Re: Multiple definition of gnulib symbols

[Simon Josefsson]

On 26 apr 2007, at 01.04, Bruno Haible wrote:

> Simon Josefsson wrote:
> > It seems clear that the problem is that both libgnutls and libgsasl
> > contains the same gnulib symbols.
>
> Uh, you are jumping to the conclusion rather quickly.

Oops.  I don't understand the error, so jumping to conclusion isn't  
unlikely.

> First of all, can the reporter reproduce the problem also when  
> building
> without the -ffunction-sections option?

Yes, I asked him to do that and there were no change.

> Second, the error message is about gc-libgcrypt.o and gc-gnulib.o in
> particular, not about gnulib in general. These two object files define
> different, but partially overlapping sets of symbols:
>   - gc-libgcrypt.o defines gc_hash_hmac_setkey, gc-gnulib.o doesn't.
>   - both define gc_init.
> Possibly there are also differences due to the version of gnulib  
> used in
> the two libraries /usr/lib/libgnutls.a and .libs/libgsasl.a . It would
> help if your reporter could give you the output of "nm" on these two
> libraries.

Bennett, could you try running 'nm' on the libraries?

But yes, gc-libgcrypt and gc-gnulib are intended to be two mutually  
exclusive modules, since they provide the same symbols, but I  
wouldn't have thought that could lead to problem between two projects  
that each use gc-libgcrypt and gc-gnulib.  I would have thought that  
these symbols would not be externally visible, but I guess there is  
no such concept with static libraries.

> > Or is there some libtool/ld/etc setting that gnulib or my
> > projects should use, to avoid causing this situation?
>
> Such errors when linking statically typically occur when you have  
> object
> files defining more than one symbol. The rest of gnulib doesn't see  
> this
> kind of error because most .o files define one and only one function.

Oh!  I had no idea that defining multiple symbols in a single object  
file could lead to trouble.  Sigh.

> How can you turn a module that defines 10 functions into a module that
> defines just 1 symbol? Combine the 10 functions into a vtable (=  
> struct
> containing function pointers). See the 'list' module for an example:
>   - The header file defines inline functions or macros that access  
> individual
>     elements of this function pointer table,
>   - Any .o file only defines a named function pointer table.
> (This is not to say that here you won't have versioning problems:  
> If at
> some moment you add an 11th function pointer, two compiled versions of
> this module will be binary incompatible.)

I see.  Seems somewhat complicated...

> > One solution might be for gnulib-tool to change the namespace of all
> > gnulib functions to 'gnutls_*' and 'gsasl_*' respectively, when
> > importing them into each project.
>
> Yes. Ralf was the first one to realize the need for such a  
> renaming. It can
> be done in a Makefile.am rule without special help from gnulib- 
> tool. See
> gettext/gettext-tools/libgettextpo/Makefile.am.

Aha!  Ok, I think that approach may be simpler, if it already can be  
automated easily.  I'll wait with implementing it until I can confirm  
and understand why it would be needed though, it seems I can learn  
something here.

Thanks,
Simon