RE: How to control to use the function static linked to a shared library

["Hongbo Li" <hongbol at nortel dot com>]

Hi Ian,

Thanks for the information. I will take a look at the manual. When you
talk about the attribute, does that mean I need to change my source
code? Do you think the new option -fvisibility=hidden in gcc 4.0.0 would
solve this issue? I am using gcc 3.3.2.

Once again, thank you,

Hongbo.



-----Original Message-----
From: Ian Lance Taylor [mailto:iant@google.com] 
Sent: Wednesday, June 28, 2006 10:09 PM
To: Li, Hongbo [CAR:PK17:EXCH]
Cc: gcc@gcc.gnu.org
Subject: Re: How to control to use the function static linked to a
shared library


"Hongbo Li" <hongbol@nortel.com> writes:

This question would be more appropriate for the gcc-help mailing list
rather than the gcc mailing list.

> 	I currently hit an issue that I would like to use a function 
> statically linked to a shared library but my program use the same 
> function from another shared library. Here is what I do:
> 
> 	1. I have toto.cxx that has one function called: toto() {cout <<

> "static toto" << endl;}
> 	2. I create an archive say toto.a has the toto.o
> 	3. I have toto1.cxx that has one functin called toto() {cout
cout 
> <<"shared toto"<<endl;}
> 	4. I create a shared libtoto1.so
> 	5. I have use_toto.cxx that has one function called use_toto() {
> toto();}:
> 	6. I create a shared libuse_toto.so that statically link to
toto.a
> 	7. My main program test.cxx calling use_toto()
> 
> 	I would like to always see the output of "static toto" but the
output 
> depends on the order of linking toto1.so and use_toto.so
> 
> 	I will see "static toto" when I do this
> 	g++ -o test -L./ -luse_toto -ltoto1.so ./test.o
> 
> 	But I see "shared toto" if I change the order:
> 	g++ -o test -L./ -ltoto1.so -luse_toto ./test.o
> 
> 
> 	My question: do we have any way during the compilation/link to 
> control the program so that toto() in toto.cxx is always used? Since I

> may not have way to control how to build the main program, is there a 
> way to build libuse_toto.so so that toto() in toto.cxx is always used?

As you have discovered, the order on the link line determines when
symbols will be used.

You can force a few other possibilities by using a linker version script
or by setting the visibility attributes.  See the linker manual for
version scripts and the gcc manual for attributes.

Ian