[ncl-talk] Unable to link to Fortran shared object created with WRAPIT

[Michael Toy]

Hi Dennis,

Thank you for your help.  I understand now to keep things “Fortran 77” in terms of what WRAPIT processes.  In this spirit, I changed my f90 program from a module to just a subroutine by eliminating the “module” statements, and just leaving “mult.f90” as:

subroutine mult(x,y,z)

implicit none

real, intent(in) :: x,y
real, intent(out) :: z

z = x*y

end subroutine mult

Using the same mult.stub file as before, a mult.so file is created and is readable by the NCL — external MLT “./mult.so” — command, and executes just fine.  Hopefully this will work for the actual Fortran code I’m hoping to execute from NCL, which is a WRF physics module (which I won’t call a module for the purposes of WRAPIT).

Thanks again.

Best regards,
Mike




> On May 13, 2018, at 8:27 AM, Dennis Shea <shea at ucar.edu> wrote:
> 
> Hello,
> 
> Once a function/subroutine is placed in a module, two 'things' must be done:
> 
> [1] A module must be compiled prior to its invocation by other program units
> [2] The program unit(s) invoking the function/subroutine contained within a module must apply the USE statement.
> 
> Attached are two fortran codes. Note the module is compiled 1st. 
> Also, a side point, these could be in one file as long as the module is compiled prior to other units. 
> 
> %> gfortran toy_module.f90 test.toy_module.f90
> %> ./a.out
> 
>  z=   6.8999996
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
> Likely, you already know the above .
> However, I thought it should be mentioned for others who might want to do something similar to what you are doing.
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
> OK ... how to accommodate using a subroutine contained within a module from NCL.
> 
> [1] *THE* issue is that NCL's  WRAPIT  understands only f77 syntax. 
> [2] The  'USE' statement is f90. Further, it must/should appear even before an 'implicit none' statement.
> [3] WRAPIT would likely fail (untested if this is true) if the USE statement were encountered between the 'C NCLFORTSTART' and 'C NCLEND' delimiters.
> [4] My opinion is that you must add a 2nd subroutine ... a bit of a nuisance. 
> 
> ---
> In the following, the 77 and 90 suffixes are used to differentiate the program subroutines. They have no language meaning.
> 
> The 1st subroutine [mult77]  contains the WRAPIT recognized delimiters:  'C NCLFORTSTART' and 'C NCLEND'.  WRAPIT will create the necessary infrastructure for argument passing between arguments between NCL  (written in C) and fortran.
> 
> The 2nd subroutine is a valid program unit invokes the 'USE' statement. 
> 
> Again, the USE statement could not be simply added to the 1st subroutine because WRAPIT would not know what to do with it!
> 
> C NCLFORTSTART
>       subroutine mult77(x,y,z)
>       implicit none
>       real x,y,z
> C NCLEND
>       call mult90(x,y,z)
>       return
>       end
> C------------
>       subroutine mult90(x,y,z)
>       use module_mult
>       implicit none
>       real, intent(in)  :: x,y
>       real, intent(out) :: z
> 
>       call mult(x,y,z)
>       return
>       end
> 
> ================
> Test the NCL call to invoke the module. Note the module is compiled 1st.
> 
> %> WRAPIT toy_module.f90 toy_mult7790.f
> 
> This will create 'toy_module.so'
> 
> The following 'toy_test.ncl' contains:
> 
> external TOY_MODULE "./toy_module.so"
> 
> 
>    xNCL = 2.3
>    yNCL = 3.0
>    zNCL = 1e20
>    TOY_MODULE::mult77(xNCL, yNCL, zNCL)  ; interface with f77 which calls f90
>    print("zNCL="+zNCL)
> 
> =====
> %> ncl toy_test.ncl
> 
> (0)    zNCL=6.9
> 
> ==================
> Hopefully, this is somewhat clear.
> 
> Good luck
> 
> On Fri, May 11, 2018 at 3:47 PM, Michael Toy <toy at ucar.edu <mailto:toy at ucar.edu>> wrote:
> Hello,
> 
> I am trying to call a fortran subroutine from an NCL script, and have followed the documentation for “WRAPIT”.  This is my first time trying it.  When I enter the following in NCL:
> ncl 0> external MLT “./mult.so"
> 
> I get the error message:
> warning:An error occurred loading the external file ./mult.so, file not loaded
> ./mult.so: undefined symbol: mult_
> warning:error at line 0
> 
> 
> I’m testing a simple subroutine which multiplies two numbers together.  My Fortran 90 code (mult.f90) is:
> 
> module module_mult
> 
> contains
> 
> subroutine mult(x,y,z)
> 
> implicit none
> 
> real, intent(in) :: x,y
> real, intent(out) :: z
> 
> z = x*y
> 
> end subroutine mult
> 
> end module module_mult
> 
> 
> My “stub” file is:
> C NCLFORTSTART
>       subroutine mult(x,y,z)
>       real x,y,z
> C NCLEND
> 
> 
> When I run “WRAPIT mult.stub mult.f90” it seems to run successfully, and produces the file:
> mult.so
> 
> 
> I am running NCL version 6.4.0 on the following system:
> Linux x86_64 x86_64 x86_64 GNU/Linux
> 
> I know this problem has come up in the NCL users’ forum before, but I’ve not seen how the issue gets resolved.  Your help would be appreciated.  Thanks.
> 
> Best regards,
> Mike
> 
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> <toy_module.f90><test.toy_module.f90><toy_mult7790.f><toy_test.ncl>

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