Problem with C calling Fortran subroutine embedded in a dynamic library

[sallestaing]

Hi all,

I am encountering a problem when running a binary under Linux: symbol lookup error.

The binary is obtained through a C main program which calls a subroutine defines in a fortran shared library.

To build the fortran shared library I used this process:

1- build the fortran source objects

ifort -fPIC -g -c -m64 -heap-arrays -O3 -ipo prog1.f90

ifort -fPIC -g -c -m64 -heap-arrays -O3 -ipo prog2.f90

...

ifort -fPIC -g -c -m64 -heap-arrays -O3 -ipo prog13.f90

ifort -fPIC -g -c -m64 -heap-arrays -O3 -ipo prog14.f90

2- Create the shared library with object files

ifort -shared -Wl,-soname,libmylib.so.1 -o libmylib.so.1.0.1 prog1.o prog2.o ...prog13.o prog14.o -lc

3- Export Library Path.

export LD_LIBRARY_PATH=$HOME/Work/myfolder/lib:$LD_LIBRARY_PATH

I've then created a fortran program that reads a fortran subroutine (called fortsub in the next example) defines in the shared library

Here is the program in fortran main.f90:

------------------------

program main

implicit none

! local variables

integer :: m

character(len=128):: finput

! get name of experiment from the argument list and create file names

m=iargc()

finput=' '

if(m.lt.1) then

write(6,*)'use: myprog '

stop

else

call getarg(1,finput) ! get experiment file name

end if

call fortsub(finput)

end

------------------------

Finally I've created the executable using the following :

> ifort -m64 -heap-arrays -O3 -ipo -o bin/myprog main.f90 lib/libmylib.so.1 -I/$HOME/Work/myfolder/modules/

I've tried the obtained binary and it works fine.

However, for distribution purpose, I would like to use a C program instead of a fortran one to call the subroutine.

Here is the C program main.c:

------------------------

#include

#include

extern void fortsub_(char*,long int);

int main(int argc, char *argv[])

{

if ( argc != 2 )

printf("use: %s \\n",argv[0]) ;

else {

long int leng = strlen(argv[1]);

fortsub_(argv[1], leng);

}

return 0;

}

------------------------

I've then compiled it using :

> icc -m64 -heap-arrays -O3 -ipo -o bin/myprog main.c lib/libmylib.so.1 -I/$HOME/Work/myfolder/modules/ -L/opt/intel_fc/10.0.023/lib/ -lifcore -limf

During compilation everything works fine however when I launch the binary I've got the following error:

>./bin/myprog ../test/example1.input

./bin/myprog: symbol lookup error: ./bin/myprog: undefined symbol: fortsub_

I've check the library dependencies as well as the binary and it sounds like nothing missing:

> ldd lib/libmylib.so.1

linux-gate.so.1 => (0xa000000000000000)

libc.so.6.1 => /lib/libc.so.6.1 (0x2000000800730000)

libifport.so.6 => /opt/intel_fc/10.0.023/lib/libifport.so.6 (0x2000000800980000)

libifcore.so.6 => /opt/intel_fc/10.0.023/lib/libifcore.so.6 (0x20000008009dc000)

libimf.so.6 => /opt/intel_cc/10.0.023/lib/libimf.so.6 (0x2000000800bcc000)

libm.so.6.1 => /lib/libm.so.6.1 (0x2000000800ea0000)

libintlc.so.6 => /opt/intel_cc/10.0.023/lib/libintlc.so.6 (0x2000000800f70000)

libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x2000000800fa4000)

libdl.so.2 => /lib/libdl.so.2 (0x2000000800fc4000)

/lib/ld-linux-ia64.so.2 (0x2000000800000000)

libunwind.so.7 => /lib/libunwind.so.7 (0x2000000800fdc000)

> ldd bin/myprog

linux-gate.so.1 => (0xa000000000000000)

libmylib.so.1 => /home/user/Work/myfolder/lib/libmylib.so.1 (0x200000000004c000)

libifcore.so.6 => /opt/intel_fc/10.0.023/lib/libifcore.so.6 (0x2000000000718000)

libimf.so.6 => /opt/intel_fc/10.0.023/lib/libimf.so.6 (0x2000000000908000)

libm.so.6.1 => /lib/libm.so.6.1 (0x2000000000bf0000)

libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x2000000000cc0000)

libc.so.6.1 => /lib/libc.so.6.1 (0x2000000000ce0000)

libdl.so.2 => /lib/libdl.so.2 (0x2000000000f30000)

libunwind.so.7 => /lib/libunwind.so.7 (0x2000000000f48000)

libifport.so.6 => /opt/intel_fc/10.0.023/lib/libifport.so.6 (0x2000000000f94000)

libintlc.so.6 => /opt/intel_fc/10.0.023/lib/libintlc.so.6 (0x2000000000ff0000)

/lib/ld-linux-ia64.so.2 (0x2000000000000000)

Do you have any ideas on what is going on here? Apparently there is a linker error, am I wrong?

It is the first time I try this kind of coupling between fortran and C so any advise will be very helpfull!

Cheers,

Tristan

[eliosh]

We have to guess how fortsub was declared. Did you use BIND ?

[sallestaing]

Hi eliosh,

Thanks for your answer, actually I have defined fortsub

subroutine fortsub(inputfile)

use mod1

use mod2

...

end subroutine fortsub

Do I need to use BIND to define it?

Cheers

Tristan

[eliosh]

Tristan,

My experience with Fortran is quite limited. However, If I understand correctly, the best way would be to use the *standard* C interoperability features of modern Fortran. In this case you should use BIND(C) in your function definition and use *interoperable* inputs/outputs. I also think that your approach is also possible, but you must take care of the different mangling conventions used in C and Fortran. In C, the compiler usually adds an underscore to the end of symbol. In Fortran, if I remember correctly, it is not standardized, you should either search the documentation or run 'nm' on your object file to see what you get.