From: Eric Wong <normalperson@...>
Date: 2012-06-25T13:24:38+09:00
Subject: Re: have_func() does not find a func in the given .h file

I単aki Baz Castillo <ibc@aliax.net> wrote:
> Hi, in my extconf.rb I check some Ruby functions (since I'm trying
> Ruby trunk with rvm). I understand that the method have_func() does
> not look into Ruby sources within my .rvm/ directory, so I call the
> method by passing the exact file as argument:
> 
> 
> /home/ibc/.rvm/repos/ruby$ grep ruby_thread_has_gvl_p vm_core.h
> int ruby_thread_has_gvl_p(void);

This is a private function, Ruby uses gcc -fvisibility=hidden to
hide them and only exposes certain functions in vm_core.h
via "#pragma GCC visibility ..."

> But have_func() does not find it:

ave_func() doesn't parse C headers to find functions, but instead
tries to link a C program to find the function.

> irb> require "mkmf"
> irb> have_func("ruby_thread_has_gvl_p", "/home/ibc/.rvm/repos/ruby/vm_core.h")
> checking for ruby_thread_has_gvl_p() in
> /home/ibc/.rvm/repos/ruby/vm_core.h... no
> 
> Am I doint something wrong?

You're relying too much on ever-changing Ruby internals :)