Re: A patch for default version and archive

["H . J . Lu" <hjl at valinux dot com>]

On Tue, Nov 14, 2000 at 09:49:50AM -0800, Ian Lance Taylor wrote:
>    Date: Tue, 14 Nov 2000 09:33:16 -0800
>    From: "H . J . Lu" <hjl@valinux.com>
> 
>    On Tue, Nov 14, 2000 at 08:59:06AM -0800, Ian Lance Taylor wrote:
>    > 
>    > What I think we really need to do is to write down the semantics of
>    > versioned symbols.  I actually asked Eric to do this long ago so that
>    > I could understand what was going on, but he never found the time to
> 
>    I have added some documentations for .symver to as:
> 
> Thanks for doing that.  But I assume you understand that this has
> nothing to do with the written semantics of versioning that I would
> like to see.  Your documentation assumes that the reader already
> understands versioning, and understands what the symbols with @ in
> their name represent.  Those are among the questions I think ought to
> be answered.
> 

I see your point. I left it out. Even Ulrich and I have different
interpretations of what the symbols with @ in their name represent :-).
Here is my take. As far as I know, symbol versioning was introduced to
solve one problem, that is to provide the backward compatibility when
the ABI in libc.so is changed. Since glibc 2.1 (?), when you do

# gcc x.c
# nm a.out| grep GLIBC
         w __cxa_finalize@@GLIBC_2.1.3
         w __deregister_frame_info@@GLIBC_2.0
         U __libc_start_main@@GLIBC_2.0
         w __register_frame_info@@GLIBC_2.0
         U fclose@@GLIBC_2.1
         U fopen@@GLIBC_2.1
         U fprintf@@GLIBC_2.0

As you can see, each reference to symbols in libc.so are bound to a
specific version. Since we don't have symbol versioning in x.c, all
references are resolved to symbols with `@@', which are symbols can
resolve references to symbols with the same version or without any
version. Normally, you won't see any references to `@' since it will
only show up with my glibc proposal. However, you can do

# nm /lib/libc.so.6 | grep GLIBC

The one with `@@' will resolve references to symbols with the same
verison or without any version. The one with `@' will only resolve
references to symbols with the same verison. There 2 different cases
for the one with `@' like foo@ver1:

1. ld.so will resolve references to foo with version ver1. You can
image those references look like foo@ver1 or foo@@ver1.
2. ld will only resolve references to foo@ver1.



-- 
H.J. Lu (hjl@valinux.com)