Cannot compile/run on macOS

[quinntpratt]

Hello, I've been following along in your book "Modern Fortran" to learn the basics of the language.
I made it all the way to chapter 11 (great book by the way!) and now I've encountered an issue with the c-binding business...

I was able to install/compile libdill with no errors following the commands given in section 11.1.2.
However, the initial versions of the files: mod_dill.f90, and server.f90 given in listings 11.2 and 11.3 in the textbook don't work for me.
I also tried jumping to the end of the chapter, cloning this repo, and following the instructions in the readme file that didn't work either (with a similar error).

I am able to compile both module/program with no issue,
>> gfortran -c mod_dill.f90 server.f90
which produces the binary files... but when it comes to linking them with,
>> gfortran mod_dill.o server.o -o server
I'm hit with:

Undefined symbols for architecture x86_64:
  "_dill_ipaddr_local", referenced from:
      _MAIN__ in server.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status

which suggests a leading underscore is being added to the libdill function dill_ipaddr_local at compile time? (I don't know C really at all), and thus bind(c,name="dill_ipaddr_local") can't find its binding?

In an effort to track this down further I wrote a simple hello_world.c program with a function to print "Hello world" and that encountered the same issue with the underscores unless I compile and link the c program with gfortran as well (instead of gcc)... but I'm not sure how I can apply this information to the compilation/binding of libdill.

Any help with this would be amazing - and I'm sure others working on macOS would benefit too.
Thank you.

Other info:
>> gfortran --version gives,

GNU Fortran (GCC) 11.2.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

My machine is a Macbook Pro (with intel CPU) running macOS 11.7.2 (big sur)

[milancurcic]

Thanks @quinntpratt! I don't know why that is. I don't own a Mac and haven't used it before.

What I think this

Undefined symbols for architecture x86_64:
  "_dill_ipaddr_local", referenced from:
      _MAIN__ in server.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status

suggests is that server.o tries to look for _dill_ipaddr_local but it's not found at link time. In other words, I think this name may be modified at the Fortran program side rather than the libdill side.

What does nm libdill.a | grep ipaddr_local output for you?

[quinntpratt]

Hi @milancurcic,

nm libdill.a | grep ipaddr_local

results in,

                 U _dill_ipaddr_local
00000000000000b0 T _dill_ipaddr_local
0000000000000960 t _dill_ipaddr_local.cold.1
00000000000009a0 t _dill_ipaddr_local.cold.2
00000000000009e0 t _dill_ipaddr_local.cold.3
0000000000000a20 t _dill_ipaddr_local.cold.4
0000000000000a60 t _dill_ipaddr_local.cold.5

[milancurcic]

OK, thanks. I don't think the underscore is our problem. I'll do some searching.

[jnorrid]

FYI: libdill now has a homebrew formula for macOS: https://formulae.brew.sh/formula/libdill

macOS users should not need to build it manually, but have the option to simply issue:

brew install libdill