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-   -   Static functions, extensions, linkage (http://www.velocityreviews.com/forums/t831988-static-functions-extensions-linkage.html)

Daniel Berger 08-02-2006 12:05 AM

Static functions, extensions, linkage
 
Hi,

How do you get at a static function from within a C extension? I tried
this snippet where I attempt to use flo_plus from numeric.c:

/* foo.c */
#include <ruby.h>

extern VALUE flo_plus(VALUE, VALUE);

static VALUE foo_test(VALUE x, VALUE y){
return flo_plus(x, y);
}

void Init_foo(){
VALUE cFoo = rb_define_class("Foo", rb_cObject);
rb_define_method(cFoo, "test", foo_test, 2);
}

# test.rb
$:unshift Dir.pwd
require 'foo'
f = Foo.new
f.test

This result is:

ruby: symbol lookup error:
/home/djberge/programming/ruby/extensions/foo.so: undefined symbol:
flo_plus

I tried linking explicitly against -lruby but that didn't help.

Regards,

Dan


Timothy Hunter 08-02-2006 12:28 AM

Re: Static functions, extensions, linkage
 
Daniel Berger wrote:
> Hi,
>
> How do you get at a static function from within a C extension? I tried
> this snippet where I attempt to use flo_plus from numeric.c:
>
> /* foo.c */
> #include <ruby.h>
>
> extern VALUE flo_plus(VALUE, VALUE);
>
> static VALUE foo_test(VALUE x, VALUE y){
> return flo_plus(x, y);
> }
>
> void Init_foo(){
> VALUE cFoo = rb_define_class("Foo", rb_cObject);
> rb_define_method(cFoo, "test", foo_test, 2);
> }
>
> # test.rb
> $:unshift Dir.pwd
> require 'foo'
> f = Foo.new
> f.test
>
> This result is:
>
> ruby: symbol lookup error:
> /home/djberge/programming/ruby/extensions/foo.so: undefined symbol:
> flo_plus
>
> I tried linking explicitly against -lruby but that didn't help.
>
> Regards,
>
> Dan
>
>
>

Where is 'flo_plus' defined?


Daniel Berger 08-02-2006 12:51 AM

Re: Static functions, extensions, linkage
 

Timothy Hunter wrote:
> Daniel Berger wrote:
> > Hi,
> >
> > How do you get at a static function from within a C extension? I tried
> > this snippet where I attempt to use flo_plus from numeric.c:
> >
> > /* foo.c */
> > #include <ruby.h>
> >
> > extern VALUE flo_plus(VALUE, VALUE);
> >
> > static VALUE foo_test(VALUE x, VALUE y){
> > return flo_plus(x, y);
> > }
> >
> > void Init_foo(){
> > VALUE cFoo = rb_define_class("Foo", rb_cObject);
> > rb_define_method(cFoo, "test", foo_test, 2);
> > }
> >
> > # test.rb
> > $:unshift Dir.pwd
> > require 'foo'
> > f = Foo.new
> > f.test
> >
> > This result is:
> >
> > ruby: symbol lookup error:
> > /home/djberge/programming/ruby/extensions/foo.so: undefined symbol:
> > flo_plus
> >
> > I tried linking explicitly against -lruby but that didn't help.
> >
> > Regards,
> >
> > Dan
> >
> >
> >

> Where is 'flo_plus' defined?


In numeric.c. Note that it *builds* fine, it just doesn't *run*.

Regards,

Dan


Timothy Hunter 08-02-2006 01:05 AM

Re: Static functions, extensions, linkage
 
Daniel Berger wrote:
> Timothy Hunter wrote:
>
>> Daniel Berger wrote:
>>
>>> Hi,
>>>
>>> How do you get at a static function from within a C extension? I tried
>>> this snippet where I attempt to use flo_plus from numeric.c:
>>>
>>> /* foo.c */
>>> #include <ruby.h>
>>>
>>> extern VALUE flo_plus(VALUE, VALUE);
>>>
>>> static VALUE foo_test(VALUE x, VALUE y){
>>> return flo_plus(x, y);
>>> }
>>>
>>> void Init_foo(){
>>> VALUE cFoo = rb_define_class("Foo", rb_cObject);
>>> rb_define_method(cFoo, "test", foo_test, 2);
>>> }
>>>
>>> # test.rb
>>> $:unshift Dir.pwd
>>> require 'foo'
>>> f = Foo.new
>>> f.test
>>>
>>> This result is:
>>>
>>> ruby: symbol lookup error:
>>> /home/djberge/programming/ruby/extensions/foo.so: undefined symbol:
>>> flo_plus
>>>
>>> I tried linking explicitly against -lruby but that didn't help.
>>>
>>> Regards,
>>>
>>> Dan
>>>
>>>
>>>
>>>

>> Where is 'flo_plus' defined?
>>

>
> In numeric.c. Note that it *builds* fine, it just doesn't *run*.
>
> Regards,
>
> Dan
>
>
>

I see. Since flo_plus has static linkage in numeric.c you can't call it
from your extension. It builds okay because you supplied a declaration
for it, and it links okay because Linux does lazy linking (that is,
external symbols aren't resolved until the .so gets loaded), but it
won't run because there's no external definition of flo_plus to match
your external reference.

You'll have to use rb_funcall to call "+".




Logan Capaldo 08-02-2006 04:03 AM

Re: Static functions, extensions, linkage
 

On Aug 1, 2006, at 8:10 PM, Daniel Berger wrote:

> Hi,
>
> How do you get at a static function from within a C extension? I
> tried
> this snippet where I attempt to use flo_plus from numeric.c:


I could be wrong, but I believe the entire purpose of a static
function is to _not_ be get at able from other code (sort of like
private in ruby).


Vincent Fourmond 08-02-2006 04:42 AM

Re: Static functions, extensions, linkage
 

Hello !

>
> This result is:
>
> ruby: symbol lookup error:
> /home/djberge/programming/ruby/extensions/foo.so: undefined symbol:
> flo_plus
>
> I tried linking explicitly against -lruby but that didn't help.


By the way, if you're interested to know which symbols are exported
from a library, just do

nm -D /usr/lib/library.so

A look to that on my computer shows no references to flo_plus, only:
nm -D /usr/lib/libruby1.8.so | grep flo
U flock
U floor
0000000000057ef0 T rb_float_new

Cheers

Vincent



Tim Hunter 08-02-2006 12:37 PM

Re: Static functions, extensions, linkage
 
Vincent Fourmond wrote:
>
> By the way, if you're interested to know which symbols are exported
> from a library, just do
>
> nm -D /usr/lib/library.so
>
> A look to that on my computer shows no references to flo_plus, only:
> nm -D /usr/lib/libruby1.8.so | grep flo
> U flock
> U floor
> 0000000000057ef0 T rb_float_new



In Ruby, the functions that are intended for use by extensions start
with the prefix "rb_" and are declared in either ruby.h or intern.h.
Since flo_plus doesn't start with "rb_" it isn't intended to be
available to extensions.


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