux-gnu/libc-2.17.so)
==2784== by 0x423B3E: findvee_ (FindVee.f95:64)
==2784== by 0x8: ???
==2784== Address 0x8000000000000008 is not stack'd, malloc'd or (recently) free'd
==2784==
==2784==
==2784== Process terminating with default action of signal 11 (SIGSEGV)
==2784== General Protection Fault
==2784== at 0x5C7FBA0: ??? (in /lib/x86_64-linux-gnu/libgcc_s.so.1)
==2784== by 0x5C80EFD: _Unwind_Backtrace (in /lib/x86_64-linux-gnu/libgcc_s.so.1)
==2784== by 0x4E4D7D7: _gfortran_backtrace (in /usr/lib/x86_64-linux-gnu/libgfortran.so.3.0.0)
==2784== by 0x4E4DDDE: ??? (in /usr/lib/x86_64-linux-gnu/libgfortran.so.3.0.0)
==2784== by 0x56A3FEF: ??? (in /lib/x86_64-linux-gnu/libc-2.17.so)
==2784== by 0x423B3E: findvee_ (FindVee.f95:64)
==2784== by 0x8: ???
==2784==
==2784== HEAP SUMMARY:
==2784== in use at exit: 3,859 bytes in 20 blocks
==2784== total heap usage: 157 allocs, 137 frees, 300,126 bytes allocated
==2784==
==2784== LEAK SUMMARY:
==2784== definitely lost: 58 bytes in 1 blocks
==2784== indirectly lost: 0 bytes in 0 blocks
==2784== possibly lost: 0 bytes in 0 blocks
==2784== still reachable: 3,801 bytes in 19 blocks
==2784== suppressed: 0 bytes in 0 blocks
==2784== Rerun with --leak-check=full to see details of leaked memory
==2784==
==2784== For counts of detected and suppressed errors, rerun with: -v
==2784== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 2 from 2)
Segmentation fault (core dumped)
Lines 64 and 66 (to which the output points) are:
64 call Objee(apmax,Val)
66 write(*,*) 'After Objee', apmax, Val
As an inexperienced user, I don't really understand how this helps me in any way, other than pointing to the portion of my code I already suspected was causing the crash. What am I missing here?
